A diagnosis of acute periapical abscess was made and the tooth was opened for drainage. After 4 days, cleaning and shaping of root canals was performed with K files, using the step-back technique and 1-2 ml of 3% sodium hypochlorite irrigant after each file used.


The presence of an invaginated deep lingual pit in the mesial root canal renders the tooth susceptible to invasion by microorganisms, and subsequent pulpal Infection with necrosis and the development of peri-apical periodontitis. The fact that there was no obvious connection between the invaginated space and the main canal suggests that the pulp necrosis in the main canal occurred as a result of dentine permeability between the two canals. Some authors have reported similar cases in the maxilla. but these were characterized as fusion or gemination (Burzynski 1973, Shifman & Tamir  1979).

In spite of difficulties faced during the root canal treatment, such as diagnosis. access preparation, and clean¬ing and shaping, the patient’s recall examination demonstrated an asymptomatic tooth with evidence of healing of the periapical lesion. Similar reports on the successful conservative management of such tomes have been published (Morfis & Lentzari 1989. Vajrabhaya 1989).

For the references, click the file below:

Dens_invaginatus.pdf

Local_anesthetics.pdf

The aims of this investigation were to determine the presence or absence of endotoxins in the pulp of symptomatic and symptom-free human carious teeth, to quantify the amount of endotoxins present, and to associate the presence of endotoxins with the acute pulpal pain.
Pulpal tissue was sampled from 28 single-rooted carious teeth (15 symptomatic, 13 symptom-free) derived from 28 patients. Samples were also taken from the pulp of 5 noncarious control teeth. During sampling an effort was made to collect an equal weight of pulpal tissue in all cases (approximately 8 mg). The extraction of endotoxins was performed with the use of phenol-water. The assay and quantitative determination of endotoxins was performed with the use of a limulus lysate test. The data were analyzed statistically by using the independent t test.
Endotoxins were detected in pulpal tissues of all carious teeth in the symptomatic (mean average, 0.15773 ng/mL; SD = 0.045811) and symptom-free group (mean average, 0.10723 ng/mL; SD = 0.010925). In noncarious control teeth, endotoxins were not detected. The presence of endotoxins was significantly higher in the group of symptomatic teeth than in the group of symptom-free teeth (P < .001).
The presence of endotoxins in the pulpal tissue of all the carious teeth indicates that they may play a major role in the pathogenesis of human pulpal diseases. Since a significantly higher level of endotoxins was detected in the pulp of symptomatic carious teeth than in that of symptom-free carious teeth, an association of endotoxins levels with severity of pulpal pain is probable.(Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;91:587-93)
As long as enamel and cementum protect the dentine, the dental pulp will remain healthy, unless an external factor such as trauma disturbs its blood microcirculation. The removal of these protective barriers as a result of caries, trauma, or iatrogenic exposure will create a communication gate between the dental pulp and the microorganisms of the oral cavity through dentinal tubules or through an immediate contact after a pulp exposure.1,2 The influence of bacterial invasion in the dental pulp in animals was studied by Kakehashi et al in 1965. Their research demonstrated that bacteria produced an extensive inflammation.3 In human beings a histologic examination revealed that whenever bacterial growth was observed on cavity dentinal walls of restored teeth, an inflammatory reaction was present in the pulp. No inflammatory reactions were observed in cavities without bacterial presence, even when silicate cement was placed directly on the exposed pulp.4
The cell wall of gram-negative bacteria such as Prevotella contains endotoxins that can be either secreted in vesicles by growing organisms or released into the environment after the death of the cell. Endotoxins are a major virulence factor capable of initiating various biological responses, such as complement activation, fever induction, macrophage activation, cytotoxicity, and bone resorption.5,6 Studies have shown that microbial byproducts (eg, endotoxins) may produce an inflammatory reaction in the dental pulp.7-9
Symptoms originating from carious teeth with vital pulp vary considerably, ranging from simple discomfort to spontaneous pain of extreme intensity.10 Endotoxins may evoke pain through activation of the Hageman factor11 or through neurotoxic properties when acting on presynaptic nerve terminals.12-14
Despite considerable interest in the mechanisms of inflammation and pain in the dental pulp of carious teeth, no direct evidence has been presented to show the presence of endotoxins in the vital and in the inflamed pulp of human beings.
Therefore, the purposes of this investigation were (1) to determine the presence or absence of endotoxins in the pulp of symptomatic and symptom-free carious teeth diagnosed as irreversible and reversible pulpitis, respectively, (2) to quantify the amount of endotoxins present in the above pulps, and (3) to study the association between the presence of endotoxins with the acute pulpal pain present in symptomatic teeth.
Patient selectionIncluded in this study were 28 single-rooted teeth (3 maxillary central incisors, 1 maxillary lateral incisor, 3 maxillary canines, 10 maxillary second premolars, 5 mandibular first premolars, 6 mandibular second premolars) with vital pulps diagnosed as having irreversible and reversible pulpitis from 28 patients, 15 to 62 years of age, who presented at the Clinic of Conservative Dentistry at the Dental School of the University of Athens. The teeth were divided into 2 groups: Group 1, symptomatic carious (n = 15); and group 2, symptom-free carious (n = 13). Moreover, a third group of single-rooted sound noncarious teeth (n = 5) was included as a control, constituted from 4 patients, 11 to 13 years of age (Table I).
The following information was noted for each patient: Age, gender, tooth, pulp vitality (electrical and thermal), nature of pain (duration, location, sharp, or dull), history of previous local treatment, periodontal status, and radiographic findings.
All the teeth in groups 1 and 2 had deep interproximal or occlusal carious lesions or secondary caries under a restoration, without exposure of the dental pulp as evaluated clinically and radiographically (at least 0.5 mm of dentine protected the pulp). None of the teeth showed radiographic evidence of periapical inflammation. Group 1 (symptomatic carious) consisted of 15 single-rooted teeth with the clinical diagnosis of irreversible pulpitis. The teeth were placed into this group on the basis of the following criteria: The teeth were currently causing spontaneous pain or had a recent history of causing severe pain that was diffused and lasted for minutes or hours when exposed to thermal stimuli; all the teeth responded to ice or electric pulp testing; and a severe, prolonged pain reaction was elicited with ice. Group 2 (symptom-free carious) consisted of 13 deeply carious and symptom-free single-rooted teeth that needed a post or dowel for their final restoration. The teeth were placed into this group on the basis of the following criteria: No history of moderate or severe pulpal pain and no pain at the time of sampling; and clinical and radiographic examination determined the presence of caries without pulpal exposure, no signs of periapical pathosis, and normal to slight reaction to the vitality test. Group 3 consisted of 5 intact teeth from 4 patients. The teeth were placed into this group on the basis of the following criteria: A verbal history confirmed no previous pulpal pain; a clinical and radiographic examination assured that these teeth had no caries, restoration, wear facets, or periodontal disease; and all the teeth were found normal after being tested by both ice and electric pulp test.
Teeth in this group included premolars extracted because of orthodontic considerations. Teeth with a history of previous local medication to manage pulpal pain, with periodontal pockets more than 3 mm, with root caries, or with an exposure of the pulp were not included in the study.
The protocol was approved and supported by a grant from the University of Athens. All patients agreed to participate in the study, and each patient signed a detailed informative consent form.
Pulp sampling After the diagnosis of reversible or irreversible pulpitis, local anesthesia was administered and the crown of the tooth to be sampled was thoroughly washed with airwater spray and dried. A rubber dam was placed and the operation field including the outer surface of the tooth, the dam, and the clamp was disinfected with tincture of iodine. Patients were excluded from the study if the application of the rubber dam was not effective. All carious dentine was removed with a sterile bur at low speed and without water spray. This was followed by a wide penetration of the pulp chamber with a new, sterile long-shanked round bur. The pulpal tissue was engaged and removed with a new, sterile barbed broach and then transferred to a preweighed pyrogen-free tube (Whittaker Bioproducts, Walkersville, Md). All the tubes were reweighed with the specimens. During the sampling an effort was made to collect an equal quantity of the pulpal tissue in all cases (approximately 8 mg). All the samples were stored at –30°C, as recommended by the manufacturer, until the next step of the procedure.

Release of endotoxins
The extraction of endotoxins was performed by the phenol-water method.15 Three millilters of a 65% phenol solution were added to the tubes containing the specimens. The samples were vortexed at room temperature for 1 minute and centrifuged at 3500 rpm for 50 minutes. The solution then formed 2 phases: The upper phase, which contained endotoxins, and the lower phase, which contained mostly phenol. The upper phase (supernatant) was removed with a pyrogen-free pipette and placed in a pyrogen-free tube for 10 minutes at 60°C to inactivate proteins that might cause falsepositive results. Heating does not affect the activity of endotoxins since they are heat stable.5,6

Measurement of endotoxins
To determine the amount of endotoxins present in the collected supernatant, the LAL method, a modified limulus amebocyte lysate and a synthetic colorproducing substrate to detect endotoxins chromogenically (Quantitative Chromogenic LAL-1000, Whittaker Bioproducts), was used. With this method a yellow color will develop if endotoxins are present in the sample.

Reagent preparation. From the endotoxins supplied in the kit (E. coli 0111:B4) with a known concentration (23 EU/mL), 4 standard endotoxin solutions were prepared with concentrations of 0.1, 0.25, 0.5, and 1.0 EU/mL, to be used as positive controls. By reading the absorbency of the above known concentrations of endotoxin in a phasmatophotometer (Spectronic 70; Bausch & Lomb) at 405 nm, the corresponding absorbance values were recorded. As a result, a standard curve was constructed from which the best fit was calculated. The absorbance at 405 nm is linear in the concentration range used (Fig 1).

Test method. The kit used was supplied with LAL reagent water, E. coli endotoxin (23 EU/mL), chromogenic substrate, and chromogenic limulus amebocyte lysate (LAL). Acetic acid (25%) was used as the stop reagent.

Different solutions were needed for the quantification of endotoxins in the samples: (1) 4 tubes with 50 µL of the above-mentioned endotoxin standards, (2) 1 blank tube containing 50 µL of LAL reagent water instead of sample to be used as a negative control, and (3) samples tubes with 50 µL of supernatant from each specimen.

At the beginning (time 0), 50 µL of LAL was added to each of the aforementioned tubes (4 tubes of endotoxin standards, one blank tube, and tubes with samples). Thorough mixing was performed, and the tubes were incubated for 10 minutes at 37°C. After 10 minutes, 100 µL of chromogenic substrate solution were added, mixed, and incubated for 6 minutes at 37°C, after which 100 µL of stop reagent (acetic acid) was added, and samples were vortexed. All samples were independently examined in a phasmatophotometer by 2 persons who were blinded to the samples (Fig 2).

Calculation of endotoxic concentration. The mean absorbance value of the blank was subtracted from the mean absorbance value of the standards and the value of samples to calculate the mean ∆ absorbance. Since this absorbance value is in direct proportion to the amount of endotoxins present, the endotoxic concentration can be calculated graphically from the standard curve.

Statistical analysis. To correlate the amount of endotoxins found in the pulp with the presence or absence of pulpal pain, we analyzed the data on the presence or absence of severe and spontaneous pulpal pain and the quantitative determination of endotoxins in the pulpal tissue statistically by means of independent t test.
Endotoxins were detected in all pulpal tissues of the teeth in groups 1 (symptomatic carious) and 2 (symptomfree carious). No endotoxins were detected in group 3 (control; intact noncarious teeth). The mean concentration of endotoxins in the experimental groups is shown in Table II.

The concentration of endotoxins in the pulpal tissue of symptomatic teeth was significantly higher (P < .001) than that of the symptom-free teeth (Table III).

The objectives of this investigation were the determination and quantification of the amount of endotoxins present in the pulp of symptomatic and symptom-free human carious teeth and the association of their presence with acute pulpal pain.

To achieve our purpose, we used the LAL method, which is the same or similar to methods used in earlier studies of endotoxins. A survey of the literature shows that Dahlen and Bergenholtz used the LAL method to identify endotoxic activity in teeth with necrotic pulps16; samples (10-15 µL) with gram-negative organisms could be diluted 104 to 106 times and still give a positive reaction. Horiba et al17 used a chromogenic substrate that reacted specifically with endotoxins in a chromogenic method to quantify endotoxins in the dentinal wall of infected root canals, using a spectrophotometer at 405 nm. They found endotoxins at the level of picograms. Thus, with the LAL method it is possible to identify a low concentration of endotoxins.18 Fukui et al19 found endotoxins in the plasma of different patients. Endotoxins were recently detected by the LAL method in middle ear effusions.20 Several other studies have used the LAL method for demonstration of endotoxins.21-24

Our results demonstrated that the mean value of endotoxins detected in approximately 8 mg of the inflamed pulpal tissue of symptomatic teeth was 0.15773 ng/mL, whereas it was 0.10723 ng/mL in symptom-free teeth. In the literature the average value of detected endotoxins ranged from approximately 1 to 100 µg/mL.16-18,21,22An exact comparison between studies was difficult because of differences in tissue samples, sampling technique, and other methodological aspects. For example, Schein and Schilder,21 using the limulus lysate test, deposited 0.1 mL of saline solution in the pulp chamber and the same amount of fluid was aspirated. In this volume of fluid endotoxins originating from both pulpal tissue and pulpal wall were dissolved, leading to the detection of a concentrated solution of endotoxins in a microgram range. In our study the amount of endotoxins contained in the removed pulp only was dissolved in 3 mL of phenol-water solution, thus resulting in a weaker concentration measured in nanograms.
Determination_of_endotoxins.pdfOther substances may induce a false-positive LAL reaction (ie, blood products). This was not the case in our study, as all these substances were inactivated through heating. With our technique the normal noncontaminated pulps were negative to endotoxic detection.

Many studies have demonstrated that the major etiologic factor for the initiation and progression of caries and pulp inflammation in human teeth is the microorganisms present in the oral cavity.3,25,26 In recent years there has been considerable interest in the role of anaerobic microorganisms plays in inflammation and pain. It has been established that application of crude bacterial extracts or specific bacterial components to exposed dentin can induce inflammation in the underlying pulp, indicating that bacterial products are probably capable of diffusing to the pulp.8 Such a hypothesis is supported by the finding that bacterial endotoxins were found to be capable of passing through 0.5 mm of dentin.27 Inflammation of the pulpal tissue may also be induced, under dental restorations by secondary caries or by marginal leakage. The results following Class V cavity preparation in monkey teeth and restoration with a poor marginal seal strongly supported the importance of bacteria as a major factor in the development of pulpal inflammation and necrosis.28 However, scanning and transmission electron microscopic examinations of human vital pulps under deep carious lesions has rarely revealed the presence of microorganisms.29,30 Moreover, bacterial penetration of noncarious dentin to the pulp has been a rare finding even after long-term exposure of the dentin to the oral microflora.31
Hoshino et al32 used an anaerobic technique to examine the microflora of the pulps of freshly extracted teeth with deep carious lesions without pulpal exposure. They detected anaerobic bacteria in 6 of 9 teeth and postulated that bacteria penetrated to the pulps through the infected dentinal tubules. Endotoxins producing gram-negative cocci were among the microorganisms found.32

In our study endotoxins were detected in the pulp of all carious teeth. Since there was no pulpal exposure in our cases, it seems logical that the origin of endotoxins is gram-negative bacteria situated in the deep carious dentin, transported to the pulp through dentinal tubules. However, endotoxins may have been produced by bacteria already existing in the pulpal tissue since, within a necrotic area of vital pulp, bacteria may be present when no or slight amounts of irregular dentin forms in a limited area under deep carious lesions.1

In a previous study we found that endotoxins are present in the carious dentin of symptomatic and symptom-free teeth with vital pulp. A greater amount of endotoxins was present in painful teeth than in those without symptoms.23 In the present study we found that the amount of endotoxins was significantly greater in the pulps of symptomatic carious teeth with irreversible pulpitis than in the painless carious teeth. Therefore, there appeared to be a strong association between the level of pain and the concentration of endotoxins in the pulp of carious teeth. A probable explanation for this phenomenon is that endotoxins activated the Hageman factor, which in turn led to the production of bradykinin, a potent pain mediator and inducer of increased vascular permeability.11 In addition, endotoxins possess neurotoxic properties that act on presynaptic nerve terminals.12-14 Matsushita et al33 recently reported that endotoxin from black-pigmented bacteria may be involved in multilesional periapical periodontitis by inducing particular cytokines and/or humoral immune responses.

Moreover, the relationship between bacterial endotoxins and pain has been demonstrated in teeth with infected root canals and periapical lesions; more endotoxins were found in the periapical areas of symptomatic teeth than in those of symptom-free teeth.21,24 In his classic work on the bacteriology of pulps rendered nonvital by trauma, Sundqvist found that a greater number of different bacterial strains were isolated from patients with pain symptoms.34 There was a significant relationship between clinical symptoms and the presence of Bacteroides melaninogenicus (Prevotella). This anaerobic endotoxin producing, gram-negative rod was isolated only from symptomatic teeth and was absent from those that were asymptomatic.34 The association of B melaninogenicus (Prevotella) and clinical symptoms was confirmed by Griffee et al35 in their study of 33 teeth with nonvital pulps. B melaninogenicus was isolated from 12 teeth, and its presence was found to correlate with pain, foul odor, and the formation of sinus tracts.35 Thus, it seems that endotoxins play a major role in the pathogenesis of the pulp and periapical tissues, since their presence in caries, inflamed pulp, infected root canals, and periapical lesions is associated with clinical symptoms.

In the present investigation it was evident that although endotoxins were detected in all pulpal tissues of all carious teeth, pain was not found in all patients but only in those who had a greater concentration of endotoxins in the pulp. The same occured in our previous study, where pain was not evident in all patients despite the detection of endotoxins in carious dentin.23 Our results have been in agreement with the results of others who have found that there is a higher level of endotoxins in symptomatic teeth than in those without symptoms.21,24,34,35 These findings suggest that the concentration of endotoxins in the pulp must exceed a certain level for pain to be clinically apparent. It is generally believed that pulp fibroblasts are able to respond to low levels of endotoxins (5 to 125 µg/mL) by increased cell division and synthesis of connective tissue matrix. In contrast, a high level of endotoxins (625 µg/mL) has been shown to be obviously toxic to connective tissue containing fibroblasts and would result in tissue necrosis.36 Nakane et al37 investigated the influence of endotoxins purified from Porphyromonas gingivalis, Porphyromonas endodontalis, Fusobacterium nucleatum, and E coli on the production of DNA and protein from human dental pulp cells. They found that a concentration of 1 µg/mL endotoxins caused no change in the production of DNA or protein. But at 10 µg/mL the amount of DNA was increased, and at 100 µg/mL it was inhibited.37 Thus, infections associated with low concentrations of endotoxins may actually stimulate repair mechanisms.11 In clinical practice, one might find that symptom-free teeth with deep carious lesions have an amount of endotoxins in their pulps that is insufficient to excite the intradental nerves or to produce an acute inflammation.

Although the cause of pulpal pain is multifactoral, our study suggests that the concentration of endotoxins in the pulp is one factor. A certain threshold level of endotoxins must be reached to have an effect on the inflamed dental pulp such that clinical pain may be observed.

Endotoxins were demonstrated in the inflamed pulp tissue of symptomatic and asymptomatic carious teeth. The amount of endotoxins in the inflamed pulp of carious teeth was significantly greater in symptomatic teeth than in symptom-free teeth. A hypothesis has been presented, suggesting that a certain threshold level of endotoxins is required for the development of pain in the inflamed pulp.

This study evaluated the effectiveness of a highly flexible endodontic brush made of polypropylene canal brush (CanalBrush; Coltène) on smear layer removal from the canal walls when used according to the manufacturer’s recommendations. Forty-four singlerooted mandibular incisors were prepared to apical size 30/0.06 and randomly divided into three groups A, B and C, where the final irrigation regimen was 10 mL 17% EDTA and 10 mL 2.5% NaOCl for group A, 10 mL EDTA, 5 mL NaOCl, CanalBrush for 20 s at 450 rpm and 5 mL NaOCl for group B, 10 mL NaOCl, CanalBrush and 10 mL NaOCl for group C. One medium-sized CanalBrush was used for each root canal and all brushes were examined under the optical microscope after application to evaluate bristle deformation. Afterwards, roots were split longitudinally and the presence of smear layer was evaluated under a scanning electron microscope. Used brushes invariably exhibited bristle deformation. Group C exhibited the highest means of smear layer in all thirds. Comparing the apical thirds in all groups, there was no statistical difference between groups A and B (3.64±0.48 and 3.68±0.62 respectively), while group C exhibited significantly higher scores (3.9±0.28) than the other two groups. In conclusion, the CanalBrush proved unable to remove smear layer from the instrumented root canals, when used according to the manufacturers’ instructions.
Endodontic treatment aims at eliminating or critically reducing the microbial load of root canal system and at removing inorganic remnants and organic tissues, which constitute a potential nutrient for microorganisms. This goal is reached by chemomechanical preparation, i.e instrumentation and irrigation.
Instrumentation, though, produces a 1-5 μm thick smear layer on the dentinal surface, consisting of dentin, predentin, pulpal remnants, odontoblast processes, irrigant remnants and bacteria, in infected teeth (1-5).
Although controversy exists among authors as to whether this layer should be removed or not, smear layer removal is proposed after chemomechanical preparation in previously infected root canals (6,7), before placing intracanal medicaments (8) and before final obturation of the root canals (9). Recently, with the introduction of adhesive dentistry to endodontics, smear layer removal is indicated in combination with resin based sealers (10,11).
In the past, several materials and methods have claimed to be successful in smear layer removal, such as chelating agents (EDTA, citric acid, etc), lasers, sonic and ultrasonic devices, all of them with conflicting results (6,12-17).
Recently, a microbrush specifically fabricated for root canal cleaning has been introduced on the market. The CanalBrush (Coltène, Germany) is available in three sizes (small, medium and large), which correspond to apical diameter of 25, 30 and 40 respectively, according to the ISO classification. The manufacturer recommends this brush to be used in conjunction with NaOCl at a maximum speed of 650 rpm for up to 30 s.
To date, a small number of investigations have evaluated the cleaning efficacy of the CanalBrush. Garip et al. (18) examined root canal cleanliness using EDTA with or without the application of the CanalBrush. Other authors compared its effectiveness to ultrasonic devices (19), or studied its cleaning efficacy after having adjusted the CanalBrush to a sonic handpiece (20). However, none of the aforementioned studies strictly follows the manufacturer’s instructions; thus, there is insufficient information concerning the usefulness of the CanalBrush in the clinical practice of Endodontics.
The purpose of this study was to evaluate the efficacy of the CanalBrush on smear layer removal from the instrumented root canals, when used according to the company’s instructions. The null hypothesis was that the use of CanalBrush after completion of chemomechanical preparation, according to the manufacturers’ instructions, contribute to obtain cleaner canal walls.
Forty-four freshly extracted mandibular human incisors, stored in 10% formalin, were radiographed in a buccoligual direction to ensure that they possessed one straight root canal. All teeth were decoronated to a standard root length of 10 mm using a diamond disc. Afterwards, a size 10 K-file (Dentsply Maillefer, Switzerland) was inserted into the canal orifice until its tip became just visible through the apical foramen and the working length was established at 1 mm shorter than the actual root length (9 mm). Finally, a small amount of Carbowax (Dow Chemical Co, Midland, MI, USA) was placed on each root tip.
Root canal instrumentation was performed with GT rotary files Series 20 and 30 (Dentsply/Maillefer), used with the handpiece of an Endo IT motor (Aseptico, Woodinville, WA, USA) with programmed torque control and speed settings, in a crown-down manner. Instruments 30/0.10, 30/0.08 and 30/0.06 were initially inserted to 2, 5 and 7 mm in the root canal, respectively. Apical preparation of the root canals was completed by a file sequence of 30/0.04, 20/0.08 and 30/0.06. Between each file change patency was confirmed by using #10 K-file and irrigation with 2 mL 2.5% NaOCl was performed.
At the end of the chemomechanical preparation, teeth were randomly divided into three groups A and B (n=15 each) and C (n=14) and irrigation with a 27 G blind-ended needle was carried out in group A using 10 mL of 17% EDTA (Vista Dental Products, Racine, WI, USA) for 3 min followed by a 10 mL flush of 2.5% NaOCl. In group B the canals were irrigated with 10 mL of 17% EDTA for 3 min and then flushed with 5 mL 2.5% NaOCl, brushed with CanalBrush at 450 rpm for 20 s, 2 mm from the working length and followed by a 5 mL flush of 2.5% NaOCl. In group C the irrigation protocol included 10 mL of 2.5% NaOCl, application of CanalBrush as in the afore-mentioned group and followed by another 10 mL flush of the same solution. All CanalBrushes were inserted to the working length. At the end, all experimental groups received a final 10 mL flush of saline to deactivate irrigant remnants. The total amount of irrigants used in each canal was 42 mL. A new medium-sized CanalBrush was used for each root canal and all brushes were examined under the optical microscope after usage to evaluate bristle deformation. Afterwards, roots were split longitudinally with a diamond disk in a buccolingual direction. The presence of smear layer was evaluated by scanning electron microscopy (QuantaTM 3D DualBeamTM Hilsboro, Oregon, USA) at 1000× magnification using a 4-cathegory scoring system as follows: score 1, smear layer covering 0-25% of the examined surface; score 2, smear layer covering 25-50% of the examined surface; score 3, smear layer covering 50-75% of the examined surface; and score 4, smear layer covering 75-100% of the examined surface (21).
Representative photos of each score taken in a pilot study were shown to the examiners before scoring (Fig 1). The scoring procedure was performed by 3 examiners and was double-blinded. First, the apical end of preparation was found at low magnification, and then every millimeter of the apical (0-3 mm), middle (4-6 mm) and coronal (7- 9mm) thirds of the root canal walls were scanned at 1000X magnification and scored (21).
Intraclass Correlation Coefficient (ICC) was calculated in order to assess the degree of agreement between observers, since our rating procedure employed multiple observers and considered ordinal data. ICC for single measure agreement was: 0.794 (95%CI 0.76-0.82), and for the average of k measures: 0.92 (95%CI 0.91-0.93).
Data were expressed as mean ± standard deviation (SD). Comparisons between more than two groups were performed by Analysis of Variance (ANOVA) and Welch’s/ Brown-Forsythe robust tests. All tests were two-sided. Differences were considered as statistically significant if the null hypothesis could be rejected with>95% confidence (p<0.05).

