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Microscopic evaluation of three endodontic files pre- and postinstrumentation
0099-2399/98/2407-0461 $03.00/0 JOURNAL OF ENDODONTICS
Printed in U.S.A.
Copyright © 1998 by The American Association of Endodontists
VoL. 24, No. 7, JULY 1998
SCIENTIFIC ARTICLES Microscopic Evaluation of Three Endodontic Files Pre- and Postinstrumentation Idomeo Bonetti Filho, DDS, PD, Roberto Miranda Esberard, DDS, PA, Renato de Toledo Leonardo, DDS, PAS, and Carlos E. del Rio, DDS
K-type files, Sureflex NiTi files, and FlexoFiles were evaluated morphometrically as they come from the manufacturer, and after being used to instrument root canals 1,3, and 5 times in maxillary premolars. Evaluation was made using a stereomicroscope at x40 magnification and photomicrographs. The abnormalities found after instrumentation were submitted for statistical analysis. It was concluded that small-sized stainless-steel instruments should be discarded after one use. On the other hand, #30 stainless-steel K-files could be used up to three times and #30 stainless-steel FlexoFUes up to five times. Sureflex NiTi instruments, even after five times, did not show appreciable abnormalities in shape. It is strongly recommended that small-sized nickel-titanium instruments should be discarded after five uses.
comparison of #15 Nitinol files with #15 stainless-steel files, Nitinol files had twice the elastic flexibility in bending and torsion and superior resistance to torsional fracture. Their results suggest that Nitinol files have a degree of flexibility appropriate for shaping curved root canals. Serene et al. (6) state that it is the perception of practitioners that NiTi files seem to get sharper with use. Their studies suggest that NiTi files increase in hardness with sterilization, can be used up to 10 times without failure, and that failure occurs due to the way the instrument is used instead of how long it is used. NiTi hand and engine-driven instrument systems are being manufactured for instrumentation of root canals. Investigations have been performed to evaluate torsional testing (9), fatigue (10), and results in the shape of canals instrumented with NiTi instruments (11, 12). As of this date, no investigation has been conducted to determine the wear characteristics of NiTi instruments while cleaning and shaping root canals. The purpose of this study was to evaluate wear characteristics under progressive use (warning signs that may occur before breakage) and the incidence of breakage during use of stainless-steel and NiTi instruments.
Endodontic files are used to explore and clean and shape the root canal space. Research has demonstrated differences between types and brands of endodontic files (1) and between their cutting and machining efficiency (2-5). In earlier studies, Stenman and Spangberg (3, 4) demonstrated that root canal instruments vary greatly in their effectiveness in removing debris. The effectiveness depends on the diameter of the instrument used (1). A large number of endodontic files of modified designs have been marketed with the purpose of attaining a high resistance to breakage, cutting efficiency, and durability. Recently, a new generation of endodontic files has been manufactured of nickel-titanium (NiTi) alloy. NiTi alloy endodontic instruments exhibit elastic memory, allowing them to return to their original shape upon unloading after substantial deformation. By contrast, other metals (such as stainless steel) sustain plastic deformation leading to permanent shape change when submitted to similar forces (6). The elastic property of NiTi has been known for about 30 yr (7). The first investigation of NiTi endodontic files (Nitinol) was reported in 1988 by Walia et al. (8). Their study showed that, in a
MATERIALS AND METHODS Seventy-five extracted human, two-rooted maxillary premolars with two separated root canals and mature apices were selected (150 roots). They were divided into three groups containing 25 teeth each. Each group was instrumented with a different type of file: K-type files (Maillefer, Ballaigues, Switzerland), FlexoFile (Maillefer), and Sureflex NiTi files (Maillefer). Each file group contained 10 files each of #15, #20, #25, and #30. These instruments were analyzed morphometrically unused (control) and after 1, 3, and 5 instrumentation cycles. After conventional coronal access, the pulpal chamber of each tooth was flooded with 2.5% NaOC1 (Clorox Company, Oakland, CA). A #10 file was used to explore and verify the anatomical diameter of apical exits of the root canals to discard teeth with root canal exits larger than 0.10 mm diameter. After verifying the diameter of the root canal, a #10 file was used to established working length 1 mm short of the anatomic apex. Each canal was instrumented with 200 strokes using a filing motion to working 461
462
Bonetti Filho et al.
