Effects of cleaning, disinfection, and sterilization procedures on the cutting efficiency of endodontic files

0099-2399/96/2212-0657503.00/0 JOURNALOF ENDODONTICS Copyright © 1996 by The American Association of Endodontists

Printed in U.S.A.

VOL. 22, No. 12, DECEMBER1996

Effects of Cleaning, Disinfection, and Sterilization Procedures on the Cutting Efficiency of Endodontic Files Youssef Ha'=~el, DCD, DSO, PhD, Ren~ Serfaty, DCD, Philippe Bleicher, Thin-Thin C. Lwin, BDS and Claude Allemann, DCD, DSO

The effects of various cleaning, chemical disinfection, and sterilization procedures on the cutting efficiency of endodontic instruments Unifile (De Trey, Bois Colombes, France), (Flexofile Maillefer, Ballaigues, Switzerland), and H-File (Maillefer)) were investigated. The cross-infection control treatment procedures investigated were as follows: chemical disinfectionmNaOCl (2.5%) for 12 and 48 h, and NH4 (5%) for 1 and 4 h; ultrasonic cleaning for 4 and 16 cycles of 15 min; and sterilization methods with chemiclave for 5 and 10 cycles of 20 min, Poupinel for 5 and 10 cycles of 120 min at 180°C and glass beads for 10 and 40 cycles of 40 at 250°C. Cutting efficiency was evaluated as the mass of Plexiglas cut per unit of energy expended by the instrument in microgram/Joule. The cutting efficiency decreased from 1 to 77%, depending on the file design and type of treatment procedures. Heat sterilization (Poupinel) did not modify the cutting efficiency of Unifile and Flexofile. The decrease in cutting efficiency was independent of frequency and duration of treatment procedures.

Reactivity of the metal in its working environment includes properties such as chemical inertness (corrosion resistance) and the effects of repeated clinical instrumentation and various cleaning, disinfection, and sterilization procedures on the mechanical properties (i.e. cutting efficiency, angular deflection, stiffness/flexibility, and ease of handling characteristics). A review of the literature shows that no study has dealt specifically with cutting efficiency loss as a result of cleaning, disinfection, and sterilization procedures. These procedures are applied to all endodontic instruments for a variable number of times during their life span to prevent cross-infection. The cause of cutting efficiency loss observed in endodontic files is multifactorial, and it would have been unrealistic to study all of them, so this study concentrated on one important cause. The aim of this study was to evaluate the effects of cleaning, disinfection, and sterilization on the cutting efficiency of three file designs (Unifile, Flexofile, and H-File).

M A T E R I A L S AND M E T H O D S

Test Equipment The cutting efficiency measurements were made using the experimental device described in another study (1). The device consisted of two removable plates onto which the test specimen parallelepids (of hardness 33 VHN) Plexiglas plates could be attached. Testing followed the 2% conicity of the instrument to achieve intimate contact along the whole 16-ram full working length. Four identical springs allowed the total tightening force of 325 × g (i.e. 162.5 g on either side of the vice) to be evenly distributed on the two Plexiglas plates and thus to the tested endodontic instrument. The apparatus holding the endodontic instrument was capable of moving in the X-Y-axis and was attached to a pulley system that allowed clinical simulation of a quarter clockwise turn and withdrawal motion along the 16-ram full working length of the endodontic instrument. Movement along the Y-axis allowed a new Plexiglas surface to be cut each time for a total of 50 items for each tested file. Water irrigation at the 85 ml/min rate was supplied to the file in between cuttings to remove any debris left over from the preceding cut.

It is essential for the endodontic clinician not only to understand the clinical aspects of root canal therapy, but also to understand the range of usefulness and limitations of the instruments involved to produce optimal results consistently. The appropriate selection of endodontic instruments to correlate with various situations that may arise in root canal therapy is an important factor in achieving quality results. However, no organized set of guidelines exists, to make this a simple task. Instead, the clinician has to acquire information concerning selection criteria from various sources to formulate a rational basis for instrument selection. One selection criterion is the effect of the working environment on the instrument.

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Journal of Endodontics

Hai~el et al.

practice. For the same reasons, the most popular sterilization techniques were investigated in this study.

1400 1200 1000 800 pg/joule

600 400 200 0

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Experimental Procedures

:i:;:i:;:i:i:i:;:!:i:!:i:i:;:i:i:i:i:i:i:!:i!:?----ii?!iii!)i)!!i!i!)i!i!~!i!iii!!i2221!!i!)!ii!

