- Email: [email protected]
Comparison in vivo of the first tapered and nontapered instruments that bind at the apical constriction
Vol. 102 No. 3 September 2006
ENDODONTOLOGY
Editor: Larz S. Spångberg
Comparison in vivo of the first tapered and nontapered instruments that bind at the apical constriction Anda Kfir, DMD,a Esther Rosenberg, DMD, and
b
Zvi Fuss, DMD,c Tel-Aviv, Israel
MAURICE AND GABRIELA GOLDSCHLEGER SCHOOL OF DENTAL MEDICINE
Objective. To compare sizes of the first instrument with or without taper that binds to the narrow apical diameter of the root canal after coronal flaring. Study design. For the study, 388 canals were examined in patients with intact apices. A standard endodontic access cavity was prepared and the coronal third flared using standardized K-files, Gates Glidden reamers, or Profile rotary instruments. Apical patency was established using K-file size 10 and working length determined using an apex locator and radiographs. Standardized K-file hand instruments were gently introduced to working length beginning with size 15. The first K-file to bind to the canal walls and reach the working length was recorded as FKFB. Nontapered instruments (Lightspeed) were then gently introduced by hand to each canal in ascending order beginning with size 20 to working length. The first instrument to bind to the canal walls and reach the working length was recorded as FLSB. Statistical analysis was carried out using univariate analysis of variance. Results. The average size of FLSB was approximately 2 ISO sizes larger than FKFB (P ⬍ .001). Minimal differences were found in the maxillary central incisors (6.7 ⫾ 3.0) and maximal differences in canals from maxillary lateral incisors (15.4 ⫾ 3.5). Conclusions. The first nontapered instruments to bind at the apical constriction were larger and reflected the actual narrow apical diameter of the canal better than the tapered instruments. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2006;102:395-8)
Thorough debridement of the root canal system and 3-dimensional obturation of the canal system are 2 main objectives of endodontic therapy.1 The vertical dimension of the root canal and the importance of the precise determination of the working length are the focus of most textbooks and much of the literature.2,3 Different methods for working length determination have been described: the tactile method, which necessitates a very pointed digital tactile sense4 and is best performed after coronal flaring,5 the radiographic a
Specialist in Endodontics, Instructor and Coordinator of the Department of Endodontology, School of Dental Medicine, Tel-Aviv University, Tel Aviv, Israel. b Specialist in Endodontics and Instructor, Department of Endodontology, School of Dental Medicine, Tel-Aviv University, Tel-Aviv, Israel. c Specialist in Endodontics, private practice. Received for publication Nov. 16, 2005; returned for revision Nov. 16, 2005; accepted for publication Nov. 16, 2005. 1079-2104/$ - see front matter © 2006 Mosby, Inc. All rights reserved. doi:10.1016/j.tripleo.2005.11.017
method, which is the most popular, and the electronic measurement. Furthermore, the horizontal dimension of the root canal and its width have also been discussed in detail.6-8 Root canals are frequently elliptical in cross section, having both narrow and large diameters.9 It is also well accepted that to achieve the best canal debridement, the enlarged canal should fit its large diameter. Moreover, the average initial large diameter of the canals at the apical constriction ranges between 0.3 and 0.4 mm, corresponding to ISO size 30-40 standardized K-files.9 The question can be asked why the canal diameter has not received proper attention.10 During instrumentation, iatrogenic procedural errors, such as zipping, canal transportation, ledging, and root perforations, occur, especially when using rigid instruments.11-13 Nickel-titanium (NiTi) instruments were introduced to alleviate procedural errors,14 to better negotiate curved root canals,15 and to reduce treatment time with the use of the automated rotary NiTi instruments.16-19 The tech395
