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Effectiveness of four methods for preparing root canals: A scanning electron microscopic evaluation
0099-2399/88/1407-0340/$02.00/0 JOURNAL OF ENDOOONTICS Copyright 9 1988 by The American Association of Endodontists
Printed in U.S.A.
VOL. 14, NO. 7, JULY 1988
Effectiveness of Four Methods for Preparing Root Canals: A Scanning Electron Microscopic Evaluation Youssef Haikel, DCD, DSO, and Claude Allemann, DCD, DSO
MATERIALS AND METHODS
In this study, 140 curved root canals of extracted teeth were prepared by one of the four following methods: 1) hand preparation using K files and H files alternately; 2) automated preparation using a sonic air handpiece fitted with Rispisonic and Hellsonic instruments or 3) fitted with Shapersonic instruments; or 4) mechanical preparation using Canal Finder instrumentation. The roots were ground saggitally and the specimens were evaluated by scanning electron microscopy. The shaping and cleaning effectiveness of the preparation methods were assessed in terms of surface condition of the canal walls at the level of their coronal, middle, and apical thirds. Each canal was evaluated according to a scale from 1 to 4. A statistical analysis was used to indicate any significant difference in surface condition among the four methods. The results obtained with the manual method were similar to those gained from the Canal Finder method, without any difference between the three parts of the canal. The surface condition of the canals prepared with both Sonic Air methods was better in the coronal and middle thirds than in the apical third where pulp residues were noticed.
Ninety extracted human premolars and molars, with curved roots (range, 20 to 60 degrees) and mature apices were utilized in this study. The straight roots of these teeth were resected away and one or two curved roots of each tooth was saved. The sample consisted of 140 root canals stored in a 10% formalin solution following extraction. All root canals were prepared by a single operator using one of the four following methods. Each method included 35 root canals selected at random: 1) hand preparation using K fries and H files alternately (controls); 2) automated preparation using a Sonic Air handpiece fitted with Rispisonic and Helisonic canal instruments or 3) fitted with canal Shaper instruments (Sonic Air; Micro-Mega, Besan~n, France); or 4) mechanical preparation using a Canal Finder contra-angle (Socirt6 EndoTechnic, Marseille, France) fitted with modified K and H flies. Mechanical Instrumentation The Sonic Air 3000 instrument is a pneumatic handpiece fitted on a high-speed air line. It provides to the root canal instrument a vibratory motion of 1,500 to 3,000 Hz frequency which is to be adjusted to each instrument in order to obtain an optimal vibratory amplitude. A fixed instrument stop on the handpiece tip fits the root canal instrument at the correct length before adjusting the frequency. The Canal Finder instrument is a slow-speed contra-angle which provides the files two types of motions: a longitudinal vibratory motion where amplitude ranges from 0.3 to 1.0 mm according to the penetration resistance of the files in the root canal; on the other hand, a rotary or helicoid motion, depending on the progression of the fries in the canal. An adjustable instrument stop is attached to the contra-angle tip.
Many comparative studies have shown that the manual method for preparing root canals using serial standardized instruments yielded better results than the automated methods. This was true in terms of shaping, respect for the apical structure, and cleaning effectiveness of the canal (1-8). However, the hand preparation leaves a smear layer on the canal walls (9, 10) and is slow and wearisome. These disadvantages led many investigators to become interested in the new automated systems developed to enhance the accuracy and the swiftness of the endodontic process ( 11-15). The aim of the present investigation was to use scanning electron microscopy to evaluate the shaping and cleaning effectiveness of hand instrumentation versus those of two recent automated systems for preparing root canals.
Root Canal Preparation The canals were manually probed to the foramen, with K files of sizes 8, 10, and 15 for groups 1, 2, and 3. The Canal Finder instrument was fitted with sizes 8 and 10 K files for group 4. The working length was obtained by measuring the 340
Automated Endodontic Devices
Vol. 14, No. 7, July 1988
length of the initial file at the apical foramen minus 1 mm for groups 1 and 4, or minus 2 mm for groups 2 and 3 prepared with the Sonic Air methods. The canals of the first three groups were instrumented with files up to size 30 whereas those of group 4 were prepared with files up to size 25. In all four groups the instrumentation was recapitulated with a #15 K file between one file and the next one of increasing size. Each canal was flushed with a 2.5% NaOCI solution. The preparation of group 1 (controls) was achieved by alternating K and H files (Micro-Mrga) into the entire canal length with the circumferential filing technique (16). Canals of group 2 were prepared with Rispisonic instruments (Micro-Mrga) in their coronal and middle thirds and with Helisonic instruments (Micro-Mrga) in their apical third whereas canals of group 3 were instrumented with Shaper files (Micro-Mrga) along their whole length. The canals of group 4 were prepared with special K files up to #15, the angles and tip of which were rounded by the manufacturer (Socirt6 Endo-Technic). Thereafter, they were fitted with modified H files, the angle of the blade of which was opened by the manufacturer (Soci&6 Endo-Technic). The motions of the files used for groups 2, 3, and 4 consisted of in and out linear movements with pressure along the walls as in the "contact shaping technique" (13). After a final flush with NaOC1 solution, the canals of all groups were dried with absorbent tips of paper.
