28/08/2018 0 Σχόλια
ENDODONTOLOGY - Evaluation of different methods for the root-end cavity preparation
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.
REFERENCES
1. Kim S. Endodontic microsurgery. In: Cohen S, Burns R, editors. Pathways of the pulp 8th ed. St Louis: Mosby Comp; 2002. p. 683-725.
2. Carr G. Ultrasonic root end preparation. Dent Clin N Am 1997; 41:541-54.
3. Bertrand G, Festal F, Barailly R. Use of ultrasound in apicoectomy. Quintessence Int 1976;7:9-12.
4. Wuchenich G, Meadows D, Torabinejad M. A comparison between two root end preparation techniques in human cadavers. J Endod 1994;20:279-82.
5. Engel T, Steiman R. Preliminary investigation of ultrasonic root end preparation. J Endod 1995;21:443-5.
6. Gorman M, Steiman R, Gartner A. Scanning electron microscopic evaluation of root end preparation. J Endod 1995;21:13-7.
7. Gutmann J, Saunders W, Nguyen L, Guo I, Saunders E. Ultrasonic root end preparation part 1. SEM analysis. Int Endod J 1994;27:318-24.
8. Waplington M, Lumley P, Walmsley D, Blunt L. Cutting ability of an ultrasonic retrograde cavity preparation instrument. Endod Dent Traumatol 1995;11:177-80.
9. Zuolo M, Perin F, Ferreira M, Faria F. Ultrasonic root end preparation with smooth and diamond-coated tips. Endod Dent Traumatol 1999;15:265-8.
10. Rainwater A, Jeansonne BG, Sarkar N. Effects of ultrasonic rootend preparation on microcrack formation and leakage. J Endod 2000;26:72-5.
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.
14. Abedi RH, Van Mierlo LB, Wilder-Smith P, Torabinejad M. Effects of ultrasonic root-end preparation on the root apex. Oral Surg Oral Med Oral Path Oral Radiol Endod 1995;80:207-13.
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.
16. Gilheany PA, Figdor D, Tyas MJ. Apical dentin permeability and microleakage associated with root end resection and retrograde filling. J Endod 1994;20:22-6.
17. Rubinstein R, Kim S. Short-term observation of the results of endodontic surgery with the use of a surgical operation microscope and super-EBA as root-end filling material. J Endod 1999;25:43-8.
18. Gray G, Hatton FJ, Holtzmann D, Jenkins D, Nielsen C. Quality of root-end preparations using ultrasonic and rotary instrumentation in cadavers. J Endod 2000;26:281-3.
19. Peters CI, Peters OA, Barbakow F. An in vitro study comparing root-end cavities prepared by diamond-coated and stainless steel ultrasonic retrotips. Int Endod J 2001;34:142-8.
20. Morgan L, Marshall J. A scanning electron microscopic study of in vivo ultrasonic root-end preparations. J Endod 1999;25:567-70.
21. Frank R, Antrim D, Bakland L. The effect of retrograde cavity preparation in the root apexes. Endod Dent Traumatol 1996;12: 100-3.
22. Von Arx T, Walker W. Microsurgical instruments for root end cavity preparation following apicoectomy: a literature review. Endod Dent Traumatol 2000;16:47-62.
23. Von Arx T, Kurt B. Root-end cavity preparation after apicoectomy using a new type of sonic and diamond-surfaced retrotip: a 1-year follow up study. Oral Maxillofac Surg 1999;57:656-61.
root_end_cavity_preparation.pdf
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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