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A systematic approach to preventing intracanal breakage of endodontic files Sotokawa T. A systematic approach to preventing intracanal breakage of endodontic files. Endod Dent Traumatol 1990; 6: 60-62. Abstract - This study was conducted to determine the effectiveness of a method to prevent intracanal breakage of endodontic files. An application schedule with a predetermined number of periods of use for K-files of all sizes was implemented at the authors clinic for a 3-year period. All the files used under this schedule were discarded after the predetermined periods of use, whether they displayed any deformity or not. During the 3-year period, 1933 files (53.7 per month) were discarded after preparation of 3269 root canals There were 5 file fractures (01 per month) compared with 1.4fi:"acturesper month before the adaption of this system. The monthly average of files discarded during the 3-year research period was 53.7 Before the adoption of the trial system, the monthly average of
discarded files was 76.5 It is concluded that the experimental system effectively reduced the incidence of intracanal instrument fi^actures and the total number of files consumed. It is an estabfished fact that endodontic files should not be used beyond a certain period of time because the wear they undergo during chnical use eventually leads to intracanal breakage (1). Sotokawa (2) has pointed out that file deformations caused by bending cause and advance metal fatigue, eventually resulting in breakage. Thus, to prevent breakage, it would be advantageous to discard files in which metal fatigue has occurred before they break. However, it is not possible to distinguish fatigued files with the naked eye. Therefore, a system has been established whereby the instruments are discarded after they have been used in the root canal a certain number of times. This study was conducted to determine the effectiveness of this system in preventing intracanal breakage of endodontic files during
clinical practice. Material and methods Table 1 shows the periods of time that each size file was used during the 3-year period. Before the adoption of the system examined in this study, all files used at the authors clinic were systematically subjected to thorough visual inspection during use as a measure against breakage. Any 60 Tadashi Sotokawa 1-2-46 Yamagishi Morioka, Iwate pref, Japan Key words: root canal therapy; root canal instrumentation; intracanal instrument fractures. Tadashi Sotokawa, 1-2-46 Yamagishi Morioka, Iwate pref., Japan Accepted for publication September 15, 1989. file exhibiting even the slightest deformity was discarded. Despite being subjected to extreme deformations, 7^08 and ^10 file sizes had very low breakage rates, considering the relatively large numbers of these files discarded. This may be attributed to frequent visual inspection of the smallest instruments. Thus, thorough visual inspection before, during, and after use was thought to be the most
effective measure to prevent breakage. File sizes j^l5 through jl25 broke frequently. Their one-month use period was derived from the fact that about one file in each of these sizes broke per month. Although no breakage was observed in p O files, many were discarded because of partial reverse twisting, indicating that they were prone to damage. Accordingly, they were assigned a one-month use period. One file each in the sizes p 5 through #45 was discarded per month on average because of deformities observed under unaided visual inspection. However, because 3 files each were always prepared in the file tray for rotational use, a 3-month use period was established for these file sizes. For the sizes #50 through #60, one file each was Preventing intracanal breakage of endodentic files Table 1. Predetermined periods of use for K-files All the files discarded during the 3-year period were recorded. The monthly numbers of discarded files and broken files were recorded and compared with
the numbers that had been attained during a 17-month period just before this system was adopted. During the previous period, the files and the instrumentation technique used by the author had been the same as the ones used in the present study. File size 08-10 15-30 35-45 50-60 70-120 Until deformity Is observed 1 month 3 months 6 months 1 year discarded every 2 months. And likewise, since 3 each of these sizes were placed in the file tray for rotational use, they were assigned a 6-month use period. File sizes /7^7O to /^120 required considerable time to show wear. However, they were dulled considerably after one year A one-year use period was thus derived for these sizes. The instruments examined in this study were Kfiles (Zipperer, Munich, FRG). They were placed in a file tray containing 68 files: 6 files each of ;^08 to 1120, 4 files each of ;^25 to §80, and 1 files each of ^90 to /^120. The instrumentation technique used by the author for root canal preparation has been the