341
Shaping The shaping effectiveness of the four preparation methods is shown in Table 1. The hand preparation (control) provided well-centered cone-shaped canals following the initial course. The apical constriction was generally respected but the apical third of the canal seemed overinstrumented when compared with the two other thirds of the same canal. To the contrary, the specimens prepared with either one of the Sonic methods, especially the Rispisonic-Helisonic method, exhibited straightenings of the curved canals, and, thus, the initial canal path was modified (Fig. 1). In addition, zipped apical foramina and ledge formation were frequently noticed with the Sonic methods (Fig. 2). As to the specimens prepared with the Canal Finder method, many of the curved canals were also straightened and the inner wall of dentin was enlarged (Fig. 3). Furthermore, destruction of the apical constriction was often seen (Fig. 4). No ledge formation was noticed with this method.
Canal Cleanliness The qualitative assessment of the canal cleanliness by method of preparation for each third of the canal is shown TABLE 1. Shaping effectiveness
Method of Evaluation After setting a guide file in each canal, each root was ground longitudinally to half-thickness in the mesiodistal plane, using a diamond bur. The prepared specimens were dehydrated and coated with a palladium-gold layer of about 300-A thick using a Hummer Junior Evaporator (Siemens, Kadsruhe, West Germany). They were examined under a JEOL scanning electron microscope (type JSM 35C; JEOL, Tokyo, Japan) by a single examiner who was unaware of the methods of preparation. The specimens were evaluated according to shaping and cleaning characteristics of the root canal preparation. Shaping effectiveness of the four methods of preparing root canals was subjectively evaluated in terms of respect for the canal course, respect for the apical constriction, and lack of ledge formation. In order to evaluate the cleaning effectiveness of the four methods, the surface condition of the coronal, middle, and apical thirds of each canal were evaluated according to the following scale: 1, "very clean" canal without predentin or smear layer; 2, "clean" canal with smear layer; 3, canal exhibiting "predentin" and surfaces without smear layer; 4, "untidy" canal with remains of pulpal tissues. A chi-square multiple comparison test was used to indicate any significant difference in surface condition among the four methods of preparation.
Group
No. of Teeth
Cu~e Maintained
Constri~ion Maintained
No Ledge
1 2 3 4
35 35 35 35
29 11 16 19
31 21
35 25 28 35
27
14
RESULTS The data concerning the four methods of preparation are presented with respect to (a) the shaping and (b) the cleaning effectiveness.
FIG 1. Specimen prepared with the Sonic method using Shaper instruments. The canal is not cone shaped and has apical enlargement (original magnification x25).
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FIG 2. Specimen prepared with the Sonic method using Rispisonic and Helisonic instruments. Notice the straightening of the canal curve (=) and also the apical zipping (-.~-) which is typical of this method. The unworked apical walls exhibit pulpal residues ( ~ ) (original magnification x16.5).
diagrammatically in Figs. 5 to 7 and is illustrated by Figs. 8 to 13. Concerning the manual preparation, 18% of the specimens at the coronal and middle thirds of the canal and 10% of the specimens at the apical third were qualified as very clean (Fig. 8). About 80% of the specimens were assessed as clean along all three thirds and exhibited a smear layer which occluded the dentinal canaliculi (Fig. 9). However, 17% of the specimens were qualified as untidy at the level of their apical third. With regard to both Sonic methods, the data obtained from the coronal and middle thirds of the specimens were different from those gained from the apical third. At the level of the coronal and middle parts, about 50% of the specimens were assessed as very clean (Figs. 10 and 11) and the rest of the sample was qualified as dean. A small number of preparations exhibited predentin and surfaces without smear layer (Fig. 12) in their coronal third. This occurred in 6% of the specimens prepared with Rispisonic-Helisonic instruments and 18% of those prepared with Shaper instruments--and also in the middle third (8%) when fitted with Shaper instruments. As to the apical third, only 8% of the specimens were assessed as very clean using the Rispisohic-Helisonic instruments and no specimen was so qualified when prepared with Shaper instruments. Only 30% of the specimens were evaluated as clean in the apical part using either one of the Sonic methods and, in addition, 58 and 73% of these with the Rispisonic-Helisonic
Journal of EndodonUcs
FIG 3. Specimen prepared with the Canal Finder method. The canal curve was straightened (_~) in its middle third and the foramen was enlarged (-~--) (original magnification x13).
