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Stereomicroscopic evaluation of canal shape following hand, sonic, and ultrasonic instrumentation
0099-2399/89/1503-0417/$02.00/0 JOURNAL OF ENDODONTICS Copyright r 1989 by The American Association of Endo0ontists
Printed in U.S.A.
VOL. 15, No. 9, SEPTEMBER 1989
Stereomicroscopic Evaluation of Canal Shape following Hand, Sonic, and Ultrasonic Instrumentation Robert J. Loushine, DDS, R. Norman Weller, DMD, MS, and Gary R. Hartwell, DDS, MS, FICD, FACD
This study evaluated the root canal shape after using sonic, ultrasonic, and hand instrumentation on the mesial canals of extracted human mandibular first and second molars. One-hundred and five mesial roots were randomly divided into six experimental groups and one untreated control group of 15 roots each. The following instrumentation techniques were evaluated in the experimental groups: hand instrumentation with K-Flex files, sonic instrumentation with the Endostar 5, sonic instrumentation with the Sonic Air MM 3000, and ultrasonic instrumentation with the Cavi-Endo unit. Each technique was directly compared with each other. The mesial roots were instrumented alternating the techniques between the buccal and lingual canals in each group so that a direct comparison could be made. All canals were instrumented to a size corresponding to a # 3 0 K-Flex file 1 mm from the anatomical apex. The roots were then sectioned perpendicular to the long axis so the apical and middle thirds could be evaluated with the stereomicroscope for canal shape. The control group was sectioned and examined without instrumentation. A significantly more regular shape was obtained at both levels with hand instrumentation than was obtained with either sonic or ultrasonic techniques. The comparisons between the sonic and ultrasonic techniques showed significantly better shapes were obtained with the Sonic Air MM 3000 instrument.
An anticurvature method of filing, proposed by Abou-Rass ct al. (4), directs the canal preparation toward the bulk of root structure in an attempt to prevent stripping in the bifurcation or trifurcation area. The ideal shape of the prepared canal to allow complete obturation should be the same as the cross-sectional shape of the gutta-percha master cone, especially in the apical 4 to 5 mm. After instrumenting the mesial canals of 100 mandibular molars, Jungmann et al. (5) concluded that no technique produced a round preparation in the apical portion of the root canal. Moreover, the further from the apex, the more irregular the shape became. Jungmann et al. (5), Vessey (6), and Curson (7) reported that a reaming action produced the roundest preparation and filing produced the least round preparation. With the introduction of sonic and ultrasonic instrumentation systems, the clinician has an alternative to conventional hand instrumentation techniques for canal preparation. Various authors (8-16) have reported on the beneficial effects of sonic and ultrasonic instrumentation techniques. Advocates report decreased instrumentation time, increased antimicrobial effects, improved root canal debridement, and increased dentin removal compared with hand instrumentation. In contrast, Weller et al. (17) and Cymerman et al. (18) both reported no significant difference in canal debridement between hand and ultrasonic instrumentation. A study by Pedicord et al. (19) compared root canal shapes following instrumentation by ultrasonics and by hand. Their results showed significantly rounder shapes were produced by hand instrumentation in the coronal and middle levels. At the apical levels, there was no significant difference; however, both techniques were shown to transport the canal toward the furcation. The purpose of this study was to compare the shape of the prepared canal following preparation by sonic, ultrasonic, and hand instrumentation in the mcsial canals ofexlracted human mandibular first and second molars.
During endodontic treatment the principle of maintaining the general shape and direction of the original canal system is often neglected. Violation of this principle when instrumenting curved canals can lead to "strip" perforations in the midroot area and foramen transportation in the apical portion (1). Subsequent obturation with gutta-percha becomes difficult, if not impossible. Conventional hand instrumentation, using the step-back technique, has been widely recommended for the preparation of curved canals to prevent ledging, to facilitate obturation with gutta-percha (2), and to decrease the incidence of the "zip" or "teardrop" enlargement of the apical foramen (3).
