0099-2399/90/1606-0279/$02.00/0 JOURNAL OF ENDODONTICS Copyright 9 1990 by The American Association of Endodontists
Printed in U.S.A,
VOL. 16, NO. 6, JUNE 1990
Scanning Electron Microscope Observation of Canal Cleanliness Ely Mandel, DCD, DSO, Pierre Machtou, DCD, DSO, and Shimon Friedman, DMD
The aim of this study was to evaluate the cleansing efficiency of three root canal preparation techniques. The distal root canals of mandibular molars, divided into three groups of four teeth each, were prepared according to the following techniques: manual (serial), ultrasonic (Cavi-Endo), and automated (Canal Finder). The canal wall surfaces were examined under a scanning electron microscope at three levels. No preparation technique was found to result in any characteristic microscopic features that distinguished it from the other techniques. The lack of such differences makes it impossible to establish objective criteria for comparing these techniques in terms of root canal cleanliness. It was established that even canals that appeared to be clean included areas coated with smear layer and having uninstrumented areas and even pulpal tissue debris.
Scanning electron microscopic studies, on the other hand, focused on observing the smear layer, the patency of dentinal tubules, instrument striations, and calcospherites. These studies have conflicting results. Manual preparation was found to be more effective than both automated preparation (10) and ultrasonic preparation (11). In other studies ultrasonic preparation resulted in cleaner canals (9). Several researchers did not find significant differences between preparation techniques (12, 13). The purpose of this study was to evaluate the cleansing efficiency of preparation techniques by comparing the results of manual serial preparation, endosonic preparation, and automated preparation with the Canal Finder System. MATERIALS AND METHODS Twelve freshly extracted mandibular molars with mature apices were selected for this study. Endodontic access cavities were prepared which allowed direct access to all root canals. The teeth were divided into three groups of four teeth each.
Thorough biomechanical preparation of the root canal is unanimously considered to be one of the major requirements for successful endodontic treatment (1). The prime objectives of this phase are to remove completely the organic substance that may be infected, or may become so, and to shape the root canal in conformity with the principles of obturation (2). A variety of techniques and instruments have been introduced for preparing root canals. Manual preparation techniques vary both in the type of instruments used and in the sequence of using them. The serial, or telescopic, technique was reported to be superior to other manual techniques (3). Automated techniques utilize devices that rotate files, displace them vertically, or that do both movements. The newest addition to this group is the Canal Finder (4), which was reported to be an efficient pathfinder in narrow, curved root canals (5, 6). The introduction of ultrasonic devices for canal preparation was followed by reports of their superior efficacy in irrigating the entire length of the canal (7, 8), cutting dentin, and cleansing the canal (9). Cleansing efficiency has been one of the issues discussed with regard to preparation techniques. It has been studied extensively, mainly by means of observation of the root canal walls and contents after preparation. Residual pulpal tissue debris is the principal criterion that has been evaluated. Removal of the predentin is the other main criterion in light microscopic studies.
FIG 1. LOW magnification of a split root specimen. The root canal space (C) is not involved by the longitudinal grooves (S) prepared for facilitating the split of the root with wood scissors. The a r r o w points to a crack resulting from preparation for scanning electron microscopy (original magnification •
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Journal of Endodontics
o
FiG 2. Coronal canal level after preparation with A (manual), B (ultrasonic), and C (Canal Finder) techniques. Pulpal tissue debris and smear layer appear similar in the three specimens. Occasionally, partial occlusion of the dentinal tubuli by the smear layer may be observed (arrows) (original magnification x3000).
FIG 3. Middle canal level after preparation with A (manual), B (ultrasonic), and C (Canal Finder) techniques. No particular differences may be observed between the three specimens, apart from diamond file marks (arrow) in the specimen from group B (original magnification x900).