FIG 4. Apical view of a specimen prepared with the Canal Finder method. The foramen was overinstrumented and enlarged (original magnification x62).
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1
100-
2 3 4
50.
i i i iJi!i!i!!
i i i!i!!!!!ii i 10' 0
ii!ii!]ii!il HAND
RH
SH
CF
FIG 5. Mean percentages of canal cleanliness at the level of the coronal third, related to the four methods of canal preparation: manual (HAND), Sonic with Rispisonic-Helisonic instruments (RH), or Sonic with Shaper instruments (SH) and Canal Finder (CF). The rating scale is 1, "very clean"; 2, "clean"; 3, "predentin"; and 4, =untidy." FiG 8. Middle third of a canal prepared with the manual method. The surface of the canal was evaluated as very clean with the lack of smear layer (original magnification • 1
100- :
2 3
mm 4
50-
100 HAND
RH
SH
CF
FIG 6. Mean percentages of canal cleanliness at the level of the middle third, related to the four methods of canal preparation: manual (HAND), Sonic with Rispisonic-Helisonic instruments (RH), or Sonic with Shaper instruments (SH) and Canal Finder (CF). The rating scale is: 1, very clean; 2, clean; 3, predentin; and 4, untidy.
1
FIG 9. Apical third of a canal prepared with the manual method. The surface of the canal was qualified as clean and exhibited smear layer which occludes the dentinal canaliculi (original magnification x500).
2 3 IBm 4
HAND
RH
SH
CF
FIG 7. Mean percentages of canal cleanliness at the level of the apical third, related to the four methods of canal preparation: manual (HAND), Sonic with Rispisonic-Helisonic instruments (RH), or Sonic with Shaper instruments (SH) and Canal Finder (CF). The rating scale is: 1, very clean; 2, clean; 3, predentin; and 4, untidy.
instruments or with the Shaper instruments, respectively, were assessed as untidy (Fig. 13). The data gained from the specimens prepared with the Canal Finder method were similar to those obtained from hand preparation. Along the three parts of the canal, 18% to 10% of the specimens were very clean and 82% to 73% of the specimens were clean and characterized by a smear layer and longitudinal striations. At the level of the middle and apical thirds, only 10% of the preparations were qualified as untidy. The statistical analysis indicated that there were no significant differences in canal cleanliness between the manual method and the Canal Finder method or between the RispiHelisonic method and the Shaper-Sonic method at the three canal third levels.
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Fte 10. Middle third of a canal prepared with the Sonic method using Shaper instruments. The surface of the canal was assessed as very clean (original magnification x135).
FiG 11. Middle third of a canal prepared with the Sonic method using Shaper instruments. Notice the very clean surface of the canal, without any smear layer (original magnification x630).
When comparing both manual and Canal Finder methods with the Sonic methods, there were significant differences concerning the rates very clean and clean at the level of the coronal third (p < 0.01) and the middle third (p < 0.001). The sonic methods removed the smear layer completely at the level of the coronal and middle thirds. Comparison of the manual and Canal Finder methods versus the Sonic methods also brought out significant differences concerning the rates very clean, clean, and untidy at the apical third (p < 0.001). With regard to the Sonic methods, there were significant differences concerning the canal cleanliness of the apical third versus the coronal and middle thirds (p < 0.001), as pulpal remnants were observed at the apical thirds. As to the rate predentin, it was only noticed on the uninstrumented surfaces of the root canals prepared with the Sonic methods.
Journal of Endodontics
FIG 12. Coronal third of a canal prepared with the Sonic method using the Rispisonic and Helisonic instruments. The unworked surface of the canal is characterized by predentin (original magnification x135).