MATERIALS AND M E T H O D S One-hundred and five extracted human mandibular first and second molars were selected. Schneider's method (20) was used to determine the degree of curvature of each mesial root. Only roots with less than a 40-degrcc curvature were used in this investigation. A groove was cut on the buccal surface of all roots for orientation prior to random placement 417
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into seven equal groups of 15 teeth: group 1, c o n t r o l - - n o instrumentation; group 2, hand instrumentation versus Endostar 5 (Syntex Dental Products, Valley Forge, PA); group 3, hand instrumentation versus Sonic Air MM 3000 (Medidenta International Inc., Woodside, NY); group 4, hand instrumentation versus Cavi-Endo (L. D. Caulk Division, Dentsply International Inc., Milford, DE); group 5, Sonic Air MM 3000 versus Cavi-Endo; group 6, Endostar 5 versus CaviEndo; and group 7, Endostar 5 versus Sonic Air MM 3000. In each group the instrumentation techniques were used the same number of times and were alternated between the mesiobuccal and mesiolingual canals. All files were discarded after use in three canals or earlier if they became unsuitable for further instrumentation. The control group received no instrumentation.
Preparation Standard access preparations were made and two patent, separate mesial canals were located by passing a #10 K-Flex file through each apical foramen. The working length was established by subtracting 1 m m from the length obtained when the file tip just appeared at the apical foramcn. The coronal thirds of all canals were enlarged with #2 and 3 Gates Glidden burs (Maillerfer, Switzerland) to facilitate straight line access to the middle and apical areas and to prevent binding of the instruments in the coronal aspect of the canal. The Gates Glidden burs were not allowed to extend into the experimental middle section of the root canal system. All canal preparations were performed by a single operator throughout this study. HAND INSTRUMENTATION This was accomplished using K-Flex files (Kerr, Romulus, MI) up to a size #30 at the working length. The following step-back technique was used to flare the canal: #30, 35, 30, 40, 30, 45 and 30 files. Each file size larger than the #30 was instrumented 1 m m short of the preceding file and used in a circumferential filing motion. Recapitulation was accomplished with the #30 file to the working length. Copious irrigation with distilled water was used between each file.
accomplished by using the #25 Endostar file in 5- to 7-ram strokes in a circumferential motion short of the working length. A continuous flow of filtered water irrigation was provided through the dental unit. Sonic instrumentation using the Sonic Air MM 3000 was accomplished according to the manufacturer's recommendations in a manner similar to the Endostar 5 technique. TrioSonic files size # 15, 20, and 25 were used to prepare the apical third of the canal until a #30 K-Flex file could be inserted to the working length. A #25 Trio-Sonic file was used in a circumferential filing motion, short of the working length, to flare the canal. Filtered water through the dental unit was used for continuous irrigation. ULTRASONIC I N S T R U M E N T A T I O N This was accomplished using the manufacturer's recommendations for the Cavi-Endo system. Using distilled water as the irrigant, the apical thirds of the canals were enlarged using #15, 20, and 25 Endosonic files until a #30 K-Flex file could be fit to the working length. Circumferential and an up and down motion with a #25 Endosonic file was used to flare the canal.
Evaluation Following canal preparation, each root was sectioned perpendicular to the long axis at the 2-ram level and at the 6m m level. Care was taken to avoid angled cuts as this could have made round canals appear to be oval. Each section was viewed under the stereomicroscope (Wild MPS 515; Wild Hccrbrugg Ltd., Hecrbrugg, Switzerland) at x6 power and the canal shape was evaluated by two independent examiners who were unaware of which instrumentation technique had been used. The evaluators assigned a shape rating of round, oval, or irregular for each of the prepared canals (Fig. 1). The scores of the independent evaluators were compared. For those sections in which there was a discrepancy in the assigned shapes, a reevaluation was done until a shape was agreed upon by the evaluators. The shape ratings were evaluated using a two-tailed sign test. A round canal preparation was considered
SONIC I N S T R U M E N T A T I O N All mechanical instrumentation was done according to the manufacturer's instructions. Following establishment of the working length with a K-Flex file to size #15, a #15 Endostar 5 file was precurved and inserted to the working length. The sonic instrumentation consisted of energizing the #15 file for approximately 10 s until the file could be freely moved up and down in the canal. Short 1- to 2-ram strokes were then used to enlarge the apical third of the canal until the #20 Endostar file would go to the working length without binding. The #20 and 25 Endostar files were then used in a similar manner until a #30 K-Flex file fit to the working length. The K-Flex file was not used to instrument the canal but only to check the size of tile apical preparation. If the #30 K-Flex file would not go to the working length, instrumentation with the #25 Endostar file was continued. Flaring of the canal was