/ [ H-FILE

FLEXOFILE

UNIFILE

FIG 1. Relative cutting efficiency of the control groups.

Three designs of ISO #030 endodontic instruments were used in this investigation: Unifile (De Trey, Bois Colombes, France), Flexofile (Maillefer, Ballaigues, Switzerland), and H-File (Maillefer). Thirty-nine groups of 10 files of ISO #030 (i.e. total of 390 files) were used. Each group was assigned to the various cleaning, disinfection, and sterilization techniques investigated, plus to a control group for each design of files. Unifile and Flexofile are both hybrid endodontic instruments and were chosen because they showed the highest cutting efficiency (1). H-File was chosen as an example of a traditional file so that comparisons could also be made between hybrid and traditional instruments. Size ISO #030 was chosen for two main reasons: it is a commonly used size in clinics, and it produces sufficient cut-off material to ensure reliability of cutting efficiency evaluation.

A total of 390 new stainless steel files of three different designs (Unifile, Flexofile, and H-File) and all ISO #030 were used (i.e. 30 files of each design). Each file type (random; new batch from manufacturer) was divided into l l groups, and each group consisted of 10 files. Three groups served as controls, with one group from each design file. Their cutting efficiency was evaluated in their new "initial" state, without undergoing any treatment procedures. The remaining 10 groups in each type file were subjected to each of the treatment techniques previously described. Therefore a total of 30 files (10 of each design) underwent each of the 10 investigated treatment techniques. The cutting efficiency was measured using the described test equipment (1). Each endodontic instrument underwent 50 runs/ cuts, and each cut was made on a new surface of the two Plexiglas plates. Cutting efficiency was evaluated as the mass removed/cut per unit of energy expended by the file in micrograms/Joule. The mass of Plexiglas cut was measured simply by direct weighing methods before and after 50 cuts. Energy used to make each cut was calculated from the printout (calibrated in millimeters) produced from the force captor device, which is connected to the vice, and measures the exerted force. Energy expended is represented by the area under force versus distance graph.

RESULTS

Treatment Procedures Control groups without instruments include: cleaning--ultrasonic for 4 and 16 cycles of 15 min; disinfection--NaOC1 (2.5%) for 12 H (NaOC1) and 48 h (NaOC1) and NH 4 (5%) for 1 h (NH4) and 4 h (NH4); and sterilization--chemiclave for 5 and 10 cycles of 20 rain at 134°C, Poupinel for 5 and 10 cycles of 120 min at 180°C, and glass bead (BDV) for 10 and 40 cycles of 40 s at

The control groups were designated as having 100% cutting efficiency, and the remaining groups' cutting efficiency was evaluated relative to the control groups for each design of files. The relative cutting efficiency of the three groups is shown in (Fig. 1) (Unifile has the highest and H-file has the lowest initial cutting efficiency values).

250°C.

Ultrasonic cleaning technique was chosen because it is a common and effective method of cleaning as opposed to gauze/sponge soaked in alcohol (2). NaOC1 (2.5%) and NH 4 (5%) were chosen for disinfection because they are commonly used formulations in

Unifile Table 1 and Fig. 2 demonstrate the effects of cleaning, disinfection, and sterilization on the cutting efficiency of the Unifile.

TABLE 1. Effects of various treatment procedures on the cutting efficiency of Unifile

No.

Treatment Procedure

1 2 3 4 5 6 7 8 9 10 11 12

Control NaOCl (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 × 20 min) NH 4 (1 h) NH 4 (4 h)

Mass Cut (#g) 132.4 31.8 40.2 125.3 124.0 37.7 37.7 134.1 138.9 38.2 35.9 36.0 39.6

_+ 0.0020 _+ 0.0030 _+ 0.0007 + 0.0009 _+ 0.0005 + 0.0002 + 0.0003 + 0.0010 _+ 0.0005 _+ 0.0005 _+ 0.0003 _+ 0.0009 +_ 0.0003

Energy Expended (J)

Cutting Efficiency (/xg/J)

Cutting Efficiency (%)

0.110 0.089 0.091 0.110 0.120 0.082 0.082 0.096 0.110 0.088 0.091 0.080 0.087

1203.6 357.3 441.8 1139.1 1033.3 459.8 459.8 1396.8 1262.7 434.1 394.6 450.0 455.2

100.0 29.7 36.7 94.6 85.9 38.2 38.2 115.9 104.9 36.1 32.9 37.4 37.8

Vol. 22, No. 12, December 1996

Effects of Sterilization Techniques

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FIG 2. Cutting efficiency (%) of Unifile after treatment procedures. U.S., ultrasonic; Chemi, Chemiclave; NH4, NH4.