FiG 13. Apical third of a canal prepared with the Sonic method using Shaper instruments. The surface of the canal was assessed as untidy and as having pulpal residues (original magnification x500).
DISCUSSION The method of evaluation of the cleanliness allowed rate comparison accurately since the chi-square test was used. This method did not eliminate the subjective assessment of the canal preparations but it avoided comparison of mean averages which are not representative of nonparametric data. The data concerning hand preparation confirmed that the manual method was reliable in terms of shaping, since it permitted respect of the canal course and the original apical structure. This method was also effective as it allowed cleaning the canals along their whole length, although it left a smear layer which might reduce the sealant property of the canal fiUing. The present data were in accordance with the results
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obtained from several comparative studies that concluded that the manual method was more effective and reliable than the automated methods for preparing root canals (1-8). With regard to the Sonic methods, their high cleaning effectiveness in the coronal and middle thirds of the canal was evident when compared with the manual method. Nevertheless, the cleaning rate was low in the apical third and left the pulpal remnants. This might result from lessened vibratory amplitude of the canal instruments since the canal path at the apex is narrow. Moreover, the Rispisonic-Helisonic method modified the original canal course by straightening the curves and widening the apical foramen, similar to canal preparation using Giromatic instrumentation (17, 18). These disadvantages were reduced when using Shapers, but they were not eliminated completely as reported by Cochet et al. (19). As to the Canal Finder method, the canal shaping also straightened the initial canal path, contrary to the data reported by several authors (20, 21). The overworked apical foramen was very likely related to the difficulty of accurately controlling the working length of the canal instrument since it has a longitudinal vibratory motion. Nevertheless, the Canal Finder preparation compared favorably with the manual preparation in terms of surface condition of the canal walls, as this automated method permitted efficient cleaning of the canals for their entire length. The cleaning effectiveness of the Canal Finder might be related to the type of canal instruments rather than to the type of motion of the files. CONCLUSIONS The Sonic and Canal Finder methods are time-saving procedures in comparison to the manual method but they present major disadvantages. The automated methods tend to straighten the curved canals and the Sonic methods especially were not suitable for preparing the apical third of the canal. If automated procedures are selected, it is advisable to use either the Canal Finder method for the entire canal preparation or one of the Sonic methods for the coronal and middle thirds in conjunction with hand preparation for the apical third. We gratefully acknowledge Dr. P. Herr for his assistance in the preparation of this manuscript. We would also like to thank Professor R. Frank for laboratory support. This study was supported under the INSERM, Unit6 157.
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345
Dr. Haikel and Dr. Allemann are associate professors, Department of Operative Dentistry and Endodontics, Faculty of Dental Surgery, University of Louis Pasteur, Strasbourg 67000, France. Address requests for reprints to Or. Y. Haikel, Centre de Recherches Odontologiques Unit6 INSERM 157, Facult6 de Chirurgie Dentaire-Universit6 Louis Pasteur, 1 Place de I'h6pital, Strasbourg 67000, France.
References 1. O'Connol DT, Brayton SM. Evaluation of root canal preparation with two automated endodontic handpieces. Oral Surg 1975;39:398-403. 2. Mizraki SJ, Tucker JW, Seltzer S. A scanning electron microscopic study of the efficacy endodontic handpieces. J Endodon 1985;1:324-33. 3. Klayman SM, Brilliant JD. A comparison of the efficacy of serial preparation versus giromatic preparation. J Endodon 1975;1:334-7. 4. Weine FS, Kelly RF, Bray BK. Effect of preparation with endodontic handpieces on original canal shape. J Endodon 1976;2:298-301. 5. Abou Rass M, Frank AL, Glick DH. The anticurvature filing method to prepare the curved root canal. J Am Dent Assoc 1980;101:792-4. 6. Lehmann JW, Gerstein H. An evaluation of a new mechanized endodontic device: the endolift. Oral Surg 1982;53:417-24. 7. 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. 8. Russel DI, Ryan W J, Towers JF. Complication of automated canal treatment. Br Dent J 1982;153:393-8. 