Bristle deformation
All used CanalBrushes invariably exhibited bristle deformation (Fig 2); however during the SEM examination no residues of those bristles were detected on the canals walls and no crushing was noticed.

Smear Layer
Mean scores for smear layer among groups in coronal, middle and apical thirds are presented in Table 1. Group C exhibited the highest overall values and group A the lowest. Regarding the apical third, no statistically significant difference was detected between groups A and B, however results were significantly inferior in group C. Among root thirds, in group A, the coronal one had the lowest statistically significant score, while the apical third demonstrated the highest one. Group B exhibited the lowest score in the coronal third but no statistically significant difference was noted between middle and apical thirds. Group C showed no differences among thirds.

The results of the present study did not show any improvement in smear layer removal when the CanalBrush was additionally used according to the manufacturer’s suggestions for the chemomechanical preparation of root canals. On the contrary, a worsening of the results was noticed, since smear layer scores were overall significantly higher in group B (where the CanalBrush was used) when compared to group A. This was not the case for the apical third, where no significant difference in smear layer scores was noticed between groups A and B. No improvement in cleanliness has also been reported by Garip et al. 2010, where no significant differences were noted between groups with or without the use of the CanalBrush (18). Furthermore, Rödig et al. 2010 reported no significant differences for smear layer scores in the apical and middle thirds of root canals with or without the use of CanalBrush (19). The aforementioned studies, though, found insignificant differences between groups, which is not in line with the present finding, that the use of the CanalBrush significantly worsened the results.
The significantly higher scores that were obtained in the coronal and middle thirds in group B could be explained by the fact that, in contrast to previously published research (18-20) EDTA was not agitated with the CanalBrush within the root canals, since this was not included in the manufacturer’s instructions. Another explanation of this discrepancy may be that previous studies advocated larger canal preparations in combination to the same or smaller CanalBrush sizes - 25/0.09 medium-sized CanalBrush (18) and 40/0.06, small-sized CanalBrush (19). It seems that the smaller canal preparation advocated in the present study (30/0.6) combined with the medium-sized CanalBrush (ISO: 30), although in line with company’s suggestions (larger than the minimum preparation suggested for the medium sized canal brush), led to an early bristle deformation and “squeezing” inside the proportionally narrow root canal. This may have resulted in an intense friction of the brush against the root canal walls, recreating what had already been cleansed by the demineralizing action of EDTA.
Although smear layer scores were significantly higher in the coronal and middle third of Group B, compared to Group A, this was not the case for the apical third, where similar scores were noticed. This was probably due to the fact that the overall CanalBrush design is not tapered. So, a parallel-form instrument is forced to rotate into a tapered space as the instrumented root canal. This means that in the smallest diameter of the cone, i.e., the apical part of the root canal, the bristle deformation might be severe with an early cessation of its action on the canal walls, resulting in no additional action of the brush on the apical third in group B compared to group A. On the other hand, in the middle third, the brush will work more intensively with a less severe deformation that enhances friction against the canal walls, thus producing more smear layer as already stated. Probably larger canal preparations or smaller CanalBrush sizes, application of the brush with EDTA, changing the brush shape into an overall tapered design and creation of shorter bristles would allow the CanalBrush to work passively inside the root canal which may improve its performance. These hypotheses need to be proved before advising the CanalBrush for clinical use.

Although, the combination of EDTA with NaOCl has long been known for its capacity for smear layer removal (1,6,22), these solutions are not able to clean completely the apical third of the root canal (23-25). This is obvious in Groups A and B, where the apical third exhibited significantly higher smear layer scores compared to the coronal third. Specifically in group A the presence of smear layer follows an ascending pattern, while running from the coronal to the apical third, with statistically significant differences among thirds. However, in Group C where chemomechanical preparation was performed without using EDTA, more smear layer accumulated in all thirds of the root canals, despite application of the CanalBrush. This suggests that it is the action of the chelating agent that contributes to cleaner canal walls rather than the action of the brush.

Judging from the above mentioned findings, it seems that the brush itself may have a positive action for root canal cleanliness, but several factors should be considered; greater canal preparations or smaller CanalBrush sizes could let the brush passively work yielding probably better results. Another parameter not tested is time; increasing working time might enhance cleanliness. This would be beneficial only after having determined the optimal brush to canal preparation size ratio. Otherwise, increased working time might result in even higher smear layer scores if intense friction occurs for a longer period of time. Finally, it is possible that changing the brush into an overall tapered design would improve its performance.

From the above results, it may be concluded that the utilization of the CanalBrush according to manufacturer’s recommendations did not contribute to produce cleaner dentinal walls. On the contrary, the traditional combination of EDTA and NaOCl proved superior to the CanalBrush in removing the smear layer.
Canal_Brush.pdf

Evaluation of different methods for the root-end cavity preparation

Marouan G. Khabbaz, DDS, Dr Dent,a Nikolaos P. Kerezoudis, DDS, Dr Med Sc,a Evanthia Aroni, DDS,b and Vasilios Tsatsas, DDS, Dr Dent, FICD,c Athens, Greece UNIVERSITY OF ATHENS

Objective. The dentinal walls of root-end cavities were examined for the presence of cracks and debris in correlation with the area of the root surfaces that remained after the resection.
Study design. One hundred extracted single-rooted teeth were endodontically treated, mounted in acrylic resin blocks, and the apical 2 mm of the root-apex was resected. According to the resected root surface area the teeth were divided into 2 groups having large ([2 mm2 ) or small (\2 mm2 ) surface area. For retrograde cavity preparation 4 devices were used: slow-speed handpiece, diamond coated stainless steel ultrasonic tip, smooth stainless steel ultrasonic tips, and sonic diamond-coated tips. Teeth were examined under a videomicroscope for the presence of fractures, dentin chips, and gutta-percha remnants on cavity walls. Preparation time was also recorded.
Results. Preparation with smooth stainless steel ultrasonic tips produced few intradentin cracks. Dentin debris was more frequently seen in rotary preparations whereas gutta-percha remnants were seen mainly at ultrasonically prepared teeth.
Conclusions. Sonic and ultrasonic devices produced cleaner, well-centered, and more conservative root-end cavities than the rotary instrumentation. Cracks do not correlate directly with the surface area of the root-end surfaces but rather with the type of retrotip used to prepare the root-end cavity.
(Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2004;98:237-42)

Today it is well established that the success rate of conventional endodontic therapy is high (85% to 95%). There are failed cases, however, which cannot be retreated conservatively and therefore an endodontic surgery is required to save the affected tooth.

Root-end filling after the preparation of a root-end cavity is an important step for successful periradicular surgery. Traditionally this cavity is prepared by means of a round bur on a micro contra angle slow-speed handpiece. However, in the clinical practice, this technique of apical preparation may exhibit a number of drawbacks such as increased risk of perforation.

In recent years the use of ultrasonic and sonic devices has been proposed to solve the above-mentioned problems. The first report of the root-end preparation using an ultrasonic technique was made by Bertrand et al. Later, endodontic microsurgical tips (retrotips) for ultrasonic devices became commercially available. Since the introduction of these retrotips, a large number of laboratory, but few clinical, studies have investigated different aspects of their application in the root-end cavity preparation. These studies evaluated the cleanliness of root-end cavities, the cutting ability of retrotips, the apical leakage of root-end filling materials, and the crack formation following rootend preparation with the amazing rate from 2% to 70%. However, until today little research has been done on the generation of dentin cracks correlated to the remaining area of dentinal surface after root resection.

The objectives of the present investigation were (1) to investigate the generation of cracks in dentinal walls after root resection as well as after root-end cavity preparation using different cutting devices, (2) to correlate the occurrence of cracks with the remaining area of root surfaces after the resection, (3) to examine the cleanliness of cavity walls after retrograde preparation with the different devices, and (4) to monitor the time of cavity preparation.

MATERIALS AND METHODS
Specimen selection
One hundred recently extracted human teeth, 43 canines of both jaws and 57 incisors of the lower jaw, having a straight single root with fully developed apices were used in this study. All teeth were immersed in a 3% NaOCl solution for 15 minutes immediately after extraction. Afterwards, remaining periapical and periodontal tissues were removed with curettes and stored in a saline solution at room temperature.
Specimen preparation
An evaluation of the existence of fractures or dentinal cracks in roots due to the extraction procedure was done, using a stereomicroscope (330) (Kaps, Germany). Teeth exhibiting cracks were discarded. Thereafter, all teeth were decoronated using a high-speed diamond bur under continuous water spray so as to obtain a common working length. Standard endodontic access preparations were made and working lengths were established 1 mm short of anatomical apex. The root canals were prepared chemomechanically according to the step-back technique, under copious irrigation with 3% sodium hypochlorite and subsequently dried with paper points. The root canals were obturated with laterally condensed gutta-percha using the Roth 801 sealer (Roth Drug Co, Chicago, Ill). Immediately, the teeth were inspected for the presence of cracks, using the same microscope. The coronal two thirds of the roots were mounted in self-curing acrylic resin blocks in such a way that the apical 2 mL of the root-apex were left beyond the resin block so as to be exposed for the subsequent surgical maneuvers. To avoid the elevation of temperature during polymerization of the acrylic, roots with the resin blocks were placed in a vial containing tap water. After setting of the acrylic, the exposed 2 mm of the apex were resected perpendicularly to the long axis of the root using high-speed diamond bur under continuous irrigation with water spray. To ensure that the cutting procedure did not cause any root fracture, the area of apicoectomy was inspected for the presence of cracks and photographed with a digital video camera (MS-500c, Micro-Scopeman, Moritex, Cambridge, UK) connected to a computer at a magnification capacity of 3100. Moreover, the surface area of the root was measured at its longest and its shortest diameter. The average value of the 2 diameters was then calculated and based on rootend surfaces the teeth were divided into large roots (more than 2 mm²) with a mean average of diameter 2.85 ±0.60 mm and small roots (less than 2 mm²) with mean average of diameter 1.74 ±0.23 mm.

Root-end preparation
The teeth were randomly divided into 4 groups (A, B, C, D) according to the method used to prepare the rootend cavity. Each group was further subdivided into 2 additional groups according to the root surface area. Group A consisted of 10 large (A1) and 14 small teeth (A2) where the micro contra angle slow-speed handpiece (KAVO, Biberach, Germany) with a round bur (No. 2) was used to prepare a 3-mm deep cavity down the long axis of the root canal. Cavities were then rinsed with 5 mL of water. Group B consisted of 12 large (B1) and 15 small teeth (B2) in which a 3-mm deep apical cavity was prepared using 1 diamond-coated ultrasonic retrotip (P14D) (Satelec Merignac, Cedex, France) on the ultrasonic device with the ‘‘Suprasson’’ handpiece at the highest power setting (grad point 8) recommended under water spray. Group C consisted of 10 large (C1) and 14 small teeth (C2) that received ultrasonic instrumentation with 2 smooth stainless steel retrotips (EMS-Piezon Master 400, LeSentier, Switzerland) to produce a 3-mm deep cavity at the power settings recommended by the manufacturer (at 8 o’clock) under water spray. At the beginning, initial penetration to the gutta-percha root filling was done with the CT-5 retrotip followed by the CT-1 for the final preparation of the retrocavity. Group D consisted of 11 large (D1) and 14 small teeth (D2) where the same depth of cavity preparation was made with the sonic instrumentation (Sonicretro, Kavo Sonic Flex, Biberach, Germany) using 2 diamondcoated retrotips, under water spray, the cylinder (No. 176-16) for the initial penetration and enlargement of the retrocavity and then the T-shape (No. 176-20) to produce the T-shape bottom of the cavity. All preparations were class I having a depth of 3 mm, which was confirmed by measuring with a periodontal probe.

Time recording
Together with the cavity preparation, the time to the nearest second, required to complete each preparation procedure was done with a stopwatch. Only the time of actual instrument contact with the root walls was measured.

Image inspection
Immediately after the root-end preparation all cavities were photographed using the same digital video camera connected to a computer. The preoperative and the postoperative digital images were coded and blinded and 3 investigators evaluated them. Images were scored for the existence of fractures on the root-end surface (Y = fracture present, N = fracture absent). The extension of fractures were recorded as follows: IC = intracanal fracture without the extension into dentin of the rootend surface, ID = fracture that may include the IC and an extension to the dentin of the root surface, DC = dentino-cementum fracture that included the IC, DC, and the fracture of cementum.

The presence or absence of debris (superficial dentinal chips and/or gutta-percha remnants) in the cavity was classified as follows: 0 = clean walls, 1 = debris on 1 wall, 2 = debris on 2 walls, 3 = debris on 3 walls, 4 = debris on 4 walls.

The direction of the cavity in relationship to the root canal was also recorded.
Statistical analysis
Our data concerning the distribution of debris (guttapercha remnants and dentinal chips) on the internal rootend cavity walls were statistically analyzed with the Kruskal Wallis test followed by the Mann-Whitney test. P values less than .05 were considered to be significant.

RESULTS
Crack formation
Close inspection of the resected root surfaces immediately after cutting the root apex did not reveal any crack formation. After the root-end cavity preparation there were no detectable complete cracks involving dentine and cementum. However, small intradentinal cracks (incomplete cracks) were detected in 7% of the small roots of group A, 20% of the large and 21% of the small roots in group C (Table I).

Debris in the cavities
All methods used produced dentine chips on the walls of cavities However, the amount of produced debris was different in the different groups in a significant dependent manner (Fig 1, Tables I and II). 

Studying the distribution of the gutta-percha remnants on the cavity walls, no gutta-percha was detected on the root canal walls of neither large nor small roots in group D, while in group A2 only 1 root (7%) showed guttapercha remnants (Fig 1). In groups B and C, moderate percentages (around 40%) were found with the exception of the large roots of group C where the percentage was high (90%) (Figs 2 and 3, Tables I and II). 

Direction of the cavities
In the micro-handpiece groups the long axis of the cavity preparations was often out of line with the root canal. In 1 case a perforation was noticed. In the ultrasonic and sonic groups cavities were well centered, following the original course of the root canal. Time needed for preparation In terms of the time needed for each preparation to be completed, the round bur preparation was more rapid than the preparation made by the sonic and ultrasonic devices. A bur required only 5 seconds for complete preparation whereas the corresponding time with a diamond ultrasonic tip required 57 seconds to 82 seconds, and with a smooth stainless steel ultrasonic tip, 71 seconds to 84 seconds. The most time-consuming device was the sonic diamond tip, ranging from 106 seconds to 154 seconds (Table I).
Time needed for preparation
In terms of the time needed for each preparation to be completed, the round bur preparation was more rapid than the preparation made by the sonic and ultrasonic devices. A bur required only 5 seconds for complete preparation whereas the corresponding time with a diamond ultrasonic tip required 57 seconds to 82 seconds, and with a smooth stainless steel ultrasonic tip, 71 seconds to 84 seconds. The most time-consuming device was the sonic diamond tip, ranging from 106 seconds to 154 seconds (Table I).

DISCUSSION
Recent studies have shown that an ideal root-end cavity preparation is very difficult to achieve with the use of burs on micro-motor, and that better results are obtained with the use of ultrasonic tips. Furthermore, an increased cavity depth can be achieved with ultrasonic tips, a significant factor for controlling apical leakage. Thus, an increase of the success rate of endodontic surgery procedure may be expected since isthmuses, fins, and other significant anatomical irregularities can be faced successfully in clinical practice. A disadvantage for the use of the ultrasonic tips during the root-end cavity preparation is the creation of cracks on the resected root surface due to the excessive vibration power produced by these devices. The problem of rootend cracking as a result of ultrasonic preparation was first noted by Saunders et al. Cracking may lead to long-term failure of the surgical procedure because of increasing risks for apical leakage. In the related literature, many research studies have compared ultrasonic preparation of the root-end cavity to the rotary preparation. Some results indicated that ultrasonic devices are responsible for generating cracks at the root-end surface, but other results indicated the opposite.

In our study an effort was done to simulate the periodontal ligament support of the root to be prepared by using the acrylic resin block. The results indicated that the area of the dentinal surfaces after the resection of the root end and the type of vibration (ultrasonic and sonic) did not affect the appearance of cracking. Even when the remaining thickness of the dentinal walls was only 0.5 mm after the root-end cavity preparation, there was no crack formation. On the contrary, the kind of the tip used (diamond-coated or smooth stainless steel) seemed to play a role in the production of cracks in the walls of the prepared cavities, since it was found that the use of a smooth stainless steel ultrasonic tip caused cracks in 5 teeth out of 24, in both large and small roots, whereas the diamond-coated ultrasonic and sonic tips did not produce any cracks at all. Therefore, the results of Abedi et al showing 75% of cracks when the remaining width of the thinnest dentine wall was thinner than 1 mm after ultrasonic root-end preparation could not be supported and may be due to the nature of the tips used. Only 1 root having cracks was found by Peters et al, who used ultrasonic diamond-coated or stainless steel smooth retrotips to prepare 48 root-end cavities in molar teeth mimicking clinical conditions. The failing cavity was prepared using a smooth stainless steel retrotips and the remaining minimum dentine thickness was less than 0.95 mm. Investigations of the effects of ultrasonic root-end preparation in cadavers found no cracks and it has been suggested that the periodontal ligament might help to dissipate stresses and thereby decrease the incidence of cracking. In a clinical study, only 1 incomplete canal crack was evident after the application of ultrasonic device to prepare root-end cavities on 25 human roots.20 Although our findings indicate that the appearance of cracks cannot directly correlate with the area of the dentinal surfaces, it is prudent to use ultrasonic tips, especially the smooth one, with caution to the power settings when a narrow root with biconcave morphology and thin fragile areas is to be root-end prepared, because these roots are more susceptible to infractions. Further research is needed to evaluate the depth and consequences of the presence of the apparently incomplete and shallow cracks after ultrasonic root-end cavity preparation.

Debris found in the cavities of our specimens consisted of superficial dentinal chips and gutta-percha remnants. Dentin chips were found on the walls of cavities, regardless of the method used, with the highest frequency on the cavity walls prepared with the bur on the micro contra angle slow-speed handpiece in both groups (large and small). This can be attributed to the fact that the bur preparations were made under no water spray, whereas the sonic and ultrasonic tips were supported by irrigation. Gutta-percha remnants were detected on the walls of both large and thin roots in most of the ultrasonically prepared cavities, regardless of the type of tip. Only 1 root in the group prepared with a bur showed gutta-percha remnants and, overall, gutta-percha was most efficiently removed with the use of sonic diamond tips. Thus, in clinical practice the root-end cavity must be cleaned from gutta-percha remnants before placement of the root-end filling. The effects of residual gutta-percha on treatment outcome is unknown and requires further clinical studies. Previous investigations concerning the direction of the root-end cavity prepared with different devices (ultrasonic and rotary) showed that ultrasonic tips produced cavities that are well centered along the axis of the root canal, with less tendency to gauge the canal wall in the thinnest areas of the root, thus reducing the risk of root perforation. These findings were confirmed by the results of the present study.

Time of preparation in the clinical practice is of major importance. Engel and Steiman found that preparation time with the bur was similar to that with ultrasonic tips. Peters et al, using diamond-coated and smooth ultrasonic tips, reported that the preparation times ranged from 25 to 361 seconds and were significantly lower for the diamond-coated than the stainless steel smooth ultrasonic tips. Our results indicated that the time needed to prepare a root-end cavity with rotary instrumentation was very short compared to the sonic and ultrasonic tips. This finding agrees with Waplindton et al, who found the rotary preparation more rapid than the ultrasonic one. Although our in vitro results showed time superiority of the round bur preparation, in clinical practice sonic or ultrasonic instruments may prove faster because they have better accessibility to the root end and require less bone removal, which in turn may result in significantly less total time of surgical procedure.

Thus, the use of sonic and ultrasonic tips to prepare root-end cavities created more clean, centered, and conservative cavities than the rotary method. The small ultrasonic tips have also eliminated the need for steep bevel angles and for larger osteotomies in clinical practice. This is important to support rapid and successful periapical healing. Overall, the ultrasonic and sonic instruments appear to be useful tools for root-end cavity preparation, particularly in cases where a high risk of perforation exists or when limited access to the root apex is of consideration.

CONCLUSION
Based on the conditions of this study, the following conclusions can be drawn: The area of the root-end dentin surfaces after resection does not influence the crack formation during the preparation of the root-end cavity with rotary, sonic, and ultrasonic instruments. Cracks were produced at the root-end face, mainly when the smooth stainless steel ultrasonic retrotips were used Dentinal chips were found in all experimental groups with the highest rate in the rotary instrument group. Gutta-percha remnants on the cavity walls were mainly detected in teeth prepared with ultrasonic retrotips. The time needed for the preparation of the root-end cavities with the sonic and ultrasonic devices was more than double compared to that of the rotary instrument group.

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11. Saunders WP, Saunders EM, Gutmann JL. Ultrasonic root-end preparation, Part 2. Microleakage of EBA root-end filling. Int Endod J 1994;27:325-9.
12. Layton C, Marshall G, Morgan L, Baumgartner J. Evaluation of cracks associated with ultrasonic root end preparation. J Endod 1996;22:157-60.
13. Waplington M, Lumley P, Walmsley D. Incidence of root face alteration after ultrasonic retrograde cavity preparation. Oral Surg Oral Med Oral Path Oral Radiol Endod 1997;83:387-92.
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15. Loyd A, Jaunberzins A, Dummer PM, Bryant S. Root-end cavity preparation using the Micro Mega retro-prep tip. SEM analysis. Int Endod J 1996;29:295-301.
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root_end_cavity_preparation.pdf

Marouan G. Khabbaz, Mersini I. Makropoulou, Alexandros A. Serafetinides, Dimitris Papadopoulos, and Eirini Papagiakoumou

Twenty-one teeth with one root canal were prepared by the step-back technique, divided into three groups, and split longitudinally. Group A served as a control. In group B, 20 to 150 pulses of 100 μs, 30 to 70 mJ per pulse at 1 to 4 Hz from a free-running Er:YAG laser were applied to the rootcanal dentin. In group C, the Q-switched Er:YAG laser, with the same energy parameters and a 190-ns pulse duration was used. Scanning electron microscopy examination revealed that control specimens had debris and smear layer obscuring the dentinal tubules at all levels in the canals without crack formation. Both groups of laser-treated dentin were clean with opened dentinal tubules except around the lased area in which there was an intact smear layer. Cracks were observed in both laser groups with higher frequency in group C. In group B, craters with different depth levels at the root canal walls were produced and the energy apparently was distributed equally, because craters were well-shaped. In contrast, the ablation efficiency in group C was questionable with the parameters used in this study. Consequently, suitable parameters of the free-running Er:YAG laser must be found before its careful use as an adjunct in endodontic therapy.

It is well established today that cleaning and shaping of the root-canal system are essential for the successful outcome of endodontic treatment. The objectives of the cleaning procedure are to eliminate microorganisms and all tissue remnants as well as inflammatory irritants from the root-canal space. Shaping creates a suitable space that facilitates debridement, irrigation, and canal obturation. Studies have shown that chemomechanical instrumentation with different instruments, methods, and techniques is unable to totally remove the debris from the root-canal walls (1–3).

Laser treatment with Er, Cr:YSGG Er:YAG CO₂, Nd:YAG Argon and other types of irradiation has been investigated on the root-canal walls by several researchers (4–13). Although some of these results are promising, some disadvantages remain evident when lasers are applied to endodontic treatment. For example, the Nd:YAG laser has the difficulty of absorption on the surface of dentin because of its wavelength, and the CO₂ laser cannot be delivered through a suitable fiber-optic system to the root canal. The diffusion of heat into adjacent tissues is a drawback for the both of these lasers (5). Excimer laser can be transmitted via fiber optic without heating damage of dentin, but using this type of laser, especially the KrF at 248 nm, there is the possibility of making a genetic changes because of the proximity to the 260 nm DNA absorption peak (14, 21).

Because water has the strongest absorption peak for electromagnetic radiation at the wavelength of 2.94 μm, the Er:YAG laser emitting at this wavelength is a suitable instrument for ablation of dentin, which consists of 12–13.5% of water. Dentin can be removed by the Er:YAG laser by a continuous vaporization process of its water resulting to high internal pressure, which leads to microexplosions in the irradiated dentin mass. Because only a small amount of water content has to be vaporized, little energy is necessary for this ablation process (15). Experimental studies on the efficacy of the Er:YAG laser irradiation for cleaning the root-canal walls demonstrated that this type of laser is more effective in removing the smear layer than other laser type and endodontic irrigants (9), and the dentinal walls were free of debris with opened dentinal tubules (6, 7). When a root canal model was drilled into a bovine dentin block it was found that the Er:YAG laser technique can have the advantage of decreasing the preparation time (11).