FIG 3. Cutting efficiency (%) of Flexofile after treatment procedures. U.S., ultrasonic; Chemi, Chemiclave; NH4, NH 4.

One can see that the chemical disinfection treatment with NaOC1 (2.5% for 12 h) caused the greatest reduction in cutting efficiency of 64 to 70% and that Poupinel sterilization methods (5 and 10 cycles) did not cause a reduction in cutting efficiency. Bead sterilization caused the lowest cutting efficiency reduction of 5 to 14%, followed by ultrasonic cleaning of 62%, then chemical disinfection with NH 4 and Chemiclave of 64 to 67%.

76%, followed by Chemiclave sterilization (5 cycles × 20 min) and ultrasonic cleaning (16 cycles X 15 min) by 68%, then NaOC1 (12 h) by 66%, ultrasonic cleaning (4 cycles x 15 rain) by 65%, NaOCI (48 h) by 63%, BDV (40 cycles × 40 s) by 59%, Poupinel (10 cycles × 2 h) by 54%, NH 4 (4 h) by 53.5%, and Chemiclave (20 cycles X 20 min), NH 4 (1 h), and Poupinel (5 cycles x 2 h) by 50%. Table 4 demonstrates the percentage of reduction in cutting efficiency from control groups for the Unifile, Flexofile, and H-Files.

Flexofile

Table 2 and Fig. 3 demonstrate the effects of various treatment techniques on the cutting efficiency of Flexofile. In this case, the Chemiclave sterilization method caused the greatest reduction in cutting efficiency of 73 to 77%. Poupinel sterilization caused the lowest cutting efficiency loss of 1 to 12%, followed by NaOC1 (2.5%) disinfection of 58 to 68%, then ultrasonic cleaning of 66 to 67%, then bead sterilization of 67%, and NH 4 (5%) chemical disinfection of 68%.

H-File

Table 3 and Fig. 4 demonstrate the effects of various treatment procedures on the cutting efficiency of H-Files. The reductions in cutting efficiency were generally lower for all methods ranging from 50 to 76%. The greatest reduction occurred with glass bead sterilization (10 cycles 5< 40 min); cutting efficiency decreased by

DISCUSSION For each type of sterilization or disinfection, two series of cycles were chosen. The first series relates a realistic clinical use, and the second series represents four times the first series of cycles to amplify the corrosion process and metallic structural modifications. If the bioburden (blood, saliva, and debris) is not removed from the instruments, any method of sterilization may be ineffective. An alternate method of cleaning uses an ultrasonic cleaner. A period of 15 rain will usually be adequate. In this study, 4 and 16 cycles were used for cleaning the instruments. Some clinicians used cold sterilization solutions for holding or storing files and reamers. Diluted bleach (NaOC1 1:10 to 1:2) has been recommended by the American Dental Association and the Environmental Protection Agency for disinfection. Sterilization of

TABLE 2, Effects of various treatment procedures on the cutting efficiency of Flexofile

No.

Treatment Procedure

1 2 3 4 5 6 7 8 9 10 11 12

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 × 2 h) Chemiclave (5 × 20 rain) Chemiclave (20 x 20 rain) NH4 (1 h) NH4 (4 h)

Mass Cut (/xg) 146.9 41.2 44.5 44.7 45.4 42.2 43.6 145.2 138.3 34.7 39.7 43.3 43.1

_+ 0.0030 _+ 0.0004 _+ 0.0005 _+ 0.0006 _+ 0.0002 _+ 0.0003 _+ 0.0004 _+ 0.0020 + 0.0009 + 0.0008 ÷ 0.0008 ± 0.0010 _+ 0.0009

Energy Expended (J)

Cutting Efficiency (/xg/J)

Cutting Efficiency (%)

0.15 0.10 0.14 0.14 0.14 0.13 0.13 0.15 0.16 0.15 0.15 0.I4 0.14

979.0 412.0 317.9 319.3 324.3 324.6 335.8 968.0 864.4 231.3 264.7 309.7 307.9

100.0 42.1 32.4 32.6 33.1 33.2 34.3 98.9 88.3 23.0 27.0 31.5 31.5

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Journal of Endodontics

Hai]~el et al. TABLE 3. Effects of various treatment procedures on the cutting efficiency of H-File No.