FIG 1. Examples of rated shapes of root canals following instrumentation. Top left, round; bottom left, oval; top right, round; bottom right, irregular (original magnification •
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5). When compared with the Cavi-Endo and the Endostar 5 (Tables 5 and 6). the Sonic Air MM 3000 method produced significantly better canal shapes at both levels (Figs. 6 and 7), with the most common shape for each technique being oval. No significant difference in canal shape was found (Table 7) when the Endostar 5 and Cavi-Endo techniques were compared with one another (Fig. 8). The Cavi-Endo system produced the largest number of irregular-shaped canals. The independent evaluators agreed 88% of the time. For
TABLE 4. Hand instrumentation versus Cavi-Endo (n = 15)
Canal Shape Level
Method
Best Shape Sign Test Round Oval Irregular
FIG 2. Representative examples of unprepared canals (controls, group 1). Left, apical section demonstrating round canals. Right, middle section demonstrating oval canals (original magnification x6),
Apical Hand Cavi-Endo Middle Hand Cavi-Endo
8 0 9 0
7 3 5 5
0 12 1 10
14 0 13 0
p < 0.001 p < 0.001
TABLE 1. Controls--no instrumentation (n = 15)
Canal Shape Level Round
Oval
Irregular
26 16
4 14
0 0
Apical Middle
TABLE 2. Hand instrumentation versus Endostar 5 (n = 15)
Canal Shape Level
Method
Best Shape Sign Test Round Oval Irregular
Apical
Hand Endostar Middle Hand Endostar
6 1 5 0
8 7 9 4
1 7 1 11
10 0 13 0
p = 0.002 p < 0.001
TABLE 3. Hand instrumentation versus Sonic Air MM 3000 (n = 15)
FIG 3. Hand instrumentation versus Endostar 5 (representative examples, group 2). Left, apical section: top, hand (round); bottom, Endostar 5 (round). Right, middle section: top, hand (oval); bottom, Endostar 5 (oval) (original magnification x6).
Canal Shape Level
Method
Best Shape Sign Test Round Oval Irregular
Apical
Hand Sonic Air Middle Hand Sonic Air
6 0 4 1
8 8 10 6
1 7 1 8
12 0 9 2
p < 0.001 p = 0.065
the best shape: however, an oval shape was considered better than an irregular shape when evaluating the sections. The Pearson r test was used to establish the interratcr correlation. RESULTS In the uninstrumented controls (Fig. 2), the predominent canal shape in the apical portion was round while an almost equal number of canals were rated as either round or oval in the middle sections (Table 1). Hand instrumentation (Tables 2 to 4) produced a significantly rounder canal shape at both the apical and middle levels when compared with thc Endostar 5, Sonic Air MM 3000, and Cavi-Endo techniques (Figs. 3 to
FIG 4. Hand instrumentation versus Sonic Air MM 3000 (representative examples, group 3). Left, apical section; top, hand (oval); bottom, Sonic Air MM 3000 (oval). Right, middle section: top, hand (round); bottom, Sonic Air MM 3000 (oval) (original magnification •
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FiG 5. Hand instrumentation versus Cavi-Endo (representative examples, group 4). Left, apical section: top, hand (round); bottom, CaviEndo (oval). Right, middle section: top, hand (round); bottom, CaviEndo (irregular) (original magnification x6).
FIG 7. Endostar 5 versus Sonic Air MM 3000 (representative examples, group 7). Left, apical section: top, Endostar 5 (round); bottom, Sonic Air MM 3000 (oval). Right, middle section: top, Endostar 5 (round); bottom, Sonic Air MM3000 (round) (original magnification x6).
TABLE 5. Sonic Air M M 3000 versus Cavi-Endo (n = 15) TABLE 7. Endostar 5 versus Cavi-Endo (n = 15)
Canal Shape Level
Method
Best Shape Sign Test Round Oval Irregular
Apical Sonic Air Cavi-Endo Middle Sonic Air Cavi-Endo
4 1 2 0
10 8 11 8
1 6 2 7
Canal Shape Level
11 0 10 0
Method
p = 0.002
Best Shape Sign Test Round Oval Irregular
p = 0.001 Apical Endostar Cavi-Endo Middle Endostar Cavi-Endo
3 1 1 0
11 9 12 10
1 5 2 5
7 0 5 0
p = 0.016 p = 0.063
TABLE 6. Endostar 5 versus Sonic Air M M 3000 (n = 15)
Canal Shape Level
Method
Best Shape Sign Test Round Oval Irregular
Apical
Endostar Sonic Air Middle Endostar Sonic Air
2 4 1 3
12 10 7 10
1 1 7 2
0 6 2 7
p = 0.031 p = 0.179
FIG 8. Endostar 5 versus Cavi-Endo (representative examples, group 6). Left, apical section: top, Endostar 5 (irregular); bottom, Cavi-endo (irregular). Right, middle section: top, Endostar 5 (irregular); bottom, Cavi-Endo (irregular) (original magnification x6).
those sections where there was initial disagrccmcnt, a reevaluation was done and a rating was then agrced upon. FIG 6. Sonic Air MM 3000 versus Cavi-Endo (representative examples, group 5). Left, apical section: top, Sonic Air MM 3000 (oval); bottom, Cavi-Endo (irregular). Right, middle section: top, Sonic Air MM 3000 (oval); bottom, Cavi-Endo (irregular) (original magnification x6).
