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Effects of cleaning, chemical disinfection, and sterilization procedures on the mechanical properties of endodontic instruments
0099-2399/97/2301-0015503.00/0 Printed in U.S.A.
JOURNAL OF ENDODONTJCS
Copyright © 1997 by The American Association of Endodontists
VOL. 23, No. 1, JANUARY1997
SCIENTIFIC ARTICLES Effects of Cleaning, Chemical Disinfection, and Sterilization Procedures on the Mechanical Properties of Endodontic Instruments Youssef Ha'fkel, DCD, DSO, PhD, Ren~ Serfaty, DCD, Philippe Bleicher, Thin-Thin C. Lwin, BDS, and Claude Allemann, DCD, DSO
The aim of this study was to test and compare the values of torsional moment, torsional angular deflection, bending moment, and permanent angular deflection of three designs of root canal files (Unifile, Flexofile, and H-File) before and after crossinfection treatment procedures, according to ANSI/ADA specification no. 28. An increase in value for all mechanical properties tested was observed after the treatment procedures, with the exception of Flexofile wherein a decrease in permanent angular deflection was evident. Unifile showed a decrease in torsional moment and bending moment. The changes in mechanical properties after treatment procedures ranged from 0.1 to 63% from the control groups. Generally, the changes in values observed were insignificant and still well within ANSI/ADA specification no. 28. Thus, they do not have any clinical significance.
the instruments. Different combinations of cross-infection control techniques and their effects on one or more of the mechanical properties have been studied (10-15). This study investigates the whole range of the most commonly used cross-infection control techniques and their effects on the mechanical properties of three different file designs (Unifile, Flexofile, and H-File), according to ANSI/ADA specification no. 28. Mechanical properties of clinical significance studied were: (a) maximum bending moment (in grams • centimeter) required to bend the instrument to 45°--this is a measure of stiffness, the inverse of flexibility in terms of moment value developed during testing; (b) permanent angular deformation (in degrees) after bending moment tests to 45°--this is a measure of the strength of the stainless steel base metal; (c) maximum torque (torsional moment) at failure (in grams • centimeter) in clockwise rotation--this is a measure of resistance to fracture; and (d) maximum angular deflection at failure (in degrees) in clockwise rotation--this is a measure of torque resistance. The purpose of this study was to evaluate quantitatively, the effects of cross-infection control techniques on the mechanical properties of the files investigated.
M A T E R I A L S AND M E T H O D S The mechanical properties of endodontic instruments are an important feature that contributes to the achievements of an optimal result in root canal therapy. Mechanical properties are directly influenced by metallurgy and the design of the instruments (crosssectional geometry, diameter and manufacturing process). There are many publications in the endodontic literature that document the cutting efficiency (1-4) and mechanical properties (5-9) of' root canal files. This has led to the modifications in the design of traditional K- and H-type files to produce hybrid instruments with superior mechanical properties. Cleaning, disinfection, and sterilization procedures minimize and prevent cross-infection, for which all endodontic treatment procedures have the potential because of their invasive nature. Much of the literature seems to indicate that cross-infection control is gained at the expense of reduction in mechanical properties of
Test Equipment and Operation Procedure Experimental procedures were based on the test methodology that was developed for ANSI/ADA specification no. 28. A digital torque meter memocouple (Maillefer SA, Ballaigues, Switzerland) measured torque with an accuracy of + 1 g • cm and angular deflection with an accuracy of +-2 °. The equipment consisted of a reversibly geared motor revolving at 2 rpm (Baure CM 2024), which drove a test instrument by means of a separate hardened steel chuck and a torque measuring device fixed on two linear ball bearings. A digital display and amplifier controlled the operation of the motor and recorded torque and angular rotation. The circuitry of the amplifier retained the information about torque and angular rotation for display, up to the point of failure. A strip chart
15
16
Hail~el et al.
Journal of Endodontics TABLE 1. Effects of various treatment procedures on the mechanical properties of Unifile
No.
1 2 3 4 5 6 7 8 9 10 11 12
Treatment Procedure Control NaOCI (12 h) NaOCI (48 h) BDV (10 × 40 s) BDV (40 × 40 s) Ultrasonic cleaning (1 h) Ultrasonic cleaning (4 h) Poupinel (5 x 2 h) Poupinel (10 x 2 h) Chemiclave (5 × 20 min) Chemiclave (20 x 20 min) NH4 (1 h) NH4 (4 h)
Torsional Moment 62.78 58.18 54.84 54.38 53.77 50.18 51.46 49.96 56.96 49.00 56.82 55.50 47.62
+_ 2.2 _+ 7.8 +_ 5.4 _+ 5.4 _ 9.6 _+ 9.7 _+ 4.0 _+ 4.2 _+ 7.4 + 2.2 + 8.2 _+ 6.0 _+ 4.5
Torsional Angular Deflection 941.6 1133.4 1111.2 1037.6 1016.7 1105.8 1280.0 1204.0 1016.2 1405.8 1052.0 1097.2 1144.0
_+ 80.8 + 193.0 _+ 107.0 + 53.2 + 64.2 _+ 100.0 +_ 227.0 _+ 167.0 _+ 83.3 _+ 74.6 _+ 76.8 _+ 88.8 _+ 131.0
Bending Moment 55.96 45.92 40.30 56.44 42.44 49.88 47.94 47.88 47.72 44.26 50.32 53.70 46.57
+ 5.17 +_ 3.89 _+ 4.27 _+ 2.08 _+ 6.45 _+ 7.77 + 6.95 _+ 8.30 _+ 2.29 _+ 5.12 + 5.08 _+ 2.11 _+ 4.59
Permanent Angular Deflection 27.8 30.2 32.2 28.0 30.2 30.4 29.8 31.8 30.4 30.0 30.2 29.4 32.2
___0.98 _+ 1.17 - 1.92 + 0.01 _+ 1.17 - 1.20 -+ 2.14 _-- 1.94 _+ 1.02 +_ 2.10 +- 2.49 _+ 0.49 +_ 1.92
BDV, glass bead sterilization.