Treatment Procedure

1 2 3 4 5 6 7 8 9 10 11 12

Control NaOCI (12 h) NaOCI (48 h) BDV (10 x 40 s) BDV (40 × 40 s) Ultrasonic cleaning (1 h) Ultrasonic cleaning (4 h) Poupinel (5 × 2 h) Poupinel (10 x 2 h) Chemiclave (5 x 20 rain) Chemiclave (20 x 20 min) NH 4 (1 h) NH 4 (4 h)

Mass Cut (/~g) 141.6 43.2 45.1 35.7 46.9 44.5 47.7 47.4 40.2 43.1 46.8 43.8 47.0

_-- 0.0020 +_ 0.0002 _+ 0.0004 _+ 0.0030 -+ 0.0007 + 0.0005 -+ 0.0010 _+ 0.0004 _+ 0.0007 +_ 0.0003 -+ 0.0003 +- 0.0010 -+ 0.0007

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FiG 4. Cutting efficiency (%) of H-file after treatment proced ures. U.S., ultrasonic; Chemi, Chemiclave; NH4, NH 4.

instruments by immersion in NaOC1 solution as a sterilant requires 6 to 10 h immersion. NaOC1 is an intermediate-level disinfectant. Intermediate-level disinfectants do not kill spores, but are capable of destroying other microbial forms, including vegetative bacteria, tubercle bacillus, and lipid and nonlipid viruses. Iverson et al. (3) immersed the endodontic instruments in cold sterilization solution for 10 cycles of 30 min (5 h). In the present study, the instruments have been immersed in germicidal solutions: NaOC1 (12 and 48 h) and NH 4 (1 and 4 h). Dry heat does not penetrate as well as moist heat; therefore, higher temperatures are required for sterilization. The usual recommendations are 160°C to 180°C for 2 h (4). However, in their study, Roulet (5) and Iverson et al. (3) used 10 cycles at 170°C for 1 h. In the present study, 5 and 10 cycles of 2 h at 180°C dry heat were used. Unsaturated chemical vapor autoclaves (chemiclave) use a mixture of alcohol formaldehyde, ketone, acetone, and water. The recommended temperature is 13 I°C for 30 min (6). Roulet (5) and Iverson et al. (3) used 10 cycles of autoclaving at - 1 2 7 ° C for 30 rain. However, Mitchell et al. (7) used <10 cycles. In the present study, the autoclaving was done in 5 and 10 cycles of 20 min at 134°C (after 20 min to reach the optimal conditions). The time required for glass bead sterilization was between 10 and 60 s. The highest time was necessary for sporicidal activity. Schutt and Starsiak (8) recommended 60 s, and Windeler and Walter (9) still found some bacteria after 60 s. In the present study, glass bead sterilization was done during 10 and 40 cycles of 40 s at 250°C. The number of cycles is variable according to different

Energy Expended (J)

Cutting Efficiency (/~g/J)

Cutting Efficiency (%)

0.21 0.19 0.18 0.22 0.17 0,19 0.22 0.14 0.13 0.21 0.14 0.13 0.15

674.3 227.4 250.5 162.3 275.9 234.2 216.8 338.6 309.2 215.5 334.3 336.9 313.3

100 33.7 37.1 24.1 41.1 34.7 32.2 50.2 45.9 31.9 49.6 50.1 46.5

authors. Chernick et al. (10) used 100 cycles of 10 s, Roulet (5) used 20 cycles of 20 s, and Iverson et al. (3) used 10 cycles of 20 s. Cutting action is the basic functional property of endodontic instruments, thus loss of this property would render the instrument useless. It was therefore in our interest to identify the factors that effect this property and evaluate the extent of such effects to avoid the complications associated with the use of inadequate files during clinical instrumentation. Yguel-Henry and von Stebut (11) studied cutting efficiency loss because of clinical instrumentation. They documented the importance of bulk material properties (mechanical strength and fracture toughness) and flaw-free surface machining to attain better efficiency and reliability of instruments. However, clinical instrumentation was not the only cause of cutting efficiency reduction. There were many variables that affected cutting efficiency and one such variable (treatment procedures to achieve asepsis) was investigated and is reported herein. The differing relative cutting efficiency values of the three control groups (Unifile, Flexofile, and H-File in their new initial state) could be accounted for by their different design and execution of the fluted portion, cross-sectional geometry, manufacturing procedures, variable amount of plastic debris, and metal spurs on new files (2). It has been shown in another study (1) that the design of the Unifile (similar to H-type instruments)--with its flutes ground into the wire shaft, creating double helix-spiraled cutting edges along the shaft that in cross-section are S-shaped--had superior cutting efficiency compared with the Flexofile (similar to K-type instruments), in which flutes were created by a twisting process resulting in triangular cross-sections (12). Based on the results of this study, a most appropriate treatment technique (the one that had the least detrimental effect on cutting efficiency) can be recommended tot each of the three file designs studied. For Unifile, heat sterilization (Poupinel) was the best method, because no cutting efficiency loss was noted for both 5 and 10 cycles. In the case of Flexofile, heat sterilization was also the best treatment procedure, because the least cutting efficiency reduction was related, ranging from a 1 to 12% decrease with 5 and 10 cycles, respectively. It would seem that, with the exception of dry heat sterilization (Poupinel) on Unifile and Flexofile, a significant detrimental cutting efficiency reduction (range of 20 to 70%) was observed on all three designs of files after the treatment procedures were studied. This fact suggested that the original metal properties of endodontic files were significantly changed to a varying extent in accordance