fiared technique as described by Weine (3). The apical part of the root canal was enlarged mainly to the sizes /^40 to ^80. All types of teeth were treated. At the end of each month, files that had reached their limited time of use were discarded, whether they displayed any deformity or not. They were then replaced with new files of the same sizes. Table 2, K-files discarded before the adoption of the experimental system (during 17-month period) File #08 #10 #15 #20 #25 #30 #35 #40 #45 #50 #55 #60 #70 #80 #90 #100 #110 #120 Discarded, but not fractured files 91 709 275 60 19 62 13 9 19 6 3 7 2 2 0 0 0 0 Total 1277 (monthly average) Discarded because of breakage Total number of discarded files 1 1 6 2 9 0 1 0 1 1 2 0 0 0 0 0 0 0 92 710 281 62 28 62 14 9 20 24 (1,4) 1301 (76.5) 7 5 7 2 2 0 0 0 0 Results The results obtained before the adoption of the experimental system (over the 17-month period) are presented in Table 2. Over this period, 1493 root canals (87.8 per month)
were prepared The total number of discarded files was 1301 (76.5 per month). Twenty-four file fractures (14 per month) were observed in file sizes )^08 to ^55. The results obtained after the adoption of the system (over the 3-year period) are presented in Table 3. Over this period, 3269 root canals (908 per month) were prepared. The total number of discarded files was 1933 (53.7 per month) Five file fractures (0.1 per month) were observed, 2 in files ^ and 3 in files ^15. No breakage was observed in the file sizes from ^20 to ^120. Discussion The total number of fractures, 5 (0.1 per month), was a remarkable decrease from the figure attained before adoption of the experimental system (1.4 Table 3, K-files discarded after the adoption of the experimental system (during 3-year period) File #08 #10 #15 ^20 #25 #30 #35 #40 #45 #50 #55 #60 m m #100 #110 #120 Discarded, but not fractured files 54 507 613 193 131 153 54 51 48 26 26 23 17 15 5 4 4 4 Total 1928 (monthly average)
Discarded because of breakage Total number of discarded 0 2 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 54 509 616 193 131 153 54 51 48 26 26 23 17 15 5 4 4 4 5 (0.1) 1933 (53,7) 0 61 Sotokawa per month). This suggested that a system with a predetermined number of periods of use may effectively reduce the incidence of intracanal instrument fractures. Broken files were found only in #10 and #15 file sizes, indicating that each of these file sizes needed a time limit of use as well. No breakage occurred in the file sizes #20 to #120, indicating that the predetermined periods of use prevented breakage in the larger files. Therefore, if the time limits of use for all the file sizes are properly set, this system could prevent breakage of all K-files during clinical use. There is obviously a connection between the periods of use for files and their frequency of use that should be taken into account before adopting this system; an increase in the latter will shorten the former. The figure (53.7
per month) attained after the adoption of the experimental system was proportionally much smaller than the one before the adoption of it, thus indicating the cost-effective potential of this system. By setting an appropriate use period for each file size, it is possible to prevent file breakage caused by bending deformations. Moreover, it can be assumed that the adoption of such a system will not significantly increase the number of files used. Undoubtedly, file use periods are influenced by 62 such factors as file type, physical properties, frequency of use, the operators techniques, and file maintenance. Consequendy, the schedule shown in Table 1 is not universally applicable. However, the findings of this study can serve as a practical and informative guide to endodontists attempting to devise their own system to prevent fracture. Adoption of such a system would conceivably ensure superior file conditions, allowing the endodontist to perform more efficient root canal therapy with