Vol. 16, No. 6, June 1990
Techniques and Canal Cleanliness
The root canals of the teeth in each group were prepared according to one technique, as follows: group A - - m a n u a l serial preparation, according to Schilder (2); group B--ultrasonic technique, according to Martin et al. (9), with the CaviEndo (Caulk-Dentsply, Milford, DE); and group C--Canal Finder System (Soeiete Endo Technic, Marseille, France), according to Levy (4). All of the teeth were prepared by the same operator. The preparation of each root canal was carried out with new instruments to ISO #25. Copious intermittent irrigation with 2.5% sodium hypochlorite was used during the preparation. At the completion of the preparation, each canal was flushed with 6 ml of sodium hypochlorite followed by 6 ml of saline solution and dried with paper points. After instrumentation, the distal roots were separated from the mesial roots by interradicular section and were used for this study (the mesial roots were used for a parallel study). The roots were grooved superficially in a longitudinal direction by discs and split by means of wood scissors (Fig. 1). The split specimens were prepared for scanning electron microscopic observation of the canal wall surfaces by undergoing fixation, dehydration, and gold coating. A low magnification (x 10 to 90) overall view of the specimens was obtained first. Further observations were carried out at the apical, middle, and coronal levels of the root canals. Individual areas at each level were observed at three magnifications, x90 to 900, x900 to 2,000, and x2000 to 4300. Altogether 442 photomicrographs were obtained. RESULTS Pulpal tissue debris, smear layer, and instrument striations were frequently observed in all of the examined specimens, regardless of the preparation technique. No specific pattern of these findings was observed in any particular group. At the coronal root level (Fig. 2) and the middle root level (Fig. 3), pulpal tissue debris and smear layer were found in abundance. In combination with the instrument striations they characterized the instrumented surfaces of the canal walls. The pulpal debris was arranged along the instrument striations. At the middle and coronal levels of all specimens, uninstrumented areas were observed alongside the instrumented surfaces (Fig. 4). These uninstrumented areas were character-
281
ized by calcospherites, by patent dentinal tubuli, and by the absence of debris, smear layer, and instrument striations. Occasionally, smeared debris was found in the uninstrumented areas, having been pushed there from the adjacent instrumented sites. At the apical levels of the specimens, all of the characteristics of the instrumented areas were observed consistently, but not the characteristics of uninstrumented areas (Fig. 5). DISCUSSION Observation of the canal walls of all of the specimens demonstrated the existence of uninstrumented surfaces, regardless of the root canal preparation technique. In earlier studies, however, uninstrumented canal surfaces were reported infrequently (13, 14) Cleansing efficiency studies of preparation techniques tend to focus on the cleaned portions of the canals, often resorting to high magnifications which limit the observed field (12, 13). Only observation of longitudinal sections of the whole canal may demonstrate uninstrumented enclaves, interspersed among the dominant instrumented surfaces (13). Uninstrumented areas were observed in the coronal and the middle root levels, but not in the apical level. This finding may be explained by the smaller diameter of the apical third of the canal, which increases the probability of instrument-wall contact. However, the marked reduction in the density of dentin tubules at the apical level does not permit the observation of calcospherites, which are the only definite evidence of uninstrumented surfaces. In the instrumented areas of the specimens, at all levels, no differences were noticed between the tested preparation techniques. The finding of abundant debris in all of the specimens is in agreement with reports in which residual debris was observed in canals after instrumentation and irrigation with sodium hypochlorite (10-16). These results do no support earlier evidence for sodium hypochlorite being a superior irrigant for the removal of debris from the canals (8, 17, 18). Our study did not compare the ability of sodium hypochlorite to remove debris with that of other irrigants. However, it suggests that sodium hypochlorite, whose cleansing efficiency depends on a direct contact with the tissue as well as on the duration of this contact and the volume of the irrigant, does not cleanse the canals completely. It has been suggested that a synergistic relationship exists
FIG 4. Instrumented and uninstrumented areas in proximity. The instrumented areas (A) are characterized by instrument striations, smear layer, and pulpal tissue debris. The uninstrumented areas (B) show calcospherites (black arrows) and patent dentinal tubuli. Smeared debris (white arrows) is occasionally pushed onto the uninstrumented areas by the instrumentation and irrigation (original magnifications: left, x36; middle, x300; right, x 1200).