Journal of Endodontics
FIG 2. Photomicrographs of defects (arrows) in endodontic files produced during instrumentation of root canals 1,3, and 5 times. (,4) Cutting edge dented. (/3) Cutting edge deformed. (C) Loss of metal sliver. (/9) Flute unwound. (E) Tip of instrument fracture. sliver or cutting edge deformed or rounded or dented or grooved. 7. Breakage of instrument. After instrumentation 1, 3, and 5 times, the files were visually inspected for defects by two endodontists, and the findings were submitted to statistical analysis using analysis of variance to determine if there were significant differences between the three groups of instruments. RESULTS FIG 1. Instrument holder for morphometric evaluation.
length. Buccal and lingual roots were used alternately. All instrumentation was performed by the same operator. During instrumentation, the root canals were irrigated using a total of 20 ml of 2.5% NaOC1 solution. Instruments were used sequentially starting with #15, followed by #20, #25, and #30. Photomicrographs were taken of the new instruments, and after the end of 1, 3, and 5 instrumentation cycles. The instrument was positioned for morphometric analysis in an instrument holder fabricated by the University of Texas Health Science Center at San Antonio Instrumentation Department (Fig. 1). Visual evaluation was performed under a stereomicroscope (Carl Zeiss, West Germany) at x40 magnification by rotating the instrument 360 degrees on its axis. New instruments were evaluated for defects in machining: deformations, grooves, metallic flashes, edge abnormalities, and fractures. These manufacturer defects were recorded to evaluate only defects that occur during instrumentation. At the end of each instrumentation cycle, visual inspection of the instruments was performed and evaluated. To supplement the visual analysis and maintain an archival record of the deformations or defects of the file, photographs were made. The following scores were given according to the degree of deformation (Fig. 2): 1. Without visual deformations. 2. Cutting edge dented. 3. Cutting edge dented and grooved. 4. Cutting edge deformed and rounded, plus dented and grooved. 5. Deformation of the tip, loss of metal sliver plus cutting edge deformed or rounded or dented or grooved. 6. Flutes unwound plus deformation of the tip or loss of metal
Most unused stainless-steel files presented manufacturer defects: either a single defect or a combination of deformations, grooves, metallic flashes, and edge abnormalities. These defects were recorded so they would not be incorporated in the final results after instrumentation. Morphometric analysis of the stainless-steel instruments (Kflies and FlexoFiles) after use showed dented cutting edges, grooves, deformed, and rounded tips with loss of metal slivers. Some stainless-steel files (especially #15 and #20) showed unwound portions of the flutes. Defects appeared in #15, #20, and #25 K-files and in #15 FlexoFiles after one use. FlexoFiles #20 and #25 and K-files #30 showed defects after three uses. FlexoFile #30 showed defects after five uses. Most of the Sureflex NiTi files did not show appreciable deformities as in the stainless-steel instruments even after being used five times. The exceptions were that some of the #15 and #20 Sureflex files showed grooves and dents in the cutting edge after being used five times. In order of performance from most resistant to least resistant to deformations, the files ranked in the following order: Sureflex (NiTi), FlexoFile, and K-type file. The data on instrument deformation after l, 3, and 5 uses were analyzed with the analysis of variance procedures. Highly significant differences (p < 0.0001) were found between the three types of files, as well as between the different sizes (#15, #20, #25, and #30) in the same type of file. The statistical results are summarized in Figs. 3 to 5. They served to compare levels of evaluation of occurred abnormalities for K-files, FlexoFiles, and Sureflex NiTi files, each type with four different diameters, before and after 1, 3, and 5 uses. K-type files showed the highest degree of deformation. Sureflex files showed the lowest deformation. The differences between these two types of files were significant in all sizes after 1, 3, and
Endodontic Instrument Evaluation
Vol. 24, No. 7, July 1998
1 K-type Rexoflls
[~
S
Sureflex
~4 "6
Q 2
15
20
25
k
463
Between different sizes of K-type files, #15 showed the highest deformation, significantly different from other sizes after one and five uses. After three uses, #15 was significantly more deformed than #25 and #30. In FlexoFile, #15 showed significantly higher deformation than the other sizes after one use. After three and five uses, the difference between the # 15 and #20 files was not significant, nor was the difference between the #25 and #30 files. However, the two smaller sizes were significantly different from the two larger sizes. Differences between sizes of Sureflex files were not significant after 1, 3, and 5 uses.