396 Kfir, Rosenberg, and Fuss nical innovations combined with correct methods enable safe enlargement of the apical third of the root canal to larger sizes when necessary.20 Safe enlargement of the root canals can present a problem—what size to enlarge the root canal? Haga21 found that mechanical preparation of the root canal to 2 sizes larger than the original was still inadequate. Grossman22 recommends 3 ISO sizes beyond the first instrument in which tactile sensation binds the root canal’s walls at working length. However, a histologic study23 has shown that canals instrumented to 3 sizes larger were still not thoroughly cleaned. Gutierrez and Garcia24 suggest that because the root canal diameter is larger than the instrument caliber used, each canal should be calibrated independently before instrumentation. The selection of the first instrument to fit the apical constriction is achieved by tactile sensation, which is possible only after coronal flaring. Any tapering discrepancy between the gauging instrument and the canal may lead to early instrumentation of the canal wall, causing a false sensation of apical binding. Instruments with a large taper might give a resistance sensation when the instrument is in friction with the coronal parts of the canal, while at the apical part there is no contact between the instrument and the canal walls. The aim of the present study was to compare, in vivo, the sizes of the first instrument with or without taper (K-file vs. Lightspeed instruments) to bind to the narrow apical diameter of the root canal following coronal flaring. MATERIALS AND METHODS The study consisted of 388 canals from teeth randomly selected by 2 evaluators (specialists in endodontology) during endodontic therapy in patients with intact apices. Teeth in the maxilla were divided into central and lateral incisors (I), canines (C), premolars with 1 (Pm-1ca) and 2 (Pm-2ca) canals, molars–palatal roots (M-p), and molars–buccal roots (M-b) (Fig. 1). Teeth in the mandible were divided into incisors (I), canines (C), premolars with 1 canal (Pm-1ca), premolars with 2 canals (Pm-2ca), molars–distal root (M-d), and molars–mesial root (M-m) (Fig. 2). A standard endodontic access cavity was prepared using cylindrical diamond (Strauss, Netanya, Israel) or tungsten (SS White, Lakewood, NJ) drills. The coronal third was flared using standardized K-files (VDW, Munich, Germany), beginning with size 60 at the orifice followed by smaller sizes, each penetrating deeper into the coronal third, or Gates Glidden reamers (VDW), beginning with size 3 at the orifice followed by sizes 2 and 1, each penetrating 2 mm deeper into the coronal third of the root canal, or by Profile .04
OOOOE September 2006
Fig. 1. Mean ISO size of the diameter of the root canal as measured by tapered or nontapered instrument in the maxilla. A significant difference was observed between the 2 groups (P ⬍ .001).
Fig. 2. Mean ISO size of the diameter of the root canal as measured by tapered or nontapered instruments in the mandible. A significant difference was observed between the 2 groups (P ⬍ .001).
rotary instruments (Dentsply Maillefer, Ballaigues, Switzerland.), beginning with size 45 at the orifice followed by size 40 and 35 until coronal flaring was completed. Apical patency was established by passing K-file size 10 through the foramen, and working length was determined using an apex locator. Radiographs were taken with the XCP system (Rinn; Dentsply, Elgin, IL) to standardize the x-ray beam. Standardized K-file hand instruments were gently introduced by the first evaluator to working length beginning with size 15. The first K-file to bind to the canal walls without pushing and to reach the working length was recorded as FKFB. The same procedure was repeated by the second evaluator. Nontapered instruments (Lightspeed; Lightspeed Technology, San Antonio, TX) were gently introduced by hand to each canal in ascending order beginning with size 20 to working length. The first Lightspeed instrument to bind at the canal walls and reach the working length was recorded as FLSB. This step was also performed by 2 separate evaluators specialized in endodontics who routinely use Lightspeed. In all instances, a larger file was introduced
OOOOE Volume 102, Number 3