(Linseis L4100) was used for recording the data. Mounted on the shaft of the device was a chuck with brass jaws (70% copper and 30% zinc) that was used to clamp the test instrument at the tip along a 3 mm length. Because the test instrument was twisted, the torque measuring device freely moved horizontally on the ball bearing, compensating for increasing and decreasing instrument length as it was twisted. For the torsion tests, the device was calibrated for the torque range of the test instrument size (i.e. ISO #030) being tested. A wire cutter was used to remove the handle of the test instrument at the point wherein the handle was attached to the shaft. The shank of the test instrument was then placed into the chuck. The torque device was slowly slid along the linear ball bearing until the tip of the instrument entered 3 mm into the brass jaws. The apparatus was activated for clockwise rotation. The recorder automatically traced the torque or angular rotation curve. Maximum torsional values and number of degrees to failure were recorded and tabulated. For the bending tests, the same equipment was used with few modifications. The tip was inserted on a 3 mm length into a chuck, which was perpendicular to the axis of the geared motor. The amplifier was set at an angular deflection of 45 °, at which point the test automatically stopped. The bending moment was then automatically measured, as was the permanent deformation that resulted from bending to 90 ° . All measurements were made automatically; therefore, operator bias was eliminated. Three designs of ISO #030 endodontic instruments were investigated: Unifile (De Trey, Bois Colombes, France), Flexofile (Maillefer), and H-File (Maillefer). Thirty-nine groups of 10 files of ISO #030 (i.e. a total of 390 files) were used. Each group was assigned to the various cleaning, disinfection, and sterilization techniques investigated, plus a control group for each design of the files. The sterilization techniques tested in the present study were documented in a previous study (16): ultrasonic cleaning for 4 and 16 cycles of 15 min; chemical disinfection with NaOCI (2.5%) for 12 and 48 h and with NH 4 (5%) for 1 and 4 h; and sterilization methods--chemiclave for 5 and 10 cycles of 20 min at 134°C, Poupinel (dryheat) for 5 and 10 cycles of 2 h at 180°C, and glass beads (BDV) for 10 and 40 cycles of 40 s at 250°C. A total of 390 files were divided into 39 groups, each consisting of 10 files. There were 11 groups for each file design plus three control groups (one from each file design). The controls were designated to undergo mechanical testings in the new initial state
without first being subjected to the different cross-infection control techniques. One group from each of the file designs was subjected to each of the treatment procedures, then they underwent mechanical testing. Four parameters were measured and tabulated: maximum torque at failure in (grams" centimeter) in clockwise rotation; maximum angular deflection at failure (in degrees) in clockwise rotation; maximum bending moment (in grams • centimeter) required to bend the instrument to 45°; and permanent angular deformation after bending test (in degrees).
RESULTS The Unifile had the highest initial values of the parameters tested (i.e. torsional moment and permanent angular deformation), and Flexofile had the highest values in the other two parameters tested (i.e. torsional angular deflection and bending moment). H-File had the lowest relative values in all parameters measured, except permanent angular deformation wherein Flexofile was found to have the lowest value. The implications are that the Unifile is most resistant to fracture (i.e. has highest torque resistance), compared with the other two files. H-File has the least resistance to fracture. This implication is made purely from torsional moment values; whether a file will undergo fracture or not in the clinical situation is unpredictable and is dependent on many variables (i.e. instrumentation technique, presence of surface flaws on file, etc.). Unifile also has the greatest initial strength, followed by H-File, then Flexofile. This statement is based on the permanent angular deformation values obtained. Based on the relative bending moment values, Flexofile in its new initial state was found to have the highest stiffness value (i.e. lowest flexibility).
Unifile Compared with the Unifile (Table 1) control group, the following results were observed: a decrease in torsional moment indicative of an increase susceptibility to fracture after treatment procedures; an increase in angular deflection indicative of a decrease in torque resistance; a decrease in bending moment indicative of a decrease in stiffness or increase flexibility; and an increase in permanent angular deformation indicative of a decrease in strength of base metal.
Vol. 23, No. 1, January 1997
Effects of Sterilization Techniques
17
TABLE 2. Effects of various treatment procedures on the mechanical properties of Flexofile No.