3O
DISCUSSION
Inst~ment size
FIG 3. Graph showing deformation of different types of instruments after one use.
I
K-type Rexofi[e
._o = s
E ~ Suref[ex
~o "6 a
One of the main purposes of instrumenting root canals during endodontic therapy is the cleaning and shaping of root canals by removal of dentin using the mechanical procedures of filing or reaming. This procedure has been referred to as "cutting efficiency." Several investigators have published articles relating to cutting efficiency, torsional flexibility, fatigue of K-type files, and other endodontic instruments (9-14). Cutting efficiency studies have been done by assessing how fast instruments were able to cut dentin. NiTi files have been shown to be less efficient when compared with stainless-steel files. This is due to the greater flexibility of the NiTi files in comparison with stainless-steel files
(6).
2
15
20
~'5
30
instrument size
FJG 4. Graph showing deformation of different types of instruments after three uses.
c o 5
I
K-type
E
Flsxofile
E ~ sureflex
o
~3 2
15
25
20 instrument size
FIG 5. Graph showing deformation of different types of instruments after five uses.
5 uses. The difference between the K-type and FlexoFile was significant at all four sizes after one use. After three uses, the difference between the K-type and FlexoFile was significant in #15 and #30 sizes. After five uses, the K-type and FlexoFile were found to be significantly different in #15 and #25 sizes. The difference between the FlexoFile and the Sureflex was significant at #15 size after one use, and in #15, #20, and #25 sizes after three uses. After five uses, they were significantly different in all sizes.
Newman et al. (14) suggest from clinical assessment of instrumentation of root canals that 450 strokes may be a realistic number of strokes to instrument a root canal. We used 200 strokes in this study, because in our pilot study it was more than sufficient to enlarge a root canal. It was not our goal to overuse endodontic files, but to test the life expectancy of endodontic files under simulated clinical conditions. Presently, a large number of types of files are available on the market. FlexoFiles and Surefiex NiTi files, evaluated in this study, are K-file types in design. K-type files #15 through #30 are twisted from stainless-steel square cross-section wire blanks and have a cutting tip. FlexoFiles #15 through #30 are twisted from stainlesssteel triangular cross-section wire blanks and have a safe-end tip. Due to their triangular cross-section, FlexoFiles are more flexible than the K-files. Sureflex NiTi files #15 through #30 are machined from square cross-section NiTi wire blanks and have a safe-end tip. Due to their flexibility, NiTi files were more effective in curved and narrow canals than in straight and large canals. Use of the NiTi files requires familiarization with the physical properties of the instrument in extracted teeth before using them in clinical cases. From our study, we may conclude that K-type files #15, #20, and #25 and FlexoFile #15 should be discarded after one use; FlexoFile #20 and #25 and K-type file #30 should not be used more than three times; and Sureflex NiTi files #15 and #20 and FlexoFile #30 should be discarded after being used five times. These findings concur with the literature that advise that smaller files should be used with caution and discarded after limited use. It was also observed that deformations in NiTi instruments were more difficult to observe clinically than deformation in stainless-steel instruments. It is strongly suggested that #15 through #30 NiTi instruments be discarded after five uses, regardless of whether they show any distortion or not. This guideline should minimize fractures and deformations and maximize cutting efficiency of the files. We also concluded that dentists should be aware that endodontic instruments come from the manufacturer with defects that may
464
Journal of Endodontics
Bonetti Filho et al.