to ensure that it could not reach the same depth (i.e., working length). Statistical analysis was carried out using univariate analysis of variance. RESULTS The mean ISO sizes of the diameter of the root canals as measured by tapered or nontapered instruments are shown in Figures 1 and 2. The average size of FLSB was larger, approximately 2 ISO sizes than the average size of FKFB (P ⬍ .001). The mean diameter of FKFB and FLSB in all root canal groups after coronal flaring was 22.1 (⫾4.7) and 33.3 (⫾6.8) (P ⬍ .001), respectively. In maxillary central incisors, minimal differences (6.7 ⫾ 3.0) were found in canals, and maximal differences (15.4 ⫾ 3.5) were found in maxillary lateral incisors. DISCUSSION After coronal flaring and working length determination, most clinicians select a file which they believe will fit the apex and reflect its apical minor diameter (FKFB). Accordingly, the decision is made regarding the extent of apical shaping and final apical canal enlargement. The present study indicates that their judgment is often incorrect. Coronal interferences and curvatures present difficulty to the clinician’s ability to sense the apical diameter with a file. They produce premature contacts with the file and interfere with its progression toward the apex. Early flaring of the coronal third, regardless of the method of instrumentation used, removes these contacts, opens the space and reduces file contact. Thus, a file progresses more easily toward the apex after flaring, as suggested by Leeb.26 Moreover, preflaring improves tactile feel and allows the operator to better sense the canal size near the apex without curvatures and irregularities.5,28 This better sense of apical diameter provides information that should result in better control of biomechanical preparation. Preflaring can be accomplished by either manual (K-files) or mechanical instrumentation (rotary flaring; Gates Glidden drills, or NiTi rotary instruments). The present study clearly indicated that FLSB can be significantly larger than the FKFB in all tooth groups (Figs. 1 and 2). This information suggests that canal interferences and curvatures are factors in the clinician’s ability to sense apical diameter with a file (tapered instrument) even after coronal flaring. The use of an endodontic instrument without taper, such as the Lightspeed instrument, enables the selection of a first instrument with better apical adaptation, better sense of resistance, plus the ability to place a larger file to the apex. The widest area is confined to its apical 2-3
Kfir, Rosenberg, and Fuss 397
mm and the remainder of the instrument is smooth with no taper. Contact between the instrument and the canal walls exists only in the 2-3 mm of the apical part of the root canal. The difference between the FKFB and FLSB was largely found in the relatively more narrow and curved canals, such as the lateral incisors, known to have a distopalatinal curve in its apical part, or in the narrow mesial root canals of mandibular molars. It was less prominent in the wide and relatively straight canals, such as the central incisors, maxillary canines, or distal roots of the mandibular molars. In root canals where there is a relatively natural large taper or where no anatomic curves are present, a tapered instrument can be introduced through to the working length without coronal interferences. In the present study, the mean initial apical narrow diameter in all root canals was 0.33 mm. The mean values of FLSB ranged from 0.25 to 0.60 mm. These measurements correspond to those of Wu et al.,9 who demonstrated that the average initial narrow diameter at the apical constriction ranges from 0.3 to 0.4 mm. To begin enlargement with 3 instruments beyond the mean values of FLSB means greater final enlargement compared with enlargement when the beginning point is FKFB (mean values range from 0.15 to 0.30 mm). This enlargement will enable better cleaning of the root canal, mechanically and chemically, and will ensure removal of more microorganisms and their substrates from the canal, thus improving the outcome of the treatment and success rate. Because determination of the initial narrow apical canal diameter plays a major factor in identifying the extent of final apical shaping, the operator should consider introducing a nontapered instrument to working length after coronal flaring. CONCLUSION Because the first nontapered instrument that binds the apical constriction is larger than the corresponding tapered instrument, it better reflects the actual narrow apical diameter of the canal. The authors wish to thank Ms. Rita Lazar for editorial assistance and preparation of the manuscript. REFERENCES 1. Schilder H. Cleaning and shaping the root canal. Dent Clin North Am 1974;18:269-96. 2. Kuttler Y. Microscopic investigation of root apices. J Am Dent Assoc 1950;50:544-52. 3. Green DA. Sterioscopic study of the root apices of 400 maxillary and mandibular anterior teeth. Oral Surg 1956;9:1224-32. 4. Seindberg BH, Alibrandi BV, Finel H, Logue B. Clinical investigation of measuring working length of root canals with an electronic device and with digital tactile sense. J Am Dent Assoc 1975;90:379-87.