The laser effects depend, among other factors, on the power setting, mode of energy delivery, type and condition of laser, and target tissue (8). Although the temperature increase during the Er:YAG laser irradiation is not significant (16), melting and fusing of the orifice of the dentinal tubules caused by 40 mJ of irradiation has been noted (11). Investigators studying the morphological changes of the root dentinal walls after their irradiation with Nd:YAG, CO₂, and Argon laser found that it was highly dependent on energy level and duration of irradiation (5). During tissue irradiation, the thermal damage may be limited when the laser intensity is high and the interaction time is short (17, 18). In this JOURNAL OF ENDODONTICS Printed in U.S.A. Copyright © 2004 by The American Association of Endodontists VOL. 30, NO. 8, AUGUST 2004 585 case, especially effective is the Q-switched mode of the laser operating with the pulse length below the thermal relaxation time of the irradiated tissue, so less thermal damage is caused to the tissue (19). However, no studies have examined the efficacy of the Q-switched Er:YAG laser on the root canal. This study was designed to evaluate the morphological changes at the root-canal walls produced by the free-running and Q-switched Er:YAG laser. In addition, the efficacy of conventional cleansing procedures and the two types of laser used, in removing debris and smear layer from the root-canal walls was studied.

MATERIALS AND METHODS Twenty-one, human permanent straight and single-rooted, freshly extracted teeth were used in this study. After extraction, the teeth were stored in phosphate-buffered saline until use. All teeth were radiographed to confirm root canal patency, the absence of complicated root-canal anatomy, and the presence of one root canal only. The crowns of the teeth were resected at the CEJ, and the working length of each root canal was established 1 mm shorter of the apical foramen. Root canals were then prepared by the step-back technique using Flexo-files (Maillefer, Switzerland) with filing motion. Apical preparation was accomplished after a file #50 had enlarged the root canal at the working length. The coronal third of the canal was prepared with Gates Glidden burs #2 and #3. The root canals were irrigated with 2 ml of 3% sodium hypochlorite solution after each file and 10 ml of the same solution at the end of the preparation. The irrigant solution was delivered with a 25-gauge needle as apically as possible without binding. The root canals were then dried with paper points, and teeth were randomly divided into three groups (A, B, and C) of seven teeth each.
Afterward the roots were grooved longitudinally with a diamond bur without penetration into the root canal and split into two halves. In group A, which served as the control, the root canal dentin was not lased. In group B, the free-running Er:YAG laser, developed in the National Technical University of Athens (NTUA), with a wavelength of 2.94 DISCUSSION
Laser irradiation on the root-canal walls for the evaluation of cleaning ability has been investigated by many researchers. Khan et al. (5) reported that the CO₂, Nd:YAG, and Argon laser produced more carbonization (thermal damage) and greater shape changes of the root canals as energy and duration of the laser treatment were increased. On the contrary, Q-switched laser application with less pulse duration than the normal spiking mode produced less thermal damage to the irradiated tissues (19). Arrastia-Jitosho et al. (13) applied the Nd:YAG Q-switched nanosecond pulsed laser on dentin and predicated that this laser cannot replace the conventional method of hand instrumentation in root canals, but it was shown that it was capable of complete removal of smear layer. Rohanizadeh et al. (20) studied the effects of the Q-switched Nd:YAG laser on dentin, enamel, bone, and cementum at different frequencies and irradiation times. They demonstrated that this type of laser can produce craters with frequency-related depths without carbonization or high-melting zones but with cracks and fractures in the irradiated tissues.

In our study, it was shown that cracks were found in the majority of surfaces that were lased with the Q-switched Er:YAG. Only the use of decreased energy, frequency, and pulse repetition rate produced acceptable shape changes of irradiated dentin. Therefore, our results taken together with those of the other previously mentioned authors (13, 20) enunciate that much work is needed to improve the parameters used with the Q-switched type of laser on dentinal root canal walls because of the creation of cracks on them. Cracks are not desirable because they can reduce the integrity of the tooth structure and the success rate of the endodontic treatment. It is believed that the crack formation as well as the reduced ablation ability of the hard dental tissue produced by the Qswitched Er:YAG laser are caused by the formation of plasma in the surface of dentin. The application of a relevant and appropriate water spray in conjunction with suitable parameters of the laser beam will prevent these problems (22).

The cleaning effect of different instrumentation techniques and irrigation solutions on the smear layer produced after the preparation of the root canal walls has been investigated by several researchers. Siqueira et al. (3) used five instrumentation techniques with copious irrigation with 5% sodium hypochlorite to evaluate their cleaning ability on the apical third of curved root canals. They found that none of the technique used totally debrided the entire root-canal system, especially when variations in the internal anatomy were present. Takeda et al. (9) used 3 ml of 5.25% sodium hypochlorite and 3% H₂O₂ alternately between each file size and final irrigation with 17% EDTA, 6% phosphoric acid, and 6% citric acid, in different teeth groups, to remove the smear layer from the prepared root canal. They demonstrated that none of the irrigation solutions used had effectively cleaned all the smear layer from the root-canal system. Mayer et al. (1) reported that ultrasonically activated irrigants (5.25% NaOCl and 17% EDTA) did not reduce debris and smear layer from rotary prepared root canal with ProFile .04 and lightspeed. Our results are similar because after the root canal preparation, using the sodium hypochlorite as irrigating solution, the root canal walls were covered with debris and smear layer. Consequently, it seems that it is very difficult to obtain clean dentinal walls in the root canal by instrumentation and irrigation only.

On the contrary, it seems that laser irradiation with different laser types (Er:YAG, Nd:YAG, Ar, and CO₂) is effective in removing debris and smear layer from the root canal walls (4–9, 12, 13). We agree with these researchers because our results indicated that it was possible to vaporize debris and smear layer from the irradiated area of the prepared root canals with the parameters used in this investigation. However, we noticed that around the irradiated area, smear layer was still existing. This SEM observation indicates that temperature increase caused by the laser beams does not diffuse from the irradiated to the nearest area, or if it does, it was not able to vaporize debris and smear layer located there. Another verification of this observation was, as the findings of Takeda et al. (7) indicated, that in specimens in which the irradiation beam did not touch the root canal walls, laser was not effective in removing debris and smear layer. Furthermore, it was demonstrated that the angle of the laser beam in relation to the target surface can be a deciding factor of how much energy will be absorbed by the dentin (4).

In this investigation, the root canals of freshly extracted teeth were prepared to a file size #50, split, and irradiated in air because an optical fiber was not used. Our results cannot be directly equated to an intact tooth or an in situ interaction; they are the nearest ones to the optimum situation when one considers the low availability of clinical endodontic fibers. Future improvements to laser fiber tips will result in suitable medium for the clinical use of the laser Er:YAG irradiation to vaporize debris and smear layer from the prepared root canal.

Supported by a grant from the secretariat of the Research Committee of the National and Kapodistrian University of Athens.

1. Mayer BE, Peters OA, Barbakow F. Effects of rotary instruments and ultrasonic irrigation on debris and smear layer scores: a scanning electron microscopic study. Int Endod J 2002;35:582–9.
2. Hulsmann M, Schade M, Schafers F. A comparative study of root canal preparation with HERO 642 and Quantec SC rotary Ni-Ti instruments. Int Endod J 2001;34:538–46.
3. Siqueira JF, Araujo MC, Garcia PF, Fraga RC, Saboia Dantas CJ. Histological evaluation of the effectiveness of five instrumentation techniques for cleaning the apical third of root canal. J Endodon 1997;23:499–502.
4. Anic I, Segovic S, Katanek D, Prskalo K, Najzar-Fleger D. Scanning electron microscopic study of dentin lased with Argon, CO₂ and Nd:YAG laser. J Endodon 1989;24:77–81.
5. Khan MA, Khan MFR, Khan MW, Wakabayashi H, Matsumoto K. Effect of laser treatment on the root canal of human teeth. Endod Dent Traumatol 1997;13:134–45.
6. Takeda FH, Harashima T, Eto JN, Kimura Y, Matsumoto K. Effect of Er:YAG laser treatment on the root canal walls of human teeth: an SEM study. Endod Dent Traumatol 1998;14:270–3.
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Laser_efficacy_on_root_canal_walls.pdf

Ioanna S. Arvaniti, DDS, MSc,* and Marouan G. Khabbaz, DDS, PhD*
Abstract Introduction: Taper is a factor that determines final root canal dimensions and, consequently, the dimensions of the space for the cleaning action of irrigants. Therefore, the aim of the present study was to investigate the influence of taper on root canal cleanliness. Methods: Root canals of 45 mandibular incisors were divided into 3 groups and prepared with GT rotary files to apical preparation size 30 and final taper 0.04, 0.06, and 0.08, respectively. Irrigation with 2.5% NaOCl was performed after each file. The final irrigation sequence was 10 mL 17% ethylenediaminetetraacetic acid, followed by 10 mL 2.5% NaOCl and 10 mL saline solution. The presence of debris and smear layer on root canal walls was evaluated under the scanning electron microscope with the use of a 4-category scale system. Results: The presence of debris was minimal in all groups. Statistical analysis for the presence of smear layer showed no significant differences between the groups, whereas a significant difference was detected between the apical and middle thirds of each group. Conclusions: Under the conditions of this study, root canal preparation with tapers 0.04, 0.06, or 0.08 did not affect canal cleanliness. Debris removal was almost complete for all tapers, whereas smear layer was not removed, especially from the apical part of the canals. (J Endod 2011;37:871–874)
Key Words Debris, EDTA, root canal preparation, root canal taper, rotary NiTi instruments, smear layer
After its mechanical preparation, root canal is a space where the irrigation fluids are placed to express their cleaning action. The dimensions of this space determine the irrigants’ volume and, consequently, their efficacy. In 1965, Wandelt(1)stated that only a small and ineffective volume of a chelator can be placed in narrow root canals. In a recent study, Brunson et al (2) confirmed Wandelt’s statement, showing that an increase in root canal dimensions leads to an increase in the mean volume of irrigant inside the canal. The clinician has the ability to alter root canal dimensions by changing the final apical preparation size and/or its taper.
In the era of ISO manufactured endodontic instruments, keeping the apical preparation as wide as possible was believed to be the only way for the irrigation fluids to reach and reduce the microbial population from the critical apical 3 mm of the root canal, thus increasing its cleanliness (3–7). Today, the manufacturers of nickeltitanium rotary systems believe that apical preparation should be kept as narrow as possible while increasing root canal taper. This decreases the preparation errors and makes root canal obturation easier and more efficient, but it also creates a greater deposit for the irrigation fluids and at the same time leads to cutting a larger amount of dentin from the canal walls, thus producing a cleaner root canal (8). Although this hypothesis seems reasonable, it has little scientific evidence; it is not yet proven whether an increase in taper leads to cleaner root canals. In a recent study, Brunson et al (2) showed that the increase in apical preparation size and taper leads to an increase in mean irrigant volume inside the canal. However, these investigators did not study the effect of increased irrigant volume on root canal cleanliness. Therefore, the purpose of the present study was to investigate the influence of taper on root canal cleanliness, which was assessed by the presence of debris and smear layer in the middle and apical thirds of canals prepared with 3 different tapers. The null hypothesis was that the increase in taper does not affect root canal cleanliness.
Materials and Methods Forty-five freshly-extracted mandibular incisors stored in 10% formalin were used for this study. Before preparation, all teeth were radiographed in buccolingual direction to ensure they had 1 straight root canal. The teeth were cut perpendicularly to their long axis by using a diamond disk 10 mm from the root tip. Patency of the root canals was ensured by using #10 K-file (Dentsply/Maillefer, Ballaigues, Switzerland). Finally, a small amount of Carbowax (Dow Chemical Co, Midland, MI) was placed on each root tip.
The roots were randomly divided into 3 experimental groups (n = 15). Root canal instrumentation was performed with GT rotary files Series 20 and 30 (Dentsply/Maillefer), placed in the handpiece of an Endo IT motor (Aseptico, Woodinville, WA) with programmed torque control and speed settings. Different protocols were used in a way that final root canal taper was 0.04, 0.06, and 0.08 for groups A, B, and C, respectively. Working length was 9 mm. The instrumentation details were as follows.
In group A (taper 0.04), GT files Series 30 were used in a crown-down manner. Files 30/0.10, 30/0.08, and 30/0.06 were placed 2, 5, and 7 mm inside the canal, respectively, and file 30/0.04 at working length. In g roup B (taper 0.06), root canals were instrumented as in group A, and at the end of preparation, files 20/0.08 and 30/ 0.06 were placed at working length. In g roup C (taper 0.08), root canals were instrumented as in group B, and at the end of preparation, files 20/0.10 and 30/0.08 were placed at working length.Between every file change, patency at working length was confirmed by using #10 K-file, and the canals were irrigated with 2.5% NaOCl. Irrigation was performed with a 27-gauge blind-ended endodontic irrigation needle (Hawe Max-I-probe; Kerr-Hawe, Bioggio, Switzerland). The volume of irrigant flushed after each file was 3 mL for group A, 2 mL for group B, and 1.5 mL for group C. The final irrigation sequence was 10 mL of 17% EDTA (Vista Dental Products, Racine, WI) for 3 minutes, followed by 10 mL of 2.5% NaOCl and 10 mL saline solution. The total amount of irrigants used in each canal was 42 mL.
After instrumentation the roots were split longitudinally with a diamond disk in a buccolingual direction. The presence of debris and smear layer was evaluated by scanning electron microscopy at 255x and 1000x magnification, respectively. A 4-category scale system was used for debris and smear layer as follows: score 1, presence of debris/smear layer that covers 0%–25% of the surface examined; score 2, presence of debris/smear layer that covers 25%–50% of the surface examined; score 3, presence of debris/smear layer that covers 50%– 75% of the surface examined; and score 4, presence of debris/smear layer that covers 75%–100% of the surface examined.
Representative photos of each score taken in a pilot study were given to the examiners before scoring (Fig. 1).
The scoring procedure was performed by 3 examiners and was double-blinded. First, the apical end of preparation was found at low magnification, and then every millimeter of the apical (0–3 mm) and middle (4–6 mm) thirds of the root canal wall was scanned at 255x and 1000x magnification and scored.
Statistical analysis with the nonparametric Kruskal-Wallis test was performed to detect any statistical differences in the presence of debris and smear layer between the 3 groups. In addition, the nonparametric Friedman test was used to assess the differences between the apical and middle thirds of the root canals of each group. The level of significance was set at P ≤ .05.
Results Debris The presence of debris in the apical and middle thirds of the root canals was found to be minimal, with a mean score of 1.1 for all groups. For this reason, debris was excluded from the statistical analysis.
Smear Layer Mean scores for the presence of smear layer in groups A, B, and C are shown in Table 1. No statistically significant differences could be found between the groups. However, a statistically significant difference between the apical and the middle thirds was detected in all groups, with the former showing the worst results (Table 2).
Discussion The objective of the present study was to evaluate the influence of taper on root canal cleanliness. To achieve this, the canals studied should have the same apical preparation size but different tapers. Therefore, the experimental protocol for the use of System GT files was designed in a way that at the end of preparation, the apical and middle thirds of the canals had a constant taper of 0.04, 0.06, or 0.08 mm/mm. In all groups, the last GT file gave its taper to the middle and apical thirds of the canals, because its flute diameters were greater than those of the former file placed at working length.
Irrigation was another factor that was controlled, because it affects root canal cleanliness. The total volume of irrigants in each tooth was 42 mL. Because the number of instrument changes differed between groups, this was achieved by flushing a different volume of irrigant after every instrument in each group. In this way, the only variable was the frequency of irrigation. However, the influence of this factor on root canal cleanliness has not yet been studied thoroughly. A pertinent study showed that the number of instrument changes and, consequently, the frequency of irrigation did not contribute to the efficacy of debridement (9).
The first finding of our study was that root canal taper did not affect its debridement. This result can be compared with those of some previous studies. Lee et al (10) and van der Sluis et al (11) prepared root canals with GT files Series 20 and studied the influence of root canal taper on debris removal. According to their results, the increase in taper led to better debridement. Albrecht et al (12) reported that when canals were prepared with GT files size 20, the increase in taper led to better debridement, whereas when the apical preparation size was 40, taper had no influence on debris removal. It was concluded that root canal debridement is mainly affected by final instrument size and to a lesser extent by canal taper. The influence of final instrument size on root canal cleanliness was also studied by Usman et al(9), who reported that root canal instrumentation with GT file 40/0.06 led to significantly better debris removal than with GT file 20/0.06. In our study, root canals were prepared with GT files size 30, and no statistically significant differences were found between groups of different taper. If this result is combined with the above findings, we could conclude that root canal taper can affect its debridement only when final instrument size is smaller than 30. However, this conclusion needs further investigation.
Our second finding was that root canal taper did not influence smear layer removal. This result cannot be confirmed, because studies regarding the influence of taper on root canal cleanliness do not deal with smear layer removal (9–12). Our study was based on early findings by Wandelt (1), according to which the effectiveness of a chelator is very much dependent on root canal’s width. We made the hypothesis that the increase in taper would lead to an increase in the volume of the chelator, making it more effective in smear layer removal. Although this was not confirmed by our findings, it is an issue that requires further investigation.
In each group, a statistically significant difference in the presence of smear layer was found between the apical and middle thirds of the canals. This is in accordance with the results of most studies regarding smear layer removal (13–18). This finding seems reasonable, because the apical is the narrowest part of the canals.
To further study the dimensions of this narrowest part, we considered that after their mechanical preparation, the apical third of the canals was a truncated cone, which for all groups had a standard height of 3 mm and a small base diameter of 0.30 mm (the same as the tip diameter of a GT file Series 30), but it differed in its large base diameter, which was 0.42, 0.48, and 0.54 mm for tapers 0.04 mm/mm, 0.06 mm/ mm, and 0.08 mm/mm, respectively. According to the formulas for the calculation of the surface area and the volume of the truncated cone, the apical dentin surface was 3.4 mm2 for group A, 3.7 mm2 for group B, and 4 mm2 for group C, whereas the volume of the apical third was 0.0003, 0.00037, and 0.00041 mL for groups A, B, and C, respectively. However, according to early findings by Fraser (19), 2 mL of ethylenediaminetetraacetic acid is needed to decalcify a dentinal surface area as small as 0.35 mm2 . Consequently, the volume-to-surface ratio in our study was extremely low for the chelator to be effective in smear layer removal.
Finally, root canal cleanliness can also be assessed by the presence of bacteria after chemomechanical preparation. Because an increase in taper leads to cutting a greater amount of dentin from the canal walls, it would be interesting to repeat the present study to investigate the influence of taper on root canal’s bacteriologic population before and after chemomechanical preparation.Conclusions
Under the conditions of the present study, root canal preparation to apical size 30 and tapers 0.04, 0.06, or 0.08 did not affect canal cleanliness. The removal of debris was almost complete for all tapers, whereas smear layer was not completely removed in any of the groups, with no statistically significant differences between them (P> .05). In all groups, the middle third was the cleanest part of the canal, with a statistically significant difference from the apical third (P ≤ .05).

Acknowledgments
This article was adapted from a thesis submitted by Dr Ioanna S. Arvaniti in partial fulfillment of the requirements for the MS degree in Endodontics at University of Athens School of Dentistry.

We acknowledge Dr Konstantinos Kalogeropoulos for his assistance in scoring the root canals under the SEM.

The authors deny any conflicts of interest related to this study.

References
1. Wandelt S. Kann man enge Wurzelkan€ale mit Komplexbildern chemisch erweitern? Experimentelle Untersuchungen und klinische Erfahrungen. Deutsche Zahn€arztliche Zeitschrift 1965;20:621–6.
2. Brunson M, Heilborn C, Johnson J, Cohenca N. Effect of apical preparation size and preparation taper on irrigant volume delivered by using negative pressure irrigation system. J Endod 2010;36:721–3.
3. Nair P, Sj€ogren U, Krey G, Kahnberg K, Sundqvist G. Intraradicular bacteria and fungi in root-filled asymptomatic human teeth with therapy resistant periapical lesions: a long-term light and electron microscopic follow up study. J Endod 1990;16:580–8.
4. Orstavik D, Kerekes K, Molven O. Effects of extensive apical reaming and calcium hydroxide dressing on bacterial infection during treatment of apical periodontitis: a pilot study. Int Endod J 1991;24:1–7.
5. Simon JH. The apex: how critical is it? Gen Dent 1994;42:330–4. 6. Wu MK, Wesselink PR. Efficacy of three techniques in cleaning the apical part of curved root canals. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1995;79: 492–6.
7. Siqueira J, Araujo M, Garcia P, Fraga R, Saboia Dantas C. Histological evaluation of the effectiveness of five instrumentation techniques for cleaning the apical third of the root canals. J Endod 1997;23:499–502.8. Buchanan LS. The standardized-taper root canal preparation: part 1—concepts for variably tapered shaping instruments. Int Endod J 2000;33:516–29.
9. Usman N, Baumgartner JC, Marshall JG. Influence of instrument size on root canal debridement. J Endod 2004;30:110–2.
10. Lee SJ, Wu MK, Wesselink PR. The efficacy of ultrasonic irrigation to remove artificially placed debris from different-sized simulated plastic root canals. Int Endod J 2004;37:607–12.
11. Van der Sluis LWM, Wu MK, Wesselink PR. The efficacy of ultrasonic irrigation to remove artificially placed dentine debris from human root canals prepared using instruments of varying taper. Int Endod J 2005;38:764–8.
12. Albrecht LJ, Baumgartner JC, Marshal JG. Evaluation of apical debris removal using various sizes and tapers of ProFile GT files. J Endod 2004;30:425–8.
13. Baker N, Eleazer P, Averbach R, Seltzer S. Scanning electron microscopic study of the efficacy of various irrigating solutions. J Endod 1975;1:127–35.
14. Mc Comb D, Smith D. A preliminary scanning electron microscopic study of root canals after endodontic procedures. J Endod 1975;1:238–42.
15. Ciucchi B, Khettabi M, Holz J. The effectiveness of different endodontic irrigation procedures on the removal of the smear layer: a scanning electron microscopic study. Int Endod J 1989;22:21–8.
16. Aktener B, Bilkay U. Smear layer removal with different concentrations of EDTAethylenediamine mixtures. J Endod 1993;19:228–31.
17. Scelza M, Antoniazzi J, Scelza P. Efficacy of final irrigation: a scanning electron microscopic evaluation. J Endod 2000;26:355–8.
18. O’Connell M, Morgan L, Beeler W, Baumgartner C. A comparative study of smear layer removal using different salts of EDTA. J Endod 2000;26: 739–43.
19. Fraser JG. Chelating agents: their softening effect on root canal dentin. Oral Surg Oral Med Oral Pathol 1974;37:803–11.
Root_Canal_Taper.pdf

Postablative surface characteristics (degree of charring, cracks and other surface deformation) were evaluated using light microscopy
(KAPS D 35614) and scanning electron microscopy (SEM; JEOL JSM 6100).
The SEM images presented in this paper correspond to the following laser parameters. For the fundamental wavelength Nd:YAG
laser pulses the laser energy was 57 mJ and the spot size 0.985 mm², resulting in an energy fluence of 5.786 J/cm². For the first harmonic
Nd:YAG laser pulses the laser energy was 28.1 mJ and the spot size 0.882 mm², resulting in an energy fluence of 3.186 J/cm².

RESULTS
Quantitative Evaluation
For quantitative evaluation of the ablational behaviour of the picosecond laser sources used in this work, dentine ablation rates versus
laser energy fluence were plotted.

The small number of dental samples irradiated for each fluence and the fact that the irradiated areas of the dental sections are not
identical (root and crown), do not allow us to add statistically significant error bars to the figures. Despite this, the maximum possible
error in our energy fluence measurements is estimated to be in the order of ±10%. Another source of variation in ablation rate reproducibility is the great inhomogeneity within individual samples and between different samples (e.g. differences in tissue density, microstructure, water content, regional thickness, mechanical strength).

Results show that the ablation rate of the infrared Nd:YAG laser pulses was low (Fig. 2), whereas the ablation rate of the visible picosecond laser pulses increases rapidly and it can be fitted with a sigmoidal fitting curve as shown in Fig. 3.

Qualitative Evaluation
Macroscopic Observations
No charring was observed with either of the wo laser wavelengths at any of the pulse energies tested.SEM Observations
The surface morphology images of the interaction of the Nd:YAG laser with dentine are shown in Figs 4–6. It is obvious from these figures that the surfaces of irradiated dentine are very clean without any smear layer andwith opened tubules. Figure 4 shows a view of a conical-shaped crater with irregular edges. 

This irregularity probably reflects tissue inhomogeneities, in combination with reduced laser beam intensity in the periphery of the spot area. No cracks are detected. A detail from the sample of Fig. 4, with greater magnification, is shown in Fig. 5. The irregular edges are obvious.

Melted materials are observed away from the edge (right upper corner of the image), and dentine tubules are opened near to the border of the crater. Also a smear layer is not detected in contact with the edge of the crater. Small grained dentine in the border of the crater with some dentine chips is presented in Fig. 6. The surface morphology images of the interaction of the first harmonic Nd:YAG laser with dentine are shown in Figs 7–9. The surfaces of irradiated dentine are melted and the tubules are sealed off. Cracks are observed. Figure 7 shows a view of a crater surrounded by irregular and rough edges; intensive cracking is evident. Dentine surrounding the crater is coated with a smear layer.

Figure 8 shows normal and irradiated dentine. Normal dentine is totally coated with a smear layer. This is evidence of the absence of thermal damage to surrounding tissues. The surface of irradiated dentine is composed of granular melted material spread uniformly throughout the surface. The edge of the crater is extremely sharp.