jeopardize the integrity of the instruments while cleaning and shaping a root canal. It is strongly suggested that new instruments be examined for defects before being used. The authors wish to thank Dr. Chen Huan for his statistical assistance. Or. Huan is a Program Analyst with the Computing Resources Department at the University of Texas Health Science Center at San Antonio, Texas. Drs. Bonetti Filho, Miranda Esberard, and de Toledo Leonardo are affiliated with the Department of Endodontics, Araraquara Dental School, Araraquara, Brazil. Dr. del Rio is a professor, Department of Endodontics, University of Texas Health Science Center, San Antonio, TX. Address requests for reprints to Dr. Carlos E. del Rio, Professor, Department of Endodontics, the University of Texas Health Science Center, San Antonio, TX 78284-7892.
References 1. Stenman E, Spangberg LSW. Root canal instruments are poorly standardized. J Endodon 1993;19:327-34. 2. Stenman E, Spangberg LSW. Machining efficiency of endodontic Kfiles and Hedstrom. J Endodon 1990;16:375-82. 3. Stenman E, Spangberg LSW. Machining efficiency of endodontic files: a new methodology. J Endodon 1990;16:151-7.
4. Stenman E, Spangberg LSW. Machining efficiency of Ftex-R, K-flex, Trio-Cut and S files. J Endodon 1990;16:575-9. 5. Kazemi RB, Stenman E, Spangberg LSW. The endodontic file is a disposable instrument. J Endodon 1995;21:451-55. 6. Serene TP, Adams JD, Saxena A. Nickel titanium instruments: applications in Endodontics. St. Louis: Ishiyaku EuroAmerica, Inc., 1995. 7. Buckler W J, Wang E. Effect of low temperature phase on the mechanical properties of alloy near composition NiTi. J Appl Phys 1963;34:1475. 8. Walia H, Brantley WA, Gerstein H. An initial investigation of the bending and torsional properties of Nitinol root canal files. J Endodon 1988;14:346-51. 9. Burgess JO, Clement DJ, del Rio CE. Torsional testing of the Lightspeed NiTi instrument system. J, Endodon 1996;22:231-5. 10. Pruett JP, Clement DJ, Carnes DL Jr. Cycling fatigue testing of nickel titanium endodontic instruments. J Endodon 1997;23:77-85. 11. Luiten DJ, Morgan LA, Baumgartner JC. A comparison of four instrumentation techniques on apical canal transportation. J Endodon 1995;21:2632. 12. Glosson CR, Hailer RH, Dove SB, del Rio CE. Comparison of root canal preparation using NiTi hand, NiTi engine-driven, and K-Flex endodontic instruments. J Endodon 1995;21:146-51. 13. Zuolo ML, Walton RE, Murgel CAF. Canal Master files: scanning electron microscope evaluation of new instruments and their wear with clinical usage. J Endodon 1992;18:336-9. 14. Newman JG, Brantley WA, Gerstein H. A study of the cutting efficiency of seven brands of endodontic files in linear motion. J Endodon 1983;9:31622.
You Might Be Interested The Framingham Study enrolled 5209 persons 25 to 62 years of age in 1948 and has monitored the survivors' health every 2 years since. We owe a considerable debt for our increased knowledge of long-term health factors to the folks who had the foresight to initiate the study and the perseverance to maintain it. After almost 50 years, the three factors that have determined longevity are (1) no cigarettes, (2) low blood pressure, and (3) high fixed vital capacity (Arch Int Med 156:505). The latter two would likely be exercise related. Having long-lived parents did help, too. M. E. Thusalah
Printed in U.S.A.