DISCUSSION Thc goal of any new instrumcntation technique should be an improvement of the cleansing and shaping procedure. One
Vol. 15, No. 9, September 1989
of the advantages of the ultrasonic system suggested by Martin et al. (9, 10) is the increased ability to remove dentin when compared with conventional hand instrumentation. This reported ability may not be dcsirablc, especially if the dentin removal is irregular and deviates from the original shape of the canal. The present study has shown that hand instrumentation produces a more rcgular preparation at both the apical and middle levels. In all cases of irregular preparations in the midroot sections, the irregularity deviated toward the furcation side of the root. Due to the root concavity on the distal surface of the mesial root, there is a danger of perforation whcn excessive dentin is removed during instrumentation. The decreased amount of tooth structure on the furcation sidc of these roots and the dangcrs encountered in canal preparation have been pointed out by several investigations (21-25). Observations in the uninstrumented control group in this invcstigation were in agreement with these studies since the majority of our canals were found to be closer to the furcation side of the root also. During instrumentation of the mesial canals of mandibular molars, the canal position must always be considered since excessive circumferential filing can lead to a strip perforation (4). In the present study, no sections showed any evidence of this occurring but many of those sections with irregular preparations closely encroached on the furcation side of the root. Time of instrumentation for each technique was excluded from statistical analysis, but it is the operator's opinion that although operator fatigue was reduced using thc sonic/uhrasonic systems, thc overall time required to completely prepare the canal is not less than with hand instrumentation. The amount of time necessary to change from one sonic file to the next must be considered and many cases require initial hand instrumentation to allow placement of the first sonic instrument to the working length. This initial prcparation is frequently the most time consuming part of canal instrumentation. Additionally, it often becomes necessary to use hand instrumentation between sonic filing to allow the next size sonic file to reach the working length. The noise lcvcl and aerosol spray crcatcd during the use of the sonic/ultrasonic units should be considered an occupational hazard when using these systems and proper barrier techniques must be used. The opinions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of Defense or the Department of the Army. Dr. Loushine is a second year endodontic resident, Dr. Weller is director. and Dr. Hartwell is the former director, Endodontic Residency Training Program.
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421
U.S. Army Dental Activity, Fort Gordon, Georgia 30905-5650. Address requests for reprints to Dr. Weller.
References 1. Weine FS. Endodontic therapy. 3rd ed. St. Louis: CV Mosby, 1982:3001. 2. Allison DA, Weber CR, Walton RE. The influence of the method of canal preparation on the quality of apical and coronal obturation. J Endodon 1979;5:298-304. 3. Weine FS, Kelly RF, Lio PJ. The effect of preparation procedures on original canal shape and on apical foramen shape. J Endodon 1975;1:255-62. 4. 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. 5. Jungmann CL, Uchin RA, Bucher JF. Effect of instrumentation on the shape of the root canal. J Endodon 1975;1:66-9. 6. Vessey RA. The effect of filing versus reaming on the shape of the prepared root canal. Oral Surg 1969;27:543-7. 7. Curson I. Endodontic techniques. Preparation of root canals. Br Dent J 1966;121:329-33. 8. Martin H. Ultrasonic disinfection of the root canal. Oral Surg 1976:42:929. 9. Martin H, Cunningham WT, Norris JP, Cotton WR. Ultrasonic versus hand filing of dentin: a quantitative study. Oral Surg 1980;49:79-81. 10. Martin H, Cunningham WT, Norris JP. A quantitative comparison of the ability of diamond and K-type files to remove dentin. Oral Surg 1980;50:5668. 11. Cunningham WT, Martin H, Forrest WR. Evaluation of root canal debridement by the endosonic synergistic system. Oral Surg 1982;53:401-4. 12. Cunningham WT, Martin H. A scanning electron microscopic evaluation of root canal debridement with the endosonic ultrasonic synergistic system. Oral Surg 1982;53:527-31. 13. Martin H, Cunningham WT. The effect of endosonic and hand manipulation on the amount of root canal material extruded. Oral Surg 1982;53:6113. 14. Cameron JA. The use of ultrasound in the cleaning of root canals: a clinical report. J Endodon 1982;8:472-4. 15. Martin H. Cunningham W. Endosonic endodontics, the ultrasonic synergistic system. In: Gerstein H, ed. Techniques in clinical endedontics. Philadelphia: WB Saunders, 1983:316-23. 