A magnification of the irradiated area, which is composed of finer beads of melted material, is illustrated in Fig. 9. There is selective ablation of intertubular dentine and the tubules are sealed off with fused and grained dentine.
DISCUSSION
It is well established that cleaning and shaping of the root canal system is an essential objective for the success of endodontic therapy. The
aim of this procedure is to eliminate all tissue remnants as well as bacteria from the root canal system. Shaping creates smooth wall surfaces of root canals and suitably shaped space that facilitates filling [12].
In a previous study we found that dentine ablation rates with near-infrared and visible picosecond laser pulses are comparable to or better than those of the excimer nanosecond lasers [11], but approximately one order of magnitude less e$cient than those of the mid-infrared HF laser [6].
Comparing the cutting efficiency of the Nd:YAG and the first harmonic Nd:YAG laser in this study, we observed that the latter creates a crater of 2 m in dentine with an energy fluence of 0.6 J/cm² (Fig. 3) whereas the Nd:YAG laser needs a higher fluence of 4.5 J/cm² to create the same crater depth (Fig. 2).
Despite the higher energy level needed for the ablation of dentine with the Nd:YAG laser, this ablation seems to create no other mechanical or thermal damage in this hard dental tissue, as revealed by SEM examinations of specimens. This result provides evidence that the ablation of hard dental tissue does not depend entirely on the energy level of the laser used; other parameters need to be considered, such as the laser wavelength and the optomechanical properties of the tissue. 
Macroscopic inspection of the ablation crater showed smooth surfaces, free of thermal damage, for both laser wavelengths used.
Detailed examination of SEM images showing the interaction of the picosecond Nd:YAG laser (λ=1064 nm) with dentine showed a  homogeneous surface with very small grains and a small increase in tubule diameter which means very little rise in the temperature of the
dentine surface with a very small degree of melting. Willms et al. [13] investigated the suitability of picosecond Nd:YLF laser, emitting at a wavelength of 1053 nm, for dentine ablation and also reported no thermal or mechanical damage.
Correlation of the pulse duration with the cutting quality of the near-infrared laser radiation requires comparison of our results with the results obtained by other researchers with longer laser pulses. Neev et al. [14] investigated the ablation e$ciency, thermal damage and surface  characteristics of dentine irradiated by the Nd:YAG laser with a pulse duration of 15 ns and found that the surface of the dentine had a glazed appearance with crack formation when an 80 mJ/pulse at 10 Hz pulse repetition rate was used. Ragot-Roy et al. [15] using the Nd:YAG laser, but with a pulse duration of 65 s, found that laser irradiation of root canal dentine surfaces induces a nonhomogeneously modified dentine layer, where melted and resolidified dentine partially closes the dentine tubules.
In an attempt to explain the basic mechanisms of ultrashort laser ablation of hard tissues, we have considered the following. The Nd:YAG laser operates at a wavelength of 1064 nm. This wavelength corresponds to an energy per single photon emission of only 1.18 eV, which is not enough to ionise tissue molecules and to break molecular bonds. Multiphoton absorption is suppressed because of the low absorption coe$cient of the tooth tissue at this wavelength (the range of 300–1300 nm is a range of low absorption for enamel and dentine [7]). However, the absorption can be enhanced and a multiphoton process can be initiated in so-called ‘plasma-mediated ablation’ [9]. Due to the high power densities per pulse (>1012 W/cm²), a multiphoton process can take place, providing initial electrons for the optical breakdown. The strong field in the laser beam focus (>106 V/cm), leads to an avalanche-like multiplication of electrons. The generated plasma is further heated by inverse
bremsstrahlung resulting in an enhanced shielding of the tissue sample. As the absorption of successive laser pulses is strongly enhanced by the plasma, interaction effects are mainly localised at the surface of the target [10]. The rapid expansion of this plasma generates an acoustic shock wave which finally enables ablation of the tissue. Therefore, in contrast to longer pulse duration, picosecond pulses at near-infrared laser wavelengths ablate tissues with no signs of thermal damage, as heat diffusion into the tissue is negligible and the energy loss into the target is minimised [10,13]. 

The interaction of visible ultrashort pulsed laser radiation with dentine was also investigated, in our study, by using the first harmonic of the Nd:YAG laser. 

As shown in Fig. 1, the first harmonic of the Nd:YAG laser in our system is produced by passing an Nd:YAG incident beam of 1064 nm through an integral BBO harmonic generator to produce an intense visible green laser light of 532 nm, with a pulse width of 100 ps. This wavelength enhances the energy absorption of blood-perfused tissues and avoids the requirement of a separate visible aiming beam [15].

In our study, ablation of dentine by the first harmonic Nd:YAG was associated with intensive cracks and melting while dentine tubules were closed. The melting of dentine demonstrates that in conjunction with the primary photomechanical mechanism secondary thermal effects are also observed. The sigmoid nature of the ablative response with increasing energy density and the conical nature of the craters produced is a result of increased laser beam absorption in the plume of ablation produced at higher fluences [16]. Tewfik et al. [17] reported on the  structural and functional changes in root dentine following exposure to KTP/532 laser, with laser energy per pulse of 1–2 J and pulse lengths of 0.2–1 s. They also found loss of the smear layer, smear plugs, and peritubular dentine, thus increasing the tubular diameter, after 10 pulses with approximately 1 min between pulses to allow for temperature dissipation. Machida et al. [18] irradiated dentine samples with di#erent laser power parameters, but with the same total laser energy, 6 J, by using the KTP:YAG laser at λ=532 nm. They reported no significant
microstructural changes of dentine when the total laser energy of 6 J was delivered with 1 W6 s, repeated five times and with 2 W3 s, repeated five times. However, after irradiation with 3 W2 s, repeated five times, SEM examination demonstrated successful removal of smear layer and debris with a few localised patches of melting. The comparison of the surface morphology of visible and near-infrared laser ablated craters in dentine indicate that di#erent ablation mechanisms are involved. In both cases, efficient ablation was observed only in the presence of plasma. However, the ablation mechanism in the case of the fundamental wavelength Nd:YAG laser could be better described as ‘plasma-mediated ablation’, whereas in the case of the first harmonic Nd:YAG laser the observed mechanical disruption indicates that the relevant mechanism could be better characterised as ‘photodisruption’. According to Niemz [10], if the ionising effect of plasma contributes more to the ablation process than the generated acoustic shock wave, the mechanism is called ‘plasma-mediated ablation’. If mechanical disruption is induced as a primary result of acoustic shock waves, the mechanism is characterised as ‘photodisruption’.

CONCLUSIONS
The macroscopic inspection of the ablated dentine in the present study shows smooth surfaces, free of thermal damage. SEM examination in the case of Nd:YAG laser, demonstrated successful ablation of dentine and removal of smear layer and debris with opened orifices. These successful properties achieved using this technique should significantly improve root canal preparation and seal and tooth longevity in a clinical situation. In contrast, the use of the first harmonic Nd:YAG laser provided an irregular surface of dentine and cracks. Consequently, it seems that the cleaning and shaping of the root canal with the application of the picosecond Nd:YAG laser may be possible and research needs to be continued.

Dentine ablation measurements with nearinfrared and visible picosecond laser pulses showed a relatively good effciency. In all systems, efficient ablation was observed only in the presence of plasma. A ‘plasma-mediated ablation’ mechanism was considered for the dentine ablation with 1064 nm laser pulses, whereas the ‘photodisruption’ process was involved mainly in the dentine irradiation with 532 nm laser pulses.

Despite the relatively slow laser efficiency for the dentine ablation rates, ultrashort-pulse laser ablation of hard dental tissues is opening up a previously unexplored field which is expected to impact on laser processing in dentistry. These investigations can exhibit new insights related to the versatility of laser surface processing in general.

ACKNOWLEDGEMENTS
The authors would like to thank the members of the Non-Linear Optics Group of the Heriot-Watt University for their help in carrying out the ablation experiments.

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Eirini Papagiakoumoua, Dimitrios N. Papadopoulos, Marouan G. Khabbazb, Mersini I. Makropoulou, Alexander A. Serafetinides
AbstractLaser based dental treatment is attractive to many researchers. Lasers in the 3 mm region, as the Er:YAG, are suitable especially for endodontic applications. In this study a pulsed free-running and Q-switched laser was used for the ablation experiments of root canal dentine. The laser beam was either directly focused on the dental tissue or delivered to it through an infrared fiber. For different spatial beam distributions, energies, number of pulses and both laser operations the quality characteristics (crater’s shape formation, ablation efficiency and surface characteristics modification) were evaluated using scanning electron microscopy (SEM).
The craters produced, generally, reflect the relevant beam profile. Inhomogeneous spatial beam profiles and short pulse duration result in cracks formation and lower tissue removal efficiency, while longer pulse durations cause hard dentine fusion. Any beam profile modification, due to laser characteristics variations and the specific delivering system properties, is directly reflected in the ablation crater shape and the tissue removal efficiency. Therefore, the laser parameters, as fluence, pulse repetition rate and number of pulses, have to be carefully adjusted in relation to the desirable result.
1. Introduction The use of lasers in dentistry was considered in the early days of medical lasers [1], as they can provide a number of clinical benefits that the conventional highspeed turbine lacks, such as pain-reduced cavity preparation, accurate and precision work and microsurgical operations.
During the last few years there is a great interest in laser treatment on the root canal dentin. Shaping of the surface of the root canal is essential for the successful outcome of the endodontic treatment. Various studies have shown that chemomechanical instrumentation, with different methods and techniques, was unable to remove totally the debris from the root canal walls [2–4].
Several laser sources have been used for dental applications, such as CO2, hydrogen-fluoride (HF) chemical laser, Er:YSSG, Er, Cr:YSSG, and Er:YAG [5,6]. To minimize the chances for thermal diffusion, during the photothermal ablation process, the laser absorption depth should be limited to the thinnest layer near the surface. The most important factors in limiting the conduction of heat from the laser exposure site to the adjoining material are: (i) the depth of energy deposition, (ii) the thermal diffusion and (iii) the change of state (i.e. vaporization). The depth of energy deposition varies with wavelength and defines the limit for minimizing thermal diffusion. If the basic absorber is water, the absorption depth is smaller for wavelengths in the mid-infrared region, where water presents maximum absorption [7]. As far as the dental hard tissue is concerned, its two other main constituents, namely, hydroxyapatite and collagen, have also absorption peaks in the 3.0 mm region [8,9]. The thermal diffusion, on the other hand, is associated with the thermal relaxation time of the material involved and the exposure duration to laser radiation. To avoid though thermal denaturation of the adjacent tissues to the laser exposed ones, high power pulses, with pulse width shorter than the thermal relaxation time, are needed [5]. But as the tissue removal per pulse is very small, high repetition rates are desirable in order to create a considerable tissue removal rate. Tissue ablation studies with picosecond and sub-picosecond laser pulses have been recently performed, providing interesting results [10–12]. These systems, emitting at wavelengths far from the main absorption peak of the water, ablate dental tissue with different mechanisms to the mid-infrared ones. Furthermore, in the majority of the cases, such systems remain rather costly for clinical use. Therefore, shorter pulses in the 3.0 mm region, at high repetition rates, are of primary importance [13]. Thus, TEA HF and Q-switched Er:YAG lasers are suitable as they can produce shorter pulses (of the order of 100 ns) than the tissue thermal relaxation time (of the order of 1 ms).
Q-switched Er:YAG laser producing 2.94 mm emission wavelength, short pulses, high power per pulse, high repetition rate, uniform reproducible beam seems to be the most advantageous, in terms of efficiency, pulse duration and spatial beam quality. Moreover, transmission of the 3.0 mm wavelength beams through flexible waveguides and fibers that is necessary for the application of lasers in dental treatments, is these days possible [14,15]. Especially as far as the transmission of the Er:YAG laser radiation is concerned, many studies have been made and several materials, appropriate for use in a clinical environment, have been tested in order to achieve low attenuation values, high power and short duration laser pulses delivery [16]. However, the transmission of laser radiation through waveguides and fibers induces changes in the temporal and mainly in the spatial beam profile. Therefore, it is very interesting to study how any alteration of the laser parameters (pulse duration, repetition rate, beam energy and spatial distribution of the beam profile) affects the cutting and ablating operations. It is expected that the result in the crater’s shape, depth and morphology is characteristic for the combination of these parameters. Especially, the laser beam quality delivered to the biological tissue may affect the crater, influencing both its shape and morphology [17,18]. The Er:YAG laser can produce a high quality beam in comparison to the HF and the CO2 laser, which are the other possible laser candidates for such applications.
The aim of this work was to investigate the influence of the Er:YAG laser beam spatial distribution in the ablation craters profile, by studying the photographic records obtained with scanning electron microscopy (SEM). The role of the mid-infrared laser pulse width was also studied and, therefore, Qswitched and free-running Er:YAG laser pulses were used, of different energies and repetition rates, delivered to the tissue either through the air or through a fiber.
2. Materials and methods 2.1. Laser sources A pulsed Er:YAG laser, emitting at 2.94 mm, in the Q-switched or free-running mode, was used, developed in our laboratory (N.T.U.A.). The laser rod was a Kigre Er:YAG rod, with dimensions 5 mm 150 mm. A laser cavity of 70 cm length was formed by an AR/75% for 2.94 mm flat/flat output coupler and a high reflector for 2.94 mm flat/flat. A Kigre K537 E. Papagiakoumou et al. / Applied Surface Science 233 (2004) 234–243 235 linear flash lamp filled with Xe (1500 Torr/5.5 in— 1850 V/56.5 J) was used to pump the crystal. In the free lasing mode, the maximum possible output energy was around 500 mJ with a pulse width of 80 ms at FWHM (full width at half maximum). The vertical and horizontal beam divergence was equal to 0.7 mrad and the maximum possible repetition rate with the available power supply was 10 Hz. By adding an frustrated total internal reflection (FTIR) prism modulator between the crystal and the output coupler inside the cavity, single Q-switched pulses were produced. The maximum possible output energy was around 80 mJ with a pulse width of 190 ns at FWHM. The beam divergence and the maximum possible repetition rate were the same as in the free lasing operation.
2.2. Sample preparation Several single rooted human teeth were used in this study. All teeth were radiographed to confirm the absence of complicated root canal anatomy and the presence of one root canal only. The crowns of the teeth were resected and root canals were measured, cleaned and shaped by the step-back preparation technique using the Flexofile (Maillefer, Switzerland) with filing motion. A 3% sodium hypochlorite solution was used as irrigant. Root canals were then dried with paper points.
Teeth were randomly divided in three groups (A, B and C). The roots were grooved longitudinally with diamond bur without penetration into the root canal and split into two halves. Teeth of group A were irradiated with Q-switched Er:YAG laser pulses of 190 ns pulse duration. Experiments were realized with different spatial distributions at several pulse energies, and thus several fluences, and the results were observed and evaluated in SEM images.
Free-running Er:YAG laser pulses of 80 ms pulse duration were applied to the root canal walls of dental samples of group B. The influence of several pulse energies and complicated spatial distributions of the beam profile, produced from different values of the pulse repetition rate was tested. The results are illustrated in SEM images.
Teeth of group C were irradiated with both Qswitched and free-running laser beams, delivered to the ablation area through sapphire optical fibers.
2.3. Er:YAG laser ablation Sequences of different fluences, in each Er:YAG laser operation, were applied to dental sample groups. In group A, the Q-switched Er:YAG laser was used, with pulse repetition rate of 1–4 Hz, energy 8–70 mJ/ pulse. Teeth were irradiated with 10–200 pulses of 190 ns duration. In group B, the free-running laser was used, with pulse repetition rate of 1–4 Hz, energy 6– 70 mJ/pulse. Teeth were irradiated with 20–200 pulses of 80 ms duration. For the irradiation of samples of group C, laser parameters in the same range with groups A and B were used. The laser beam was delivered to the tissue through 425 mm core diameter sapphire fibers of 25 cm length, with effective NA 0.1 and attenuation values of 2 dB/m. The evaluation of this kind of fibers and their performance details have been reported elsewhere [19]. Transmission rates of 88% were measured.
The laser beam was focused on the sample by means of a focusing lens (f ¼ 15:0 cm). Whenever the fiber was used, the beam was focused through a 300 mm diameter pinhole fixed in the focal plane, in order to achieve a nearly TEM00-like input beam. The fiber was aligned in contact to the pinhole and the tooth was placed very close or in contact to the fiber’s end. The laser energy was measured using calibrated laser pyroelectric detectors (model ED-200, Gen Tec). Images of the respective laser beam spatial profiles were acquired using a Pyrocam I pyroelectric array (from Spiricon) connected to a PC laser beam analyzer. During the laser irradiation, the root canal was kept constantly wet with saline solution irrigation (3 ml/min) to avoid dehydration of the tissue. After the laser irradiation all teeth were prepared for scanning electron microscopy (SEM) examination, for the evaluation of the ablation crater morphology.
3. Results 3.1. Q-switched Er:YAG laser Samples irradiated with TEM00 mode profile Qswitched laser beam showed the formation of round well-shaped craters, with dentinal tubules opened at the crater edge. Cracks were clearly observed during the SEM examination in the majority of the samples.
​​​​​​​In all teeth used no carbonization or extended melting zones were observed. The ablation started at a fluence value of 2.3 J/cm² . At higher pulse fluences the ablation rates increased quickly quasi-logarithmically while plasma formation was macroscopically observed accompanied by abrupt saturation of the ablation rates for energy fluence more than 10 J/cm² .

In Figs. 1 and 2, SEM images of samples irradiated with beam of irregular spatial energy distribution (TEM01 and TEM03 mode profile beam, respectively), are presented. The spatial beam distribution changes, from the one of Fig. 1 to that of Fig. 2, due to the higher repetition rate, while the energy remains almost the same (50 and 40 mJ/pulse, respectively). In these images, as we can see, the crater shape represents more or less, depending on the energy and the number of pulses, the beam profile. More efficient tissue ablation has occurred by the main lobes of the beam. Dentinal tubules were clear without any obscurity from fused dentine. However, cracks were observed in most of the samples even for lower energies (3.5 40 mJ/pulse).

At this point we should notice that when a higher order multimode beam profile was used the degree of delineation was strongly depended on the applied energy. For a multimode profile the definition of an overall fluence based on the ratio of total energy to total area, although retains its practical meaning, becomes inaccurate. Different parts of multimode beams may show ‘‘local’’ fluences with great difference between them. Thus, above a certain energy level, related to the specific spatial distribution of the beam, it is possible that most parts of the beam exceed the saturation fluence threshold (due to plasma shielding) exhibiting, therefore, similar ablation results. In this way, even high multimode beams may produce smoothed crater’s shape. In case of lower energy, so that the fluences of the different parts of the beam are not in the saturation area, their partial ablation efficiency per pulse follows a quick quasilogarithmic rise. This results in the characteristic delineation of the beam profile on the tissue. The above effect is clearly presented in Fig. 2, where in the first case (Fig. 2a) smoothing of the tissue surface is observed from a multimode beam of 70 mJ/pulse energy, while Fig. 2b shows strong delineation of the same beam profile but for 40 mJ/pulse energy.

Measurements with samples of croup C have been made by transmitting the Q-switched Er:YAG laser radiation through a sapphire fiber of 425 mm core diameter and 25 cm length. The output beam exhibited a strongly spiking, highly multimode, profile. At these fiber experiments we did not sprinkle the root canal as the tooth was placed too close or in contact to the fiber. This procedure caused deep cracks on the tissue when a large number of pulses were applied.
Fig. 3a shows an example, where the ablation crater is the result of 200 pulses with 10 mJ energy each and the pulse repetition rate set to 1 Hz. In this case the tooth were placed at 2 mm distance from the fiber output end. No plasma formation was macroscopically observed during the irradiation. All the energy was absorbed from the tissue and considerable material removal happened, while deep cracks were produced. On the contrary, when the tooth was placed in contact to the fiber output end, with the same laser parameters, plasma was created in the fiber-tissue interface. A minimal tissue removal has occurred and no cracks were observed when a small number of pulses was used. An example of this case is shown in Fig. 3b, where the tissue was irradiated with 100 pulses but no sufficient tissue material was removed.
3.2. Free-running Er:YAG laser
For the comparison of the root canal ablation results with laser pulses of the same wavelength but different pulse duration, experiments were performed with freerunning Er:YAG laser. When a TEM00 laser beam profile was applied on the tissue well-shaped craters were formed. The ablation started at a fluence value of 3.5 J/cm² . At higher pulse fluences the behavior of the ablation rates was the same as in the case of the Qswitched laser. A quick increment was observed and abrupt saturation of the ablation rates with increasing fluence more than 6 J/cm² was noticed. In Figs. 4 and 5, samples irradiated with free-running Er:YAG laser are presented. Obscured dentinal tubules at all levels of the crater’s wall led to a periodical rippled structure on the tissue surface. This ripple formation was present in all the samples irradiated with free running laser pulses. Small cracks were also observed only in few samples, when energies from 50-70 mJ/pulse or large number of pulses (over 150) were used (Fig. 5).
Once more, as happened also when the Q-switched laser was employed, the degree of delineation was depended on the energy level. When low energy (20 mJ/pulse) was applied the crater’s shape resembled that of the beam profile (Fig. 5a). By increasing the energy (70 mJ/pulse) the abnormalities, caused by the odd profile, became smoother (Fig. 5b).
Finally, experiments with transmission of the free-running Er:YAG laser radiation through the 425 mm core diameter sapphire fiber, have been performed, resulting to the same spiking character of the crater’s shape, as in the case of the Q-switched Er:YAG laser.
4. Discussion The main objective of this study was to evaluate the influence of the Q-switched Er:YAG (190 ns duration) spatial beam energy distribution on the ablation efficiency per pulse of the laser. The fluence and the repetition rate involvement on the root canal surface ablation were also investigated. For comparison, irradiation of samples with 80 ms free-running Er:YAG laser beam pulses, with similar experimental parameters, has been performed. From our results it was shown that the ablation started at a fluence value of 2.3 J/cm² for the Q-switched Er:YAG laser and at 3.5 J/cm² for the free-running laser. Previous studies by Majaron et al. [20] concluded that a change in the pulse duration in the range of 50 ms to 1 ms had no effect on the ablation threshold of dentine. However, in the study of Apel et al. [21] is shown that the ablation threshold value 10 J/cm² was reduced to 6 J/ cm² when shorter pulses were applied during experiments in the 100–700 ms time range. In our study, a clear reduction of the ablation rate threshold of about 30% was also observed for the ns pulses of the Qswitched Er:YAG laser, a pulse duration well below the 100 ms of the previous study.
At higher pulse fluences the ablation rates increased quickly quasi-logarithmically. This phenomenon is a result of absorption and scattering of the laser beam by the ejected debris, as it was also reported by others [17,22]. Abrupt saturation of the ablation rates with increasing fluence above 6 J/cm² for the free-running Er:YAG laser and 10 J/cm² for the Q-switched Er:YAG laser reveals plasma formation. Plasma absorbs most of the incident laser radiation, thereby decreasing the energy available for ablation, as it has been also suggested for CO² laser beam tissue ablation [23].
Generally, experiments showed that the degree of delineation of odd spatial energy distributions depends on the energy level. Thus, quick rise to a saturation level in the ablation rates, due to the different fluence levels in a multimode beam profile, is clearly reflected in the beam profile delineation on the tissue. Consequently, in a clinical application one should know the saturation levels of the ablation rates of the specific tissue that wants to irradiate, in order to choose the appropriate laser parameters. The fact that in a clinical application the laser pulses are not delivered to the same position, due to both patient and dentist movements, accentuate the necessity of careful laser use. The ablated tissue irregularities, like those observed in Figs. 2b and 5a, could randomly overlap due to pulse to pulse movement and thus influence the successful shaping of root canal walls.
It has been recommended that adjusting the pulse repetition rate minimizes thermal injury of the surrounding tissues by ensuring that the inter-pulse period is longer than the thermal relaxation time of the substrate and thus allows cooling between pulses [24,25]. Cooling of the tissue, in order to avoid thermal injuries, may also be aided by reducing the pulse duration [26]. The Q-switched Er:YAG laser, with 500 times shorter pulse width than the freerunning laser, is of great interest for applications in which extremely high surface quality of the irradiated biological tissue is the main concern. Free-running laser ablation is based on a quasi-continuous vaporization of tissue water during the laser pulse [27]. Therefore, some of the dehydrated collagen matrix still remains on the irradiated surface [28]. In contrast the Q-switched laser ablation is an explosive removal of the collagen matrix by rapidly evaporated tissue water due to the very high intensity and the short interaction time [29]. Only a small amount of heat penetrates the adjacent tissue, as the pulse mid-infrared lasers (λ ≈ 3:0 mm) exhibit strong absorption by hard dental tissues, restricting residual thermal damage to a minimum zone [30]. In our experiments, the only form of thermal alteration that we observed was fusion of dentine, which resulted in obscurity of dentinal tubules. And, according to the pre-mentioned theoretical predictions, this effect was observed only in samples irradiated in the free-lasing mode, independently of energy distribution and pulse repetition rates.
A very interesting pattern of the ablation surface, observed in several dental samples, was the circular ripple aspect of the crater. The spatial period of this rippled structure, which was closed to the irradiation wavelength (~3 mm) (shown very clearly in Fig. 4), probably indicates the occurrence of coherent structure formation processes [31]. Therefore, this ripple morphology could be considered as a result of interference between the incident and the reflected laser light with the scattered light near the interface [31]. The ripple aspect of the crater wall (grating-like patterns) was very common in polymer surfaces irradiated with laser light, particularly polarized light [32]. This formation was attributed to a periodic electromagnetic field which also results from interference of the incident beam with surface scattered radiation. To the best of our knowledge, this aspect was recorded for the first time in hard biological tissue surface.
As far as the crack formation is concerned, shorter pulses did create more and deeper cracks than those produced in few cases with the free-running Er:YAG laser. This is probably the result of stress transients produced during the short-pulsed ablation process. The laser-induced temperature rise in the primary zone of energy deposition, for pulse duration tp < d=us, where d is the primary zone of energy deposition and us is the velocity of sound in tissue, causes thermoelastic expansion of the tissue, which yields mechanical stress [33]. This procedure can be accompanied by plasma formation in the air–tissue surface. Actually, the macroscopic observations during the experimental procedure indicate that the higher Er:YAG laser power per pulse, in the Q-switched laser, created luminous and sounded plasma.
Besides the reduced thermal damage, another consequence of the short duration high power pulses is the reduction of the ablation rates to few micrometers per pulse at moderate fluences. In all the samples of group A the Q-switched Er:YAG laser demonstrated lower efficiency in tissue removal rates than the free-lasing one, at similar laser parameters. The ablation efficiency decreases when plasma is initiated on the sample surface. Plasma initiates due to the high stress transients induced by short laser pulses and ionization of the ablated material by the incident laser beam. This plasma shields the composite surface from the remaining laser energy in the tail of the incident laser pulse. The energy in the tail of the laser pulses is absorbed and reflected by the plasma plume in front of the sample, and it never reaches the surface to contribute to ablation [34]. Thus, a first consideration could be that the lower efficiency of Q-switched Er:YAG laser seems to be an obstacle for some clinical applications. However, another approximation could also be that shallower craters are created in this way and this permits a controlled ablation of the tissue.
The application of the Er:YAG laser in a clinical environment demands the efficient delivery of the laser beam through non-toxic fibers or waveguides. The propagation properties of the laser beam through large-core/multimode fibers and preexistent or induced by the use, input/output end and bulk fiber imperfections result in multimode output laser beam even when a TEM00 input laser beam is launched into the fiber. This consists the motivation for the investigation of the beam profile delineation on the tissue when fibers are used.
The use of optical fibers to transmit the laser beam to the tissue, in an effort to simulate real clinical conditions, gave us encouraging preliminary results. From the craters observed in both Q-switched and free-running Er:YAG laser seems that the result depends a lot on whether the laser radiation is delivered in the form of a free beam or whether comes through a fiber in contact with the tissue surface. According to Mu¨ller et al. [35], in the first case the microscale fast thermal explosion can expand into the open hemisphere and the ablation products will take a large amount of the energy away. In the fiber contact case the explosion happens in a closed chamber and the energy cannot escape. Therefore, the pressure increases much more and in addition to the direct photoablation effect the non-irradiated surrounding tissue becomes destroyed by a photohydraulic effect [36].
It should be noted that there are differences in holes created with the fiber in contact and not in contact with the tissue. A restriction factor of the ablation efficiency is the intense plasma formation in the area between the fiber’s output end and the tissue’s surface, which is strongly related to their distance. The above should be taken into account in consideration with the cone/cave crater’s shape observations by Mu¨ller [35].
5. Conclusions The interest in laser based endodontic treatment procedures (e.g. root canal enlargement) is continuously increasing, especially during the last years, as lasers offer convenient, fast and almost painless application and their experimental use is very encouraging. Promising hard dental tissue laser ablation systems are considered to be the mid-infrared lasers, like the Er:YAG laser. Ablation of root canal dentine using Er:YAG laser is an efficient procedure resulting in a very good crater quality, when the appropriate parameters are used. Moreover, short pulse durations provided by Q-switched Er:YAG laser systems seem to improve the ablation process in terms of reduced thermal damage.
The ablation rates were measured with the application of gaussian-like laser profiles to the tissue for both free-running and Q-switched laser operations. The ablation threshold values defined were 3.5 J/cm² for the Q-switched laser and 2.3 J/cm² for the free-running laser, while, in both cases, saturation, due to plasma formation, was observed above 10 J/cm² and 6 J/cm² fluences, respectively.
Well-defined, spatially uniform laser pulses allow accurate determination of material removal with good post-ablative tissue characteristics. Any beam profile modification, due to laser fatigue, resonator instabilities, misalignment, or elevated energy output characteristics, is directly reflected in the ablation crater shape and influences the tissue removal efficiency.
As a result of the different nature of the laser-tissue interaction between the two different laser operations, Q-switched and free-lasing, two main advantages of the short pulse ablation are deduced. First, the ablation rates with giant pulses are reduced to few micrometers per pulse at moderate fluences. This means that shallower craters are created and the ablation rate can be controlled more easily. Adjusting the pulse energy and/or the number of pulses can produce desirable crater depths. Secondly, the tissue ablation is performed with reduced lateral thermal damage and effects like fusion or carbonization are unlikely to happen.
However, giant pulses increase the possibility of stress transients creation due to stress confinement and this may lead to cracks formation in the crater’s edge or even at the bottom of the crater, when high powers or a large number of pulses are used. Still, a detailed histological analysis of the irradiated tissue has to be performed in order to detect deeper deteriorations that could be due to mechanical stress.
Use of fiber optics to enable laser beam propagation into the oral cavity clinical application of laser based dental treatment, is desirable. Results of the present study showed that someone has to be very careful, since a damaged end surface, defective points of the fiber core, variations of the core diameter, microbends, launching conditions and other numerous reasons are responsible for the extensive mode coupling in a fiber, which spoils the homogenous energy distribution applied on the tissue. Higher order modes can be excited and propagated even when a TEM00 input beam is used. This inevitable restriction on the beam profile quality in a clinical application necessitates the very careful control of the laser parameters (fluence, pulse duration, repetition rate, number of pulses) for the desirable result.
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M. G. Khabbaz, E. Protogerou & E. Douka
Department of Endodontics, Faculty of Dentistry, University of Athens, Athens, Greece