1 2 3 4 5 6 7 8 9 10 11 12
Treatment Probedure Control NaOCI (12 h) NaOCL (48 h) BDV (10 × 40 s) BDV (40 x 40 s) Ultrasonic cleaning (1 h) Ultrasonic cleaning (4 h) Poupinel (5 x 2 h) Poupinel (10 × 2 h) Chemiclave (5 x 20 min) Chemiclave (20 x 20 min) NH4 (1 h) NH4 (4 h)
Torsional Moment 56.28 55.25 61.74 58.48 53.46 57.02 55.10 54.46 58.20 53.90 58.34 56.24 54.42
± 5.36 ± 3.14 ± 6.11 __+3.75 ± 3.62 ± 5.67 +_ 2.66 ± 3.42 ± 2.06 -+ 2.88 ± 6.45 ± 3.44 +_ 2.67
Torsional Angular Deflection 1262.2 1366.5 1473.0 1322.6 1344.6 1470.8 1520.5 1340.2 1420.6 1458.2 1249.2 1717.6 1446,4
Permanent Angular
Bending Moment
+_ 293 _+ 399 ± 256 ± 240 _+ 441 _+ 379 ± 417 +_ 97 _+ 379 _± 602 _+ 176 _+ 424 ± 199
59.60 56.26 58.94 65.28 61.43 59.84 59.68 64.52 62.52 60.04 64.68 57.72 58.06
Deflection
-+ 1.92 _+ 2.42 ± 2.26 ± 2.56 _+ 2.10 _+ 3.79 ± 1.73 _+ 3.89 _+ 2.19 _+ 1.80 ± 1.02 _+ 2.08 ± 2.76
9,0 9.0 8.4 8.6 7.0 8.6 8.8 7.7 6.4 6.8 7.6 8.7 8.8
+_ 0.01 +_ 0.71 ± 0.49 + 0.49 ± 0.01 _+ 0.49 ± 0.75 +_ 0.43 _+ 0.49 +_ 1.17 ± 0.80 ± 0.43 _+ 0.40
BOV, glass bead sterilization.
TABLE 3. Effects of various treatment procedures on the mechanical properties of Heliofile Number
1 2 3 4 5 6 7 8 9 20 11 12
Treatment Procedure Control NaOCI (12 h) NaOCI (48 h) BDV (10 x 40 s) BDV (40 x 40 s) Ultrasonic cleaning (1 h) Ultrasonic cleaning (4 h) Poupinel (5 x 2 h) Poupinel (10 x 2 h) Chemiclave (5 x 20 min) Chemiclave (20 x 20 min) NH4 (1 h) NH4 (4 h)
Torsional Moment 53.5 51.1 59.3 57.1 54.0 56.4 52.2 53.2 54.3 53.0 56.3 54.9 57.1
+ 1.7 _+ 1.5 _+ 6.7 ± 7.8 ± 3.4 ± 3.5 ± 1.3 ± 3.3 _+ 2.9 ± 3.2 ± 2.4 ± 3.6 _+ 2,8
Torsional
717.0 808.6 755.8 798.2 789.8 806.6 778.0 610.8 669.2 765.4 723.0 796.8 896.2
Permanent
Bending Moment
Angular Deflection -+ 81.9 -+ 188.2 _+ 152.0 ± 226.8 _+ 145.5 ± 194.0 _+ 119.7 ± 89.1 +- 88.9 _+ 231.2 ± 124.9 ± 239.4 -+ 228,1
54.8 56.6 61.2 61.2 60.8 60.9 57.6 54.9 56.7 56.6 60.3 60.0 59.6
Angular Deflection
_+ 2.4 _+ 4.4 _+ 2.5 _+ 2.8 ± 2.1 +_ 4.3 _+ 2.8 ± 3.4 _+ 2.3 ± 2.8 ± 3.0 ± 2.2 -4- 3.3
17.6 18.6 19.0 17.8 17.6 19.6 19.2 28.6 28.7 19.2 18.6 18.4 19.2
_+ 0.9 _+ 0.9 _+ 1.2 _+ 1.3 ± 1,1 ± 1.1 ± 0.5 ± 0.8 _+ 0.9 _+ 1.1 ± 0.5 ± 0.6 +_ 0.8
BDV, glass bead sterilizaion.
Flexofile Compared with the Flexofile (Table 2) control group, the following results were evident: an increase in torsional moment; an increase in torsional angular deflection; an increase in bending moment; and a decrease in permanent angular deformation.
H-File Compared with the H-File (Table 3) control group, the following results were found: an increase in torsional moment; an increase in torsional angular deflection; an increase in bending moment; and an increase in permanent angular deformation. The degree or extent of increase and decrease in the tested mechanical properties varied according to the file type and treatment procedure they underwent. The aforementioned changes are tabulated in Table 4.
DISCUSSION The results provide a comprehensive, comparative description of the effects that cleaning, disinfection, and sterilization methods have on the mechanical properties of the three file designs inves-
TABLE 4. Comparison of the percentage change in mechanical properties after treatment procedures Range of Change in % Mechanical Property Torsional moment Torsional angular deflection Bending moment Permanent angular deformation
A
Unifile
A
Flexofile
A
H-File
J, 1"
7-24 8-49
1" 1"
5-9 1-36
1" 1'
0-11 0-25
$ 1"
0-28 0-16
I' J,
5-10 0-29
1' 1"
0.2-12 0-63
tigated. There have been other reports of changes observed in mechanical propertie~ as a result of sterilization techniques (11). Iverson et al. (15) indicated that torque strength and angular deflection do not affect endodontic files subjected to 10 cycles of autoclaving at 127°C for 30 min, 10 cycles of glass bead sterilization for 20 s, or 10 cycles at 171°C for 1 h at dry heat sterilization. These findings are in agreement with those of other studies (13, 14). However, Mitchell et al. (13) found that sterilization affected a significant decrease in angular deflection after autoclaving after 10 cycles, although in their study a simulated clinical usage procedure was incorporated in the test regimen. The present study included the whole range of cross-infection
18
Journal of Endodontics
Hdtl(el et al.