9. Cergneux M, Ciucchi B, Dietschi JM, Holz J. Etude de I'influenca de la smear layer sur 1'6tanch6it6 de I'obturation canalaire. Inf Dent 1986;18:1699702. 10. Kennedy WA, Walker III WA, Gough RW. Smear layer removal effects on apical leakage. J Endodon 1986;12:21-7. 11. Levy G. Une nouvelle instrumentation pour r6aUser m6caniquement I'ensemble de la proc(~dure endodontique: le Canal Finder. Rev Fran(; Ended 1984;2:11-8. 12. Martin H, Cunningham W. Endosonic endodontics: the ultrasonic synergetic system. Int Dent J 1984;34:198-203. 13. Laurichesse JM. La technique de I'appui parietal (TAP). Rev Fran~: Ended 1985;3:19-33. 14. Tronstad L, Barnett F, Schwartzben C, Frasca P. Effectiveness and safety of a sonic vibratory endodontic instrument. Endod Dent Traumatol 1985;1:69-76. 15. Barnett F, Godick B, Tronstad L. Clinical suitability of a sonic vibratory endodontic instrument. Ended Dent Traumato11985;1:77-81. t6. Bence R. Handbook of clinical endedontics. St. Louis: CV Mosby, 1976:110-33. 17. Frank AL. An evaluation of the Giromatic endodontic handpiece. Oral Surg 1967;24:419-21. 18. Harty FJ, Stock CJ. The giromatic system compared with hand instrumentation in endodontics. Br Dent J 1974;137:239-44. 19. Cochet JY, Barrit l, Laudchesse JM. Etude exp~rimentale du respect de la trajectoire canalaire pour les instruments soniques. Rev Fran~: Endod 1986;3:21-3. 20. Tronstad L, Niemczyk SP. Efficacy and safety test of six automated devices for root canal instrumentation. Endod Dent Traumato11986;2:270-6. 21. Sakurai-Fuse E, Goldman M, Tenca J. A comparison of two methods of instrumenting curved canals [Abstract]. J Dent Res 1986;65(special issue):253.
Printed in U.S.A.
VOL. 14, NO. 7, JULY 1988
Effectiveness of Four Methods for Preparing Root Canals: A Scanning Electron Microscopic Evaluation Youssef Haikel, DCD, DSO, and Claude Allemann, DCD, DSO
MATERIALS AND METHODS
In this study, 140 curved root canals of extracted teeth were prepared by one of the four following methods: 1) hand preparation using K files and H files alternately; 2) automated preparation using a sonic air handpiece fitted with Rispisonic and Hellsonic instruments or 3) fitted with Shapersonic instruments; or 4) mechanical preparation using Canal Finder instrumentation. The roots were ground saggitally and the specimens were evaluated by scanning electron microscopy. The shaping and cleaning effectiveness of the preparation methods were assessed in terms of surface condition of the canal walls at the level of their coronal, middle, and apical thirds. Each canal was evaluated according to a scale from 1 to 4. A statistical analysis was used to indicate any significant difference in surface condition among the four methods. The results obtained with the manual method were similar to those gained from the Canal Finder method, without any difference between the three parts of the canal. The surface condition of the canals prepared with both Sonic Air methods was better in the coronal and middle thirds than in the apical third where pulp residues were noticed.
Ninety extracted human premolars and molars, with curved roots (range, 20 to 60 degrees) and mature apices were utilized in this study. The straight roots of these teeth were resected away and one or two curved roots of each tooth was saved. The sample consisted of 140 root canals stored in a 10% formalin solution following extraction. All root canals were prepared by a single operator using one of the four following methods. Each method included 35 root canals selected at random: 1) hand preparation using K fries and H files alternately (controls); 2) automated preparation using a Sonic Air handpiece fitted with Rispisonic and Helisonic canal instruments or 3) fitted with canal Shaper instruments (Sonic Air; Micro-Mega, Besan~n, France); or 4) mechanical preparation using a Canal Finder contra-angle (Socirt6 EndoTechnic, Marseille, France) fitted with modified K and H flies. Mechanical Instrumentation The Sonic Air 3000 instrument is a pneumatic handpiece fitted on a high-speed air line. It provides to the root canal instrument a vibratory motion of 1,500 to 3,000 Hz frequency which is to be adjusted to each instrument in order to obtain an optimal vibratory amplitude. A fixed instrument stop on the handpiece tip fits the root canal instrument at the correct length before adjusting the frequency. The Canal Finder instrument is a slow-speed contra-angle which provides the files two types of motions: a longitudinal vibratory motion where amplitude ranges from 0.3 to 1.0 mm according to the penetration resistance of the files in the root canal; on the other hand, a rotary or helicoid motion, depending on the progression of the fries in the canal. An adjustable instrument stop is attached to the contra-angle tip.