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between ultrasonic vibration and sodium hypochlorite (8, 9), that improves the elimination of debris from the prepared canals (9, 18). This ultrasonic activation of sodium hypochlorite was attributed to the effects of cavitation and acoustic streaming (7-9). Furthermore, an improved cleansing effect of ultrasonic preparation in the apical portion of the canal was attributed to facilitated irrigation by the ultrasonic devices at the apical level (7-14). The finding of debris at all root levels of all of the specimens in our study, including the ones prepared ultrasonically in combination with sodium hypochlorite, does not support these suggestions. Recent reports dismissed the cavitation and acoustic streaming effects as being minimal in the root canal, existing only when the files are not loaded by wall contact (14, 16, 19). These reports may explain our findings, which are in agreement with earlier reports that questioned the ability of the ultrasonic system to affect the entire root canal volume, particularly the apical area (11-13). It appears that even ultrasonically energized continuous irrigation does not allow the sodium hypochlorite the necessary conditions for optimal activity on pulpal tissue debris. It has also been reported that ultrasonic preparation with sodium hypochlorite resulted in the elimination of the smear layer (8, 9, 14, 15). In our experiment, the ultrasonic endodontic system had no effect on the presence or absence of smear layer on the canal walls. Our findings confirm previous reports in which smear layer was found on instrumented canal surfaces regardless of the preparation technique (20). It appears that only the use of EDTA during preparation may reduce the amount of smear layer (16, 17). Although some prep~ratibn techniques have been considered to have advantages over others, several studies failed to demonstrate any such advantages (10, 12, 13). Turek and Langeland (10) concluded that the efficacy of cleaning the canal depends on the endodontic anatomy rather than on the technique used. In a later report Langeland et al. (13) confirmed the lack of differences among preparation techniques. They suggested that some of the published histological material that demonstrated the advantages of specific techniques could not be trusted to represent the factual condition of the canals. In the present study the new automated device, the Canal Finder System, was not found to be superior or inferior to the manual or the ultrasonic techniques. In fact, its design does not offer an advantage in this aspect of canal preparation. However, recent reports suggest that it may be advantageous in other respects, namely, pathfinding (6) and speeding the preparation (5) of narrow, curved canals and conforming to canal curvatures without altering them (5, 6). Our study was not intended to examine these aspects of the tested techniques and therefore does not demonstrate them. Under the conditions of the present study, it was not possible to distinguish between the results of the different canal preparation techniques in terms of canal wall surface appearance. The same characteristics of the prepared surfaces were found in association with each of the tested techniques. This fact and the subjectivity of interpretation of the observed image are the factors that make comparative studies based on canal wall surfaces inconclusive. Thus, it appears from this study, as from other studies, that scanning electron microscopic observation of canal walls is unsuitable for qualitative comparison of the cleansing efficiency of preparation techniques. Furthermore, a thoroughly instrumented and cleansed root canal should not be expected to be free of smear layer,
Journal of Endodontics
FIG 5. Apical canal level after preparation with A (manual), B (ultrasonic), and C (Canal Finder) techniques. The three specimens appear similar, with evidence of instrument striations, pulpal tissue debris, and smear layer (original magnification x900).
Techniques and Canal Cleanliness
Vol. 16, No. 6, June 1990
uninstrumented areas, and even pulpal tissue debris. These factors should not be considered as dominant reasons for preferring one preparation technique over another. We thank Professor Henry Boulekbache, Laboratory of Comparative Anatomy, University of Paris VII, for his valuable help in the realization of the experimental protocol. Drs. Mandel and Machtou are affiliated with the School of Dentistry, University of Paris VII, Paris, France. Dr. Friedman is affiliated with the Hebrew Llniversity-Hadassah School of Dental Medicine, Jerusalem, Israel.
References 1. Guttman JL, Dumsha T. Cleaning and shaping the root canal system. Pathways of the pulp. 4th ed. St. Louis: CV Mosby, 1987. 2. Schilder H. Cleaning and shaping the root canal. Dent Clin North Am 1974;18:269. 3. Walton RE. Histologic evaluation of different methods of enlarging the pulp canal space. J Endedon 1976;2:304-11. 4. Levy G. Une nouvelle instrumentation pour realiser mecaniquement rensemble de la procedure endodontique. Rev Fr Endod 1984; 13:11-8. 5. Tronstad L, Niemczyk SP. Efficacy and safety tests of six automated devices for root canal instrumentation. Ended Dent Traumato11986;2:270-6. 6. Goldman M, Sakurai E, Kronman J, Tenca JI. An in vitro study of the pathfinding ability of a new automated handpiece. J Endodon 1987;13:42933. 7. Teplitsky PE, Chenail BL, Mack B, Machnee CH. Endodontic irrigationa comparison of endosonic and syringe delivery systems. Int Endod J 1987;20:233-41.