OOOOE September 2006
398 Kfir, Rosenberg, and Fuss 5. Stabholtz A, Rotstein I, Torabinejad M. Effect of preflaring on tactile detection of the apical constriction. J Endod 1995;21:92-9. 6. Green EN. Microscopic investigation of root canal diameter. J Am Dent Assoc 1958;57:636-44. 7. Kerekes K, Tronstad L. Morphometric observations on the root canals of human molars. J Endod 1977;3:114-8. 8. Jou Y, Karabukak B, Levin J. Endodontic working width: current concepts and techniques. Dent Clin North Am 2004;48: 323-35. 9. Wu MK, R’oris A, Barkis D, Wesselink PR. Prevalence and extent of long oval canals in the apical third. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;89:739-43. 10. Senia ES. Canal diameter: the forgotten dimension. Endod Pract 2000;3:34-8. 11. Cattoni M. Common failures in endodontics and their corrections. Dent Clin North Am 1963;7:383-99. 12. Walton R, Torabinejad M. Principles and practice of endodontics. 2nd ed. Philadelphia: WB Saunders; 1996. p. 201–33. 13. Bakland LK. Endodontic misshapes: perforations. Calif Dent Assoc J 1991;19:41-8. 14. Walia H, Brantley WA, Gerstein H. An initial investigation of the bending and torsional properties of Nitinol root canal files. J Endod 1988;14:346-51. 15. Pettiette MT, Metzger Z, Phillips C, Trope M. Endodontic complications of root canal therapy performed by dental students with stainless-steel K-files and nickel-titanium hand files. J Endod 1999;25:230-4. 16. Roig-Cayon M, Basilio-Monne’ J, Abo’s-Herra’ndiz R, BrauAguade’ E, Canalda-Sahli CA. Comparison of molar root canal preparations using six instruments and instrumentation techniques. J Endod 1997;23:383-6. 17. Thompson SA, Dummer PMH. Shaping ability of Lightspeed rotary nickel-titanium instruments in simulated root canals. Part 1. J Endod 1997;23:698-702. 18. Thompson SA, Dummer PMH. Shaping ability of Lightspeed rotary nickel-titanium instruments in simulated root canals. Part 2. J Endod 1997;23:742-7.
19. Spanberg LW. Instruments, materials and devices. In: Cohen S, Burns RC, editors. Pathways of the pulp. 7th ed. St. Louis: Mosby; 1998. p. 476-95. 20. Kfir A, Rosenberg E, Zuckerman O, Tamse A, Fuss Z. Comparison of procedural errors resulting during root canal preparations completed by junior dental students in patients using an “8-step method” versus “serial step-back technique.” Int Endod J 2003; 36:49-53. 21. Haga CS. Microscopic measurements of root canal preparations following instrumentation. J Br Endod Soc 1968;2:41. 22. Grossman L. Endodontic practice. 10th ed. Philadelphia: Lea & Febiger; 1985. p. 207. 23. Walton RE. Histologic evaluation of different methods of enlarging pulp canal space. J Endod 1976;2:304-11. 24. Gutierrez JH, Garcia J, Microscopic and macroscopic investigation on results of mechanical preparation of root canals. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1968; 25:108-16. 25. Contreras MAL, Zinman EH, Kaplan SK. Comparison of the first file that fits at the apex before and after early flaring. J Endod 2001;27:713-6. 26. Leeb J. Canal orifice enlargement as related to biomechanical preparation. J Endod 1983;9:463-70. 27. Weine FS. Endodontic therapy. 5th ed. St. Louis: CV Mosby; 1996. 28. Morgan LF, Montgomery S. An evaluation of the crown-down pressureless technique. J Endod 1984;10:491-8. Reprint requests: Dr. Anda Kfir, Coordinator Department of Endodontology School of Dental Medicine Tel Aviv University Tel Aviv, Israel [email protected]
ENDODONTOLOGY
Editor: Larz S. Spångberg
Comparison in vivo of the first tapered and nontapered instruments that bind at the apical constriction Anda Kfir, DMD,a Esther Rosenberg, DMD, and
b
Zvi Fuss, DMD,c Tel-Aviv, Israel
MAURICE AND GABRIELA GOLDSCHLEGER SCHOOL OF DENTAL MEDICINE