control techniques. The file size used was restricted to ISO #030 to present a more comprehensive assessment of the effects of various treatment procedures on the mechanical properties under investigation. The revised form of A D A specification no. 28 has requirements at only a single bend angle of 45 ° and a single twist angle of 360 ° (17). There is no counterclockwise torsion requirement in the ANSI/ADA specification no. 28, although, this addition was proposed several years ago by Chemick et al. (14). At present, the recommendation is not to twist instruments more than one-quarter revolution (90°), in the counterclockwise direction, to stay within the safety limits of the files. The use of the new torsion instrument (Torquemeter Memocouple, Maillefer) indicated in the revised ANSI/ADA specification no. 28 allowed measurements to be made automatically; therefore, operator bias was eliminated. All of the file groups examined in this investigation met or far exceeded the limits set by the revised ANSI/ADA specification no. 28, both initially and after treatment procedures, although changes in values for the four mechanical properties were evident to a varying extent, depending on the treatment procedure they underwent. The relative differences evident in the initial values of the four mechanical properties for the different files have been well-documented in the endodontic literature as being attributable to crosssectional geometry or section modulus, method of manufacture, and metallurgical differences caused by varying alloy composition of stainless steel instruments (5, 11). The changes in mechanical properties after treatment procedures ranged from 0.2 to 63%, depending on design of file and type of cross-infection technique. It is not possible to predict the clinical performance of the files based on the mechanical property values obtained as there are many other factors. The 63% increase from the control group value was observed in the permanent angular deflection of the H-File. Although this seems to be a significant change, its clinical implications are insignificant. This is because permanent angular deformation is a reflection of the strength of the base metal (i.e. an increase in value would indicate that the metal has decreased in strength and consequently a higher angle of deformation is recorded), and a reduction in this value is not necessarily a disadvantage in all clinical situations (e.g. useful in severely curved canals as long as cutting efficiency is still adequate for canal preparation). Perhaps it is for this reason that there is no permanent angular deformation requirement in the ANSI/ADA specification no. 28, because a change in its value does not have a detrimental effect in the clinical situation.
All of the other changes observed in the four mechanical properties investigated in this study, as a result of different treatment procedures, were insignificant because they remained within the limits set by ADA specification no. 28. Dr. Ha~tl~el,Dr. Serfaty, Mr. Bleicher, and Dr. Allemann are affiliated with the Department of Endodontics, CRO, University Louis Pasteur, Strasbourg, France. Mrs Thin-Thin was affiliated with the ERASMUS Exchange Programme, University of Glasgow, Glasgow, Scotland. Address requests for reprints to Dr. Youssef Hat, el, INSERM U-424, UFR Odontologie, University Louis Pasteur, 1, Place de I'H6pital, 67000 Strasbourg, France.
References 1. 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. 2. Neal RG, Craig RG, Powers JM. Cutting ability of K-type endodontic files. J Endodon 1983;9:52-7. 3. Machian GR, Peters DD, Lorton L. The comparative efficiency of four types of endodontic instruments. J Endodon 1982;8:398-402. 4. Webber J, Moser JB, Heuer MA. A method to determine the cutting efficiency of root canal instruments in linear motion. J Endodon 1980;6:82934. 5. Krupp JD, Brantley WA, Gerstein H. An investigation of the torsional and bending properties of seven brands of endodontic files. J Endodon 1984;10: 372-80. 6. Roth WC, Gough RW, Grandich RA, Walker WA. A study of the strength of endodontic files' potential for torsional breakage and relative flexibility. J Endodon 1983;9:228-32. 7. Dolan DW, Craig RG. Bending and torsion of endodontic files with rhombus cross-sections. J Endodon 1982;8:260-4. 8. Lentine FN. A study of torsional and angular deflection of endodontic files and reamers. J Endodon 1979;5:181-91. 9. Craig RG, Mcllwain ED, Peyton FA. Bending and torsion properties of endodontic instruments. Oral Surg 1968;25:239-54. 10. Chenail BL, Brantley WA, Gerstein H. Clockwise torsional properties of intracanal instruments. Oral Surg 1977;43:130-4. 11. Younis O. The effects of sterilization techniques on the properties of intracanal instruments. Oral Sur9 1977;43:130-4. 12. Roulet JF. Dynamic fracture of conventional endodontic instruments vs experimental files. J Endodon 1983;9:12-6. 13. Mitchell BF, James GA, Nelson RC. The effects of autoclave sterilization on endodontic files. Oral Surg 1983;55:204-7. 14. Chemick LB, Jacobs J J, Lautenschlager EP, Heuer MA. Torsional failure of endodontic files. J Endodon 1976;2:94-7. 15. Iverson GW, von Fraunhofer JA, Herrmann JW. The effects of various sterilization methods on the torsional strength of endodontic files. J Endodon 1985;11:266-8. 16. Halt(el Y, Serfaty R, Bleicher PH, Thin-Thin CL, Allemann C. Effects of cleaning, disinfection, and sterilization procedures on the cutting efficiency of endodontic files. J Endodon (in press). 17. Council on Dental Materials, Instruments and Equipment. Revised American National Standards Institute/American Dental Association Specification No. 28 for root canal files and reamers, type K & H {approved October 1981).