Copyright © 1998 by The American Association of Endodontists
VoL. 24, No. 7, JULY 1998
SCIENTIFIC ARTICLES Microscopic Evaluation of Three Endodontic Files Pre- and Postinstrumentation Idomeo Bonetti Filho, DDS, PD, Roberto Miranda Esberard, DDS, PA, Renato de Toledo Leonardo, DDS, PAS, and Carlos E. del Rio, DDS
K-type files, Sureflex NiTi files, and FlexoFiles were evaluated morphometrically as they come from the manufacturer, and after being used to instrument root canals 1,3, and 5 times in maxillary premolars. Evaluation was made using a stereomicroscope at x40 magnification and photomicrographs. The abnormalities found after instrumentation were submitted for statistical analysis. It was concluded that small-sized stainless-steel instruments should be discarded after one use. On the other hand, #30 stainless-steel K-files could be used up to three times and #30 stainless-steel FlexoFUes up to five times. Sureflex NiTi instruments, even after five times, did not show appreciable abnormalities in shape. It is strongly recommended that small-sized nickel-titanium instruments should be discarded after five uses.
comparison of #15 Nitinol files with #15 stainless-steel files, Nitinol files had twice the elastic flexibility in bending and torsion and superior resistance to torsional fracture. Their results suggest that Nitinol files have a degree of flexibility appropriate for shaping curved root canals. Serene et al. (6) state that it is the perception of practitioners that NiTi files seem to get sharper with use. Their studies suggest that NiTi files increase in hardness with sterilization, can be used up to 10 times without failure, and that failure occurs due to the way the instrument is used instead of how long it is used. NiTi hand and engine-driven instrument systems are being manufactured for instrumentation of root canals. Investigations have been performed to evaluate torsional testing (9), fatigue (10), and results in the shape of canals instrumented with NiTi instruments (11, 12). As of this date, no investigation has been conducted to determine the wear characteristics of NiTi instruments while cleaning and shaping root canals. The purpose of this study was to evaluate wear characteristics under progressive use (warning signs that may occur before breakage) and the incidence of breakage during use of stainless-steel and NiTi instruments.
Endodontic files are used to explore and clean and shape the root canal space. Research has demonstrated differences between types and brands of endodontic files (1) and between their cutting and machining efficiency (2-5). In earlier studies, Stenman and Spangberg (3, 4) demonstrated that root canal instruments vary greatly in their effectiveness in removing debris. The effectiveness depends on the diameter of the instrument used (1). A large number of endodontic files of modified designs have been marketed with the purpose of attaining a high resistance to breakage, cutting efficiency, and durability. Recently, a new generation of endodontic files has been manufactured of nickel-titanium (NiTi) alloy. NiTi alloy endodontic instruments exhibit elastic memory, allowing them to return to their original shape upon unloading after substantial deformation. By contrast, other metals (such as stainless steel) sustain plastic deformation leading to permanent shape change when submitted to similar forces (6). The elastic property of NiTi has been known for about 30 yr (7). The first investigation of NiTi endodontic files (Nitinol) was reported in 1988 by Walia et al. (8). Their study showed that, in a
MATERIALS AND METHODS Seventy-five extracted human, two-rooted maxillary premolars with two separated root canals and mature apices were selected (150 roots). They were divided into three groups containing 25 teeth each. Each group was instrumented with a different type of file: K-type files (Maillefer, Ballaigues, Switzerland), FlexoFile (Maillefer), and Sureflex NiTi files (Maillefer). Each file group contained 10 files each of #15, #20, #25, and #30. These instruments were analyzed morphometrically unused (control) and after 1, 3, and 5 instrumentation cycles. After conventional coronal access, the pulpal chamber of each tooth was flooded with 2.5% NaOC1 (Clorox Company, Oakland, CA). A #10 file was used to explore and verify the anatomical diameter of apical exits of the root canals to discard teeth with root canal exits larger than 0.10 mm diameter. After verifying the diameter of the root canal, a #10 file was used to established working length 1 mm short of the anatomic apex. Each canal was instrumented with 200 strokes using a filing motion to working 461
462
Bonetti Filho et al.