283
8. Cameron JA. The synergistic relationship between ultrasound and sodium hypochlorite: a scanning electron microscope evaluation. J Endodon 1987; 13:541-5. 9. Martin H, Cunningham W. Endosonics- the ultrasonic synergistic system of endodontics. Ended Dent Traumato11985;1:201-6. 10. Turek T, Langeland K. A light microscopic study of the efficacy of the telescopic and the Giromatic preparation of root canals. J Endodon 1982;8:437-43. 11. Reynolds MC, Madison S, WaJton RE, Krell KV, Rittman BRJ. An in vitro histological comparison of the step-back, sonic and ultrasonic instrumentation technique in small curved root canals. J Endodon 1987;13:307-14. 12. Tauber R, Morse DR, Sinai IA, Furst ML. A magnifying lens comparative evaluation of conventionaJ and ultrasonically energized filing. J Endodon 1983;9:269-74. 13. Langeland K, Liao K, Pascon EA. Work saving devices in endodontics: efficacy of sonic and ultrasonic techniques. J Endodon 1985; 11:499-510. 14. Ahmad M, Pitt Ford TR, Crum LA. Ultrasonic debridement of root canals: acoustic streaming and its possible role. J Endedon 1987;13:490-9. 15. Ahmad M, Pitt Ford TR, Crum LA. Ultrasonic debridement of root canals: an insight into the mechanisms involved. J Endodon 1987;13:93-101. 16. Goldman LB, Goldman M, Kronman JH, SunLin P. The efficacy of several irrigating solutions for endodontics: a scanning electron microscopic study. Oral Surg 1981 ;52:197-204. 17. Yameda RS, Armas A, Goldman M, SunLin P. A scanning electron microscopic comparison of a high volume final flush with several irrigating solutions; Part 3. J Endodon 1983;9:137-41. 18. Griffiths BM, Stock CJR. The efficiency of irrigants in removing root canal debris when used with an ultrasonic preparation technique. Int Endod J 1986;19:277-84. 19. Walmsley AD. Ultrasound and root canal treatment: the need for scientific evaluation. Int Ended J 1987;20:105-11. 20. Goldberg F, Soares I. Massone EJ, Soares IM. Comparative debridement study between hand and sonic instrumentation of the root canal. Endod Dent Traumato11988;4:229-34.
Printed in U.S.A,
VOL. 16, NO. 6, JUNE 1990
Scanning Electron Microscope Observation of Canal Cleanliness Ely Mandel, DCD, DSO, Pierre Machtou, DCD, DSO, and Shimon Friedman, DMD
The aim of this study was to evaluate the cleansing efficiency of three root canal preparation techniques. The distal root canals of mandibular molars, divided into three groups of four teeth each, were prepared according to the following techniques: manual (serial), ultrasonic (Cavi-Endo), and automated (Canal Finder). The canal wall surfaces were examined under a scanning electron microscope at three levels. No preparation technique was found to result in any characteristic microscopic features that distinguished it from the other techniques. The lack of such differences makes it impossible to establish objective criteria for comparing these techniques in terms of root canal cleanliness. It was established that even canals that appeared to be clean included areas coated with smear layer and having uninstrumented areas and even pulpal tissue debris.
Scanning electron microscopic studies, on the other hand, focused on observing the smear layer, the patency of dentinal tubules, instrument striations, and calcospherites. These studies have conflicting results. Manual preparation was found to be more effective than both automated preparation (10) and ultrasonic preparation (11). In other studies ultrasonic preparation resulted in cleaner canals (9). Several researchers did not find significant differences between preparation techniques (12, 13). The purpose of this study was to evaluate the cleansing efficiency of preparation techniques by comparing the results of manual serial preparation, endosonic preparation, and automated preparation with the Canal Finder System. MATERIALS AND METHODS Twelve freshly extracted mandibular molars with mature apices were selected for this study. Endodontic access cavities were prepared which allowed direct access to all root canals. The teeth were divided into three groups of four teeth each.