Many comparative studies have shown that the manual method for preparing root canals using serial standardized instruments yielded better results than the automated methods. This was true in terms of shaping, respect for the apical structure, and cleaning effectiveness of the canal (1-8). However, the hand preparation leaves a smear layer on the canal walls (9, 10) and is slow and wearisome. These disadvantages led many investigators to become interested in the new automated systems developed to enhance the accuracy and the swiftness of the endodontic process ( 11-15). The aim of the present investigation was to use scanning electron microscopy to evaluate the shaping and cleaning effectiveness of hand instrumentation versus those of two recent automated systems for preparing root canals.
Root Canal Preparation The canals were manually probed to the foramen, with K files of sizes 8, 10, and 15 for groups 1, 2, and 3. The Canal Finder instrument was fitted with sizes 8 and 10 K files for group 4. The working length was obtained by measuring the 340
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Vol. 14, No. 7, July 1988
length of the initial file at the apical foramen minus 1 mm for groups 1 and 4, or minus 2 mm for groups 2 and 3 prepared with the Sonic Air methods. The canals of the first three groups were instrumented with files up to size 30 whereas those of group 4 were prepared with files up to size 25. In all four groups the instrumentation was recapitulated with a #15 K file between one file and the next one of increasing size. Each canal was flushed with a 2.5% NaOCI solution. The preparation of group 1 (controls) was achieved by alternating K and H files (Micro-Mrga) into the entire canal length with the circumferential filing technique (16). Canals of group 2 were prepared with Rispisonic instruments (Micro-Mrga) in their coronal and middle thirds and with Helisonic instruments (Micro-Mrga) in their apical third whereas canals of group 3 were instrumented with Shaper files (Micro-Mrga) along their whole length. The canals of group 4 were prepared with special K files up to #15, the angles and tip of which were rounded by the manufacturer (Socirt6 Endo-Technic). Thereafter, they were fitted with modified H files, the angle of the blade of which was opened by the manufacturer (Soci&6 Endo-Technic). The motions of the files used for groups 2, 3, and 4 consisted of in and out linear movements with pressure along the walls as in the "contact shaping technique" (13). After a final flush with NaOC1 solution, the canals of all groups were dried with absorbent tips of paper.
341
Shaping The shaping effectiveness of the four preparation methods is shown in Table 1. The hand preparation (control) provided well-centered cone-shaped canals following the initial course. The apical constriction was generally respected but the apical third of the canal seemed overinstrumented when compared with the two other thirds of the same canal. To the contrary, the specimens prepared with either one of the Sonic methods, especially the Rispisonic-Helisonic method, exhibited straightenings of the curved canals, and, thus, the initial canal path was modified (Fig. 1). In addition, zipped apical foramina and ledge formation were frequently noticed with the Sonic methods (Fig. 2). As to the specimens prepared with the Canal Finder method, many of the curved canals were also straightened and the inner wall of dentin was enlarged (Fig. 3). Furthermore, destruction of the apical constriction was often seen (Fig. 4). No ledge formation was noticed with this method.
Canal Cleanliness The qualitative assessment of the canal cleanliness by method of preparation for each third of the canal is shown TABLE 1. Shaping effectiveness
Method of Evaluation After setting a guide file in each canal, each root was ground longitudinally to half-thickness in the mesiodistal plane, using a diamond bur. The prepared specimens were dehydrated and coated with a palladium-gold layer of about 300-A thick using a Hummer Junior Evaporator (Siemens, Kadsruhe, West Germany). They were examined under a JEOL scanning electron microscope (type JSM 35C; JEOL, Tokyo, Japan) by a single examiner who was unaware of the methods of preparation. The specimens were evaluated according to shaping and cleaning characteristics of the root canal preparation. Shaping effectiveness of the four methods of preparing root canals was subjectively evaluated in terms of respect for the canal course, respect for the apical constriction, and lack of ledge formation. In order to evaluate the cleaning effectiveness of the four methods, the surface condition of the coronal, middle, and apical thirds of each canal were evaluated according to the following scale: 1, "very clean" canal without predentin or smear layer; 2, "clean" canal with smear layer; 3, canal exhibiting "predentin" and surfaces without smear layer; 4, "untidy" canal with remains of pulpal tissues. A chi-square multiple comparison test was used to indicate any significant difference in surface condition among the four methods of preparation.
