Physical dimensions and torsional properties of rotary endodontic instruments. I. Gates glidden drills

Physical dimensions and torsional properties of rotary endodontic instruments. I. Gates glidden drills

0099-2399/90/1609-0438/$02.00/0 JOURNAL OF ENDODONTICS Copyright 9 1990 by The American Association of Endodontists Printed in U.S.A. VOL. 16, NO. 9...

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0099-2399/90/1609-0438/$02.00/0 JOURNAL OF ENDODONTICS Copyright 9 1990 by The American Association of Endodontists

Printed in U.S.A.

VOL. 16, NO. 9, SEPTEMBER1990

Physical Dimensions and Torsional Properties of Rotary Endodontic Instruments. I. Gates Glidden Drills Neill H. Luebke, DDS, MS, and William A. Brantley, PhD

A laboratory study was performed on Gates Glidden drills to determine their physical dimensions and torsional properties. Five samples of sizes # 1 to # 6 drills from two brands distributed in the United States were measured for physical dimensions. Five samples of the most commonly used sizes #1, #2, and # 3 drills from these two brands were tested at failure in both the clockwise and counterclockwise directions using an analog torque meter. The values for the bur head dimensions of both brands correspond closely to those established by the ISO. The mean values for torque at failure for both the clockwise and counterclockwise directions showed no statistically significant difference for each brandsize combination. However, some instrument groups had separation or fracture sites near the bur head, while other groups underwent failure near the handpiece end. This study is the first part of a continuing investigation to establish standards for rotary endodontic instruments.

Gates Glidden drill sizes and to investigate the torsional properties of the most commonly used sizes. M A T E R I A L S AND M E T H O D S Two brands of Gates Glidden drills (Union Broach, Long Island, NY and Brasseler USA, Inc., Savannah, GA) were utilized in this study. Physical measurements of the diameter of the milled shaft and the maximum width of the bur head were made utilizing five samples for drill sizes #1 to #6. This was accomplished by rotation of the drill to find the widest diameter of the shaft and bur head. The shaft diameter was measured three times while the bur head width was measured four times, rotating between each observation, utilizing a traveling stage microscope (Gaertner Scientific Co., Chicago, IL) with a precision of about 0.001 mm. Five samples from each brand of drill sizes # 1, #2, and #3 were tested with clockwise loading, and five samples of drill sizes # I, #2, and #3 were tested with counterclockwise loading, utilizing a general procedure based upon the original version of the American Dental Association (ADA) Specification No. 28 for K-type hand files and reamers (15). The rationale was that no performance guidelines have been established for the Gates Glidden drill by either the ISO or the ADA (8). A manually operated analog torque meter (Power Instruments, Inc., Skokie, IL), shown in Figure 1, and previously used in our laboratory (14), provided measurements of torsional moment. The sample drills were clamped at the final 3 mm of the bur head by polished brass plates fastened in the vise of the torque meter apparatus. The torsional moment was recorded in ounce 9 inches at 45-degree increments for the first 360 degrees and thereafter in 90-degree increments until failure. The torsional properties of the drills were evaluated for both the clockwise and counterclockwise twisting modes, and moment values at fracture were converted from ounce 9 inch to gram 9 centimeter. Mean values and standard deviations were obtained for both the clockwise and counterclockwise torque values and the angular deflections noted prior to failure. After each test, the separation site of the fracture was observed for each drill using the traveling stage microscope.

The Gates Glidden drill is a rotary instrument which has been used since the end of the last century (1). This instrument is milled from a single shank of metal (carbon steel or Stainless steel). It comes in sizes # 1 through #6 and is used with a slowspeed handpiece. The literature reflects an increase in its use for endodontic applications including flaring and post preparation (2-7). The most c o m m o n Gates Glidden drills used are sizes #I through #3 (5). One potential hazard in using the Gates Glidden drill is that it can separate within the canal. The International Organization for Standardization (ISO) through cooperation of the manufacturers has established manufacturing or physical standards for Gates Glidden drills (8). However, there is little information in the literature concerning the mechanical properties of these instruments (9, 10). Considerably more research has been performed to determine the bending and torsional properties of files and reamers ( 11-14). The Gates Glidden drills used in the United States market are provided by two manufacturers. There are more distributors than manufacturers, so only samples from the two manufacturers were tested in this study. The purpose of this study was to report the physical dimensions for all