Abstract
Khabbaz MG, Protogerou E, Douka E. Radiographic quality of root fillings performed by undergraduate students. International Endodontic Journal, 43, 499–508, 2010.

Aim
To evaluate the radiographic technical quality of root fillings and the incidence of iatrogenic errors in treatment provided by undergraduate students.

Methodology
Endodontic records and periapical radiographs of 759 root filled teeth were selected following exclusion of 25 (3.3%). A final total of 734 cases were used to assess the technical quality of root fillings in 1109 root canals performed by 4th and 5th undergraduate students. Two variables were examined: the length and the density of the fillings, categorized as acceptable and non-acceptable. The presence of ledges, root perforation, foramen perforation and fractured instruments were also investigated. Chi-square tests were used for statistical analysis.

Results
Acceptable root fillings were found in 55% of canals. More ‘acceptable’ root fillings occurred in maxillary compared to mandibular teeth (58 and 51% respectively) (P < 0.05) and in anterior compared with premolar (71 and 61%) and molar root canals (39% respectively) (P < 0.05). Insignificantly more (5.4%) acceptable root fillings were provided by 5th year students. Most of the underfillings and iatrogenic errors were detected in molars for both academic years (53 and 65% respectively). Ledges were noted in 55% of cases treated by both academic years and significantly more foramen perforations were detected in the 5th compared with the 4th year students (P < 0.05).

Conclusions
There is a need to improve the technical quality of root fillings performed by the undergraduate students, especially in molar teeth.

Keywords: dental education, radiographic evaluation, root canal treatment, root filling, iatrogenic errors, undergraduate students.

Introduction
The technical quality of root canal treatment and the coronal restoration have an important bearing on the periapical health of root-filled teeth (Ng et al. 2008).

The European Society of Endodontology has published Undergraduate Curriculum Guidelines for Endodontology to encourage the development of highquality undergraduate dental education and acceptable standards of care in clinical endodontics (European Society of Endodontology 1994, 2001). These guidelines state that the graduating student will be expected to demonstrate the ability to perform satisfactory nonsurgical root canal treatment on single and multirooted teeth. This must include cleaning, shaping and filling of the root canal system. The student is also expected to understand the iatrogenic errors that may occur during nonsurgical root canal treatment and how to avoid them. Yet, in ‘Profile and Competences for the European Dentist’ published in November 2004 by the Association for Dental Education in Europe and the DentEd III Thematic Network Project, it was declared that Dentists are expected to act for the achievement of the total health of their patients through oral health management without supervision. These skills should be taught during the clinical semesters of their studies, where they have to reach a level of performance requiring some degree of accuracy consistent with patient well-being (Association for Dental Education in Europe and the DentEd III Thematic Network Plasschaert et al. 2004). Despite the aforementioned statements, there is evidence that inadequate root canal treatment performed by dentists, in many countries, is not the exception but the rule (Table 1). Furthermore, iatrogenic complications or procedural errors during root canal treatment performed either by undergraduate students or dentists, such as ledges, canal transportation, instrument separation etc., may result in incomplete cleaning and shaping of the canals with a severe consequence on the outcome (Crump & Natkin 1970, Kapalas & Lambrianidis 2000, Lambrianidis 2001, Peters 2004, Eleftheriadis & Lambrianidis 2005).

At the Dentistry School of Athens, undergraduate students in Endodontics must complete a pre-clinical course, which includes both theoretical and practical training. This course is held during the 5th and 6th semester of the third year of the dental degree program, which lasts for 5 years overall. During the completion of this study (2004–2006), the course included 26 h of lectures and 39 h of laboratory practical training for the 5th semester and 26 h of lectures and 26 h of laboratory practical training for the 6th semester. The teacher to students ratio was 1/15 and neither Ni–Ti instruments nor apex locators were employed at that time. Success in one written examination was required in order to proceed to clinical training in the 7th –10th semester. During the 4th year (7th and 8th semesters), which represent the 1st clinical year in endodontics, students had to attend 26 h of clinical seminars in conjunction with their clinical practice on patients. During the 2nd clinical year (9th and 10th semesters), students worked in multidisciplinary clinics to fulfil the
clinical requirements that include Periodontology, Operative Dentistry, fixed and removable Prosthetic Dentistry and Endodontics.

One reason cited for the relatively poor technical standards of root canal treatment amongst general practitioners may be the limited endodontic teaching received at Dental Schools (Qualtrough et al. 1999, Barrieshi-Nusair et al. 2004). Subsequently, an investigation of the possible relationship between pre-clinical education in endodontics and the effectiveness of the clinical work provided by undergraduate students would be of great interest.

The aim of this study was to evaluate the results of pre-clinical educational approaches in Endodontics for undergraduate students in the Dental School of the University of Athens, Greece. This was undertaken by examining the radiographic quality of root fillings and the incidence of iatrogenic errors caused by the 4th and 5th year undergraduate students during their clinical practice.

Materials and methods
Endodontic records from 759 completed root canal treatments (RCT) performed by undergraduate students with the same pre-clinical training at the Dental School of the University of Athens, between 2004 and 2006, were randomly selected for examination. The inclusion criteria for this selection were:

1 All root canal treatments performed by 4th and 5th year undergraduate dental students on completely formed permanent teeth.

2 Teeth treated using at least three, long cone/ paralleling technique, radiographs (preoperative, working-length (intermediate) and postoperative) of good quality that showed the entire length of the root and the periapical area. Cases with unreadable radiographs were excluded.

Treatments were conducted by students according to the following protocol: After consideration of the medical and dental history of each patient, local anaesthesia was administered if needed. Afterwards, rubber dam isolation, access preparation and determination of the working length using K-files with an intermediate radiograph was performed. Each root canal was instrumented with the step back technique, using stainless steel hand instruments (K–files of 0.02 taper), whilst in some cases Gates-Glidden drills were used in the coronal third of the root canals in order to facilitate straight line access. Root canals were irrigated with 3% NaOCl, whilst in cases of narrow and calcified canals Rc-Prep paste (Premier Dental Products Comp. Norristown, Philadelphia, USA) was also used.

All root canals were filled during a second session with gutta-percha cones and cement (Roth root canal cement type 811 elite grade, Chicago, IL. USA) with the technique of cold lateral condensation. All gutta-percha cones and spreaders were of 2% taper.

Evaluation of the technical quality of root filling was based on the immediate postoperative radiograph. Two variables were examined, the length and the density of the root canal fillings. Iatrogenic errors included ledges, perforations (root and apical foramen) and fractured instruments were also recorded. The detection of these errors was based on the comparison of initial, intermediate and final radiographs.

Evaluation of the final root filling was performed through magnifying lenses on a diaphanascope by three independent investigators. All investigators examined all cases. In cases of interexaminer disagreement (52 root canals), examiners came to a consensus. Measurements were recorded using a transparent ruler of 0.5 mm accuracy. In cases of maxillary premolars and mandibular molars, exposed with alteration in horizontal angulation by the students, it was considered that they had been exposed with a mesial angulation. Consequently, this fact rendered it possible to differentiate the palatal from the buccal root canal in maxillary premolars and the mesiobuccal from the mesiolingual root canal in mandibular molars according to Clark’s rule (Georig & Neaverth 1987).

Evaluation criteria
The technical quality of the root fillings and the presence of iatrogenic errors found on radiographs were evaluated, classified and recorded; root canal was the unit of assessment.

The criteria for radiographic classification of the technical quality of root fillings were based on two variables; length and density. They were classified as acceptable and unacceptable as follows:

1 Acceptable: The filling material ends 0–2 mm short of the radiographic apex with no voids visible within the material or between material and the root canal walls.
2 Unacceptable:
A Under-filled: The filling material ends more than 2 mm from the radiographic apex.
B Density problem: The filling material ends 0–2 mm short from the radiographic apex with visible voids within or between the material and the root canal walls.
C Over-filled: Materials extruded beyond the apex.

The criteria for radiographic classification of the iatrogenic errors were based on:
1 Ledge: A ledge was considered present if the apical extent of gutta-percha in the final radiograph deviated from the original curvature compared with the working-length radiograph.
2 Perforation: A perforation was diagnosed when extrusion of materials was detected in any area of the root (lateral wall or the foramen of the root).
3 Fractured instrument: They were diagnosed through observation of the final radiograph and according to the radiopacity between the filling material and fractured instrument.

Statistical analysis
Data were expressed as frequencies and percentages. Differences in categorical variables were assessed using Pearson’s chi square test. Bonferroni–Holmes correction was applied in order to maintain a familywise a < 0.05, in cases of multiple comparisons. All tests were two sided. Differences were considered as statistically significant if the null hypothesis could be rejected with>95% confidence ( P < 0.05).

Results
The total number of collected cases that received root canal treatment by the 4th and 5th year students was 759. From those 25 (3.3%) were excluded because of radiographic deficiencies such as over-exposure or over-development, under-fixing or abrasion, superimposition of root canals and anatomical noise from overlying structures. Finally, 734 teeth corresponding to 1109 root canals were included. The distribution of this sample according to the tooth type and location is detailed in Table 2. More maxillary teeth (395 teeth) and root canals (595 canals) were treated than mandibular teeth (339 teeth) and canals (514 canals). The difference was not significant ( P> 0.05). However, the distribution of frequencies of the various treated tooth types differed significantly between the arches (P < 0.001). In the maxilla, the most common tooth types were incisors and premolars. In the mandible, the pre-dominant types were premolars and molars. The frequencies of RCT amongst different tooth types differed significantly ( P < 0.001). Molars exhibited the highest number of completed RCT (42.5%), even though they were the third most commonly treated group of teeth. Specifically, 2.9 root canals on average
per tooth were treated in the molar group, a more than 200% increased frequency, compared to the other groups in both arches. From the same table, it can be noted that 4th and 5th year students performed 438 and 671 RCT on 255 and 479 teeth, respectively, which means that 5th year students operated on 88% more teeth and 53% more root canals than 4th year students.

Technical quality of root fillings
From 438 RCTs performed in the 4th year of study, acceptable fillings were detected in 226 (51.6%). From 671 RCTs performed in the 5th year of study, acceptable fillings were detected in 382 (57%) and in both academic years the percentage of acceptable fillings was (54.8%) (Table 3).

From the 1109 root canals treated by the students in both academic years, 595 were in the maxilla, from which 345 (58%) were acceptable. Of the 514 in the mandible, 263 (51.2%) were acceptable. Significantly more acceptable root fillings were detected in the maxilla than in the mandible (P < 0.05) (Table 4).

In both academic years, unacceptable root fillings were detected in 501 root canals, from which 250 were in the maxilla and 251 in the mandible. Even though the frequency of unacceptable root fillings was almost identical between maxilla and mandible (250 vs 251), the distribution of fault subgroups significantly differed between the two arches. Maxillary root canals exhibited a similar frequency of under-filling and canals with density problems (38.4% and 36%, respectively), which were the pre-dominant causes for unacceptable fillings. On the other hand, in mandibular canals, under-filling was by far the most common cause, responsible for 49.4% of unacceptable root fillings. Fillings with density problems only and over-fillings were detected respectively, in 90 (36%) and 64 (25.6%) root canals in the maxilla, in 78 (31.1%) and 49 (19.5%) respectively in the mandible with no significant differences between them (P> 0.05) (Table 4).

Of the 1109 root canals receiving treatment by the students of both academic years, 339 were anterior teeth, 299 pre-molars and 471 molars. Acceptable fillings were found respectively in 241 (71%), 182 (60.9%) and 185 (39.3%). Students of both years exhibited a significantly lower ratio of acceptable root fillings in molars, compared to anterior teeth (P < 0.05) and pre-molars (P < 0.05).

Thus, there was a statistically significant difference (P < 0.05) between acceptable root fillings performed in anterior, pre-molars and molars with descending tendency, with the best in anterior and the worst in molar teeth, for both academic years (Table 5). The total of unacceptable root fillings and the causes of the inadequacy are shown for 4th and 5th year students in Table 5.

Iatrogenic errors
During their clinical training on patients, students of the 4th year created iatrogenic errors in 144 root canals out of 438 (32.9%) and of the 5th year in 203
out of 671 (30.3%). The difference was not significant (P> 0.05) (Table 6). The distribution of frequencies of different types of iatrogenic errors differed significantly between 4th and 5th year students (P < 0.01). Even though the percentages of ledges in root canals with iatrogenic errors were similar (P> 0.05), 5th year students created root perforations in only 14 root canals (6.9%), which was 63.1% fewer than the 4th year students (P < 0.05). However, they created foramen perforations in 76 root canals (37.4%), which was 40% higher than foramen perforations created by the 4th year students (37 root canals 25.7%) (P < 0.05) (Table 6).

Iatrogenic errors were detected in 347 root canals for both academic years from which 48 (13.8%) were in anterior teeth, 72 (20.8%) in pre-molars and 227 (65.4%) in molars. The frequency of iatrogenic errors differed significantly between tooth types (P < 0.001). Molars exhibited the highest frequency of iatrogenic errors and anterior teeth the lowest. All differences between frequencies amongst the various tooth types were statistically significant (P < 0.05) (Table 7).

Discussion
The material used in this study consisted of selected endodontic records and periapical radiographs of patients who received RCT. Only periapical radiographs were used and at least three preoperative, intermediate and postoperative were needed for each case to be included. In total 1109 RCT were considered in both jaws with no significant difference between the number of RCT performed in the maxilla or in the mandible. In this sample, it was found that students of both academic years treated more root canals in molars than in any other tooth group and, they conducted more RCT in 5th than in 4th year. In several studies, periapical health and improved outcome of RCT were most likely to be associated with dense root fillings, 0 to within 2 mm from the radiographic apex (Saunders et al. 1997, Chugal et al. 2003, Ng et al. 2008). These radiographic criteria were used in the present study to assess the quality of root fillings performed by undergraduate students. Similar criteria were used by others (Buckley & Spangberg 1995, Boltacz-Rzepkowska & Pawlicka 2003, Barrieshi-Nusair et al. 2004).
The evaluation of the radiographic technical quality of root fillings in anterior and posterior teeth, performed by 4th and 5th year dental students, revealed that overall 54.8% were technically acceptable. Whilst it is difficult to compare this finding with other educational institutes, the trend appears similar to some (Eleftheriadis & Lambrianidis 2005) and at variance to others (Hayes et al. 2001, Barrieshi-Nusair et al. 2004, Lynch & Burke 2006, Er et al. 2006, Moussa-Badran et al. 2008). These differences may occur because of different criteria used in evaluation, materials, educational system, methods etc. For example, in the study of Lynch & Burke (2006) 63 root fillings out of 100 (63%) performed on single-rooted teeth were acceptable. In this study, the evaluation of the radiographic technical quality of the root fillings was performed on a small number of teeth with one straight root canal. Although the ratio in the present study on anterior teeth only was higher (71%), this figure does not reflect the real situation of the clinical skill of the undergraduate students, because they also have to complete endodontic therapy and show their skill on multi-rooted teeth (European Society of Endodontology 1994, 2001).

Comparing the present results with others (see Table 1), it seems that the mean percentage of adequate fillings performed by undergraduate students (54.8%) was relatively high. However, under-reporting of problems may have occurred because of the twodimensional radiographic images and the unknown number of cases referred to the post-graduate clinic as a result of difficulties or because of technically impairment by the under-graduate students.

Different surveys have demonstrated that general practitioners, even the recently qualified, do not follow guidelines taught during their basic education (Helminen et al. 2000, Stewardson 2001, 2002, Hill & Rubel 2008). Thus, it can be speculated that the percentage of 54.8% will probably be decreased amongst graduates. Undoubtedly, this needs to be improved. However, it is already known from an investigation of the frequency and distribution of root-filled teeth and apical periodontitis in a Greek population that the prevalence of apical periodontitis associated with the root-filled teeth was 60% (Georgopoulou et al. 2005). It is well established that the presence of apical periodontitis in root-filled teeth is often associated with inadequate root fillings.

For both academic years, the highest percentage of acceptable root fillings was noted in anterior teeth and the lowest in posterior teeth, especially molars. Similar results were found in other educational institutes (Barrieshi-Nusair et al. 2004, Eleftheriadis & Lambrianidis 2005). Furthermore, in several studies concerning national populations, it was detected that molar teeth had significantly higher levels of apical periodontitis compared with other teeth (Kirkevang et al. 2001, Jimenez-Pinzon et al. 2004, Georgopoulou et al. 2005, Loftus et al. 2005, Ridell et al. 2006). Thus, it is apparent that in Dental Schools and dental practice, it is difficult to treat molar teeth successfully. Accordingly, modification of the educational program needs to take place to emphasize the differences between treating molars versus anterior teeth and to acquire the clinical skill requested. Specifically, the introduction of hand and rotary Ni–Ti instruments for the instrumentation of molar root canals may be of benefit. Clinical research has demonstrated that there was a higher incidence of procedural errors and a lower success rate for primary RCT of molar teeth prepared with stainless steel files compared with the use of Ni–Ti instruments in a continuous reaming action (Cheung & Liu 2009).

The percentage of unacceptable root fillings was 45.2%. The reason for this high percentage is probably correlated to inadequate chemomechanical preparation or/and the filling of the root canals. The technique taught for chemomechanical preparation was traditional serial step-back with stainless steel K-files used in a filing motion and for the filling of root canals was lateral condensation of cold gutta-percha. It is known that the step-back technique used by inexperienced students may produce procedural errors such as ledges, blocking and transportation of the root canal, which may lead to incomplete cleaning and underfilling (Greene & Krell 1990, Gambarini 1999, Kfir et al. 2004). Moreover, the usage of stainless steel instruments may produce a high incidence of procedural errors, which may reduce the prognosis (Cheung & Liu 2009).

Furthermore, the lateral condensation of cold guttapercha in a nonflared or minimally flared root canal may create voids. Following this study, it was decided to emphasize on using Ni–Ti instruments and preflaring of the root canal before the measurement of the working length and to recapitulate between instruments with a small file to loosen the accumulated debris in the apical portion of the root canal.

One of the aims of academic teachers must be to improve knowledge and skills through the improvement of the educational program. The educational level offered in Endodontics has been a topic of great interest (Qualtrough & Dummer 1997, Qualtrough et al. 1999, Hayes et al. 2001, Petersson et al. 2002, BarrieshiNusair et al. 2004, Eleftheriadis & Lambrianidis 2005, Lynch & Burke 2006, Er et al. 2006, Sonntag et al. 2008). The quality of education is a resultant of many factors such as time devoted to theoretical and practical teaching and training (pre-clinical and clinical), the ratio of supervisors: students, the clinical and scientific level of teachers if they are specialized or not, the teaching aids, the assessment methods, etc.

Aiming to enhance the clinical performance of undergraduate students in endodontics, changes have already been made to the pre-clinical course. These include better theoretical teaching and laboratory exercises and better training of teachers because of special staff-seminars organized by the administration of our School. These changes have led to the following:
1 Increase in laboratory training time,
2 Improvement of the teacher to student ratio from 1/ 15 to 1/6,
3 Involvement of specialist endodontists and third year postgraduate students in pre-clinical education,
4 Insertion of flexible laboratory seminars that are supported by practical demonstrations of each exercise immediately before training,
5 Implementation of audiovisual technology in education,
6 Use of new technology such as the rotary instrumentation and the electronic measurement of working length,
7 Addition of seminars on molar endodontics and increasing the number of molars treated in the laboratory,
8 Application of an assessment system that includes student self-assessment and staff assessment, theoretical and practical examination on an extracted tooth at the end of the 5th and the 6th semester
9 Adoption of flexible examinations that consist of the summation of three written test with the mean average degree of the theoretical and practical assessment in the laboratory.

Finally, it will be of great interest to repeat the same research in the future to assure the predictability of the new educational measures.

Conclusions
The radiographic quality of RCT performed by the 4th and the 5th year undergraduate students in the School of Dentistry of the University of Athens was acceptable in 54.8% of cases. As a result, there is a need to improve the quality of the RCTs performed by undergraduate students, through the revision of the preclinical educational program in Endodontics. Special emphasis must be placed on the educational methods and training of students providing root filling on molar teeth.