Group
No. of Teeth
Cu~e Maintained
Constri~ion Maintained
No Ledge
1 2 3 4
35 35 35 35
29 11 16 19
31 21
35 25 28 35
27
14
RESULTS The data concerning the four methods of preparation are presented with respect to (a) the shaping and (b) the cleaning effectiveness.
FIG 1. Specimen prepared with the Sonic method using Shaper instruments. The canal is not cone shaped and has apical enlargement (original magnification x25).
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Haikel and Allemann
FIG 2. Specimen prepared with the Sonic method using Rispisonic and Helisonic instruments. Notice the straightening of the canal curve (=) and also the apical zipping (-.~-) which is typical of this method. The unworked apical walls exhibit pulpal residues ( ~ ) (original magnification x16.5).
diagrammatically in Figs. 5 to 7 and is illustrated by Figs. 8 to 13. Concerning the manual preparation, 18% of the specimens at the coronal and middle thirds of the canal and 10% of the specimens at the apical third were qualified as very clean (Fig. 8). About 80% of the specimens were assessed as clean along all three thirds and exhibited a smear layer which occluded the dentinal canaliculi (Fig. 9). However, 17% of the specimens were qualified as untidy at the level of their apical third. With regard to both Sonic methods, the data obtained from the coronal and middle thirds of the specimens were different from those gained from the apical third. At the level of the coronal and middle parts, about 50% of the specimens were assessed as very clean (Figs. 10 and 11) and the rest of the sample was qualified as dean. A small number of preparations exhibited predentin and surfaces without smear layer (Fig. 12) in their coronal third. This occurred in 6% of the specimens prepared with Rispisonic-Helisonic instruments and 18% of those prepared with Shaper instruments--and also in the middle third (8%) when fitted with Shaper instruments. As to the apical third, only 8% of the specimens were assessed as very clean using the Rispisohic-Helisonic instruments and no specimen was so qualified when prepared with Shaper instruments. Only 30% of the specimens were evaluated as clean in the apical part using either one of the Sonic methods and, in addition, 58 and 73% of these with the Rispisonic-Helisonic
Journal of EndodonUcs
FIG 3. Specimen prepared with the Canal Finder method. The canal curve was straightened (_~) in its middle third and the foramen was enlarged (-~--) (original magnification x13).
FIG 4. Apical view of a specimen prepared with the Canal Finder method. The foramen was overinstrumented and enlarged (original magnification x62).
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1
100-
2 3 4
50.
i i i iJi!i!i!!
i i i!i!!!!!ii i 10' 0
ii!ii!]ii!il HAND
RH
SH
CF
FIG 5. Mean percentages of canal cleanliness at the level of the coronal third, related to the four methods of canal preparation: manual (HAND), Sonic with Rispisonic-Helisonic instruments (RH), or Sonic with Shaper instruments (SH) and Canal Finder (CF). The rating scale is 1, "very clean"; 2, "clean"; 3, "predentin"; and 4, =untidy." FiG 8. Middle third of a canal prepared with the manual method. The surface of the canal was evaluated as very clean with the lack of smear layer (original magnification • 1
100- :
2 3
mm 4
50-
100 HAND
RH
SH
CF
FIG 6. Mean percentages of canal cleanliness at the level of the middle third, related to the four methods of canal preparation: manual (HAND), Sonic with Rispisonic-Helisonic instruments (RH), or Sonic with Shaper instruments (SH) and Canal Finder (CF). The rating scale is: 1, very clean; 2, clean; 3, predentin; and 4, untidy.
1
FIG 9. Apical third of a canal prepared with the manual method. The surface of the canal was qualified as clean and exhibited smear layer which occludes the dentinal canaliculi (original magnification x500).
2 3 IBm 4
HAND
RH
SH
CF
FIG 7. Mean percentages of canal cleanliness at the level of the apical third, related to the four methods of canal preparation: manual (HAND), Sonic with Rispisonic-Helisonic instruments (RH), or Sonic with Shaper instruments (SH) and Canal Finder (CF). The rating scale is: 1, very clean; 2, clean; 3, predentin; and 4, untidy.
instruments or with the Shaper instruments, respectively, were assessed as untidy (Fig. 13). The data gained from the specimens prepared with the Canal Finder method were similar to those obtained from hand preparation. Along the three parts of the canal, 18% to 10% of the specimens were very clean and 82% to 73% of the specimens were clean and characterized by a smear layer and longitudinal striations. At the level of the middle and apical thirds, only 10% of the preparations were qualified as untidy. The statistical analysis indicated that there were no significant differences in canal cleanliness between the manual method and the Canal Finder method or between the RispiHelisonic method and the Shaper-Sonic method at the three canal third levels.