16. Martin H, Cunningham W. Endosonics-the ultrasonic synergistic system of endodontics. Endod Dent Traumato11985;1 ;201-6. 17. Weller RN, Brady JM, Bernier WE. Efficacy of ultrasonic cleaning. J Endodon 1980;6:740-3. 18. Cymerman JJ, Jerome LA, Moodnick R M A scanning electron microscope study comparing the efficacy of hand instrumentation with ultrasonic instrumentation of the root canal. J Endodon 1983;9:327-31. 19. Pedicord D, EIDeeb ME, Messer HH. Hand versus ultrasonic instrumentation: its effect on canal shape and instrumentation time. J Endodon 1986;12:375-81. 20. Schneider SW. Comparison of canal preparations in straight and curved root canals. Oral Surg 1971 ;32:271-5. 21. Kessler JR, Peters DD, Lorton L. Comparison of the relative risk of molar root perforations using various endedontic instrumentation techniques.J Endodon 1983;9:439-47. 22. Bower RC. Furcation morphology relative to periodontal treatment. J Periodonto11979;50:366-74. 23. Goerig AC, Michelich RJ, Schultz HH. Instrumentation of root canals in molar using the step-down technique. J Endodon 1982;8:550-4. 24. Tidmarsh BG. Preparation of the root canal. Int Endod J 1982;15:5361. 25. Lim SS, Stock CJR. The risk of perforation in the curved canal: anticurvature filing compared with the stepback technique. Int Endod J 1987;20:33-9.
Printed in U.S.A.
VOL. 15, No. 9, SEPTEMBER 1989
Stereomicroscopic Evaluation of Canal Shape following Hand, Sonic, and Ultrasonic Instrumentation Robert J. Loushine, DDS, R. Norman Weller, DMD, MS, and Gary R. Hartwell, DDS, MS, FICD, FACD
This study evaluated the root canal shape after using sonic, ultrasonic, and hand instrumentation on the mesial canals of extracted human mandibular first and second molars. One-hundred and five mesial roots were randomly divided into six experimental groups and one untreated control group of 15 roots each. The following instrumentation techniques were evaluated in the experimental groups: hand instrumentation with K-Flex files, sonic instrumentation with the Endostar 5, sonic instrumentation with the Sonic Air MM 3000, and ultrasonic instrumentation with the Cavi-Endo unit. Each technique was directly compared with each other. The mesial roots were instrumented alternating the techniques between the buccal and lingual canals in each group so that a direct comparison could be made. All canals were instrumented to a size corresponding to a # 3 0 K-Flex file 1 mm from the anatomical apex. The roots were then sectioned perpendicular to the long axis so the apical and middle thirds could be evaluated with the stereomicroscope for canal shape. The control group was sectioned and examined without instrumentation. A significantly more regular shape was obtained at both levels with hand instrumentation than was obtained with either sonic or ultrasonic techniques. The comparisons between the sonic and ultrasonic techniques showed significantly better shapes were obtained with the Sonic Air MM 3000 instrument.
An anticurvature method of filing, proposed by Abou-Rass ct al. (4), directs the canal preparation toward the bulk of root structure in an attempt to prevent stripping in the bifurcation or trifurcation area. The ideal shape of the prepared canal to allow complete obturation should be the same as the cross-sectional shape of the gutta-percha master cone, especially in the apical 4 to 5 mm. After instrumenting the mesial canals of 100 mandibular molars, Jungmann et al. (5) concluded that no technique produced a round preparation in the apical portion of the root canal. Moreover, the further from the apex, the more irregular the shape became. Jungmann et al. (5), Vessey (6), and Curson (7) reported that a reaming action produced the roundest preparation and filing produced the least round preparation. With the introduction of sonic and ultrasonic instrumentation systems, the clinician has an alternative to conventional hand instrumentation techniques for canal preparation. Various authors (8-16) have reported on the beneficial effects of sonic and ultrasonic instrumentation techniques. Advocates report decreased instrumentation time, increased antimicrobial effects, improved root canal debridement, and increased dentin removal compared with hand instrumentation. In contrast, Weller et al. (17) and Cymerman et al. (18) both reported no significant difference in canal debridement between hand and ultrasonic instrumentation. A study by Pedicord et al. (19) compared root canal shapes following instrumentation by ultrasonics and by hand. Their results showed significantly rounder shapes were produced by hand instrumentation in the coronal and middle levels. At the apical levels, there was no significant difference; however, both techniques were shown to transport the canal toward the furcation. The purpose of this study was to compare the shape of the prepared canal following preparation by sonic, ultrasonic, and hand instrumentation in the mcsial canals ofexlracted human mandibular first and second molars.