JOURNAL OF ENDODONTJCS
Copyright © 1997 by The American Association of Endodontists
VOL. 23, No. 1, JANUARY1997
SCIENTIFIC ARTICLES Effects of Cleaning, Chemical Disinfection, and Sterilization Procedures on the Mechanical Properties of Endodontic Instruments Youssef Ha'fkel, DCD, DSO, PhD, Ren~ Serfaty, DCD, Philippe Bleicher, Thin-Thin C. Lwin, BDS, and Claude Allemann, DCD, DSO
The aim of this study was to test and compare the values of torsional moment, torsional angular deflection, bending moment, and permanent angular deflection of three designs of root canal files (Unifile, Flexofile, and H-File) before and after crossinfection treatment procedures, according to ANSI/ADA specification no. 28. An increase in value for all mechanical properties tested was observed after the treatment procedures, with the exception of Flexofile wherein a decrease in permanent angular deflection was evident. Unifile showed a decrease in torsional moment and bending moment. The changes in mechanical properties after treatment procedures ranged from 0.1 to 63% from the control groups. Generally, the changes in values observed were insignificant and still well within ANSI/ADA specification no. 28. Thus, they do not have any clinical significance.
the instruments. Different combinations of cross-infection control techniques and their effects on one or more of the mechanical properties have been studied (10-15). This study investigates the whole range of the most commonly used cross-infection control techniques and their effects on the mechanical properties of three different file designs (Unifile, Flexofile, and H-File), according to ANSI/ADA specification no. 28. Mechanical properties of clinical significance studied were: (a) maximum bending moment (in grams • centimeter) required to bend the instrument to 45°--this is a measure of stiffness, the inverse of flexibility in terms of moment value developed during testing; (b) permanent angular deformation (in degrees) after bending moment tests to 45°--this is a measure of the strength of the stainless steel base metal; (c) maximum torque (torsional moment) at failure (in grams • centimeter) in clockwise rotation--this is a measure of resistance to fracture; and (d) maximum angular deflection at failure (in degrees) in clockwise rotation--this is a measure of torque resistance. The purpose of this study was to evaluate quantitatively, the effects of cross-infection control techniques on the mechanical properties of the files investigated.
M A T E R I A L S AND M E T H O D S The mechanical properties of endodontic instruments are an important feature that contributes to the achievements of an optimal result in root canal therapy. Mechanical properties are directly influenced by metallurgy and the design of the instruments (crosssectional geometry, diameter and manufacturing process). There are many publications in the endodontic literature that document the cutting efficiency (1-4) and mechanical properties (5-9) of' root canal files. This has led to the modifications in the design of traditional K- and H-type files to produce hybrid instruments with superior mechanical properties. Cleaning, disinfection, and sterilization procedures minimize and prevent cross-infection, for which all endodontic treatment procedures have the potential because of their invasive nature. Much of the literature seems to indicate that cross-infection control is gained at the expense of reduction in mechanical properties of
Test Equipment and Operation Procedure Experimental procedures were based on the test methodology that was developed for ANSI/ADA specification no. 28. A digital torque meter memocouple (Maillefer SA, Ballaigues, Switzerland) measured torque with an accuracy of + 1 g • cm and angular deflection with an accuracy of +-2 °. The equipment consisted of a reversibly geared motor revolving at 2 rpm (Baure CM 2024), which drove a test instrument by means of a separate hardened steel chuck and a torque measuring device fixed on two linear ball bearings. A digital display and amplifier controlled the operation of the motor and recorded torque and angular rotation. The circuitry of the amplifier retained the information about torque and angular rotation for display, up to the point of failure. A strip chart
15
16
Hail~el et al.
Journal of Endodontics TABLE 1. Effects of various treatment procedures on the mechanical properties of Unifile
No.
1 2 3 4 5 6 7 8 9 10 11 12
Treatment Procedure Control NaOCI (12 h) NaOCI (48 h) BDV (10 × 40 s) BDV (40 × 40 s) Ultrasonic cleaning (1 h) Ultrasonic cleaning (4 h) Poupinel (5 x 2 h) Poupinel (10 x 2 h) Chemiclave (5 × 20 min) Chemiclave (20 x 20 min) NH4 (1 h) NH4 (4 h)
Torsional Moment 62.78 58.18 54.84 54.38 53.77 50.18 51.46 49.96 56.96 49.00 56.82 55.50 47.62
+_ 2.2 _+ 7.8 +_ 5.4 _+ 5.4 _ 9.6 _+ 9.7 _+ 4.0 _+ 4.2 _+ 7.4 + 2.2 + 8.2 _+ 6.0 _+ 4.5
Torsional Angular Deflection 941.6 1133.4 1111.2 1037.6 1016.7 1105.8 1280.0 1204.0 1016.2 1405.8 1052.0 1097.2 1144.0
_+ 80.8 + 193.0 _+ 107.0 + 53.2 + 64.2 _+ 100.0 +_ 227.0 _+ 167.0 _+ 83.3 _+ 74.6 _+ 76.8 _+ 88.8 _+ 131.0
Bending Moment 55.96 45.92 40.30 56.44 42.44 49.88 47.94 47.88 47.72 44.26 50.32 53.70 46.57
+ 5.17 +_ 3.89 _+ 4.27 _+ 2.08 _+ 6.45 _+ 7.77 + 6.95 _+ 8.30 _+ 2.29 _+ 5.12 + 5.08 _+ 2.11 _+ 4.59
Permanent Angular Deflection 27.8 30.2 32.2 28.0 30.2 30.4 29.8 31.8 30.4 30.0 30.2 29.4 32.2
___0.98 _+ 1.17 - 1.92 + 0.01 _+ 1.17 - 1.20 -+ 2.14 _-- 1.94 _+ 1.02 +_ 2.10 +- 2.49 _+ 0.49 +_ 1.92
BDV, glass bead sterilization.