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Haikel and Allemann
Fte 10. Middle third of a canal prepared with the Sonic method using Shaper instruments. The surface of the canal was assessed as very clean (original magnification x135).
FiG 11. Middle third of a canal prepared with the Sonic method using Shaper instruments. Notice the very clean surface of the canal, without any smear layer (original magnification x630).
When comparing both manual and Canal Finder methods with the Sonic methods, there were significant differences concerning the rates very clean and clean at the level of the coronal third (p < 0.01) and the middle third (p < 0.001). The sonic methods removed the smear layer completely at the level of the coronal and middle thirds. Comparison of the manual and Canal Finder methods versus the Sonic methods also brought out significant differences concerning the rates very clean, clean, and untidy at the apical third (p < 0.001). With regard to the Sonic methods, there were significant differences concerning the canal cleanliness of the apical third versus the coronal and middle thirds (p < 0.001), as pulpal remnants were observed at the apical thirds. As to the rate predentin, it was only noticed on the uninstrumented surfaces of the root canals prepared with the Sonic methods.
Journal of Endodontics
FIG 12. Coronal third of a canal prepared with the Sonic method using the Rispisonic and Helisonic instruments. The unworked surface of the canal is characterized by predentin (original magnification x135).
FiG 13. Apical third of a canal prepared with the Sonic method using Shaper instruments. The surface of the canal was assessed as untidy and as having pulpal residues (original magnification x500).
DISCUSSION The method of evaluation of the cleanliness allowed rate comparison accurately since the chi-square test was used. This method did not eliminate the subjective assessment of the canal preparations but it avoided comparison of mean averages which are not representative of nonparametric data. The data concerning hand preparation confirmed that the manual method was reliable in terms of shaping, since it permitted respect of the canal course and the original apical structure. This method was also effective as it allowed cleaning the canals along their whole length, although it left a smear layer which might reduce the sealant property of the canal fiUing. The present data were in accordance with the results
Vol. 14, No. 7, July 1988
obtained from several comparative studies that concluded that the manual method was more effective and reliable than the automated methods for preparing root canals (1-8). With regard to the Sonic methods, their high cleaning effectiveness in the coronal and middle thirds of the canal was evident when compared with the manual method. Nevertheless, the cleaning rate was low in the apical third and left the pulpal remnants. This might result from lessened vibratory amplitude of the canal instruments since the canal path at the apex is narrow. Moreover, the Rispisonic-Helisonic method modified the original canal course by straightening the curves and widening the apical foramen, similar to canal preparation using Giromatic instrumentation (17, 18). These disadvantages were reduced when using Shapers, but they were not eliminated completely as reported by Cochet et al. (19). As to the Canal Finder method, the canal shaping also straightened the initial canal path, contrary to the data reported by several authors (20, 21). The overworked apical foramen was very likely related to the difficulty of accurately controlling the working length of the canal instrument since it has a longitudinal vibratory motion. Nevertheless, the Canal Finder preparation compared favorably with the manual preparation in terms of surface condition of the canal walls, as this automated method permitted efficient cleaning of the canals for their entire length. The cleaning effectiveness of the Canal Finder might be related to the type of canal instruments rather than to the type of motion of the files. CONCLUSIONS The Sonic and Canal Finder methods are time-saving procedures in comparison to the manual method but they present major disadvantages. The automated methods tend to straighten the curved canals and the Sonic methods especially were not suitable for preparing the apical third of the canal. If automated procedures are selected, it is advisable to use either the Canal Finder method for the entire canal preparation or one of the Sonic methods for the coronal and middle thirds in conjunction with hand preparation for the apical third. We gratefully acknowledge Dr. P. Herr for his assistance in the preparation of this manuscript. We would also like to thank Professor R. Frank for laboratory support. This study was supported under the INSERM, Unit6 157.
Automated Endodontic Devices
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Dr. Haikel and Dr. Allemann are associate professors, Department of Operative Dentistry and Endodontics, Faculty of Dental Surgery, University of Louis Pasteur, Strasbourg 67000, France. Address requests for reprints to Or. Y. Haikel, Centre de Recherches Odontologiques Unit6 INSERM 157, Facult6 de Chirurgie Dentaire-Universit6 Louis Pasteur, 1 Place de I'h6pital, Strasbourg 67000, France.
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