Vol. 22, No. 12, December 1996

Effects of Sterilization Techniques

661

TABLE 4. Percentage reduction in the cutting efficiency from control groups Reduction of Cutting Efficiency in % No.

Treatment Procedure

1 2 3 4 5 6 7 8 9 10 11 12

NaOCI (12 h) NaOCI (48 h) BDV (10 × 40 s) BDV (40 × 40 s) Ultrasonic cleaning (1 h) Ultrasonic cleaning (4 h) Poupinel (5 × 2 h) Poupinel (10 x 2 h) Chemiclave (5 × 20 min) Chemiclave (20 x 20 min) NH 4 (1 h) NH 4 (4 h)

with various treatment procedures. The reason for such observations is not clear and requires further study. Dr. Haikel, Dr. Serfaty, Mr. Bleicher, and Dr. Allemann are affiliated with the Department of Endodontics, CRO, University Louis Pasteur, Strasbourg, France. Miss Thin-Thin was affiliated with the ERASMUS Exchange Programme, University of Glasgow, Glasgow, Scotland. Address requests for reprints to Dr. Youssef Ha;lkel, INSERM U-424, UFR Odontologie, University Louis Pastuer, 1, Place de I'H6pital, 67000 Strasbourg, France.

References 1. Ha'i'kel Y, Serfaty R, Thin-Thin CL, Allemann C. Measurement of the cutting efficiency of endodontic instruments: A new concept. J Endodon 1996;22:651-56. 2. Murgel CAF, Walton RE, Rittman B, Pecora JD. A comparison of technique for cleaning endodontic files after usage; a quantitative scanning electron microscopic study. J Endodon 1990;16:214-7. 3. Iverson GW, von Fraunhofer JA, Herrmann JW. The effects of various

Unifile

Flexofile

H-File

70.30 63.30 5.40 14.10 61.80 61.80 Nil Nil 63.90 67.10 62.60 62.20

57.90 67.60 67.40 66.90 66.80 65.70 1.10 11.70 77.00 73.00 68.50 68.50

66.30 62.90 76.00 59.00 65.30 97.80 49.80 54.10 68.10 50.40 50.00 53.50

sterilization methods on the torsional strength of endodontic files. J Endodon 1985;11:266-8. 4. Reams G J, Baumgartner JC, Kulild JC. Practical application of infection control in endodontics. J Endodon 1995;21:281-4. 5. Roulet JF. Dynamic fracture of conventional endodontic instruments versus experimental files. J Endodon 1983;9:12-6. 6. Cottone J, Terezhalmy G, Molinari J. Practical infection control in dentistry. Philadelphia: Lea & Febiger, 1991. 7. Mitchell BF, James GA, Nelson RC. The effects of autoclave sterilization on endodontic files. Oral Surg 1983;55:204-7. 8. Schutt RW, Starsiak WJ. Glass bead sterilization of surgical dental burs. Naval Dental Res Inst Surg 1990;19:250-1. 9. Windeler AS, Walter RG. The sporicidal activity of glass bead sterilizers. J Endodon 1975;1:237-42. 10. Chernick LB, Jacobs J J, Lautenschlager EP, Heuer MA. Torsional failure of endodontic files. J Endodon 1976;2:94-7. 11. YgueI-Henry S, von Stebut J. Cutting efficiency loss of root canal instruments due to bulk plastic deformation, surface damage and wear. J Endodon 1994;20:367-72. 12. Ha~l'kelY, Gasser P, Allemann C. Dynamic fracture of hybrid endodontic hand instruments compared with traditional files. J Endodon 1991 ;17:21720.