Acknowledgements
The authors thank Dr Stefaniotis Theodoros for his assistance in the statistical analysis of this study.

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Radiographic_quality_of_root_fillings.pdf

M. G. Khabbaz, P. L. Anastasiadis & S. N. Sykaras Department of Endodontics, University of Athens, Dental School, Athens, Greece
Abstract Khabbaz MG, Anastasiadis PL, Sykaras SN. Determination of endotoxins in caries: association with pulpal pain. International Endodontic Journal, 33, 132±137, 2000.
Aim The aims of this study were: (i) to determine the presence or absence of endotoxins in the superficial and deep layers of carious lesions of symptomatic and asymptomatic teeth with vital pulps; (ii) to quantify the amount of endotoxin present; and (iii) to associate the presence of endotoxins with the acute pulpal pain derived from the irreversible pulpitis.
Methodology Two specimens of carious dentine were taken under aseptic conditions from symptomatic teeth with irreversible pulpitis (n = 9) and asymptomatic teeth with reversible pulpitis (n = 11). The first specimen was taken from a layer of superficial caries and the second from a deeper one. Sound dentine was also collected from intact teeth without restoration and used as a noncarious control group (n = 4). During the patient sampling procedure an effort was made to collect an equal quantity of caries and sound dentine in all cases (approximately 6 mg).
The extraction of endotoxins was performed using the Phenol-water method. The assay and quantitative determination of endotoxins was performed by the Quantitative Chromogenic test using Limulus Lysate. Data were analysed statistically using either independent or paired t-tests.
Results The results indicated that endotoxins were present in the superficial and deep layers of caries of all symptomatic teeth with irreversible pulpitis (0.15078 and 0.12111 ng mL-¹, respectively), with significantly greater amount (P < 0.01) in the superficial compared to the deep layer. Endotoxins were found in superficial and deep layer of caries of all asymptomatic teeth with reversible pulpitis (0.12091 and 0.07163 ng mL-¹, respectively), with significantly greater amounts (P < 0.001) in the superficial compared to the deep layer.
The results also demonstrated that significantly greater concentrations (P < 0.005) of endotoxins were present in the superficial carious layer of symptomatic compared with asymptomatic teeth (0.15078 and 0.12091 ng mL-¹, respectively). Likewise, significantly greater amounts (P < 0.001) of endotoxins were present in the deep carious layer of symptomatic compared with asymptomatic teeth (0.12111 and 0.07163 ng mL-¹, respectively). In sound dentine no endotoxins were detected.
Conclusions This study demonstrates that endotoxins are present in carious lesions of symptomatic and asymptomatic teeth. The amount of endotoxin was significantly greater in the superficial compared to the deep layer of carious dentine. More endotoxins are present in caries of painful teeth compared with those without symptoms.
Keywords: caries, endotoxin, pulpal pain.
Introduction Endotoxins are the lipopolysaccharide complex that constitute the cell wall component of Gram-negative bacteria. Endotoxins can be either secreted in vesicles by growing organisms or released into the environment after cell death. They are capable of initiating various biological responses such as complement activation, fever induction, macrophage activation, cytotoxicity and bone resorption (Davis et al. 1973, McKane & Kandel 1986).
It is well established that microorganisms are implicated in the aetiology of dental caries. In animals, many microbial strains have been shown to be capable of inducing caries (Orland et al. 1954, 1955, Edwardsson 1986). In humans the presence of grampositive (Streptococci, Lactobacilli, Actinomyces) and gram-negative (Cocci, Bacilli, Fusiforms, Bacteroides) microorganisms have been reported in carious dentine (Bibby & Hine 1938, Roth 1957, Hoshino 1985, Hahn et al. 1991, Schupbach et al. 1996).
Sarnat & Massler (1965) in an electron microscopic study emphasized the differentiation of two distinct layers in active carious lesions in humans: the bacteria rich layer (infected zone) with necrotic dentine and the deeper bacteria free layer where decalcification was present. Seltzer & Bender (1990) concurred with this view and reported that in the superficial layer irreversible denaturation of dentine and microbial infection existed whilst in the deeper layer the denaturation was reversible and without infection.
Nevertheless, many studies (Edwardsson 1974, Hoshino 1985, Hahn et al. 1991) have reported that the deep layers of carious dentine contain microorganisms. In some cases anaerobic bacteria were isolated from deep cavities even after the application of Ca(OH)2 for 6±9 months (Bjorndal et al. 1995).
Although many investigations have been carried out on the composition and genera of bacteria of carious dentine, little information is yet available regarding the existence of endotoxins. This information is important in understanding the role of endotoxins in mediating pulpal pain and/or inflammation.
The aims of this research were: (i) to determine the presence or absence of endotoxins in the superficial and deep layers of carious lesions of symptomatic and asymptomatic teeth diagnosed as irreversible and reversible pulpitis, respectively; (ii) to quantify the amount of endotoxin present; and (iii) to associate the presence of endotoxins with the acute pulpal pain derived from the irreversible pulpitis.
Materials and methods Patient selection Twenty-four teeth diagnosed as having irreversible and reversible pulpitis (nine molars and 15 premolars) from 21 patients (12-63 years old) who presented at the Clinic of Conservative Dentistry at the Dental School of the University of Athens, were included in this study. The teeth were divided into three groups, 1-Symptomatic carious (n = 9), 2-Asymptomatic carious (n = 11) and 3-Sound noncarious (control group, n ˆ 4). All patients agreed to participate in the study.

Clinical features
The following features were noted for each patient: age, gender, tooth, pulp vitality (electrical and thermal), nature of pain (duration, diffusion, sharp or dull), history of previous cavity preparation and local dentine-medication, periodontal status and radiographic findings.

All teeth in groups 1 and 2 had deep interproximal carious lesions in the crown without exposure of the dental pulp which was evaluated clinically and radiographically (at least 0.5 mm of dentine between pulpal space and caries seen in the radiograph). None of the teeth showed radiographic evidence of periapical inflammation. Group 1 (symptomatic carious) consisted of nine teeth with the clinical diagnosis of irreversible pulpitis. Teeth were placed into this group based on the following criteria: the teeth were currently causing spontaneous pain or had a recent history of causing severe pain to thermal stimuli which was diffused and lasted for minutes or for hours. All teeth responded to ice or electric pulp testing; a severe, prolonged pain reaction was elicited with ice. Group 2 (asymptomatic carious) consisted of 11 asymptomatic teeth with caries. Teeth were placed into this group based on the following criteria: no history of moderate or severe pulpal pain and no pain at the time of sampling. Clinical and radiographic examination determined the presence of caries without pulpal exposure, no signs of periapical pathosis and with normal to slight reaction to the vitality test. Group 3 (noncarious) consisted of four intact premolars of the maxilla from three patients aged 12-13 years that were scheduled to be extracted for orthodontic reasons. Teeth were placed into this group based on the following criteria: no history of pulpal pain; a clinical and radiographic examination that revealed no caries or restoration. Pulp testing revealed the pulp to be intact and healthy.

Teeth with a history of previous cavity preparation and local medication of dentine, or with periodontal pockets more than 3 mm, or with root caries, or which, after the excavation of the carious lesion, had an exposure of the pulp were not included in the study.
Patient sampling
All instruments used in this investigation were sterilized at 1808C for 4 h. All tubes used for the collection of specimens and experimental procedures were sterile (Whittaker Bioproducts, Inc. Walkersville, MD, USA.). The tips of the pipette were also sterile, ATP free and DNA free (Eurotips of Eppendorf, Hamburg, Germany).

After the diagnosis of reversible or irreversible pulpitis was made, local anaesthesia was administered and the appropriate tooth was thoroughly washed with air-water spray and dried. The rubber dam was placed and the outer surface of the tooth and the dam were disinfected with tincture of iodine and 70% ethyl alcohol. To avoid specimen contamination with dental plaque, less than 0.5 mm of carious dentine was removed, with a new and sterile bur on a low-speed motor without water spray.

The first specimen of carious dentine was taken with an excavator (No 82; Dentsply Maillefer, Ballaigues, Switzerland) from the superficial caries approximately 1 mm beneath the edges of the cavity and transfered into a sterile preweighed tube under aseptic conditions. Subsequently caries was removed from the cavity with a new sterile round bur on the low-speed motor until the deeper layer was exposed approximately 1.5±2 mm below the superficial layer. A second specimen was taken at this level and immediately transfered into a second tube.

To collect specimens from sound noncarious dentine, local anaesthesia was administered and rubber dam applied to the maxillary premolars. Initially, enamel was removed with a diamond without water spray. Afterwards, a sterile tube was placed in close proximity beneath the tooth and dentine was ground with a sterile round bur in the low-speed motor. During grinding sound dentinal chips were collected in the tube.

All tubes were reweighed with the specimens. During sampling an effort was made to collect an equal quantity of caries and sound dentine in all cases (approximately 6 mg).

Release of endotoxins
The extraction of endotoxins was performed using phenol-water (Westphal & Jann 1965). Three millilitres of a 65% phenol solution were added to the tube containing the specimen. The samples were shaken at room temperature for 1 min with a vortex mixer. After centrifugation at 3500 r.p.m. for 50 min, the supernatant was removed with a pipette and placed in a sterile tube for 10 min in a 608C water bath to disintegrate the proteins that may induce false positive results. Heating did not affect the endotoxin activity, since the endotoxin molecule is heat stable (Davis et al. 1973, McKane & Kandel 1986).

Measurement of endotoxins
The assay and quantitative determination of endotoxins was performed using a Limulus Lysate Test (Levin & Bang 1968). The Quantitative Chromogenic LAL-1000 (QCL-1000) was used as recommended by the manufacturer (Whittaker Biobroducts, Inc. Walkersville, MD, USA).

A phasmatophotometer (Spectronic 70, Bausch & Lomb, USA) was used at 405 nm to read the absorbance rate of endotoxins. The tubes were read by two persons in a blind test. A calibration curve was constructed initially and the concentration of endotoxins determined from this curve by linear regression.

Statistical analysis
Data on the presence or absence of severe and spontaneous pulpal pain, the quantitative determination of endotoxins in superficial and deep layers of caries were analysed statistically using the independent t-test and the paired t-test to compare the amount of endotoxins found in each layer of caries with the presence or absence of pulpal pain.

Results
Endotoxins were detected in all layers of caries of group 1 (symptomatic carious teeth) and group 2 (asymptomatic carious teeth). In group 3 (control noncarious teeth) endotoxins were not detected. The mean concentration of endotoxins in groups 1 and 2 is showed in Table 1.

Endotoxin concentration in symptomatic teeth
Endotoxins were detected in the superficial and deep layers of all symptomatic teeth. The endotoxin content in the superficial layer of carious dentine (average value 0.15078 ng mL-¹, SD = 0.02183) was significantly greater (P < 0.01) than in the deeper layer (average value 0.12111 ng mL-¹, SD = 0.01024).
Endotoxin concentration in asymptomatic teeth
Endotoxins were detected in superficial and in deep layers of all asymptomatic teeth. The endotoxin content in the superficial layer of carious dentine (average value 0.12091 ng mL-¹, SD = 0.01800) was significantly greater (P < 0.001) than in the deeper layer (average value 0.07163 ng mL-¹, SD = 0.01271).

Comparison of endotoxin concentration between symptomatic and asymptomatic teeth
The concentration of endotoxins in the superficial layer of symptomatic teeth (average value 0.15078 ng mL-¹, SD = 0.02183) was significantly greater (P < 0.005) than in asymptomatic teeth (average value 0.12091 ng mL-¹, SD = 0.01800) (Table 2).

The endotoxin concentration of deep layers in symptomatic teeth (average value 0.12111 ng mL-¹, SD = 0.01024) was significantly greater (P < 0.001) than in asymptomatic teeth (average value 0.07163 ng mL1 , SD = 0.01271) (Table 2).

Discussion
It is well documented, that oral microorganisms play an important role in the initiation and progression of caries and pulpal inflammation in human teeth (Kakehashi et al. 1965, Loesche & Syed 1973, Hoshino 1985, Hahn et al. 1991). Previous studies reported that there was no infection in the deep layer of carious dentine (Sarnat & Massler 1965, Wirthlin 1970). However, our results indicate that endotoxins are present not only in the superficial but also in the deep layers of caries. On the basis that endotoxin probably reflects the gram-negative microbial flora (Schein & Schilder 1975, Fine et al. 1992), these results confirm the findings of earlier reports that when soft dentine is left in deep cavities, microorganisms are present in most cases (Seltzer 1940, Shovelton 1968).

The results of this investigation demonstrated that the amount of endotoxin in superficial layers of carious dentine was significantly greater than in the deep layers. These results are in agreement with the results of Hoshino (1985) who found that after aerobic and anaerobic incubation of specimens taken from carious dentine, the number of microorganisms recovered was greater in shallow than in deeper layers. It seems that in superficial caries, where dentine is totally denatured, conditions are suitable for the multiplication of bacteria, whilst in deeper layers conditions may be different because of the reduced permeability of carious dentine (Miller & Massler 1962) or because of the differences in the oxygen concentration between the shallow and the deep layer of caries; this hypothesis has to be tested with further investigation.

Administration of endotoxin to experimental animals produces inflammation in the pulpal tissue (Warfvinge et al. 1985, Hirafuji & Shinoda 1994). When endotoxins were topically applied to freshly exposed dentine, Warfvinge et al. (1985) demonstrated that they were capable of provoking inflammatory cell migration in the dental pulp. Furthermore, when endotoxins were injected intravenously in the rat, Hirafuji & Shinoda (1994) demonstrated that they increased the production of prostaglandin I2 and thromboxane A2 in the dental pulp.
Endotoxins may evoke pain through activation of the Hageman factor that leads to the production of bradykinin, a potent pain mediator (Seltzer & Farber 1994). Similarly, a number of studies have reported that endotoxins possess neurotoxic properties acting on presynaptic nerve terminals (Penner & Bernheim 1960, Palmiero et al. 1962, Parnas et al. 1971). However, clinical symptoms were strongly associated with the presence of Bacteroides melaninogenicus (prevotella), an anaerobic gram-negative rod that produces endotoxin in the root canal of symptomatic nonvital teeth (Sundqvist 1976, Griffee et al. 1980, Gomes et al. 1994). Previous studies (Schein & Schilder 1975, Schonfeld et al. 1982, Horiba et al. 1991) found a correlation between bacterial endotoxins and pulpal or periradicular pain, because there was a higher endotoxin level in symptomatic teeth compared to those without symptoms.

In our study, endotoxin concentration in the superficial and deep layers of carious dentine was significantly greater in symptomatic teeth with irreversible pulpitis compared with asymptomatic teeth. Since the endotoxins have inflammatory and neurotoxic properties, the higher level of endotoxins in the caries of symptomatic teeth perhaps constitutes one factor amongst many others involved in the mechanism of pulpal pain.

To prove this hypothesis, penetration of endotoxin into dentinal tubules and their diffusion to the pulp through dentine must be proved. Application of crude bacterial extracts or specific bacterial components to exposed dentine can induce inflammation in the underlying pulp, indicating that bacterial products are probably capable of diffusing to the pulp (Bergenholtz 1977). Further evidence was provided when endotoxin was applied to the pulpal floor of class V cavities in monkeys (Warfvinge et al. 1985); accumulation of neutrophils in the pulp beneath exposed dentinal tubules suggested that endotoxin diffused into the pulp and activated the complement system, thus producing C5a, a chemotactic factor for neutrophils. Also Nissan et al. (1995), studying the ability of bacterial endotoxin to diffuse through human dentine, found that it was capable of passing through 0.5 mm of dentine. Despite these laboratory studies, the presence of endotoxins in the human dental pulp is yet to be proved.

The high molecular weight of endotoxins may be one factor that slows the passage of endotoxins through dentine (Segal et al. 1990). However, it has been well established that carious dentine is much less permeable than sound dentine (Miller & Massler 1962, Trowbridge 1981, Arends et al. 1995). The recovery of endotoxin in superficial and deep layers of caries and the association with the clinical symptoms despite the decreased permeability of the carious dentine is an important finding.

Conclusion
In conclusion, this study shows that: Endotoxins exist in caries of symptomatic and asymptomatic vital teeth. The amount of endotoxin is significantly greater in the superficial compared to the deep layer of carious dentine. More endotoxins are present in caries of painful teeth than in those without symptoms.

Acknowledgements
This study was supported by a grant from the University of Athens. The authors thank Ms Mantzarea K. for her technical support.

References
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Miller W, Massler M (1962) Permeability and staining of active and arrested lesions in dentine. British Dental Journal 112, 187-97.
Nissan R, Segal H, Pashley D, Stevens R, Trowbridge H (1995) Ability of bacteria to diffuse through human dentin. Journal of Endodontics 21, 62-4.
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endotoxins_and_pulpal_pain.pdf

Abstract

After the extraction the root was placed in 5% NaOCI for 1 h before processing, to remove any soft tissue remnants attached to the root surface, and was kept in tap water. The root was air-dried in a desiccator, fixed on microscope studs, sputter-coated with gold and examined and photographed in the Cambridge Stereoscan S-150 SEM (Cambridge Instruments, Cambridge, UK).
The SEM examination revealed the presence of calcified tissue extending from the surface of the root around the apex to the extruded gutta-percha cone, forming a bridge between them (Fig. 3). A clear contact line was noticed between the newly formed tissue and the apex (Fig. 4). The surface of this tissue was smooth and had a similar appearance to the surface of the cementum of the root to which it appeared to be tightly attached (Fig. 5). The formed tissue adapted closely to the extending gutta-percha but small voids were also observed. The remainder of the surface of the root around the apex had a rough appearance (Fig. 3).Despite 4-5 mm of gutta-percha that were pushed into the periradicular tissues and the fmal 1 min overfill, there was healing of the periradicular tissues 4 years after the completion of the root canal treatment and the patient remained asymptomatic. The case was considered successful according to the criteria for evaluating the success of endodontic therapy (Bender et al. 1966).
The healing of the periapical lesion in this case was attributed to the successful control of the infection through root canal preparation and debridement as well as the obturation of the root canal. This healing process was not affected by the presence of filling materials in the periradicular tissues, which is in agreement with studies that report gutta-percha to be well tolerated (Wolfson & Seltzer 1975, Olsson & Wennberg 1985).
In clinical endodontics, it is well established that the absence of irritants in the root canal and the periradi¬cular tissues creates favourable conditions for healing, i.e. bone deposition in the periapical lesions and hard tissue formation on the root surface around the apex together with the absence of clinical symptoms. (Seltzer 1988, Weine 1996).

In teeth of animals with induced periapical lesions, cementum deposition was apparent at the root apex 12 weeks after root canal treatment. This deposition was considered as early histological proof of healing (Fouad et al. 1993). Deposition of hard tissue has also been demonstrated histologically in the root canal space of overinstrumented and underfilled root canals in animals (Davis et al. 1971, Benatti et al. 1985). Ad-ditionally, in long-term follow-up radiographs of successful cases of root-canal-treated teeth with periapical lesions and apical resorption, cementum deposition is obvious at the root apex (Weine 1996). In the present case the SEM examination of the extracted root revealed evidence of deposition of hard tissue at the root apex despite the fact that there was overfilling. This tissue resembled the cementum of the root and appeared to be calcified. Furthermore, it seemed to be tightly attached to the surface of the cementum and it adapted closely to the overextended gutta-percha. The rough appearance of the rest of the root surface around the apex led to an assumption that, on this rough surface, more of this tissue may have been attached and had possibly been destroyed during the extraction of the root. Although a histological examination of this newly formed hard tissue was not performed, it is believed to be secondary cementum which was deposited in the areas of the root resorption. Possibly this deposition constituted an effort by the local defence mechanisms of the periapical tissues to isolate the foreign materials (gutta-percha and sealer). Finally, although in the postoperative radiograph the root canal filling in the apical third appears to be complete, in the SEM photographs a gap is evident between the newly formed tissue and the gutta-percha master cone. This gap was possibly created when the tooth was extracted or during specimen preparation for the SEM. In conclusion, although there was substantial extrusion of filling materials in the periapical area, long-term healing with secondary cementum deposition at the apex and resolution of lesion occurred and the case was considered to be successful. Obviously, these findings should not encourage dentists to overfill root canals, but they confirm the importance of chemomechanical preparation and complete obturation of the root canal, as well as the low toxicity of gutta-percha.
case_report.pdf

Ενδοδοντική_θεραπεία_σε_μία_συνεδρία.pdf

Επανάληψη_ενδοδοντικής_θεραπείας.pdf

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Περίληψη
Στην κλινική πράξη, πολλές φορές, επικρατεί σύγχυση προς την αναγκαιότητα της ενδοδοντικής θεραπείας πριν από την αποκατάσταση των τερηδονισμένων δοντιών. Τούτο συμβαίνει επειδή τα όρια αυτού του θέματος δεν είναι σαφώς ξεκαθαρισμένα ή τουλάχιστον όταν υπάρχουν δεν τηρούνται από τους κλινικούς οδοντιάτρους. Παράδειγμα είναι η αποκατάσταση να γίνεται χωρίς τις δοκιμασίες ζωτικότητας του πολφού και τη λήψη οπισθοφατνιακού ακτινογραφήματος, πράγμα απαραίτητο για τη μελέτη της κατάστασης του πολφού και των περιακρορριζικών ιστών των τερηδονισμένων δοντιών. Σκοπός αυτής της βιβλιογραφικής ανασκόπησης είναι η προσπάθεια οριοθέτησης της τέλεσης της ενδοδοντικής θεραπείας ή μη σε τερηδονισμένα δόντια που προορίζονται για αποκατάσταση στην κλινική πράξη, με ταυτόχρονη παρουσίαση δικών μας περιστατικών. Η αποκατάσταση  των δοντιών με βαθιά τερηδόνα έχει άμεση σχέση: 1ον με το οδοντιατρικό ιστορικό της περίπτωσης (π.χ. παρουσία πόνου, ζωτικότητα πολφού, προηγούμενη θεραπευτική αντιμετώπιση κ.ά.), 2ον με την έκταση και το βάθος της κοιλότητας (αυξημένη διαπερατότητα της οδοντίνης στις βαθιές κοιλότητες με αποτέλεσμα τη σοβαρότερη βλάβη του πολφού) και 3ον με το ακτινογραφικό μέγεθος του μυλικού θαλάμου στα δόντια με βαθιά τερηδόνα (η σμίκρυνση των διαστάσεων του μυλικού θαλάμου στην περίπτωση της ενασβεστίωσής του μπορεί να σημαίνει μείωση της άμυνας του πολφού).

Από τη βιβλιογραφική αυτή μελέτη προκύπτει, μεταξύ άλλων, ότι στην αποκατάσταση των τερηδονισμένων δοντιών επιβάλλεται ο πλήρης κλινικός και ακτινογραφικός έλεγχος της περίπτωσης με σκοπό την πρόληψη των βλαβών του πολφού και των περιακρορριζικών ιστών αλλά και την αποφυγή της ταλαιπωρίας του ασθενούς.


Εικ. 1: Αποκατάσταση τερηδόνας μετρίου βάθους.
Α. Φωτογραφία του 42 με τερηδόνα παρειακά, εγγύς και άπω χωρίς κανένα κλινικό σύμπτωμα, σε ασθενή ηλικίας 34 ετών. Οι δοκιμασίες ζωτικότητας ήταν φυσιολογικές.
Β. Ακτινογραφική εικόνα του ιδίου δοντιού. Παρατηρείται ότι οι διαστάσεις της πολφικής κοιλότητας και οι περιακρορριζικοί ιστοί είναι στα φυσιολογικά επίπεδα.
Γ. Επάλειψη της οδοντίνης και της αδαμαντίνης με τον συγκολλητικό παράγοντα, μετά την αφαίρεση της τερηδόνας.
Δ. Φωτογραφία του ιδίου δοντιού μετά την έμφραξή του με σύνθετη ρητίνη.
Ε. Ακτινογραφική εικόνα του ιδίου δοντιού μετά την τριπλή έμφραξη. (Από το αρχείο του συναδέλφου Χ. Χρυσαφίδη.)

Εικ. 2: Μηχανική αποκάλυψη πολφού. Μετά την πλήρη αφαίρεση της τερηδόνας και κατά τη διάρκεια παρασκευής της κοιλότητας, πολφός αποκαλύπτεται, τυχαία. Η τοποθέτηση του απομονωτήρα είναι απαραίτητη για τη σωστή κάλυψή του.Επομένως ο πολφικός ιστός, αμυνόμενος με διάφορους τρόπους, προσπαθεί: 1ον να εκδιώξει τον εισβολέα μικροβιακό παράγοντα με την εκροή του υγρού των οδοντινοσωληναρίων από τον πολφό προς το εξωτερικό περιβάλλον, 2ον να περιορίσει την είσοδο των μικροβίων ή των τοξινών τους με τη σκληρωτική οδοντίνη και 3ον να απομακρυνθεί, ο ίδιος, από το σημείο του ερεθισμού με τη δημιουργία «αδιαπέραστων τοίχων» της αντιδραστικής τριτογενούς οδοντίνης. 