(Linseis L4100) was used for recording the data. Mounted on the shaft of the device was a chuck with brass jaws (70% copper and 30% zinc) that was used to clamp the test instrument at the tip along a 3 mm length. Because the test instrument was twisted, the torque measuring device freely moved horizontally on the ball bearing, compensating for increasing and decreasing instrument length as it was twisted. For the torsion tests, the device was calibrated for the torque range of the test instrument size (i.e. ISO #030) being tested. A wire cutter was used to remove the handle of the test instrument at the point wherein the handle was attached to the shaft. The shank of the test instrument was then placed into the chuck. The torque device was slowly slid along the linear ball bearing until the tip of the instrument entered 3 mm into the brass jaws. The apparatus was activated for clockwise rotation. The recorder automatically traced the torque or angular rotation curve. Maximum torsional values and number of degrees to failure were recorded and tabulated. For the bending tests, the same equipment was used with few modifications. The tip was inserted on a 3 mm length into a chuck, which was perpendicular to the axis of the geared motor. The amplifier was set at an angular deflection of 45 °, at which point the test automatically stopped. The bending moment was then automatically measured, as was the permanent deformation that resulted from bending to 90 ° . All measurements were made automatically; therefore, operator bias was eliminated. Three designs of ISO #030 endodontic instruments were investigated: Unifile (De Trey, Bois Colombes, France), Flexofile (Maillefer), and H-File (Maillefer). Thirty-nine groups of 10 files of ISO #030 (i.e. a total of 390 files) were used. Each group was assigned to the various cleaning, disinfection, and sterilization techniques investigated, plus a control group for each design of the files. The sterilization techniques tested in the present study were documented in a previous study (16): ultrasonic cleaning for 4 and 16 cycles of 15 min; chemical disinfection with NaOCI (2.5%) for 12 and 48 h and with NH 4 (5%) for 1 and 4 h; and sterilization methods--chemiclave for 5 and 10 cycles of 20 min at 134°C, Poupinel (dryheat) for 5 and 10 cycles of 2 h at 180°C, and glass beads (BDV) for 10 and 40 cycles of 40 s at 250°C. A total of 390 files were divided into 39 groups, each consisting of 10 files. There were 11 groups for each file design plus three control groups (one from each file design). The controls were designated to undergo mechanical testings in the new initial state
without first being subjected to the different cross-infection control techniques. One group from each of the file designs was subjected to each of the treatment procedures, then they underwent mechanical testing. Four parameters were measured and tabulated: maximum torque at failure in (grams" centimeter) in clockwise rotation; maximum angular deflection at failure (in degrees) in clockwise rotation; maximum bending moment (in grams • centimeter) required to bend the instrument to 45°; and permanent angular deformation after bending test (in degrees).
RESULTS The Unifile had the highest initial values of the parameters tested (i.e. torsional moment and permanent angular deformation), and Flexofile had the highest values in the other two parameters tested (i.e. torsional angular deflection and bending moment). H-File had the lowest relative values in all parameters measured, except permanent angular deformation wherein Flexofile was found to have the lowest value. The implications are that the Unifile is most resistant to fracture (i.e. has highest torque resistance), compared with the other two files. H-File has the least resistance to fracture. This implication is made purely from torsional moment values; whether a file will undergo fracture or not in the clinical situation is unpredictable and is dependent on many variables (i.e. instrumentation technique, presence of surface flaws on file, etc.). Unifile also has the greatest initial strength, followed by H-File, then Flexofile. This statement is based on the permanent angular deformation values obtained. Based on the relative bending moment values, Flexofile in its new initial state was found to have the highest stiffness value (i.e. lowest flexibility).
Unifile Compared with the Unifile (Table 1) control group, the following results were observed: a decrease in torsional moment indicative of an increase susceptibility to fracture after treatment procedures; an increase in angular deflection indicative of a decrease in torque resistance; a decrease in bending moment indicative of a decrease in stiffness or increase flexibility; and an increase in permanent angular deformation indicative of a decrease in strength of base metal.
Vol. 23, No. 1, January 1997
Effects of Sterilization Techniques
17
TABLE 2. Effects of various treatment procedures on the mechanical properties of Flexofile No.