Journal of Endodontics
FIG 2. Photomicrographs of defects (arrows) in endodontic files produced during instrumentation of root canals 1,3, and 5 times. (,4) Cutting edge dented. (/3) Cutting edge deformed. (C) Loss of metal sliver. (/9) Flute unwound. (E) Tip of instrument fracture. sliver or cutting edge deformed or rounded or dented or grooved. 7. Breakage of instrument. After instrumentation 1, 3, and 5 times, the files were visually inspected for defects by two endodontists, and the findings were submitted to statistical analysis using analysis of variance to determine if there were significant differences between the three groups of instruments. RESULTS FIG 1. Instrument holder for morphometric evaluation.
length. Buccal and lingual roots were used alternately. All instrumentation was performed by the same operator. During instrumentation, the root canals were irrigated using a total of 20 ml of 2.5% NaOC1 solution. Instruments were used sequentially starting with #15, followed by #20, #25, and #30. Photomicrographs were taken of the new instruments, and after the end of 1, 3, and 5 instrumentation cycles. The instrument was positioned for morphometric analysis in an instrument holder fabricated by the University of Texas Health Science Center at San Antonio Instrumentation Department (Fig. 1). Visual evaluation was performed under a stereomicroscope (Carl Zeiss, West Germany) at x40 magnification by rotating the instrument 360 degrees on its axis. New instruments were evaluated for defects in machining: deformations, grooves, metallic flashes, edge abnormalities, and fractures. These manufacturer defects were recorded to evaluate only defects that occur during instrumentation. At the end of each instrumentation cycle, visual inspection of the instruments was performed and evaluated. To supplement the visual analysis and maintain an archival record of the deformations or defects of the file, photographs were made. The following scores were given according to the degree of deformation (Fig. 2): 1. Without visual deformations. 2. Cutting edge dented. 3. Cutting edge dented and grooved. 4. Cutting edge deformed and rounded, plus dented and grooved. 5. Deformation of the tip, loss of metal sliver plus cutting edge deformed or rounded or dented or grooved. 6. Flutes unwound plus deformation of the tip or loss of metal
Most unused stainless-steel files presented manufacturer defects: either a single defect or a combination of deformations, grooves, metallic flashes, and edge abnormalities. These defects were recorded so they would not be incorporated in the final results after instrumentation. Morphometric analysis of the stainless-steel instruments (Kflies and FlexoFiles) after use showed dented cutting edges, grooves, deformed, and rounded tips with loss of metal slivers. Some stainless-steel files (especially #15 and #20) showed unwound portions of the flutes. Defects appeared in #15, #20, and #25 K-files and in #15 FlexoFiles after one use. FlexoFiles #20 and #25 and K-files #30 showed defects after three uses. FlexoFile #30 showed defects after five uses. Most of the Sureflex NiTi files did not show appreciable deformities as in the stainless-steel instruments even after being used five times. The exceptions were that some of the #15 and #20 Sureflex files showed grooves and dents in the cutting edge after being used five times. In order of performance from most resistant to least resistant to deformations, the files ranked in the following order: Sureflex (NiTi), FlexoFile, and K-type file. The data on instrument deformation after l, 3, and 5 uses were analyzed with the analysis of variance procedures. Highly significant differences (p < 0.0001) were found between the three types of files, as well as between the different sizes (#15, #20, #25, and #30) in the same type of file. The statistical results are summarized in Figs. 3 to 5. They served to compare levels of evaluation of occurred abnormalities for K-files, FlexoFiles, and Sureflex NiTi files, each type with four different diameters, before and after 1, 3, and 5 uses. K-type files showed the highest degree of deformation. Sureflex files showed the lowest deformation. The differences between these two types of files were significant in all sizes after 1, 3, and
Endodontic Instrument Evaluation
Vol. 24, No. 7, July 1998
1 K-type Rexoflls
[~
S
Sureflex
~4 "6
Q 2
15
20
25
k
463
Between different sizes of K-type files, #15 showed the highest deformation, significantly different from other sizes after one and five uses. After three uses, #15 was significantly more deformed than #25 and #30. In FlexoFile, #15 showed significantly higher deformation than the other sizes after one use. After three and five uses, the difference between the # 15 and #20 files was not significant, nor was the difference between the #25 and #30 files. However, the two smaller sizes were significantly different from the two larger sizes. Differences between sizes of Sureflex files were not significant after 1, 3, and 5 uses.