Thorough biomechanical preparation of the root canal is unanimously considered to be one of the major requirements for successful endodontic treatment (1). The prime objectives of this phase are to remove completely the organic substance that may be infected, or may become so, and to shape the root canal in conformity with the principles of obturation (2). A variety of techniques and instruments have been introduced for preparing root canals. Manual preparation techniques vary both in the type of instruments used and in the sequence of using them. The serial, or telescopic, technique was reported to be superior to other manual techniques (3). Automated techniques utilize devices that rotate files, displace them vertically, or that do both movements. The newest addition to this group is the Canal Finder (4), which was reported to be an efficient pathfinder in narrow, curved root canals (5, 6). The introduction of ultrasonic devices for canal preparation was followed by reports of their superior efficacy in irrigating the entire length of the canal (7, 8), cutting dentin, and cleansing the canal (9). Cleansing efficiency has been one of the issues discussed with regard to preparation techniques. It has been studied extensively, mainly by means of observation of the root canal walls and contents after preparation. Residual pulpal tissue debris is the principal criterion that has been evaluated. Removal of the predentin is the other main criterion in light microscopic studies.
FIG 1. LOW magnification of a split root specimen. The root canal space (C) is not involved by the longitudinal grooves (S) prepared for facilitating the split of the root with wood scissors. The a r r o w points to a crack resulting from preparation for scanning electron microscopy (original magnification •
279
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Mandel et al.
Journal of Endodontics
o
FiG 2. Coronal canal level after preparation with A (manual), B (ultrasonic), and C (Canal Finder) techniques. Pulpal tissue debris and smear layer appear similar in the three specimens. Occasionally, partial occlusion of the dentinal tubuli by the smear layer may be observed (arrows) (original magnification x3000).
FIG 3. Middle canal level after preparation with A (manual), B (ultrasonic), and C (Canal Finder) techniques. No particular differences may be observed between the three specimens, apart from diamond file marks (arrow) in the specimen from group B (original magnification x900).
Vol. 16, No. 6, June 1990
Techniques and Canal Cleanliness
The root canals of the teeth in each group were prepared according to one technique, as follows: group A - - m a n u a l serial preparation, according to Schilder (2); group B--ultrasonic technique, according to Martin et al. (9), with the CaviEndo (Caulk-Dentsply, Milford, DE); and group C--Canal Finder System (Soeiete Endo Technic, Marseille, France), according to Levy (4). All of the teeth were prepared by the same operator. The preparation of each root canal was carried out with new instruments to ISO #25. Copious intermittent irrigation with 2.5% sodium hypochlorite was used during the preparation. At the completion of the preparation, each canal was flushed with 6 ml of sodium hypochlorite followed by 6 ml of saline solution and dried with paper points. After instrumentation, the distal roots were separated from the mesial roots by interradicular section and were used for this study (the mesial roots were used for a parallel study). The roots were grooved superficially in a longitudinal direction by discs and split by means of wood scissors (Fig. 1). The split specimens were prepared for scanning electron microscopic observation of the canal wall surfaces by undergoing fixation, dehydration, and gold coating. A low magnification (x 10 to 90) overall view of the specimens was obtained first. Further observations were carried out at the apical, middle, and coronal levels of the root canals. Individual areas at each level were observed at three magnifications, x90 to 900, x900 to 2,000, and x2000 to 4300. Altogether 442 photomicrographs were obtained. RESULTS Pulpal tissue debris, smear layer, and instrument striations were frequently observed in all of the examined specimens, regardless of the preparation technique. No specific pattern of these findings was observed in any particular group. At the coronal root level (Fig. 2) and the middle root level (Fig. 3), pulpal tissue debris and smear layer were found in abundance. In combination with the instrument striations they characterized the instrumented surfaces of the canal walls. The pulpal debris was arranged along the instrument striations. At the middle and coronal levels of all specimens, uninstrumented areas were observed alongside the instrumented surfaces (Fig. 4). These uninstrumented areas were character-
281
ized by calcospherites, by patent dentinal tubuli, and by the absence of debris, smear layer, and instrument striations. Occasionally, smeared debris was found in the uninstrumented areas, having been pushed there from the adjacent instrumented sites. At the apical levels of the specimens, all of the characteristics of the instrumented areas were observed consistently, but not the characteristics of uninstrumented areas (Fig. 5). DISCUSSION Observation of the canal walls of all of the specimens demonstrated the existence of uninstrumented surfaces, regardless of the root canal preparation technique. In earlier studies, however, uninstrumented canal surfaces were reported infrequently (13, 14) Cleansing efficiency studies of preparation techniques tend to focus on the cleaned portions of the canals, often resorting to high magnifications which limit the observed field (12, 13). Only observation of longitudinal sections of the whole canal may demonstrate uninstrumented enclaves, interspersed among the