Αποκατάσταση της μετρίου βάθους τερηδόνας
Βασική προϋπόθεση για την επίτευξη των προαναφερθέντων αμυντικών μηχανισμών είναι η παρουσία της μικροκυκλοφορίας του αί-ματος απ’ όπου ο πολφός αντλεί τα αμυντικά του στοιχεία και διατηρεί τη ζωτικότητά του. Δα λεμφοκύτταρα, πλασματοκύτταρα και τα μακροφάγα «καθαρίζουν» τον πολφικό ιστό από τα μικρόβια ή από τα παράγωγά τους, εφόσον αυτά περάσουν από τις προαναφερθείσες αμυντικές γραμμές και στη συνέχεια αποβάλλονται μαζί, μέσω της φλεβικής και της λεμφικής οδού. Εφ’ όσον η ροή του αίματος παραμένει εντός των φυσιολογικών ορίων και εάν ληφθεί υπόψη ότι ο όγκος του αίματος του πολφού ανανεώνεται 5 έως 14 φορές το λεπτό, συμπεραίνεται ότι η συγκέντρωση των βλαπτικών παραγόντων εντός αυτού παραμένει μικρή, μη δυνάμενη να προκαλέσει σοβαρή λειτουργική βλάβη. Τούτο ισχύει εφόσον η τερηδόνα είναι χρόνια, αβαθής ή μετρίου βάθους, πράγμα που σημαίνει ότι η ένταση του ερεθίσματος παραμένει μικρή. Σε αυτές τις περιπτώσεις η μόνη ιστολογική απόδειξη του ερεθισμού του πολφού είναι ο εντοπισμός της τριτογενούς αντιδραστικής οδοντίνης στα τοιχώματα του πολφικού θαλάμου. Έρευνες έχουν δείξει ότι 7-8 μέρες μετά την άρση της μικροβιακής αιτίας της φλεγμονής του πολφού επέρχεται η αποκατάσταση με τη μορφή της αυξημένης παραγωγής της προοδοντίνης.

Από τα ανωτέρω φαίνεται ότι η αντιμετώπιση της αβαθούς ή μετρίου βάθους τερηδόνας, εφόσον ο πολφός διατηρείται φυσιολογικός, δεν μπορεί να είναι άλλη από τον καθαρισμό της τερηδονισμένης οδοντικής ουσίας και την έμφραξη της κοιλότητας με τα γνωστά υλικά που χρησιμοποιούνται στην κλινική πράξη (αμάλγαμα, ρητίνη κ.ά.) χωρίς, φυσικά, την τέλεση της ενδοδοντικής θεραπείας (Εικ. 1).

Με σκοπό την πρόληψη της διείσδυσης μικροβίων μέσω του περιεμφρακτικού χώρου, του επανατερηδονισμού αλλά και με σκοπό την προστασία του πολφού από νέα προσβολή εφαρμόζονται, σήμερα, οι συγκολλητικοί παράγοντες κάτω από τα υλικά της αποκατάστασης, ειδικά της ρητίνης. Η συγκόλληση των εμφρακτικών υλικών γίνεται στην αδαμαντίνη και στην οδοντίνη μετά την αδροποίησή τους. Στη συνέχεια το υλικό του συγκολλητικού παράγοντα εισχωρεί στους πόρους της αδαμαντίνης και στα ανοικτά στόμια των οδοντινοσωληναρίων σχηματίζοντας εσωτερικές προσεκβολές που πραγματοποιούν απόφραξη των σκληρών οδοντικών ουσιών, σε βάθος 20- 40 μm. Το γεγονός αυτό πιστεύεται ότι προσφέρει την καλύτερη προστασία του πολφού για αρκετό καιρό.

Εικ. 3: Αποτυχία της άμεσης κάλυψης του πολφού σε άτομο μέσης ηλικίας. Α. Ακτινογραφική εικόνα του 36, όπου φαίνεται η δευτερογενής τερηδόνα κάτω από μια έμφραξη αμαλγάματος. Ο πολφός ήταν ζωντανός χωρίς κλινικά συμπτώματα, ενώ παρατηρείται ενασβεστίωση του μυλικού θαλάμου.
Β. Δύο χρόνια μετά την άμεση κάλυψη του πολφού και την αντικατάσταση της έμφραξης. Οι δοκιμασίες ζωτικότητας είναι αρνητικές και στο ακτινογράφημα εμφανίζονται περιακρορριζικές αλλοιώσεις στην εγγύς και άπω ρίζα του γομφίου.

Εικ. 4: Αποκάλυψη πολφού (βέλος), έπειτα από τρόχισμα, σε δόντι που προορίζεται να γίνει στήριγμα προσθετικής αποκατάστασης. Η περίπτωση αποτελεί ένδειξη για ενδοδοντική θεραπεία.
γ) Η προηγούμενη θεραπευτική αντιμετώπιση
Αναφέρθηκε προηγουμένως ότι ο πολφός των δοντιών αντιδρά στην παρουσία της χρόνιας τερηδόνας με την παραγωγή της αντιδραστικής οδοντίνης μέσα στον μυλικό θάλαμο. Η ίδια αντίδραση εμφανίζεται και μετά την παρασκευή της κοιλότητας προς αποκατάσταση ακόμα και σε περιπτώσεις με αβαθείς μασητικές εμφράξεις. Γενικότερα όμως, η αντιδραστική οδοντίνη παράγεται μετά την εφαρμογή ερεθιστικού παράγοντα στην οδοντίνη π.χ. τροχισμού, υλικών κ.ά. Το τελικό αποτέλεσμα όλων αυτών των διεργασιών, εφόσον ο πολφός διατηρείται ζωντανός, είναι η σμίκρυνση του μυλικού θαλάμου εις βάρος του πολφικού ιστού, γεγονός που έχει σαν συνέπεια τη μείωση των κυτταρικών και αγγειακών του στοιχείων. Τούτο, πιθανόν, να προκαλέσει τη μείωση της άμυνας του πολφού, έτσι ώστε να αντέχει λιγότερο σε νέους ερεθισμούς, ειδικά σε άτομα της τρίτης ηλικίας.Εικ. 5: Πολλαπλές οδοντιατρικές πράξεις σε ένα δόντι, που οδηγούν στη νόσο του πολφού.
Α. Εικόνα από πανοραμικό ακτινογράφημα (1997) όπου φαίνεται η ήδη υπάρχουσα έμφραξη αμαλγάματος στον 16.
Β. Εικόνα από πανοραμικό ακτινογράφημα (2001) όπου, μετά την αντικατάσταση της πρώτης έμφραξης, παρατηρείται δευτερογενής τερηδόνα στην αυχενική μοίρα της εγγύς επιφάνειας (βέλος).
Γ. Τοποθέτηση στεφάνης (2002).
Δ. Έξι μήνες μετά την τοποθέτηση της στεφάνης (2002) εκδηλώθηκαν συμπτώματα πολφίτιδας που οδήγησαν στην τέλεση της ενδοδοντικής θεραπείας.
Εικ. 6: Στόμια οδοντινοσωληναρίων στο Ηλεκτρονικό Μικροσκόπιο Σάρωσης (x 10.000). Μέσω ενός επιφανειακού στομίου (βέλη) παρατηρείται, στο βάΘος της οδοντίνης, η παρουσία τριών άλλων στομίων (Σ).
Εικ. 7: Μέγεθος μυλικού θαλάμου και ενδοδοντική θεραπεία.
Α. Κλινική εικόνα του 36. Περιφερικά της έμφραξης αμαλγάματος παρατηρείται μεγάλος περιεμφρακτικός χώρος που επιβάλλει την αντικατάστασή της. Οι δοκιμασίες ζωτικότητας είναι θετικές και δεν αναφέρονται κλινικά συμπτώματα από τον ασθενή ηλικίας 62 ετών.
Β. Ο ακτινογραφικός έλεγχος έδειξε ενασβεστίωση μεγάλου τμήματος του μυλικού θαλάμου. Γ. Ενδοδοντική θεραπεία του δοντιού.

Eικ. 8: Διάτρηση κατά τη διάνοιξη λόγω ενασβεστίωσης.
Α. Γομφίος της κάτω γνάθου με μεγάλη καταστροφή της μύλης και ενασβεστίωση των εγγύς ριζικών σωλήνων.
Β. Διάτρηση του υποπολφικού τοιχώματος κατά τη διάρκεια του εντοπισμού των στο¬μίων των εγγύς ριζικών σωλήνων.
Γ. Διάτρηση πλάγιου τοιχώματος σε προγόμφιο της άνω με ενασβεστίωση του μυλικού θαλάμου και του ριζικού σωλήνα.

Συμπεράσματα
1)Το μέγεθος της αποκάλυψης του πολφού δεν παίζει ρόλο στην επούλωσή του εφόσον α) αποκλεισθεί ο μικροβιακός παράγοντας και β) ο πολφός διαθέτει τους αμυντικούς μηχανισμούς.
2)Στην αποκατάσταση των δοντιών με βαθιά τερηδόνα, η χρήση και εφαρμογή του απομονωτήρα προάγει τη δημιουργία επανορθωτικής οδοντίνης στην περίπτωση της αποκάλυψης του πολφού.
3) Στην αποκατάσταση δοντιών με βαθιά τερηδόνα πρέπει να λαμβάνεται υπ’ όψιν η ζωτικότητα του πολφού, η παρουσία ή η απουσία του πόνου, η προηγούμενη θεραπευτική αγωγή, η ηλικία του ασθενούς, το πάχος της παραμένουσας οδοντίνης μετά την παρασκευή της κοιλότητας και το μέγεθος του μυλικού θαλάμου που διαπιστώνεται από την οπισθοφατνιακή ακτινογραφία.
4)Στις περιπτώσεις αυτές και εφόσον διαπιστωθεί ενασβεστίωση του μυλικού θαλάμου, η τέλεση της ενδοδοντικής θεραπείας πριν από την αποκατάσταση πιθανόν να συμβάλει θετικά στην πρόληψη των νόσων των περιακρορριζικών ιστών αφ’ ενός και αφ’ ετέρου στην αποφυγή της ταλαιπωρίας και της δυσαρέσκειας του ασθενούς.

Αποκατάσταση_τερηδονισμένων_δοντιών.pdf

ΕισαγωγηΕίναι γνωστό ότι τα ποσοστά επιτυχίας της ενδοδοντικής θεραπείας σήμερα κυμαίνονται από 80 έως 95%. Συχνά όμως παρατηρούνται, στην κλινική πράξη, δόντια με επιτυχημένη ενδοδοντική θεραπεία που χρειάζονται όμως εξαγωγή λόγω αποτυχίας της αποκατάστασής τους. Επομένως, φαίνεται ότι η πρόγνωση της ενδοδοντικής θεραπείας εξαρτάται και από τη σωστή αποκατάσταση των ενδοδοντικά θεραπευμένων δοντιών. Τούτο επιβεβαιώνεται από μία κλινικοστατιστική έρευνα όπου εξετάσθηκαν 116 δόντια με αποτυχημένες ενδοδοντικές θεραπείες και διαπιστώθηκε ότι η αιτία της αποτυχίας οφείλεται κυρίως στην προσθετική αποκατάσταση με ποσοστό 59,4 % και πολύ λιγότερο στην ίδια την ενδοδοντική θεραπεία όπου το ποσοστό ήταν 8,6%. Κατά αυτόν τον τρόπο, σήμερα πιστεύεται ότι η επιτυχία της ενδοδοντικής θεραπείας και η παραμονή του ενδοδοντικά θεραπευμένου δοντιού στο φραγμό δεν εξαρτάται μόνο από τη σωστή τέλεση της θεραπείας αλλά και από τη σωστή, ασφαλή και πλήρη αποκατάσταση της λειτουργικότητας του ενδοδοντικά θεραπευμένου δοντιού (1-7).Α. Αναγκαιότητα αποκατάστασης των ενδοδοντικά θεραπευμένων δοντιώνΣε γραπτά του κείμενα το 1747 ο Pierre Fauchard, περιέγραψε τη μεθοδολογία αποκατάστασης άπολφων δοντιών με τη βοήθεια αξόνων και στεφάνών (7). Σήμερα, μετά από 250 χρόνια και πλέον, η ανάγκη της αποκατάστασης των ενδοδοντικά θεραπευμένων δοντιών συνεχίζει να είναι επιβεβλημένη.Συνήθως, στη κλινική πράξη, η ενδοδοντική θεραπεία εκτελείται σε δόντια που έχουν μεγάλη καταστροφή της μύλης τους εξ αιτίας κατάγματος, τερηδόνας, οδοντικής παρασκευής κ.ά. Επιπλέον με την διαδικασία της διάνοιξης και της χημικό μηχανικής επεξεργασίας των ριζικών σωλήνων (ρ.σ.) αφαιρείται οδοντίνη από τη μύλη αλλά και από τη ρίζα του δοντιού. Βέβαια μελέτες απέδειξαν ότι η διαδικασία της ενδοδοντικής θεραπείας δεν ευθύνεται για την αποδυνάμωση της ακεραιότητας του δοντιού. Οι Reeh et al. το 1989 διαπίστωσαν ότι με την ενδοδοντική θεραπεία η ακεραιότητα του δοντιού μειώνεται μόνο κατά 5%, ενώ όταν συνδυασθεί και με εγγύς-άπω κοιλότητα η ανθεκτικότητα του δοντιού στη θραύση μειώνεται κατά 63% (8) (Πίνακας 1).

Είδος Κοιλότητας	Ποσοστιαία Μείωση Αντοχής
Κοιλότητα διάνοιξης για ενδοδοντική θεραπεία	5%
Κοιλότητα 1ης ομάδας με πλάτος ισθμού το 1/3 της διαφυματικής απόστασης	20%
Κοιλότητα 2ης ομάδας με ένα όμορο κιβωτίδιο	46%
Κοιλότητα 2ης ομάδας με δύο όμορα κιβωτίδια	63%

ΠΙΝΑΚΑΣ 1. Στον Πίνακα φαίνεται η ποσοστιαία μείωση της αντοχής ενός δοντιού ανάλογα με τον αριθμό των τοιχωμάτων μύλης που λείπουν (Reeh et al 1989).

Οι Hwoe C. & Mc Kendry D. το 1990 πειραματίσθηκαν με την άσκηση βάρους στη μασητική επιφάνεια γομφίων όπου οι ακέραιοι έσπασαν στο επίπεδο των 341,4 κιλών, οι γομφίοι με διάνοιξη για ενδοδοντική θεραπεία στα 225,5 κιλά και οι γομφίοι με διάνοιξη και με εγγύς-άπω κοιλότητα στα 121,7 κιλά (9) (Πίνακας 2).

ΟΜΑΔΕΣ ΔΟΝΤΙΩΝ	ΒΑΡΟΣ ΣΤΗ ΜΑΣΗΤΙΚΗ ΕΠΙΦΑΝΕΙΑ
Άθικτα δόντια	341,4
Διάνοιξη για Ε. Θ.	225,5
Κοιλότητα II ομάδας	222,4
Διάνοιξη + κοιλότητα	121,7

ΠΙΝΑΚΑΣ 2. Στον Πίνακα φαίνεται η βαθμιαία μείωση του φορτίου που προκαλεί κατάγματα των δοντιών ανάλογα με την αύξηση του βαθμού απώλειας των σκληρών οδοντικών ουσιών (Hwoe C. & Mc Kendry D. 1990).

Από τις προαναφερθείσες έρευνες διαπιστώνεται ότι η διαδικασία της ενδοδοντικής θεραπείας, μόνη της, ελάχιστα μειώνει την αντοχή του δοντιού στα κατάγματα. Αντίθετα όταν συνδυασθεί και με απώλεια της συνέχειας των οδοντικών ουσιών, ιδιαίτερα στις όμορες επιφάνειες, η αντοχή αυτών των δοντιών στα κατάγματα εμφανίζεται πολύ μειωμένη. Τούτο οφείλεται στην αυξημένη παραμόρφωση των φυμάτων ή/και των τοιχωμάτων του ενδοδοντικά θεραπευμένου δοντιού κατά τη διάρκεια της μάσησης. Επιπλέον, η αφαίρεση του υπερπολφικού τοιχώματος το οποίο συνδέει τα φύματα μεταξύ τους κάτω από φυσιολογικές συνθήκες, αυξάνει το βαθμό της παραμόρφωσης και κατά συνέπεια συμβάλλει στην εμφάνιση καταγμάτων της μιύλης των ενδοδοντικά θεραπευμένων δοντιών (10) (.Εικόνα 1).​​​​​​​

Εκτός όμως από την απώλεια της δομικής ακεραιότητας των ενδοδοντικά θεραπευμένων δοντιών, διάφορες μεταβολές στην υγρασία της οδοντίνης και στη δομή του οργανικού υποστρώματός της ενοχοποιούνται από ορισμένους συγγραφείς για την αυξημένη ευθραυστότητά τους. Άλλοι ερευνητές όμως, που διαφωνούν με τους προηγούμενους, ισχυρίζονται ότι προς το παρόν δεν είμαστε σε θέση να γνωρίζουμε κατά πόσο αυτές οι μεταβολές επηρεάζουν την συμπεριφορά των οδοντικών ουσιών κατά την άσκηση μασητικών πιέσεων (11-14).
Παρά ταύτα ο συνδυασμός όλων των προαναφερθέντων παραγόντων (απώλεια οδοντικής ουσίας, μεταβολές στις φυσικές ιδιότητες της οδοντίνης, κ.ά.) υπαγορεύουν την ανάγκη ιδιαίτερης πρόνοιας για την αποκατάσταση των ενδοδοντικά θεραπευμένων δοντιών (14).
Μία επίσης αναγκαιότητα για την αποκατάσταση των ενδοδοντικά θεραπευμένων δοντιών αποτελεί η δυσχρωμία, ειδικά των προσθίων δοντιών, που εμφανίζεται ενίοτε στην κλινική πράξη. Η αποκατάσταση τέτοιων δοντιών γίνεται συνήθως αφού έχει αποτύχει ο αποχρωματισμός τους με τις γνωστές μεθόδους (4-6).
Επομένως υπάρχει μεγάλη ανάγκη για τη λειτουργική και αισθητική αποκατάσταση των ενδοδοντικά θεραπευμένων δοντιών και επιπλέον υπάρχει ανάγκη για την προστασία των παραμεινάντων οδοντικών ουσιών από περαιτέρω καταστροφή. Το είδος αυτής της αποκατάστασης καθορίζεται κυρίως από την έκταση της απώλειας των οδοντικών ουσιών. Σε δόντια με μικρές απώλειες ενδείκνυνται μικρής έκτασης αποκαταστάσεις με εμφράξεις ενός, δύο ή τριών τοιχωμάτων. Η χρήση σύνθετων ρητινών στα πρόσθια δόντια είναι επιβεβλημένη λόγω αισθητικής ενώ η χρήση αμαλγάματος ή σύνθετων ρητινών στα οπίσθια δόντια αποτελεί σημείο αντιπαράθεσης στην οδοντιατρική κοινότητα. Σε περιπτώσεις όπου η απώλεια των οδοντικών ιστών είναι εκτεταμένη η ανάγκη ανασύστασης της μύλης καθιστά αναγκαία την τοποθέτηση ενδορριζικού άξονα και την κατασκευή στεφάνης ολικής επικάλυψης, ιδιαίτερα εάν το δόντι αποτελεί στήριγμα γέφυρας ή μερικής οδοντοστοιχίας (1, 4).​​​​​​​
Β. Η αποκατάσταση των ενδοδοντικά θεραπευμένων δοντιών ως παράγοντας που συμβάλει στην επιτυχία της ενδοδοντικής θεραπείας
Είναι γνωστό ότι τα ποσοστά επιτυχίας της ενδοδοντικής θεραπείας είναι πολύ μεγάλα ειδικά όταν πρόκειται για δόντια με ζωντανό πολφό όπου δεν παρατηρείται η μικροβιακή παρουσία στη πολφική κοιλότητα. Η επιτυχία αυτή εξαρτάται βεβαίως από την ερμητικότητα της έμφραξης των ρ.σ. αλλά και από άλλους παράγοντες όπως και από το βαθμό ερμητικότητας της αποκατάστασης της μύλης των δοντιών αυτών. Έτσι σε μία έρευνα αφού εξετάσθηκαν 1010 ενδοδοντικά θεραπευμένα δόντια που τελικά οδηγήθηκαν στην εξαγωγή, οι ερευνητές συμπέραναν ότι η ποιότητα της αποκατάστασης της μύλης αυτών των δοντιών έχει καθοριστική σημασία για την επιτυχία της ενδοδοντικής θεραπείας (15). Το γεγονός αυτό οφείλεται στην απουσία μικροβίων και άλλων βλαπτικών παραγόντων κάτω από την σωστή και υψηλής ποιότητας αποκατάσταση, που θα μπορούσαν να εισχωρήσουν μέσω του υλικού της έμφραξης των ρ.σ., να φθάσουν και να προκαλέσουν βλάβη στους περιακρορριζικούς ιστούς. Πράγματι έχει αποδειχθεί σε εργαστηριακές μελέτες ότι διάφορα μικρόβια ή/και παράγωγα τους π.χ. S. Epidermidis, ενδοτοξίνες, κ.α. μπορούν να διαπεράσουν καλά εμφραγμένους ρ.σ. σε όλο τους το μήκος (16, 17). Στην κλινική πράξη λοιπόν, όταν υπάρχει δευτερογενής τερηδόνα ή αποκατάσταση που δεν εφαρμόζει καλά στα όρια της κοιλότητας και γενικότερα όταν υπάρχει μεγάλος περιεμφρακτικός χώρος λόγω π.χ. θραύσης της αποκατάστασης, στη μύλη ενός ενδοδοντικά θεραπευμένου δοντιού, παρατηρείται συνεχής έκθεση του υλικού της έμφραξης του ρ.σ. στα υγρά του στόματος. Το γεγονός αυτό προκαλεί διάλυση του φυράματος που περιβάλει την γουταπέρκα μέσα στο ρ.σ. και ακολουθεί μικροδιείσδυση στοματικών υγρών, μικροβίων και παραγώγων τους κατά μήκος του μέχρι να φθάσουν σε σημείο απ' όπου μπορούν να επηρεάζουν βλαπτικά τους περιακρορριζικούς ιστούς. (Εικόνα 2).Εδώ γεννάται το ερώτημα, πόσο καιρό μπορεί να παραμείνει ένα ενδοδοντικά θεραπευμένο δόντι χωρίς αποκατάσταση της μύλης του; Δυστυχώς στη βιβλιογραφία δεν υπάρχουν σαφείς αναφορές για την ταχύτητα με την οποία μετακινούνται τα μικρόβια κατά μήκος ενός εμφραγμένου ρ.σ. έτσι ώστε να έχει ο οδοντίατρος τη δυνατότητα υπολογισμού της χρονικής περιόδου που μπορεί να είναι χαριστική. Ενδεικτικά αναφέρουμε ότι οι Torabinejad και συν το 1990 παρατήρησαν πλήρη διείσδυση μικροβίων κατά μήκος των εμφραγμένων ρ.σ. στο 50°/ο των δειγμάτων τους μετά από 19 ημέρες μόνο (19). Αν και Θεωρούμε ότι το πρόβλημα αυτό έχει πολλούς αστάθμητούς παράγοντες π.χ. το είδος και η διαλυτότητα του φυράματος που χρησιμοποιήθηκε (ενγελονούχο, ρητινούχο κ.ά.), το μέγεθος της επικοινωνίας μεταξύ των εμφρακτικών υλικών του ρ.σ. και των στοματικών υγρών κ.ά. πιστεύουμε ότι ο οδοντίατρος θα πρέπει να φροντίσει για την ταχύτερη και ασφαλέστερη αποκατάσταση του ενδοδοντικά θεραπευμένου δοντιού.

'Ενας ακόμη σοβαρός παράγοντας που καθορίζει την επιτυχία της ενδοδοντικής θεραπείας μετά την αποκατάσταση του δοντιού είναι η αποφυγή ιατρογενών σφαλμάτων ή/και συμβαμάτων κατά την τοποθέτηση προσθετικών ιδίως αποκαταστάσεων. Αν και το αντικείμενο αυτό εκφεύγει ταν σκοπού αυτού του κεφαλαίου, δεν μπορούμε παρά να παραδεχθούμε ότι δόντια με κατά τα άλλα αποδεκτές ενδοδοντικές θεραπείες, χάνονται στην  κλινική πράξη, όπως προαναφέρθηκε, κυρίως για λόγους κακής προσθετικής αποκατάστασης π.χ. διατρήσεις, κατάγματα δοντιών κ.ά. (Εικόνα 3).

Από τα προαναφερθέντα αποδεικνύεται ότι η σωστή αποκατάσταση της μύλης των ενδοδοντικά θεραπευμένων δοντιών, παίζει σημαντικό ρόλο στην επιτυχία της ίδιας της ενδοδοντικής θεραπείας. Βεβαίως τα όσα προαναφέρθηκαν δεν πρέπει, σε καμία περίπτωση, να υποβαθμίσουν την σημασία και την αξία της ερμητικής έμφραξης των ριζικών σωλήνων. Αντίθετα ο κλινικός οδοντίατρος θα πρέπει να είναι επιφυλακτικός όταν κληθεί να αποκαταστήσει κάποιο ενδοδοντικά Θεραπευμένο δόντι και επιβάλλεται πριν την έναρξη της αποκατάστασης να εκτιμήσει και να αξιολογήσει όχι μόνο την τωρινή επιτυχία της περίπτωσης αλλά και τη διατήρηση αυτής στο μέλλον, με σκοπό την πρόληψη των νόσων των περιακρορριζικών ιστών και την αποφυγή της ταλαιπωρίας του ασθενή και του ιδίου.
Περιπτώσεις που χρειάζονται ιδιαίτερη προσοχή είναι όταν ο ασθενής δεν αισθάνεται αυτόματο ή προκλητό πόνο αλλά παρατηρείται στη κλινική εξέταση η παρουσία συριγγίου ή επικοινωνίας του εμφρακτικού υλικού με το στοματικό περιβάλλον για αρκετό καιρό. Επίσης μπορεί στην ακτινογραφική εξέταση να παρατηρηθεί διαύγαση των περιακρορριζικών ιστών, απορρόφηση ρίζας, μη εμφραγμένο ή ατελώς εμφραγμένο ρ.σ., κ.α. (Εικόνα 4). 'Ολα τα προαναφερθέντα ευρήματα αποτελούν ισχυρό κίνητρο για την αυστηρή αξιολόγηση της επιτυχίας της ενδοδοντικής Θεραπείας από τον οδοντίατρο ο οποίος και Θα αποφασίσει πότε και σε ποιες περιπτώσεις Θα προβεί στην επανάληψή της πριν την τοποθέτηση της τελικής αποκατάστασης της μύλης.