less labor and strain. Acknowledgements - I am grateful to Professor Masumi Ishibashi, Department of Endodontology, Iwate Medical University School of Dentistry, for critical review of the manuscript, and to Dr. Takeshi Kawabata, the Research Institue for Iron Steel and Other Metals, Tohoku University, for technical advice. References 1. GROSSMAN LI. Endodontic practice 10th ed Philadelphia: Lea & Febiger, 1981; 206-7. 2. SOTOKAWA T An analysis of clinical breakage of root canal instruments. J Endod 1988; 14: 75-82 3. WEINE FS Endodontic therapy St Louis: Mosby, 1972; 203-5
discarded files was 76.5 It is concluded that the experimental system effectively reduced the incidence of intracanal instrument fi^actures and the total number of files consumed. It is an estabfished fact that endodontic files should not be used beyond a certain period of time because the wear they undergo during chnical use eventually leads to intracanal breakage (1). Sotokawa (2) has pointed out that file deformations caused by bending cause and advance metal fatigue, eventually resulting in breakage. Thus, to prevent breakage, it would be advantageous to discard files in which metal fatigue has occurred before they break. However, it is not possible to distinguish fatigued files with the naked eye. Therefore, a system has been established whereby the instruments are discarded after they have been used in the root canal a certain number of times. This study was conducted to determine the effectiveness of this system in preventing intracanal breakage of endodontic files during
clinical practice. Material and methods Table 1 shows the periods of time that each size file was used during the 3-year period. Before the adoption of the system examined in this study, all files used at the authors clinic were systematically subjected to thorough visual inspection during use as a measure against breakage. Any 60 Tadashi Sotokawa 1-2-46 Yamagishi Morioka, Iwate pref, Japan Key words: root canal therapy; root canal instrumentation; intracanal instrument fractures. Tadashi Sotokawa, 1-2-46 Yamagishi Morioka, Iwate pref., Japan Accepted for publication September 15, 1989. file exhibiting even the slightest deformity was discarded. Despite being subjected to extreme deformations, 7^08 and ^10 file sizes had very low breakage rates, considering the relatively large numbers of these files discarded. This may be attributed to frequent visual inspection of the smallest instruments. Thus, thorough visual inspection before, during, and after use was thought to be the most
effective measure to prevent breakage. File sizes j^l5 through jl25 broke frequently. Their one-month use period was derived from the fact that about one file in each of these sizes broke per month. Although no breakage was observed in p O files, many were discarded because of partial reverse twisting, indicating that they were prone to damage. Accordingly, they were assigned a one-month use period. One file each in the sizes p 5 through #45 was discarded per month on average because of deformities observed under unaided visual inspection. However, because 3 files each were always prepared in the file tray for rotational use, a 3-month use period was established for these file sizes. For the sizes #50 through #60, one file each was Preventing intracanal breakage of endodentic files Table 1. Predetermined periods of use for K-files All the files discarded during the 3-year period were recorded. The monthly numbers of discarded files and broken files were recorded and compared with
the numbers that had been attained during a 17-month period just before this system was adopted. During the previous period, the files and the instrumentation technique used by the author had been the same as the ones used in the present study. File size 08-10 15-30 35-45 50-60 70-120 Until deformity Is observed 1 month 3 months 6 months 1 year discarded every 2 months. And likewise, since 3 each of these sizes were placed in the file tray for rotational use, they were assigned a 6-month use period. File sizes /7^7O to /^120 required considerable time to show wear. However, they were dulled considerably after one year A one-year use period was thus derived for these sizes. The instruments examined in this study were Kfiles (Zipperer, Munich, FRG). They were placed in a file tray containing 68 files: 6 files each of ;^08 to 1120, 4 files each of ;^25 to §80, and 1 files each of ^90 to /^120. The instrumentation technique used by the author for root canal preparation has been the