dominant instrumented surfaces (13). Uninstrumented areas were observed in the coronal and the middle root levels, but not in the apical level. This finding may be explained by the smaller diameter of the apical third of the canal, which increases the probability of instrument-wall contact. However, the marked reduction in the density of dentin tubules at the apical level does not permit the observation of calcospherites, which are the only definite evidence of uninstrumented surfaces. In the instrumented areas of the specimens, at all levels, no differences were noticed between the tested preparation techniques. The finding of abundant debris in all of the specimens is in agreement with reports in which residual debris was observed in canals after instrumentation and irrigation with sodium hypochlorite (10-16). These results do no support earlier evidence for sodium hypochlorite being a superior irrigant for the removal of debris from the canals (8, 17, 18). Our study did not compare the ability of sodium hypochlorite to remove debris with that of other irrigants. However, it suggests that sodium hypochlorite, whose cleansing efficiency depends on a direct contact with the tissue as well as on the duration of this contact and the volume of the irrigant, does not cleanse the canals completely. It has been suggested that a synergistic relationship exists
FIG 4. Instrumented and uninstrumented areas in proximity. The instrumented areas (A) are characterized by instrument striations, smear layer, and pulpal tissue debris. The uninstrumented areas (B) show calcospherites (black arrows) and patent dentinal tubuli. Smeared debris (white arrows) is occasionally pushed onto the uninstrumented areas by the instrumentation and irrigation (original magnifications: left, x36; middle, x300; right, x 1200).
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Mandel et al.
between ultrasonic vibration and sodium hypochlorite (8, 9), that improves the elimination of debris from the prepared canals (9, 18). This ultrasonic activation of sodium hypochlorite was attributed to the effects of cavitation and acoustic streaming (7-9). Furthermore, an improved cleansing effect of ultrasonic preparation in the apical portion of the canal was attributed to facilitated irrigation by the ultrasonic devices at the apical level (7-14). The finding of debris at all root levels of all of the specimens in our study, including the ones prepared ultrasonically in combination with sodium hypochlorite, does not support these suggestions. Recent reports dismissed the cavitation and acoustic streaming effects as being minimal in the root canal, existing only when the files are not loaded by wall contact (14, 16, 19). These reports may explain our findings, which are in agreement with earlier reports that questioned the ability of the ultrasonic system to affect the entire root canal volume, particularly the apical area (11-13). It appears that even ultrasonically energized continuous irrigation does not allow the sodium hypochlorite the necessary conditions for optimal activity on pulpal tissue debris. It has also been reported that ultrasonic preparation with sodium hypochlorite resulted in the elimination of the smear layer (8, 9, 14, 15). In our experiment, the ultrasonic endodontic system had no effect on the presence or absence of smear layer on the canal walls. Our findings confirm previous reports in which smear layer was found on instrumented canal surfaces regardless of the preparation technique (20). It appears that only the use of EDTA during preparation may reduce the amount of smear layer (16, 17). Although some prep~ratibn techniques have been considered to have advantages over others, several studies failed to demonstrate any such advantages (10, 12, 13). Turek and Langeland (10) concluded that the efficacy of cleaning the canal depends on the endodontic anatomy rather than on the technique used. In a later report Langeland et al. (13) confirmed the lack of differences among preparation techniques. They suggested that some of the published histological material that demonstrated the advantages of specific techniques could not be trusted to represent the factual condition of the canals. In the present study the new automated device, the Canal Finder System, was not found to be superior or inferior to the manual or the ultrasonic techniques. In fact, its design does not offer an advantage in this aspect of canal preparation. However, recent reports suggest that it may be advantageous in other respects, namely, pathfinding (6) and speeding the preparation (5) of narrow, curved canals and conforming to canal curvatures without altering them (5, 6). Our study was not intended to examine these aspects of the tested techniques and therefore does not demonstrate them. Under the conditions of the present study, it was not possible to distinguish between the results of the different canal preparation techniques in terms of canal wall surface appearance. The same characteristics of the prepared surfaces were found in association with each of the tested techniques. This fact and the subjectivity of interpretation of the observed image are the factors that make comparative studies based on canal wall surfaces inconclusive. Thus, it appears from this study, as from other studies, that scanning electron microscopic observation of canal walls is unsuitable for qualitative comparison of the cleansing efficiency of preparation techniques. Furthermore, a thoroughly instrumented and cleansed root canal should not be expected to be free of smear layer,
Journal of Endodontics
FIG 5. Apical canal level after preparation with A (manual), B (ultrasonic), and C (Canal Finder) techniques. The three specimens appear similar, with evidence of instrument striations, pulpal tissue debris, and smear layer (original magnification x900).