Γ. Χρόνος εκτέλεσης της αποκατάστασης των ενδοδοντικά θεραπευμένων δοντιών
Είναι γενικά παραδεκτό σήμερα ότι η μόνιμη αποκατάσταση των ενδοδοντικά θεραπευμένων δοντιών θα πρέπει να γίνεται το συντομότερο δυνατόν (4-6). Οι παράγοντες που καθορίζουν του χρόνο έναρξης της μόνιμης αποκατάστασης των ενδοδοντικά θεραπευμένων δοντιών μπορεί να έχουν σχέση με α) την παρουσία κλινικών συμπτωμάτων μετά την τελική έμφραξη των ρ.σ., β) τη διείσδυση μικροβίων μεταξύ των υλικών της προσωρινής έμφραξης και των τοιχωμάτων της μύλης του δοντιού, γ) την επούλωση των περιακρορριζικών ιστών και δ) την ύπαρξη μειωμένης πρόγνωσης της ενδοδοντικής θεραπείας.
α) Παρουσία κλινικών συμπτωμάτων μετά την τελική έμφραξη των ριζικών σωλήνων
Τα κλινικά συμπτώματα τα οποία παρατηρούνται μετά την έμφραξη των ρ.σ. μπορεί να είναι πόνος διαφορετικής εντάσεως, ο οποίος είναι δυνατόν να συνδυασθεί και με οίδημα (18). Ο μετεμφρακτικός πόνος παρατηρείται σε συχνότητα που κυμαίνεται από 1,8 έως 38%, ειδικά στα άπολφα δόντια. Συνήθως όμως η ένταση και η διάρκεια αυτού του πόνου είναι μικρές δηλαδή ήπιος πόνος για 2-3 ημέρες και η αποκατάσταση μπορεί να αρχίσει αμέσως μετά. Αξιοσημείωτο είναι ότι όταν αυτή η αποκατάσταση είναι απλή, π.χ. έμφραξη αμαλγάματος ή ρητίνης, είναι δυνατόν να γίνει στην ίδια συνεδρία με την έμφραξη των ρ.σ (19, 20).
'Ομως εφόσον μετά την τελική έμφραξη των ρ.σ. εμφανισθεί έντονος πόνος, οίδημα ή συρίγγιο, Θα πρέπει να εξετασθεί η αιτία των συμπτωμάτων αυτών και να αξιολογηθεί η επιτυχία της ενδοδοντικής θεραπείας. Φυσικά η μόνιμη αποκατάσταση της μύλης του δοντιού θα πρέπει να αναβληθεί, σε αυτές τις περιπτώσεις, μέχρι την αντιμετώπιση και την πλήρη υποχώρηση των προαναφερθέντων συμπτωμάτων.
β) Διείσδυση μικροβίων μεταξύ των υλικών της προσωρινής έμφραξης και των τοιχωμάτων της μύλης του δοντιού
Κύριος σκοπός της προσωρινής έμφραξης της μύλης του ενδοδοντικά θεραπευμένου δοντιού θεωρείται η προστασία της πολφικής κοιλότητας από την μικροβιακή επιμόλυνση μετά από τις κοπιώδεις προσπάθειες απολύμανσής της. Κατά αυτό τον τρόπο παρεμποδίζεται η είσοδος στην πολφική κοιλότητα υπολειμμάτων τροφής, υγρών και μικροβίων της στοματικής κοιλότητας. Επίσης διατηρείται το αποτέλεσμα της χημικομηχανικής επεξεργασίας και έμφραξης των ρ. σωλήνων. Τα υλικά που συνήθως χρησιμοποιούνται για τον σκοπό αυτό είναι υλικά προσωρινών εμφράξεων π.χ. Cavit ή διάφορες κονίες όπως η φωσφορική, πολυκαρβοξυλική, υαλοινομερής, φύραμα ταυ οξειδίου του ψευδαργύρου με ευγενόλη κ.ά.).
Διάφοροι παράγοντες που επικρατούν στην στοματική κοιλότητα όπως οι δυνάμεις της μάσησης, η συχνή μεταβολή της θερμότητας κ.ά. επηρεάζουν την συμπεριφορά των προσωρινών εμφρακτικών υλικών. Γι' αυτόν τον λόγο, είναι αναγκαία η εκλογή εκείνου του υλικού που χαρακτηρίζεται από μεταβολές των διαστάσεών του, ανάλογες με εκείνες των οδοντικών ουσιών κατά τις θερμοκρασιακές εναλλαγές της στοματικής κοιλότητας. Επίσης, το ιδανικό προσωρινό υλικό θα πρέπει να παρουσιάζει έλλειψη πόρων στη δομή του, καλή πρόσφυση στα τοιχώματα της κοιλότητας διάνοιξης, αντίσταση στην σύνθλιψη και γενικά στην μηχανική καταπόνηση κ.ά. Από τη μελέτη της σχετικής βιβλιογραφίας φαίνεται ότι η ενισχυμένη κονία με ΖηΟΕ, η οξυφωσφορική και η πολυκαρβοξυλική κονία δεν συγκεντρώνουν τις προαναφερόμενες προϋποθέσεις, ενώ η υαλοϊονομερής κονία μπορεί να χρησιμοποιηθεί εφόσον προηγηθεί η αδροποίηση των οδοντικών ουσιών. "Όμως το Cavit φαίνεται να συγκεντρώνει την προτίμηση των περισσοτέρων ερευνητών εφόσον χρησιμοποιηθεί σε ικανό πάχος (3,5-4 χιλ.) μέσα στην κοιλότητα διάνοιξης και για χρονικό διάστημα που δεν ξεπερνά την μίαν εβδομάδα. Επίσης έχει αποδειχθεί ερευνητικά ότι όταν το Cavit αντικαθιστά την γοντταπέρκα στα 3 χιλ του στομίου του ρ.σ., η μικροδιείσδυση εντός αυτού μειώνεται σημαντικά, και τείνει να εκμηδενισθεί όταν αυτί για Caνit τοποθετηθεί αμάλγαμα (21, 22).
Σε έρευνες βρέθηκε ότι η αποτυχία της ενδοδοντικής θεραπείας είναι μεγάλη εκεί όπου  παρατηρείται μικροδιείσδυση, απώλεια των εμφρακτικών υλικών ή των τοιχωμάτων της μύλης του ενδοδοντικά θεραπευμένου δοντιού όπως και εκεί όπου παρατηρείται παραμονή  του προσωρινού εμφρακτικού υλικού για μεγάλο χρονικό διάστημα πριν τη μόνιμη αποκατάστασή του (15, 21, 22) (Εικόνα 5).
Επομένως, μετά τα τέλος της σωστής ενδοδοντικής Θεραπεία και εφόσον η τελική αποκατάσταση της μύλης πρόκειται να γίνει με απλή έμφραξη, ενδείκνυται η άμεση τοποθέτησή της στην ίδια συνεδρία της έμφραξης των ρ. σωλήνων όπως προαναφέρθηκε.
Όταν όμως η αποκατάσταση Θεωρείται πολύπλοκη, εμφράσσεται προσωρινά το δόντι με  Cavit, που Θα έχει ικανό πάχος (3-4 χιλ.) και μόνο για μερικές μέρες έως ότου αρχίσει το συντομότερο η τελική αποκατάσταση της μύλης.
γ} Επούλωση των περιακρορριζικών ιστών
Είναι γενικά παραδεκτό ότι η αποκατάσταση των ενδοδοντικά θεραπευμένων δοντιών που περιείχαν ζωντανό πολφό, θα πρέπει να αρχίσει τα συντομότερο δυνατόν. Σε ότι αφορά την αποκατάσταση των ενδοδοντικά θεραπευμένων δοντιών με περιακρορριζική βλάβη, δυστυχώς επικρατεί στον οδοντιατρικό κόσμο μία ανυποστήρικτη επιστημονικά άποψη, ότι δηλαδή η αποκατάσταση θα πρέπει να καθυστερήσει για απροσδιόριστο χρονικό διάστημα. Όμως η διάρκεια της επούλωσης των περιακρορριζικών ιστών, σε καλά Θεραπευμένα δόντια, μπορεί να κυμαίνεται από λίγούς μήνες έως και χρόνια (5) και είναι αυτονόητο ότι η αποκατάσταση δεν μπορεί να ακολουθήσει τον ίδιο ρυθμό για τους λόγους που προαναφέρθηκαν. Επομένως, εφόσον ο οδοντίατρος κρίνει, βάσει του ιστορικού, της παρουσία ή μη της περιακρορριζικής βλάβης.
Σήμερα, με την εξέλιξη της τεχνολογίας ο κλινικός οδοντίατρος έχει τη δυνατότητα να διαγνώσει σε πολύ σύντομο χρονικό διάστημα (2-3 μήνες), την εναπόθεση ή μη του οστίτου  ιστού στις περιακρορριζικές βλάβες μετά από μια ενδοδοντική θεραπεία. Έτσι μπορεί να την επαναλάβει σε περίπτωση αποτυχίας της ή να προχωρήσει στην αποκατάσταση της περίπτωσης. Τούτο πραγματοποιείται με την εφαρμογή της ψηφιακής αφαιρετικής ακτινογραφίας (Εικόνα 6).
δ) Ύπαρξη μειωμένης πρόγνωσης της ενδοδοντικής θεραπείας
Με το τέλος της ενδοδοντικής θεραπείας θα πρέπει να εκτιμηθεί η πρόγνωσή της όπως και η μελλοντική θεραπευτική αντιμετώπιση στην περίπτωση αποτυχίας της. Όταν  πιστεύεται ότι η επανάληψη θα βελτιώσει την πρόγνωση της ενδοδοντικής θεραπείας τότε αυτή πραγματοποιείται πριν την τοποθέτηση οποιασδήποτε αποκατάστασης. Στην περίπτωση όπου αφενός η επανάληψη δεν μπορεί να βελτιώσει την ποιότητα της έμφραξης και αφετέρου η μελλοντική λύση στην περίπτωση αποτυχίας της ενδοδοντικής θεραπείας, θα είναι η χειρουργική, τότε η αποκατάσταση του δοντιού Θα πρέπει να ολοκληρωθεί σύντομα. Εάν αντίθετα η μελλοντική λύση θα είναι η εξαγωγή του δοντιού, τότε η μόνιμη αποκατάσταση αναβάλλεται μέχρις ότου σταθεροποιηθεί η κλινική εικόνα.

Περιπτώσεις όπου πράγματι παρατηρείται μειωμένη πρόγνωση της ενδοδοντικής θεραπείας μπορεί να είναι δόντια με αδυναμία επεξεργασίας και έμφραξης ταυ συστήματος των ριζικών σωλήνων. Τέτοιες περιπτώσεις μπορεί να είναι η ενασβεστίωση ρ.σ, η παρουσία σπασμένου εργαλείου που παρεμποδίζει την πλήρη επεξεργασία του ρ.σ., «σκαλοπάτι» στα τοιχώματα του ρ.σ. που δεν μπορεί να προσπεραστεί κ.ά. Επιβαρυντικό στοιχείο σε όλες τις προαναφερθείσες περιπτώσεις αποτελεί η παρουσία και περιακρορριζικής βλάβης. Επίσης μειωμένη πρόγνωση μπορεί να έχει δόντι με καλή ενδοδοντική θεραπεία αλλά με κακή περιοδοντική στήριξη, ειδικά όταν πρόκειται να αποτελέσει στήριγμα γέφυρας.
Σε όλες τις προαναφερθείσες περιπτώσεις, εάν και όταν αποφασισθεί η αναβολή της μόνιμης αποκατάστασης, το δόντι θα πρέπει να δεχθεί μίαν «ενισχυμένη προσωρινή αποκατάσταση» που θα προσφέρει, για όσο χρόνο χρειασθεί, λειτουργικότητα, αισθητική και προστασία έναντι της μικροδιείσδυσης και των καταγμάτων. Τούτο μπορεί να επιτευχθεί όταν τοποθετηθεί στα οπίσθια δόντια μίαν επένθετη έμφραξη αμαλγάματος στην οποία τα φύματα του δοντιού αντικαθίστανται με το υλικό της έμφραξης και στα πρόσθια μίαν έμφραξη από σύνθετη ρητίνη σε συνδυασμό με προσωρινή στεφάνη, εφόσον χρειασθεί (23).
Δ. Οι ενδορριζικοί άξονες από τη σκοπιά της Ενδοδοντολογίας
Η χρήση ενδορριζικών αξόνων για την αποκατάσταση της μύλης ενός ενδοδοντικά θεραπευμένου δοντιού έχει ερευνηθεί και αναλυθεί διεξοδικά στο παρελθόν. Παλαιότερα, υπήρχε η άποψη ότι ο ενδορριζικός άξονας ενισχύει το δόντι και την αποκατάσταση συνολικά και αποτρέπει την εμφάνιση καταγμάτων της ρίζας. Σήμερα πιστεύεται, ότι η τοποθέτηση ενδορριζικού άξονα δεν ενισχύει την ρίζα του δοντιού και δεν μειώνει την πιθανότητα κατάγματος, αντίθετα, σε περιπτώσεις αλόγιστης αφαίρεσης οδοντίνης, την αυξάνει γεγονός που έχει αποδειχθεί με πληθώρα εργαστηριακών μελετών (25, 26). Παρά ταύτα, η τοποθέτηση ενδορριζικών αξόνων (χυτών ή προκατασκευασμένων) στα ενδοδοντικά θεραπευμένα δόντια αποτελεί καθημερινή αναγκαιότητα και πρακτική σε πολλές περιπτώσεις. Οι ενδείξεις για την τοποθέτηση των ενδορριζικών αξόνων στα ενδοδοντικά θεραπευμένα δόντια είναι λίγες και περιορίζονται σε περιπτώσεις όπου υπάρχει μεγάλη απώλεια των σκληρών οδοντικών ουσιών για την ανασύσταση της μύλης τους, την εξασφάλιση σταθερότητας στην προσθετική αποκατάσταση και την προστασία των εναπομεινάντων τοιχωμάτων της μύλης στην περίπτωση των χυτών αξόνων.
α. Προετοιμασία του ριζικού σωλήνα για ενδορριζικό άξονα
Μετά το τέλος της ενδοδοντικής θεραπείας γίνεται εκτίμηση των παραμειυάντων οδοντικών τοιχωμάτων κατ το είδος της αποκατάστασης του δοντιού που απαιτείται. Εφόσον κριθεί απαραίτητη η τοποθέτηση ενός ή περισσοτέρων ενδορριζικών αξόνων θα πρέπει πρώτα να παρασκευασθεί κατάλληλα ο ριζικός σωλήνας. Η διαδικασία της προετοιμασίας του ριζικού σωλήνα για να δεχθεί ενδορριζικό άξονα συμπεριλαμβάνει: 1) την αφαίρεση της γουταπέρκας και 2) την παρασκευή του ριζικού σωλήνα.
α.1)    Αφαίρεση της γουταπέρκας
Ή διαδικασία αυτή μπορεί να ολοκληρωθεί αμέσως μετά την τελική έμφραξη του ρ.σ., ενώ το δόντι βρίσκεται υπό απομόνωση και χωρίς να διαταραχθεί η ερμητικότητά της. Για την αφαίρεση της γουτταπέρκας, ως καλύτερο μέσο προτείνεται η χρήση ζεστού εργαλείου  εφόσον αυτό γίνεται αμέσως μετά την τελική έμφραξη και πριν πήξει το φύραμα. Τούτο συστήνεται για να μη διαταραχθεί η ερμητικότητα της έμφραξης των ριζικών σωλήνων. Επίσης συστήνεται η χρήση της εγγλυφίδας Gates-G1idden εφόσον προγραμματισθεί η διαδικασία της αφαίρεσης να γίνει μετά από μερικές ημέρες (27, 28). Σήμερα όμως με τη χρήση σύγχρονων συσκευών έμφραξης των ρ.σ. όπως είναι το «System Β», δεν χρειάζεται να γίνει η διαδικασία αφαίρεσης της γουταπέρκας, δεδομένου ότι με την τεχνική αυτή εξασφαλίζεται αυτόματα ο ελεύθερος χώρος που απαιτείται για την τοποθέτηση του άξονα.
Η γουταπέρκα αφαιρείται από το αυχενικό και μέσο τριτημόριο του ρ.σ. και παραμένει στο ακρορριζικό. Η έκταση της παραμένουσας γουταπέρκας εντός του ρ.σ. θα πρέπει να είναι τουλάχιστον 4-5 χιλ., είτε χρησιμοποιηθεί η μία ή η άλλη τεχνική αφαίρεσης ή και ο συνδυασμός και των δύο τεχνικών. Μελέτες έδειξαν ότι μικρότερη έκταση της γουταπέρκας αυξάνει την πιθανότητα μικροδιείσδυσης από το ακρορρίζιο με αποτέλεσμα την αποτυχία της ενδοδοντικής θεραπείας. Αξιοσημείωτο είναι ότι το είδος της μεθόδου έμφραξης του ρ.σ. που χρησιμοποιείται (πλάγια ή κάθετη συμπύκνωση ή η τεχνική  θερμοπλαστικοποιημένης γουταπέρκας) δεν συσχετίζεται με την εμφάνιση μικροδιείσδυσης  μετά την αφαίρεσή της προκειμένου να κατασκευασθεί ενδορριζικός άξονας (27-29).
α.2)    Παρασκευή του ριζικού σωλήνα
Είναι γνωστό ότι μετά την αφαίρεση της γουταπέρκας από τον ρ.σ. υπάρχει συνήθως η ανάγκη διαμόρφωσής του προκειμένου να δεχθεί έναν άξονα. Η διαδικασία αυτή συνήθως  πραγματοποιείται με εγγλυφίδες Gates-Glidden και Pesso εφόσον προγραμματίζεται η τοποθέτηση χυτού άξονα. Για την τοποθέτηση προκατασκευασμένων αξόνων, συνήθως ο ρ.σ. παρασκευάζεται με ειδικές εγγλνφίδες που παρέχονται μαζί με τους άξονες και οι οποίες έχουν ανάλογη διάμετρο.
Κατά την παρασκευή χώρου για ενδορριζικό άξονα σε ένα ριζικό σωλήνα εκτός από την παραμονή 4-5 χιλ. γουταπέρκας στο ακρορριζικό του τμήμα, πράγμα που κατά κάποιον τρόπο καθορίζει το μήκος του άξονα, είναι πολύ σημαντικό να τηρούνται και άλλες προϋποθέσεις:
α.2.1) Η προετοιμασία να γίνεται με απομόνωση του δοντιού επειδή η εφαρμογή του απομονωτήρα κατά την παρασκευή του ρ.σ., διατηρεί τις συνθήκες ασηψίας του και προσφέρει σοβαρά πλεονεκτήματα (Εικόνα 7). Εφόσον το υπό θεραπεία δόντι δεν μπορεί να απομονωθεί, ο απομονωτήρας τοποθετείται στα διπλανά δόντια. Μετά το τέλος της συνεδρίας αυτής και μέχρι να γίνει η συγκόλληση του άξονα, το δόντι εμφράσσεται από τον οδοντίατρο με τον τρόπο που προαναφέρθηκε αφού εγκλεισθεί κατάλληλο για τον ρ.σ. αντισηπτικό φάρμακο.

α.2.2) Η παρασκευή του ρ.σ. να είναι συντηρητική χωρίς υπέρμετρη αφαίρεση οδοντίνης. Επιβάλλεται δε η παραμονή τουλάχιστον 1 -1.5 χιλ υγιούς οδοντικής ουσίας περιφερικά του άξονα στο αυχενικό τμήμα, ενώ στο ακρορριζικό θα πρέπει να αφαιρείται όσο το δυνατόν λιγότερη οδοντίνη. Έρευνες απέδειξαν ότι όσο αφαιρείται οδοντίνη με σκοπό την τοποθέτηση άξονα με μεγάλη διάμετρο, τόσο αυξάνονται οι τάσεις που ασκούνται στα τοιχώματα της ρίζας και επόμενο είναι να αυξάνεται ταυτόχρονα και η πιθανότητα κατάγματός της. Αξιοσημείωτο είναι ότι η μείωση της διαμέτρου της ρίζας κατά 1 χιλ. αυξάνει κατά έξι φορές την πιθανότητα κατάγματός της από έναν ενδορριζικό άξονα (30), γεγονός που στην κλινική πράξη σημαίνει ότι πρέπει να δοθεί μεγάλη προσοχή όταν παρασκευάζονται δόντια ή ρίζες δοντιών με μικρή διάμετρο (π.χ. τομείς της κάτω γνάθου, άπω ρίζα γομφίου άνω κ.ά.) προς αποφυγήν κλινικών συμβαμάτων. Αξιοσημείωτο είναι ότι το πάχος της υγιούς οδοντικής ουσίας, που προαναφέρθηκε, και το οποίο περιβάλλει τον άξονα καθορίζει σε πολλές περιπτώσεις και τη διάμετρό του που πρέπει να τηρείται από τον επεμβαίνοντα προς αποφυγήν καταγμάτων.
α.2.3) Η παρασκευή να γίνεται παράλληλα προς τον επιμήκη άξονα της συγκεκριμένης ρίζας του δοντιού όπου επιδιώκεται η τοποθέτηση του άξονα. Τούτο επιβάλλει την κλινική και ακτινογραφική εξέταση για τη διαπίστωση της θέσης και της φοράς της ρίζας. Η παρέκκλιση από αυτήν την προϋπόθεση πιθανόν να δημιουργήσει σοβαρό κλινικό πρόβλημα όπως η διάτρηση (Εικόνα 8).ΕΙΚΟΝΑ 8. Διάτρηση άπω ρίζας του 36 από χυτό ενδορριζικό άξονα. Η φορά ένθεσης του άξονα δεν είναι παράλληλη προς τον επιμήκη άξονα της συγκεκριμένης ρίζαςα.2.4) Η δημιουργία περιφερικής απόφραξης στο αυχενικό άκρο της μύλης, συγκράτηση «στεφάνης βαρελιού», αντισταθμίζει τις τάσεις που παράγονται κατά τη τοποθέτηση και λειτουργία των χυτών αξόνων αλλά και προστατεύει τα εναπομείναντα τοιχώματα της μύλης (31). Άμεσο αποτέλεσμα είναι η παύση της λειτουργίας της σφήνας που ασκεί ο άξονας στα τοιχώματα του ρ.σ. και η πρόληψη καταγμάτων μύλης και ρίζας των ενδοδοντικά θεραπευμένων δοντιών (Εικόνα 9).
ΕΙΚΟΝΑ 9. Α. Ο άξονας δημιουργεί τάσεις εντός του σωλήνα και λειτουργεί ως σφήνα με αποτέλεσμα τα κάταγμα της ρίζας. Β. Η περιφερική απόφραξη προστατεύει τους σκληρούς οδοντικούς ιστούς.Η περιφερική απόφραξη ή συγκράτηση συνίσταται στη δημιουργία αύλακας περιφερικά του στομίου του ριζικού σωλήνα και την επικάλυψη των τοιχωμάτων οδοντίνης από το κράμα του άξονα έως την περιφερική αύλακα. Η πρόγνωση του δοντιού θεωρείται καλύτερη όταν ο άξονας απολήγει σε απόσταση 1 - 2 mm από το όριο παρασκευής ενώ η  στεφάνη ολικής κάλυψης απολήγει στον αυχένα του δοντιού και σε απόσταση 1-2 χιλ από τα  όρια του άξονα. Κατά αυτόν τον τρόπο εξασφαλίζεται διπλή συγκράτηση των τοιχωμάτων του δοντιού από τον άξονα και τη στεφάνη (Εικόνα 10). Πρόσφατες εργαστηριακές έρευνες απέδειξαν ότι η παρουσία της περιφερικής συγκράτησης ενισχύει τις μηχανικές ιδιότητες του  συστήματος δόντι-άξονας-στεφάνη και αυξάνει την αντίσταση του δοντιού στη θραύση (32, 33, 34). Αξιοσημείωτο είναι ότι όταν έχει καταστραφεί όλη σχεδόν η μύλη του υπό αποκατάσταση δοντιού, επιβάλλεται η χειρουργική επιμήκυνσή της προκειμένου να επιτευχθεί η περιφερική απόφραξη.ΕΙΚΟΝΑ 10. Α. Η περιφερική αύλακα. Β. Ο χυτός ενδορριζικός άξονας εφαρμόζει  και αποφράζει το στόμιο του ρ.σ. και την αύλακα. Γ. Η στεφάνη ολικής κάλυψης εφαρμόζει στην οδοντίνη 1-2 χιλ πέραν  του άξονα.Το πλεονέκτημα αυτό δεν μπορεί να εφαρμοστεί στους προκατασκευασμένους άξονες.  Εάν ο άξονας απολήγει στο όριο της παρασκευής και παρουσιαστεί χαλάρωσή του, συχνά, εμφανίζεται κάταγμα του δοντιού (35, 36).

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