fiared technique as described by Weine (3). The apical part of the root canal was enlarged mainly to the sizes /^40 to ^80. All types of teeth were treated. At the end of each month, files that had reached their limited time of use were discarded, whether they displayed any deformity or not. They were then replaced with new files of the same sizes. Table 2, K-files discarded before the adoption of the experimental system (during 17-month period) File #08 #10 #15 #20 #25 #30 #35 #40 #45 #50 #55 #60 #70 #80 #90 #100 #110 #120 Discarded, but not fractured files 91 709 275 60 19 62 13 9 19 6 3 7 2 2 0 0 0 0 Total 1277 (monthly average) Discarded because of breakage Total number of discarded files 1 1 6 2 9 0 1 0 1 1 2 0 0 0 0 0 0 0 92 710 281 62 28 62 14 9 20 24 (1,4) 1301 (76.5) 7 5 7 2 2 0 0 0 0 Results The results obtained before the adoption of the experimental system (over the 17-month period) are presented in Table 2. Over this period, 1493 root canals (87.8 per month)
were prepared The total number of discarded files was 1301 (76.5 per month). Twenty-four file fractures (14 per month) were observed in file sizes )^08 to ^55. The results obtained after the adoption of the system (over the 3-year period) are presented in Table 3. Over this period, 3269 root canals (908 per month) were prepared. The total number of discarded files was 1933 (53.7 per month) Five file fractures (0.1 per month) were observed, 2 in files ^ and 3 in files ^15. No breakage was observed in the file sizes from ^20 to ^120. Discussion The total number of fractures, 5 (0.1 per month), was a remarkable decrease from the figure attained before adoption of the experimental system (1.4 Table 3, K-files discarded after the adoption of the experimental system (during 3-year period) File #08 #10 #15 ^20 #25 #30 #35 #40 #45 #50 #55 #60 m m #100 #110 #120 Discarded, but not fractured files 54 507 613 193 131 153 54 51 48 26 26 23 17 15 5 4 4 4 Total 1928 (monthly average)
Discarded because of breakage Total number of discarded 0 2 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 54 509 616 193 131 153 54 51 48 26 26 23 17 15 5 4 4 4 5 (0.1) 1933 (53,7) 0 61 Sotokawa per month). This suggested that a system with a predetermined number of periods of use may effectively reduce the incidence of intracanal instrument fractures. Broken files were found only in #10 and #15 file sizes, indicating that each of these file sizes needed a time limit of use as well. No breakage occurred in the file sizes #20 to #120, indicating that the predetermined periods of use prevented breakage in the larger files. Therefore, if the time limits of use for all the file sizes are properly set, this system could prevent breakage of all K-files during clinical use. There is obviously a connection between the periods of use for files and their frequency of use that should be taken into account before adopting this system; an increase in the latter will shorten the former. The figure (53.7
per month) attained after the adoption of the experimental system was proportionally much smaller than the one before the adoption of it, thus indicating the cost-effective potential of this system. By setting an appropriate use period for each file size, it is possible to prevent file breakage caused by bending deformations. Moreover, it can be assumed that the adoption of such a system will not significantly increase the number of files used. Undoubtedly, file use periods are influenced by 62 such factors as file type, physical properties, frequency of use, the operators techniques, and file maintenance. Consequendy, the schedule shown in Table 1 is not universally applicable. However, the findings of this study can serve as a practical and informative guide to endodontists attempting to devise their own system to prevent fracture. Adoption of such a system would conceivably ensure superior file conditions, allowing the endodontist to perform more efficient root canal therapy with
less labor and strain. Acknowledgements - I am grateful to Professor Masumi Ishibashi, Department of Endodontology, Iwate Medical University School of Dentistry, for critical review of the manuscript, and to Dr. Takeshi Kawabata, the Research Institue for Iron Steel and Other Metals, Tohoku University, for technical advice. References 1. GROSSMAN LI. Endodontic practice 10th ed Philadelphia: Lea & Febiger, 1981; 206-7. 2. SOTOKAWA T An analysis of clinical breakage of root canal instruments. J Endod 1988; 14: 75-82 3. WEINE FS Endodontic therapy St Louis: Mosby, 1972; 203-5