Techniques and Canal Cleanliness
Vol. 16, No. 6, June 1990
uninstrumented areas, and even pulpal tissue debris. These factors should not be considered as dominant reasons for preferring one preparation technique over another. We thank Professor Henry Boulekbache, Laboratory of Comparative Anatomy, University of Paris VII, for his valuable help in the realization of the experimental protocol. Drs. Mandel and Machtou are affiliated with the School of Dentistry, University of Paris VII, Paris, France. Dr. Friedman is affiliated with the Hebrew Llniversity-Hadassah School of Dental Medicine, Jerusalem, Israel.
References 1. Guttman JL, Dumsha T. Cleaning and shaping the root canal system. Pathways of the pulp. 4th ed. St. Louis: CV Mosby, 1987. 2. Schilder H. Cleaning and shaping the root canal. Dent Clin North Am 1974;18:269. 3. Walton RE. Histologic evaluation of different methods of enlarging the pulp canal space. J Endedon 1976;2:304-11. 4. Levy G. Une nouvelle instrumentation pour realiser mecaniquement rensemble de la procedure endodontique. Rev Fr Endod 1984; 13:11-8. 5. Tronstad L, Niemczyk SP. Efficacy and safety tests of six automated devices for root canal instrumentation. Ended Dent Traumato11986;2:270-6. 6. Goldman M, Sakurai E, Kronman J, Tenca JI. An in vitro study of the pathfinding ability of a new automated handpiece. J Endodon 1987;13:42933. 7. Teplitsky PE, Chenail BL, Mack B, Machnee CH. Endodontic irrigationa comparison of endosonic and syringe delivery systems. Int Endod J 1987;20:233-41.
283
8. Cameron JA. The synergistic relationship between ultrasound and sodium hypochlorite: a scanning electron microscope evaluation. J Endodon 1987; 13:541-5. 9. Martin H, Cunningham W. Endosonics- the ultrasonic synergistic system of endodontics. Ended Dent Traumato11985;1:201-6. 10. Turek T, Langeland K. A light microscopic study of the efficacy of the telescopic and the Giromatic preparation of root canals. J Endodon 1982;8:437-43. 11. Reynolds MC, Madison S, WaJton RE, Krell KV, Rittman BRJ. An in vitro histological comparison of the step-back, sonic and ultrasonic instrumentation technique in small curved root canals. J Endodon 1987;13:307-14. 12. Tauber R, Morse DR, Sinai IA, Furst ML. A magnifying lens comparative evaluation of conventionaJ and ultrasonically energized filing. J Endodon 1983;9:269-74. 13. Langeland K, Liao K, Pascon EA. Work saving devices in endodontics: efficacy of sonic and ultrasonic techniques. J Endodon 1985; 11:499-510. 14. Ahmad M, Pitt Ford TR, Crum LA. Ultrasonic debridement of root canals: acoustic streaming and its possible role. J Endedon 1987;13:490-9. 15. Ahmad M, Pitt Ford TR, Crum LA. Ultrasonic debridement of root canals: an insight into the mechanisms involved. J Endodon 1987;13:93-101. 16. Goldman LB, Goldman M, Kronman JH, SunLin P. The efficacy of several irrigating solutions for endodontics: a scanning electron microscopic study. Oral Surg 1981 ;52:197-204. 17. Yameda RS, Armas A, Goldman M, SunLin P. A scanning electron microscopic comparison of a high volume final flush with several irrigating solutions; Part 3. J Endodon 1983;9:137-41. 18. Griffiths BM, Stock CJR. The efficiency of irrigants in removing root canal debris when used with an ultrasonic preparation technique. Int Endod J 1986;19:277-84. 19. Walmsley AD. Ultrasound and root canal treatment: the need for scientific evaluation. Int Ended J 1987;20:105-11. 20. Goldberg F, Soares I. Massone EJ, Soares IM. Comparative debridement study between hand and sonic instrumentation of the root canal. Endod Dent Traumato11988;4:229-34.