During endodontic treatment the principle of maintaining the general shape and direction of the original canal system is often neglected. Violation of this principle when instrumenting curved canals can lead to "strip" perforations in the midroot area and foramen transportation in the apical portion (1). Subsequent obturation with gutta-percha becomes difficult, if not impossible. Conventional hand instrumentation, using the step-back technique, has been widely recommended for the preparation of curved canals to prevent ledging, to facilitate obturation with gutta-percha (2), and to decrease the incidence of the "zip" or "teardrop" enlargement of the apical foramen (3).
MATERIALS AND M E T H O D S One-hundred and five extracted human mandibular first and second molars were selected. Schneider's method (20) was used to determine the degree of curvature of each mesial root. Only roots with less than a 40-degrcc curvature were used in this investigation. A groove was cut on the buccal surface of all roots for orientation prior to random placement 417
418
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Journal of Endodontics
into seven equal groups of 15 teeth: group 1, c o n t r o l - - n o instrumentation; group 2, hand instrumentation versus Endostar 5 (Syntex Dental Products, Valley Forge, PA); group 3, hand instrumentation versus Sonic Air MM 3000 (Medidenta International Inc., Woodside, NY); group 4, hand instrumentation versus Cavi-Endo (L. D. Caulk Division, Dentsply International Inc., Milford, DE); group 5, Sonic Air MM 3000 versus Cavi-Endo; group 6, Endostar 5 versus CaviEndo; and group 7, Endostar 5 versus Sonic Air MM 3000. In each group the instrumentation techniques were used the same number of times and were alternated between the mesiobuccal and mesiolingual canals. All files were discarded after use in three canals or earlier if they became unsuitable for further instrumentation. The control group received no instrumentation.
Preparation Standard access preparations were made and two patent, separate mesial canals were located by passing a #10 K-Flex file through each apical foramen. The working length was established by subtracting 1 m m from the length obtained when the file tip just appeared at the apical foramcn. The coronal thirds of all canals were enlarged with #2 and 3 Gates Glidden burs (Maillerfer, Switzerland) to facilitate straight line access to the middle and apical areas and to prevent binding of the instruments in the coronal aspect of the canal. The Gates Glidden burs were not allowed to extend into the experimental middle section of the root canal system. All canal preparations were performed by a single operator throughout this study. HAND INSTRUMENTATION This was accomplished using K-Flex files (Kerr, Romulus, MI) up to a size #30 at the working length. The following step-back technique was used to flare the canal: #30, 35, 30, 40, 30, 45 and 30 files. Each file size larger than the #30 was instrumented 1 m m short of the preceding file and used in a circumferential filing motion. Recapitulation was accomplished with the #30 file to the working length. Copious irrigation with distilled water was used between each file.
accomplished by using the #25 Endostar file in 5- to 7-ram strokes in a circumferential motion short of the working length. A continuous flow of filtered water irrigation was provided through the dental unit. Sonic instrumentation using the Sonic Air MM 3000 was accomplished according to the manufacturer's recommendations in a manner similar to the Endostar 5 technique. TrioSonic files size # 15, 20, and 25 were used to prepare the apical third of the canal until a #30 K-Flex file could be inserted to the working length. A #25 Trio-Sonic file was used in a circumferential filing motion, short of the working length, to flare the canal. Filtered water through the dental unit was used for continuous irrigation. ULTRASONIC I N S T R U M E N T A T I O N This was accomplished using the manufacturer's recommendations for the Cavi-Endo system. Using distilled water as the irrigant, the apical thirds of the canals were enlarged using #15, 20, and 25 Endosonic files until a #30 K-Flex file could be fit to the working length. Circumferential and an up and down motion with a #25 Endosonic file was used to flare the canal.