Objective. To compare sizes of the first instrument with or without taper that binds to the narrow apical diameter of the root canal after coronal flaring. Study design. For the study, 388 canals were examined in patients with intact apices. A standard endodontic access cavity was prepared and the coronal third flared using standardized K-files, Gates Glidden reamers, or Profile rotary instruments. Apical patency was established using K-file size 10 and working length determined using an apex locator and radiographs. Standardized K-file hand instruments were gently introduced to working length beginning with size 15. The first K-file to bind to the canal walls and reach the working length was recorded as FKFB. Nontapered instruments (Lightspeed) were then gently introduced by hand to each canal in ascending order beginning with size 20 to working length. The first instrument to bind to the canal walls and reach the working length was recorded as FLSB. Statistical analysis was carried out using univariate analysis of variance. Results. The average size of FLSB was approximately 2 ISO sizes larger than FKFB (P ⬍ .001). Minimal differences were found in the maxillary central incisors (6.7 ⫾ 3.0) and maximal differences in canals from maxillary lateral incisors (15.4 ⫾ 3.5). Conclusions. The first nontapered instruments to bind at the apical constriction were larger and reflected the actual narrow apical diameter of the canal better than the tapered instruments. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2006;102:395-8)
Thorough debridement of the root canal system and 3-dimensional obturation of the canal system are 2 main objectives of endodontic therapy.1 The vertical dimension of the root canal and the importance of the precise determination of the working length are the focus of most textbooks and much of the literature.2,3 Different methods for working length determination have been described: the tactile method, which necessitates a very pointed digital tactile sense4 and is best performed after coronal flaring,5 the radiographic a
Specialist in Endodontics, Instructor and Coordinator of the Department of Endodontology, School of Dental Medicine, Tel-Aviv University, Tel Aviv, Israel. b Specialist in Endodontics and Instructor, Department of Endodontology, School of Dental Medicine, Tel-Aviv University, Tel-Aviv, Israel. c Specialist in Endodontics, private practice. Received for publication Nov. 16, 2005; returned for revision Nov. 16, 2005; accepted for publication Nov. 16, 2005. 1079-2104/$ - see front matter © 2006 Mosby, Inc. All rights reserved. doi:10.1016/j.tripleo.2005.11.017
method, which is the most popular, and the electronic measurement. Furthermore, the horizontal dimension of the root canal and its width have also been discussed in detail.6-8 Root canals are frequently elliptical in cross section, having both narrow and large diameters.9 It is also well accepted that to achieve the best canal debridement, the enlarged canal should fit its large diameter. Moreover, the average initial large diameter of the canals at the apical constriction ranges between 0.3 and 0.4 mm, corresponding to ISO size 30-40 standardized K-files.9 The question can be asked why the canal diameter has not received proper attention.10 During instrumentation, iatrogenic procedural errors, such as zipping, canal transportation, ledging, and root perforations, occur, especially when using rigid instruments.11-13 Nickel-titanium (NiTi) instruments were introduced to alleviate procedural errors,14 to better negotiate curved root canals,15 and to reduce treatment time with the use of the automated rotary NiTi instruments.16-19 The tech395
396 Kfir, Rosenberg, and Fuss nical innovations combined with correct methods enable safe enlargement of the apical third of the root canal to larger sizes when necessary.20 Safe enlargement of the root canals can present a problem—what size to enlarge the root canal? Haga21 found that mechanical preparation of the root canal to 2 sizes larger than the original was still inadequate. Grossman22 recommends 3 ISO sizes beyond the first instrument in which tactile sensation binds the root canal’s walls at working length. However, a histologic study23 has shown that canals instrumented to 3 sizes larger were still not thoroughly cleaned. Gutierrez and Garcia24 suggest that because the root canal diameter is larger than the instrument caliber used, each canal should be calibrated independently before instrumentation. The selection of the first instrument to fit the apical constriction is achieved by tactile sensation, which is possible only after coronal flaring. Any tapering discrepancy between the gauging instrument