3O
DISCUSSION
Inst~ment size
FIG 3. Graph showing deformation of different types of instruments after one use.
I
K-type Rexofi[e
._o = s
E ~ Suref[ex
~o "6 a
One of the main purposes of instrumenting root canals during endodontic therapy is the cleaning and shaping of root canals by removal of dentin using the mechanical procedures of filing or reaming. This procedure has been referred to as "cutting efficiency." Several investigators have published articles relating to cutting efficiency, torsional flexibility, fatigue of K-type files, and other endodontic instruments (9-14). Cutting efficiency studies have been done by assessing how fast instruments were able to cut dentin. NiTi files have been shown to be less efficient when compared with stainless-steel files. This is due to the greater flexibility of the NiTi files in comparison with stainless-steel files
(6).
2
15
20
~'5
30
instrument size
FJG 4. Graph showing deformation of different types of instruments after three uses.
c o 5
I
K-type
E
Flsxofile
E ~ sureflex
o
~3 2
15
25
20 instrument size
FIG 5. Graph showing deformation of different types of instruments after five uses.
5 uses. The difference between the K-type and FlexoFile was significant at all four sizes after one use. After three uses, the difference between the K-type and FlexoFile was significant in #15 and #30 sizes. After five uses, the K-type and FlexoFile were found to be significantly different in #15 and #25 sizes. The difference between the FlexoFile and the Sureflex was significant at #15 size after one use, and in #15, #20, and #25 sizes after three uses. After five uses, they were significantly different in all sizes.
Newman et al. (14) suggest from clinical assessment of instrumentation of root canals that 450 strokes may be a realistic number of strokes to instrument a root canal. We used 200 strokes in this study, because in our pilot study it was more than sufficient to enlarge a root canal. It was not our goal to overuse endodontic files, but to test the life expectancy of endodontic files under simulated clinical conditions. Presently, a large number of types of files are available on the market. FlexoFiles and Surefiex NiTi files, evaluated in this study, are K-file types in design. K-type files #15 through #30 are twisted from stainless-steel square cross-section wire blanks and have a cutting tip. FlexoFiles #15 through #30 are twisted from stainlesssteel triangular cross-section wire blanks and have a safe-end tip. Due to their triangular cross-section, FlexoFiles are more flexible than the K-files. Sureflex NiTi files #15 through #30 are machined from square cross-section NiTi wire blanks and have a safe-end tip. Due to their flexibility, NiTi files were more effective in curved and narrow canals than in straight and large canals. Use of the NiTi files requires familiarization with the physical properties of the instrument in extracted teeth before using them in clinical cases. From our study, we may conclude that K-type files #15, #20, and #25 and FlexoFile #15 should be discarded after one use; FlexoFile #20 and #25 and K-type file #30 should not be used more than three times; and Sureflex NiTi files #15 and #20 and FlexoFile #30 should be discarded after being used five times. These findings concur with the literature that advise that smaller files should be used with caution and discarded after limited use. It was also observed that deformations in NiTi instruments were more difficult to observe clinically than deformation in stainless-steel instruments. It is strongly suggested that #15 through #30 NiTi instruments be discarded after five uses, regardless of whether they show any distortion or not. This guideline should minimize fractures and deformations and maximize cutting efficiency of the files. We also concluded that dentists should be aware that endodontic instruments come from the manufacturer with defects that may
464
Journal of Endodontics
Bonetti Filho et al.