Evaluation Following canal preparation, each root was sectioned perpendicular to the long axis at the 2-ram level and at the 6m m level. Care was taken to avoid angled cuts as this could have made round canals appear to be oval. Each section was viewed under the stereomicroscope (Wild MPS 515; Wild Hccrbrugg Ltd., Hecrbrugg, Switzerland) at x6 power and the canal shape was evaluated by two independent examiners who were unaware of which instrumentation technique had been used. The evaluators assigned a shape rating of round, oval, or irregular for each of the prepared canals (Fig. 1). The scores of the independent evaluators were compared. For those sections in which there was a discrepancy in the assigned shapes, a reevaluation was done until a shape was agreed upon by the evaluators. The shape ratings were evaluated using a two-tailed sign test. A round canal preparation was considered
SONIC I N S T R U M E N T A T I O N All mechanical instrumentation was done according to the manufacturer's instructions. Following establishment of the working length with a K-Flex file to size #15, a #15 Endostar 5 file was precurved and inserted to the working length. The sonic instrumentation consisted of energizing the #15 file for approximately 10 s until the file could be freely moved up and down in the canal. Short 1- to 2-ram strokes were then used to enlarge the apical third of the canal until the #20 Endostar file would go to the working length without binding. The #20 and 25 Endostar files were then used in a similar manner until a #30 K-Flex file fit to the working length. The K-Flex file was not used to instrument the canal but only to check the size of tile apical preparation. If the #30 K-Flex file would not go to the working length, instrumentation with the #25 Endostar file was continued. Flaring of the canal was
FIG 1. Examples of rated shapes of root canals following instrumentation. Top left, round; bottom left, oval; top right, round; bottom right, irregular (original magnification •
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5). When compared with the Cavi-Endo and the Endostar 5 (Tables 5 and 6). the Sonic Air MM 3000 method produced significantly better canal shapes at both levels (Figs. 6 and 7), with the most common shape for each technique being oval. No significant difference in canal shape was found (Table 7) when the Endostar 5 and Cavi-Endo techniques were compared with one another (Fig. 8). The Cavi-Endo system produced the largest number of irregular-shaped canals. The independent evaluators agreed 88% of the time. For
TABLE 4. Hand instrumentation versus Cavi-Endo (n = 15)
Canal Shape Level
Method
Best Shape Sign Test Round Oval Irregular
FIG 2. Representative examples of unprepared canals (controls, group 1). Left, apical section demonstrating round canals. Right, middle section demonstrating oval canals (original magnification x6),
Apical Hand Cavi-Endo Middle Hand Cavi-Endo
8 0 9 0
7 3 5 5
0 12 1 10
14 0 13 0
p < 0.001 p < 0.001
TABLE 1. Controls--no instrumentation (n = 15)
Canal Shape Level Round
Oval
Irregular
26 16
4 14
0 0
Apical Middle
TABLE 2. Hand instrumentation versus Endostar 5 (n = 15)
Canal Shape Level
Method
Best Shape Sign Test Round Oval Irregular
Apical
Hand Endostar Middle Hand Endostar
6 1 5 0
8 7 9 4
1 7 1 11
10 0 13 0
p = 0.002 p < 0.001
TABLE 3. Hand instrumentation versus Sonic Air MM 3000 (n = 15)
FIG 3. Hand instrumentation versus Endostar 5 (representative examples, group 2). Left, apical section: top, hand (round); bottom, Endostar 5 (round). Right, middle section: top, hand (oval); bottom, Endostar 5 (oval) (original magnification x6).
Canal Shape Level
Method
Best Shape Sign Test Round Oval Irregular
Apical
Hand Sonic Air Middle Hand Sonic Air
6 0 4 1
8 8 10 6
1 7 1 8
12 0 9 2
p < 0.001 p = 0.065
the best shape: however, an oval shape was considered better than an irregular shape when evaluating the sections. The Pearson r test was used to establish the interratcr correlation. RESULTS In the uninstrumented controls (Fig. 2), the predominent canal shape in the apical portion was round while an almost equal number of canals were rated as either round or oval in the middle sections (Table 1). Hand instrumentation (Tables 2 to 4) produced a significantly rounder canal shape at both the apical and middle levels when compared with thc Endostar 5, Sonic Air MM 3000, and Cavi-Endo techniques (Figs. 3 to
FIG 4. Hand instrumentation versus Sonic Air MM 3000 (representative examples, group 3). Left, apical section; top, hand (oval); bottom, Sonic Air MM 3000 (oval). Right, middle section: top, hand (round); bottom, Sonic Air MM 3000 (oval) (original magnification •
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FiG 5. Hand instrumentation versus Cavi-Endo (representative examples, group 4). Left, apical section: top, hand (round); bottom, CaviEndo (oval). Right, middle section: top, hand (round); bottom, CaviEndo (irregular) (original magnification x6).