and the canal may lead to early instrumentation of the canal wall, causing a false sensation of apical binding. Instruments with a large taper might give a resistance sensation when the instrument is in friction with the coronal parts of the canal, while at the apical part there is no contact between the instrument and the canal walls. The aim of the present study was to compare, in vivo, the sizes of the first instrument with or without taper (K-file vs. Lightspeed instruments) to bind to the narrow apical diameter of the root canal following coronal flaring. MATERIALS AND METHODS The study consisted of 388 canals from teeth randomly selected by 2 evaluators (specialists in endodontology) during endodontic therapy in patients with intact apices. Teeth in the maxilla were divided into central and lateral incisors (I), canines (C), premolars with 1 (Pm-1ca) and 2 (Pm-2ca) canals, molars–palatal roots (M-p), and molars–buccal roots (M-b) (Fig. 1). Teeth in the mandible were divided into incisors (I), canines (C), premolars with 1 canal (Pm-1ca), premolars with 2 canals (Pm-2ca), molars–distal root (M-d), and molars–mesial root (M-m) (Fig. 2). A standard endodontic access cavity was prepared using cylindrical diamond (Strauss, Netanya, Israel) or tungsten (SS White, Lakewood, NJ) drills. The coronal third was flared using standardized K-files (VDW, Munich, Germany), beginning with size 60 at the orifice followed by smaller sizes, each penetrating deeper into the coronal third, or Gates Glidden reamers (VDW), beginning with size 3 at the orifice followed by sizes 2 and 1, each penetrating 2 mm deeper into the coronal third of the root canal, or by Profile .04
OOOOE September 2006
Fig. 1. Mean ISO size of the diameter of the root canal as measured by tapered or nontapered instrument in the maxilla. A significant difference was observed between the 2 groups (P ⬍ .001).
Fig. 2. Mean ISO size of the diameter of the root canal as measured by tapered or nontapered instruments in the mandible. A significant difference was observed between the 2 groups (P ⬍ .001).
rotary instruments (Dentsply Maillefer, Ballaigues, Switzerland.), beginning with size 45 at the orifice followed by size 40 and 35 until coronal flaring was completed. Apical patency was established by passing K-file size 10 through the foramen, and working length was determined using an apex locator. Radiographs were taken with the XCP system (Rinn; Dentsply, Elgin, IL) to standardize the x-ray beam. Standardized K-file hand instruments were gently introduced by the first evaluator to working length beginning with size 15. The first K-file to bind to the canal walls without pushing and to reach the working length was recorded as FKFB. The same procedure was repeated by the second evaluator. Nontapered instruments (Lightspeed; Lightspeed Technology, San Antonio, TX) were gently introduced by hand to each canal in ascending order beginning with size 20 to working length. The first Lightspeed instrument to bind at the canal walls and reach the working length was recorded as FLSB. This step was also performed by 2 separate evaluators specialized in endodontics who routinely use Lightspeed. In all instances, a larger file was introduced
OOOOE Volume 102, Number 3
to ensure that it could not reach the same depth (i.e., working length). Statistical analysis was carried out using univariate analysis of variance. RESULTS The mean ISO sizes of the diameter of the root canals as measured by tapered or nontapered instruments are shown in Figures 1 and 2. The average size of FLSB was larger, approximately 2 ISO sizes than the average size of FKFB (P ⬍ .001). The mean diameter of FKFB and FLSB in all root canal groups after coronal flaring was 22.1 (⫾4.7) and 33.3 (⫾6.8) (P ⬍ .001), respectively. In maxillary central incisors, minimal differences (6.7 ⫾ 3.0) were found in canals, and maximal differences (15.4 ⫾ 3.5) were found in maxillary lateral incisors. DISCUSSION After coronal flaring and working length determination, most clinicians select a file which they believe will fit the apex and reflect its apical minor diameter (FKFB). Accordingly, the decision is made regarding the extent of apical shaping and final apical