RESULTS The dimensions of the bur heads and the shank or shaft diameters for the Gates Glidden drill sizes #1 to #6 are listed

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Properties of the Gates Glidden Drill

in Table 1. Included in this table are the nearest standardized K-type file sizes for comparison (15, 16). From Table 1 it can be seen that, when the same drill sizes are compared for the two brands, the differences in bur head width are minimal. This is consistent with the right-hand column, where each of the drill sizes for the two brands, with two exceptions, lies within the same nominal size category of the ISO standard (8). The mean torque values at failure for the drill sizes # 1, #2, and #3 are reported in Table 2 along with the standard deviations. Utilizing Student's t test, there is no statistical difference for each instrument size of the two brands between the mean clockwise and counterclockwise torsional moments at failure, except for the Brasseler drill size # 1 (p < 0.01). The corresponding mean values for angular deflection at failure are reported in Table 3 along with the standard deviations. There is no statistical difference in torque angle at fracture for each instrument size of the two brands between the clockwise and counterclockwise directions of loading. The locations of the separation sites of the sample drills for sizes

FiG 1. Photograph of analog torque meter.

#1 through #3, as measured from the working tip, are noted in Table 4. These failure locations were, in general, very similar for the clockwise and counterclockwise loading of the same drill size for each brand. However, the fractures occurred near the bur heads for the Union Broach size #1 and for Brasseler sizes #2 and #3, whereas the failures were near the handpiece end for the Union Broach sizes #2 and #3 and for the Brasseler size # 1. Figure 2 shows the Gates Glidden drills as they would appear prior to testing. Figure 3 shows representative samples after separation for clockwise loading. Similar results were observed for counterclockwise loading (Fig. 4). DISCUSSION The first portion of this study was performed to corroborate the standards as proposed by the ISO. When considering the physical size of the bur head diameters, we felt that a comparison to the standardized K-type files was appropriate. However, the bur head for the Gates Glidden drill is triangular in shape, and this size measurement can be difficult to ascertain. As a result, the measurements on the bur head were repeated four times with a rotation between each reading on the same drill. Our findings generally agree with the existing ISO standard (8) as noted in Table 1. There are only two differences for the same drill size, the Brasseler #5 and #6 drills, of the two brands when comparisons were made to the ISO nominal size (8). We also attempted to establish some baseline torsional property information on the Gates Glidden drills, as there are presently no performance standards either from the ADA or ISO. The working portions of the drills are 18-mm long, and the smaller sizes are slender from the handpiece portion to the bur end (Fig. 2). Clinical utilization o f these drills which have a narrow shaft may result in fracture. If such clinical fracture does occur, the separation site is supposed to be near the handpiece so the drills can be removed easily from the root canal. A fracture that occurs near the bur head. as was found with the #1 Union Broach drill, the #2 Brasseler drill, and the #3 Brasseler drill, will cause the clinician a time-

TABLE 1. Physical dimensions of Gates Glidden Drills

Drill Size

Union Broach (n = 5)* #1 #2 #3 #4 #5 #6 Brasseler (n = 5)* #1 #2 #3 #4 #5 #6 * N u m b e r of test drills per size.