1 2 3 4 5 6 7 8 9 10 11 12
Treatment Probedure Control NaOCI (12 h) NaOCL (48 h) BDV (10 × 40 s) BDV (40 x 40 s) Ultrasonic cleaning (1 h) Ultrasonic cleaning (4 h) Poupinel (5 x 2 h) Poupinel (10 × 2 h) Chemiclave (5 x 20 min) Chemiclave (20 x 20 min) NH4 (1 h) NH4 (4 h)
Torsional Moment 56.28 55.25 61.74 58.48 53.46 57.02 55.10 54.46 58.20 53.90 58.34 56.24 54.42
± 5.36 ± 3.14 ± 6.11 __+3.75 ± 3.62 ± 5.67 +_ 2.66 ± 3.42 ± 2.06 -+ 2.88 ± 6.45 ± 3.44 +_ 2.67
Torsional Angular Deflection 1262.2 1366.5 1473.0 1322.6 1344.6 1470.8 1520.5 1340.2 1420.6 1458.2 1249.2 1717.6 1446,4
Permanent Angular
Bending Moment
+_ 293 _+ 399 ± 256 ± 240 _+ 441 _+ 379 ± 417 +_ 97 _+ 379 _± 602 _+ 176 _+ 424 ± 199
59.60 56.26 58.94 65.28 61.43 59.84 59.68 64.52 62.52 60.04 64.68 57.72 58.06
Deflection
-+ 1.92 _+ 2.42 ± 2.26 ± 2.56 _+ 2.10 _+ 3.79 ± 1.73 _+ 3.89 _+ 2.19 _+ 1.80 ± 1.02 _+ 2.08 ± 2.76
9,0 9.0 8.4 8.6 7.0 8.6 8.8 7.7 6.4 6.8 7.6 8.7 8.8
+_ 0.01 +_ 0.71 ± 0.49 + 0.49 ± 0.01 _+ 0.49 ± 0.75 +_ 0.43 _+ 0.49 +_ 1.17 ± 0.80 ± 0.43 _+ 0.40
BOV, glass bead sterilization.
TABLE 3. Effects of various treatment procedures on the mechanical properties of Heliofile Number
1 2 3 4 5 6 7 8 9 20 11 12
Treatment Procedure Control NaOCI (12 h) NaOCI (48 h) BDV (10 x 40 s) BDV (40 x 40 s) Ultrasonic cleaning (1 h) Ultrasonic cleaning (4 h) Poupinel (5 x 2 h) Poupinel (10 x 2 h) Chemiclave (5 x 20 min) Chemiclave (20 x 20 min) NH4 (1 h) NH4 (4 h)
Torsional Moment 53.5 51.1 59.3 57.1 54.0 56.4 52.2 53.2 54.3 53.0 56.3 54.9 57.1
+ 1.7 _+ 1.5 _+ 6.7 ± 7.8 ± 3.4 ± 3.5 ± 1.3 ± 3.3 _+ 2.9 ± 3.2 ± 2.4 ± 3.6 _+ 2,8
Torsional
717.0 808.6 755.8 798.2 789.8 806.6 778.0 610.8 669.2 765.4 723.0 796.8 896.2
Permanent
Bending Moment
Angular Deflection -+ 81.9 -+ 188.2 _+ 152.0 ± 226.8 _+ 145.5 ± 194.0 _+ 119.7 ± 89.1 +- 88.9 _+ 231.2 ± 124.9 ± 239.4 -+ 228,1
54.8 56.6 61.2 61.2 60.8 60.9 57.6 54.9 56.7 56.6 60.3 60.0 59.6
Angular Deflection
_+ 2.4 _+ 4.4 _+ 2.5 _+ 2.8 ± 2.1 +_ 4.3 _+ 2.8 ± 3.4 _+ 2.3 ± 2.8 ± 3.0 ± 2.2 -4- 3.3
17.6 18.6 19.0 17.8 17.6 19.6 19.2 28.6 28.7 19.2 18.6 18.4 19.2
_+ 0.9 _+ 0.9 _+ 1.2 _+ 1.3 ± 1,1 ± 1.1 ± 0.5 ± 0.8 _+ 0.9 _+ 1.1 ± 0.5 ± 0.6 +_ 0.8
BDV, glass bead sterilizaion.
Flexofile Compared with the Flexofile (Table 2) control group, the following results were evident: an increase in torsional moment; an increase in torsional angular deflection; an increase in bending moment; and a decrease in permanent angular deformation.
H-File Compared with the H-File (Table 3) control group, the following results were found: an increase in torsional moment; an increase in torsional angular deflection; an increase in bending moment; and an increase in permanent angular deformation. The degree or extent of increase and decrease in the tested mechanical properties varied according to the file type and treatment procedure they underwent. The aforementioned changes are tabulated in Table 4.
DISCUSSION The results provide a comprehensive, comparative description of the effects that cleaning, disinfection, and sterilization methods have on the mechanical properties of the three file designs inves-
TABLE 4. Comparison of the percentage change in mechanical properties after treatment procedures Range of Change in % Mechanical Property Torsional moment Torsional angular deflection Bending moment Permanent angular deformation
A
Unifile
A
Flexofile
A
H-File
J, 1"
7-24 8-49
1" 1"
5-9 1-36
1" 1'
0-11 0-25
$ 1"
0-28 0-16
I' J,
5-10 0-29
1' 1"
0.2-12 0-63
tigated. There have been other reports of changes observed in mechanical propertie~ as a result of sterilization techniques (11). Iverson et al. (15) indicated that torque strength and angular deflection do not affect endodontic files subjected to 10 cycles of autoclaving at 127°C for 30 min, 10 cycles of glass bead sterilization for 20 s, or 10 cycles at 171°C for 1 h at dry heat sterilization. These findings are in agreement with those of other studies (13, 14). However, Mitchell et al. (13) found that sterilization affected a significant decrease in angular deflection after autoclaving after 10 cycles, although in their study a simulated clinical usage procedure was incorporated in the test regimen. The present study included the whole range of cross-infection
18
Journal of Endodontics
Hdtl(el et al.