canal enlargement. The present study indicates that their judgment is often incorrect. Coronal interferences and curvatures present difficulty to the clinician’s ability to sense the apical diameter with a file. They produce premature contacts with the file and interfere with its progression toward the apex. Early flaring of the coronal third, regardless of the method of instrumentation used, removes these contacts, opens the space and reduces file contact. Thus, a file progresses more easily toward the apex after flaring, as suggested by Leeb.26 Moreover, preflaring improves tactile feel and allows the operator to better sense the canal size near the apex without curvatures and irregularities.5,28 This better sense of apical diameter provides information that should result in better control of biomechanical preparation. Preflaring can be accomplished by either manual (K-files) or mechanical instrumentation (rotary flaring; Gates Glidden drills, or NiTi rotary instruments). The present study clearly indicated that FLSB can be significantly larger than the FKFB in all tooth groups (Figs. 1 and 2). This information suggests that canal interferences and curvatures are factors in the clinician’s ability to sense apical diameter with a file (tapered instrument) even after coronal flaring. The use of an endodontic instrument without taper, such as the Lightspeed instrument, enables the selection of a first instrument with better apical adaptation, better sense of resistance, plus the ability to place a larger file to the apex. The widest area is confined to its apical 2-3
Kfir, Rosenberg, and Fuss 397
mm and the remainder of the instrument is smooth with no taper. Contact between the instrument and the canal walls exists only in the 2-3 mm of the apical part of the root canal. The difference between the FKFB and FLSB was largely found in the relatively more narrow and curved canals, such as the lateral incisors, known to have a distopalatinal curve in its apical part, or in the narrow mesial root canals of mandibular molars. It was less prominent in the wide and relatively straight canals, such as the central incisors, maxillary canines, or distal roots of the mandibular molars. In root canals where there is a relatively natural large taper or where no anatomic curves are present, a tapered instrument can be introduced through to the working length without coronal interferences. In the present study, the mean initial apical narrow diameter in all root canals was 0.33 mm. The mean values of FLSB ranged from 0.25 to 0.60 mm. These measurements correspond to those of Wu et al.,9 who demonstrated that the average initial narrow diameter at the apical constriction ranges from 0.3 to 0.4 mm. To begin enlargement with 3 instruments beyond the mean values of FLSB means greater final enlargement compared with enlargement when the beginning point is FKFB (mean values range from 0.15 to 0.30 mm). This enlargement will enable better cleaning of the root canal, mechanically and chemically, and will ensure removal of more microorganisms and their substrates from the canal, thus improving the outcome of the treatment and success rate. Because determination of the initial narrow apical canal diameter plays a major factor in identifying the extent of final apical shaping, the operator should consider introducing a nontapered instrument to working length after coronal flaring. CONCLUSION Because the first nontapered instrument that binds the apical constriction is larger than the corresponding tapered instrument, it better reflects the actual narrow apical diameter of the canal. The authors wish to thank Ms. Rita Lazar for editorial assistance and preparation of the manuscript. REFERENCES 1. Schilder H. Cleaning and shaping the root canal. Dent Clin North Am 1974;18:269-96. 2. Kuttler Y. Microscopic investigation of root apices. J Am Dent Assoc 1950;50:544-52. 3. Green DA. Sterioscopic study of the root apices of 400 maxillary and mandibular anterior teeth. Oral Surg 1956;9:1224-32. 4. Seindberg BH, Alibrandi BV, Finel H, Logue B. Clinical investigation of measuring working length of root canals with an electronic device and with digital tactile sense. J Am Dent Assoc 1975;90:379-87.