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Mean of Maximum Head Width (mm)

SD (mm)

Mean Shaft Diameter (mm)

SD (mm)

Closest ADA Standardized File Size (16)

ISO Standard (8) Nominal Size

0,571 0,744 0.894 1.135 1.226 1.446

0,035 0.014 0,028 0.027 0,068 0.035

0,399 0,451 0,599 0.694 0.802 0.855

0.021 0,031 0.014 0.044 0.041 0.008

#50 #70 #90 #110 #130 #150

#50 #70 #90 #110 #130 #150

0.485 0.643 0,841 1.049 1.173 1.329

0.032 0.027 0.024 0.033 0,060 0.062

0.381 0.513 0.604 0.687 0.773 0.872

0.017 0.009 0.025 0.018 0.019 0.016

#50 #70 #90 #110 #120 #140

#50 #70 #90 #110 #130 #150

440

Luebke and Brantley

Journal of Endodontics TABLE 2. Mean torque values at failure Clockwise

Drill Size Union Broach (n = 5)* #1 #2 #3 Brasseler (n = 5)* #1 #2 #3

Counterclockwise

Mean oz inch

Mean g cm

SD oz inch

2.40 4.30 5.50

173 310 396

2.03 4.88 7.24

146 351 521

Drill Size

Mean oz inch

Mean g cm

SD oz inch

0.17 0.15 0.23

#1 #2 #3

2.34 4.22 5.25

168 304 378

0.09 0.13 0.21

0.096 0.70 0.77

#1 #2 #3

1.70 4.22 8.22

122 304 592

0.17 0.51 0.79

* N u m b e r of t e s t drills per size.

TABLE 3. Mean values of angular deflection at failure Clockwise Drill Size Union Broach (n = 5)* #1 #2 #3 Brasseler

Counterclockwise

Mean (deg)

SD (deg)

Drill Size

Mean (deg)

SD (deg)

297 450 450

22 0 0

#1 #2 #3

324 450 441

18 0 18

576 504 477

146 335 144

#1 #2 #3

414 297 342

217 97 54

(n = 5)*

#1 #2 #3

* N u m b e r of t e s t drills per size.

TABLE 4. Summary of separation sites (measured from the working tip) Clockwise Drill Size

FIG 2. Gates Glidden drills #1, #2, and # 3 as received from the manufacturer.

Counterclockwise

Mean (mm)

SD (mm)

Drill Size

Mean (mm)

SD (mm)

2.21 15.26 13.60

0.04 0.04 1.08

#1 #2 #3

2.30 15.16 13.66

0.05 0.28 0.56

14,08 1.84 2.43

1.55 0.54 0.39

#1 #2 #3

14.02 2.34 2.59

1.57 0.16 0.29

Union Broach (n = 5)*

#1 #2 #3 Brasseler (n = 5)*

#1 #2 #3

* N u m b e r of test drills p e r size.

consuming problem in retrieving the instrument. Our personal communications with endodontists have revealed that this problem has in fact occurred. The measurement of an exact twist angle at instrument failure was not possible with the analog torque meter system. This was because the torque meter is spring loaded and returns to the "zero" position when the drill fractures. Therefore, the angular deflection at failure was measured as the last previous 45- or 90-degree increment recorded. Comparing the data in Tables 2 and 3, this study showed that for a given brand the clockwise and counterclockwise

FIG 3. Gates Glidden drills after separation in a clockwise direction.

torque moments and angles at fracture o f each instrument size in general were not significantly different. The equivalence of the two testing modes was further supported by the very similar separation sites for the clockwise and counterclockwise loading o f each brand-size combination as shown in Table 4. It would therefore be sufficient that all further studies of the Gates Glidden drill be performed in a clockwise manner.

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F~G 4. Gates Glidden drills after separation in a counterclockwise direction.

Previous data for K-type files and reamers indicate much greater clockwise torsional ductility (14) than found in the present study for the Gates Glidden drills. It is tempting to conjecture that there are a greater number of surface flaws in these milled instruments, compared with the K-type files and reamers, which are manufactured by twisting the starting wire blank in the counterclockwise direction. The latter manufacturing process does significantly decrease the counterclockwise torsional ductility for the K-type instruments. This may be due to work-hardening residual stresses along with the further decrease in interflute separation during twisting. The manufacture of the Gates Glidden drill is done by a symmetric process of milling the metal shank, and no fluted surface configuration is created as is for the files and reamers. It is plausible that the clockwise and counterclockwise torsional properties of the Gates Glidden drills would be similar, since the surface geometry and flaw distributions for these instruments should not have any bias to the sense of twisting. Detailed examination of the fracture surfaces of the Gates Glidden drills with the scanning electron microscope may provide direct evidence that the torsional separation of these instruments is initiated at minute surface flaws from the milling process. The much greater extent of strain hardening expected for the K-type files manufactured by twisting, compared with the milled Gates Glidden drills, should not be expected to account for the differences in clockwise torsional ductility of the two general classes of instruments. This is because the usual behavior of metals is that ductility decreases with increases in the amount of work hardening. Conclusive proof in the present context, however, would require torsional testing of the same instrument sizes of the two general classes, fabricated from the same metallurgical compositions of carbon steel and stainless steel.