control techniques. The file size used was restricted to ISO #030 to present a more comprehensive assessment of the effects of various treatment procedures on the mechanical properties under investigation. The revised form of A D A specification no. 28 has requirements at only a single bend angle of 45 ° and a single twist angle of 360 ° (17). There is no counterclockwise torsion requirement in the ANSI/ADA specification no. 28, although, this addition was proposed several years ago by Chemick et al. (14). At present, the recommendation is not to twist instruments more than one-quarter revolution (90°), in the counterclockwise direction, to stay within the safety limits of the files. The use of the new torsion instrument (Torquemeter Memocouple, Maillefer) indicated in the revised ANSI/ADA specification no. 28 allowed measurements to be made automatically; therefore, operator bias was eliminated. All of the file groups examined in this investigation met or far exceeded the limits set by the revised ANSI/ADA specification no. 28, both initially and after treatment procedures, although changes in values for the four mechanical properties were evident to a varying extent, depending on the treatment procedure they underwent. The relative differences evident in the initial values of the four mechanical properties for the different files have been well-documented in the endodontic literature as being attributable to crosssectional geometry or section modulus, method of manufacture, and metallurgical differences caused by varying alloy composition of stainless steel instruments (5, 11). The changes in mechanical properties after treatment procedures ranged from 0.2 to 63%, depending on design of file and type of cross-infection technique. It is not possible to predict the clinical performance of the files based on the mechanical property values obtained as there are many other factors. The 63% increase from the control group value was observed in the permanent angular deflection of the H-File. Although this seems to be a significant change, its clinical implications are insignificant. This is because permanent angular deformation is a reflection of the strength of the base metal (i.e. an increase in value would indicate that the metal has decreased in strength and consequently a higher angle of deformation is recorded), and a reduction in this value is not necessarily a disadvantage in all clinical situations (e.g. useful in severely curved canals as long as cutting efficiency is still adequate for canal preparation). Perhaps it is for this reason that there is no permanent angular deformation requirement in the ANSI/ADA specification no. 28, because a change in its value does not have a detrimental effect in the clinical situation.
All of the other changes observed in the four mechanical properties investigated in this study, as a result of different treatment procedures, were insignificant because they remained within the limits set by ADA specification no. 28. Dr. Ha~tl~el,Dr. Serfaty, Mr. Bleicher, and Dr. Allemann are affiliated with the Department of Endodontics, CRO, University Louis Pasteur, Strasbourg, France. Mrs Thin-Thin was affiliated with the ERASMUS Exchange Programme, University of Glasgow, Glasgow, Scotland. Address requests for reprints to Dr. Youssef Hat, el, INSERM U-424, UFR Odontologie, University Louis Pasteur, 1, Place de I'H6pital, 67000 Strasbourg, France.
References 1. 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. 2. Neal RG, Craig RG, Powers JM. Cutting ability of K-type endodontic files. J Endodon 1983;9:52-7. 3. Machian GR, Peters DD, Lorton L. The comparative efficiency of four types of endodontic instruments. J Endodon 1982;8:398-402. 4. Webber J, Moser JB, Heuer MA. A method to determine the cutting efficiency of root canal instruments in linear motion. J Endodon 1980;6:82934. 5. Krupp JD, Brantley WA, Gerstein H. An investigation of the torsional and bending properties of seven brands of endodontic files. J Endodon 1984;10: 372-80. 6. Roth WC, Gough RW, Grandich RA, Walker WA. A study of the strength of endodontic files' potential for torsional breakage and relative flexibility. J Endodon 1983;9:228-32. 7. Dolan DW, Craig RG. Bending and torsion of endodontic files with rhombus cross-sections. J Endodon 1982;8:260-4. 8. Lentine FN. A study of torsional and angular deflection of endodontic files and reamers. J Endodon 1979;5:181-91. 9. Craig RG, Mcllwain ED, Peyton FA. Bending and torsion properties of endodontic instruments. Oral Surg 1968;25:239-54. 10. Chenail BL, Brantley WA, Gerstein H. Clockwise torsional properties of intracanal instruments. Oral Surg 1977;43:130-4. 11. Younis O. The effects of sterilization techniques on the properties of intracanal instruments. Oral Sur9 1977;43:130-4. 12. Roulet JF. Dynamic fracture of conventional endodontic instruments vs experimental files. J Endodon 1983;9:12-6. 13. Mitchell BF, James GA, Nelson RC. The effects of autoclave sterilization on endodontic files. Oral Surg 1983;55:204-7. 14. Chemick LB, Jacobs J J, Lautenschlager EP, Heuer MA. Torsional failure of endodontic files. J Endodon 1976;2:94-7. 15. Iverson GW, von Fraunhofer JA, Herrmann JW. The effects of various sterilization methods on the torsional strength of endodontic files. J Endodon 1985;11:266-8. 16. Halt(el Y, Serfaty R, Bleicher PH, Thin-Thin CL, Allemann C. Effects of cleaning, disinfection, and sterilization procedures on the cutting efficiency of endodontic files. J Endodon (in press). 17. Council on Dental Materials, Instruments and Equipment. Revised American National Standards Institute/American Dental Association Specification No. 28 for root canal files and reamers, type K & H {approved October 1981).