jeopardize the integrity of the instruments while cleaning and shaping a root canal. It is strongly suggested that new instruments be examined for defects before being used. The authors wish to thank Dr. Chen Huan for his statistical assistance. Or. Huan is a Program Analyst with the Computing Resources Department at the University of Texas Health Science Center at San Antonio, Texas. Drs. Bonetti Filho, Miranda Esberard, and de Toledo Leonardo are affiliated with the Department of Endodontics, Araraquara Dental School, Araraquara, Brazil. Dr. del Rio is a professor, Department of Endodontics, University of Texas Health Science Center, San Antonio, TX. Address requests for reprints to Dr. Carlos E. del Rio, Professor, Department of Endodontics, the University of Texas Health Science Center, San Antonio, TX 78284-7892.
References 1. Stenman E, Spangberg LSW. Root canal instruments are poorly standardized. J Endodon 1993;19:327-34. 2. Stenman E, Spangberg LSW. Machining efficiency of endodontic Kfiles and Hedstrom. J Endodon 1990;16:375-82. 3. Stenman E, Spangberg LSW. Machining efficiency of endodontic files: a new methodology. J Endodon 1990;16:151-7.
4. Stenman E, Spangberg LSW. Machining efficiency of Ftex-R, K-flex, Trio-Cut and S files. J Endodon 1990;16:575-9. 5. Kazemi RB, Stenman E, Spangberg LSW. The endodontic file is a disposable instrument. J Endodon 1995;21:451-55. 6. Serene TP, Adams JD, Saxena A. Nickel titanium instruments: applications in Endodontics. St. Louis: Ishiyaku EuroAmerica, Inc., 1995. 7. Buckler W J, Wang E. Effect of low temperature phase on the mechanical properties of alloy near composition NiTi. J Appl Phys 1963;34:1475. 8. Walia H, Brantley WA, Gerstein H. An initial investigation of the bending and torsional properties of Nitinol root canal files. J Endodon 1988;14:346-51. 9. Burgess JO, Clement DJ, del Rio CE. Torsional testing of the Lightspeed NiTi instrument system. J, Endodon 1996;22:231-5. 10. Pruett JP, Clement DJ, Carnes DL Jr. Cycling fatigue testing of nickel titanium endodontic instruments. J Endodon 1997;23:77-85. 11. Luiten DJ, Morgan LA, Baumgartner JC. A comparison of four instrumentation techniques on apical canal transportation. J Endodon 1995;21:2632. 12. Glosson CR, Hailer RH, Dove SB, del Rio CE. Comparison of root canal preparation using NiTi hand, NiTi engine-driven, and K-Flex endodontic instruments. J Endodon 1995;21:146-51. 13. Zuolo ML, Walton RE, Murgel CAF. Canal Master files: scanning electron microscope evaluation of new instruments and their wear with clinical usage. J Endodon 1992;18:336-9. 14. Newman JG, Brantley WA, Gerstein H. A study of the cutting efficiency of seven brands of endodontic files in linear motion. J Endodon 1983;9:31622.
You Might Be Interested The Framingham Study enrolled 5209 persons 25 to 62 years of age in 1948 and has monitored the survivors' health every 2 years since. We owe a considerable debt for our increased knowledge of long-term health factors to the folks who had the foresight to initiate the study and the perseverance to maintain it. After almost 50 years, the three factors that have determined longevity are (1) no cigarettes, (2) low blood pressure, and (3) high fixed vital capacity (Arch Int Med 156:505). The latter two would likely be exercise related. Having long-lived parents did help, too. M. E. Thusalah