FIG 7. Endostar 5 versus Sonic Air MM 3000 (representative examples, group 7). Left, apical section: top, Endostar 5 (round); bottom, Sonic Air MM 3000 (oval). Right, middle section: top, Endostar 5 (round); bottom, Sonic Air MM3000 (round) (original magnification x6).
TABLE 5. Sonic Air M M 3000 versus Cavi-Endo (n = 15) TABLE 7. Endostar 5 versus Cavi-Endo (n = 15)
Canal Shape Level
Method
Best Shape Sign Test Round Oval Irregular
Apical Sonic Air Cavi-Endo Middle Sonic Air Cavi-Endo
4 1 2 0
10 8 11 8
1 6 2 7
Canal Shape Level
11 0 10 0
Method
p = 0.002
Best Shape Sign Test Round Oval Irregular
p = 0.001 Apical Endostar Cavi-Endo Middle Endostar Cavi-Endo
3 1 1 0
11 9 12 10
1 5 2 5
7 0 5 0
p = 0.016 p = 0.063
TABLE 6. Endostar 5 versus Sonic Air M M 3000 (n = 15)
Canal Shape Level
Method
Best Shape Sign Test Round Oval Irregular
Apical
Endostar Sonic Air Middle Endostar Sonic Air
2 4 1 3
12 10 7 10
1 1 7 2
0 6 2 7
p = 0.031 p = 0.179
FIG 8. Endostar 5 versus Cavi-Endo (representative examples, group 6). Left, apical section: top, Endostar 5 (irregular); bottom, Cavi-endo (irregular). Right, middle section: top, Endostar 5 (irregular); bottom, Cavi-Endo (irregular) (original magnification x6).
those sections where there was initial disagrccmcnt, a reevaluation was done and a rating was then agrced upon. FIG 6. Sonic Air MM 3000 versus Cavi-Endo (representative examples, group 5). Left, apical section: top, Sonic Air MM 3000 (oval); bottom, Cavi-Endo (irregular). Right, middle section: top, Sonic Air MM 3000 (oval); bottom, Cavi-Endo (irregular) (original magnification x6).
DISCUSSION Thc goal of any new instrumcntation technique should be an improvement of the cleansing and shaping procedure. One
Vol. 15, No. 9, September 1989
of the advantages of the ultrasonic system suggested by Martin et al. (9, 10) is the increased ability to remove dentin when compared with conventional hand instrumentation. This reported ability may not be dcsirablc, especially if the dentin removal is irregular and deviates from the original shape of the canal. The present study has shown that hand instrumentation produces a more rcgular preparation at both the apical and middle levels. In all cases of irregular preparations in the midroot sections, the irregularity deviated toward the furcation side of the root. Due to the root concavity on the distal surface of the mesial root, there is a danger of perforation whcn excessive dentin is removed during instrumentation. The decreased amount of tooth structure on the furcation sidc of these roots and the dangcrs encountered in canal preparation have been pointed out by several investigations (21-25). Observations in the uninstrumented control group in this invcstigation were in agreement with these studies since the majority of our canals were found to be closer to the furcation side of the root also. During instrumentation of the mesial canals of mandibular molars, the canal position must always be considered since excessive circumferential filing can lead to a strip perforation (4). In the present study, no sections showed any evidence of this occurring but many of those sections with irregular preparations closely encroached on the furcation side of the root. Time of instrumentation for each technique was excluded from statistical analysis, but it is the operator's opinion that although operator fatigue was reduced using thc sonic/uhrasonic systems, thc overall time required to completely prepare the canal is not less than with hand instrumentation. The amount of time necessary to change from one sonic file to the next must be considered and many cases require initial hand instrumentation to allow placement of the first sonic instrument to the working length. This initial prcparation is frequently the most time consuming part of canal instrumentation. Additionally, it often becomes necessary to use hand instrumentation between sonic filing to allow the next size sonic file to reach the working length. The noise lcvcl and aerosol spray crcatcd during the use of the sonic/ultrasonic units should be considered an occupational hazard when using these systems and proper barrier techniques must be used. The opinions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of Defense or the Department of the Army. Dr. Loushine is a second year endodontic resident, Dr. Weller is director. and Dr. Hartwell is the former director, Endodontic Residency Training Program.
Hand versus Sonic Instrumentation
421
U.S. Army Dental Activity, Fort Gordon, Georgia 30905-5650. Address requests for reprints to Dr. Weller.
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