OOOOE September 2006
398 Kfir, Rosenberg, and Fuss 5. Stabholtz A, Rotstein I, Torabinejad M. Effect of preflaring on tactile detection of the apical constriction. J Endod 1995;21:92-9. 6. Green EN. Microscopic investigation of root canal diameter. J Am Dent Assoc 1958;57:636-44. 7. Kerekes K, Tronstad L. Morphometric observations on the root canals of human molars. J Endod 1977;3:114-8. 8. Jou Y, Karabukak B, Levin J. Endodontic working width: current concepts and techniques. Dent Clin North Am 2004;48: 323-35. 9. Wu MK, R’oris A, Barkis D, Wesselink PR. Prevalence and extent of long oval canals in the apical third. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;89:739-43. 10. Senia ES. Canal diameter: the forgotten dimension. Endod Pract 2000;3:34-8. 11. Cattoni M. Common failures in endodontics and their corrections. Dent Clin North Am 1963;7:383-99. 12. Walton R, Torabinejad M. Principles and practice of endodontics. 2nd ed. Philadelphia: WB Saunders; 1996. p. 201–33. 13. Bakland LK. Endodontic misshapes: perforations. Calif Dent Assoc J 1991;19:41-8. 14. Walia H, Brantley WA, Gerstein H. An initial investigation of the bending and torsional properties of Nitinol root canal files. J Endod 1988;14:346-51. 15. Pettiette MT, Metzger Z, Phillips C, Trope M. Endodontic complications of root canal therapy performed by dental students with stainless-steel K-files and nickel-titanium hand files. J Endod 1999;25:230-4. 16. Roig-Cayon M, Basilio-Monne’ J, Abo’s-Herra’ndiz R, BrauAguade’ E, Canalda-Sahli CA. Comparison of molar root canal preparations using six instruments and instrumentation techniques. J Endod 1997;23:383-6. 17. Thompson SA, Dummer PMH. Shaping ability of Lightspeed rotary nickel-titanium instruments in simulated root canals. Part 1. J Endod 1997;23:698-702. 18. Thompson SA, Dummer PMH. Shaping ability of Lightspeed rotary nickel-titanium instruments in simulated root canals. Part 2. J Endod 1997;23:742-7.
19. Spanberg LW. Instruments, materials and devices. In: Cohen S, Burns RC, editors. Pathways of the pulp. 7th ed. St. Louis: Mosby; 1998. p. 476-95. 20. Kfir A, Rosenberg E, Zuckerman O, Tamse A, Fuss Z. Comparison of procedural errors resulting during root canal preparations completed by junior dental students in patients using an “8-step method” versus “serial step-back technique.” Int Endod J 2003; 36:49-53. 21. Haga CS. Microscopic measurements of root canal preparations following instrumentation. J Br Endod Soc 1968;2:41. 22. Grossman L. Endodontic practice. 10th ed. Philadelphia: Lea & Febiger; 1985. p. 207. 23. Walton RE. Histologic evaluation of different methods of enlarging pulp canal space. J Endod 1976;2:304-11. 24. Gutierrez JH, Garcia J, Microscopic and macroscopic investigation on results of mechanical preparation of root canals. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1968; 25:108-16. 25. Contreras MAL, Zinman EH, Kaplan SK. Comparison of the first file that fits at the apex before and after early flaring. J Endod 2001;27:713-6. 26. Leeb J. Canal orifice enlargement as related to biomechanical preparation. J Endod 1983;9:463-70. 27. Weine FS. Endodontic therapy. 5th ed. St. Louis: CV Mosby; 1996. 28. Morgan LF, Montgomery S. An evaluation of the crown-down pressureless technique. J Endod 1984;10:491-8. Reprint requests: Dr. Anda Kfir, Coordinator Department of Endodontology School of Dental Medicine Tel Aviv University Tel Aviv, Israel [email protected]