441

We have utilized the same torsional testing procedures as in an extensive previous study of several brands and sizes of K-type files (14). Even though there may be a difference in the detailed torsional data for the Gates Glidden drills and the K-type files, the results should be similar when compared with the larger size K-type files. These larger K-type instruments were not evaluated in our earlier laboratory study (14) and should be included in future research. Further studies will investigate the mechanical properties of the stainless steel Gates Glidden drill in all sizes (#1 to #6), utilizing the automatic torsion meter equipment outlined for the revised ADA Specification No. 28 (16), and include discussions of scanning electron microscopic observations of the fractured instruments. The authors thank Brasseler USA, Inc. and Union Broach for supplying the test samples. Dr. Luebke is assistant professor, Department of Endodontics, Marquette University School of Dentistry, Milwaukee, WI. Dr. Brantley is professor, Section of Restorative and Prosthetic Dentistry, College of Dentistry, Ohio State University, Columbus, OH, and was formerly chairman, Department of Dental Materials, Marquette University School of Dentistry, Milwaukee, WI.

References 1. Ottolengui R. Methods of filling teeth. Dent Cosmos 1892;34:807-23. 2. Abou-Rass M, Jastrab RJ. The use of rotary instruments as ancillary aids to root canal preparation of molars. J Endodon 1982;8:78-82. 3. Gordon FL. Post preparations: a comparison of three systems. J Mich Dent Assoc 1982;64:303-4. 4. Goerig AC, Michelich RJ, Schultz HH. Instrumentation of root canals in molars using the step-down techr,,que. J Endodon 1982;8:550-4. 5. Cohen SC, Bums RC (eds.). Pathways of the pulp. 4th ed. St. Louis: CV Mosby, 1987:88-9, 172-3. 6. Calhoun G, Montgomery S. The effects of four instrumentation techniques on root canal shape. J Endodon 1988;14:273-7. 7. Gegauff AG, Kerby RE, Rosenstiel SF. A comparative study of post preparation diameters and deviations using Para-post and Gates Glidden drills. J Endodon 1988; 14:377-80. 8. International Organization for Standardization. International standard 3630/2 dental root canal instruments. Part 2: Enlargers. ISO bulletins Ref No. ISO 3630/2-1986(E),1986. 9. Luebke N, Walia H, Brantley W. Torsional properties of the GatesGlidden bur [Abstract]. J Dent Res 1988;67:382. 10. Luebke N, Walia H, Brantley W. A preliminary investigation of the torsional properties of the Gates Glidden bur [Abstract]. J Endodon 1988;14:199-200. 11. Lentine F. A study of torsional and angular deflection of endodontic files and reamers. J Endodon 1979;5:181-91. 12. Dolan D, Craig R. Bending and torsion of endodontic files with rhombus cross-sections. J Endodon 1982;8:260-4. 13. Mueller H, Suchak A, Stanford W, Stanford J, Stanford S. Comparison of some root canal instruments in bending and torsion to newly formed or draft specifications. J Endodon 1984;10:182-7. 14. Krupp J, Brantley W, Gerstein H. An investigation of the torsional and bending properties of seven brands of endodontic files. J Endodon 1984;10:372-80. 15. Council of Dental Materials and Devices, American Dental Association. New American Dental Association specification number 28 for root canal files and reamers. J Am Dent Assoc 1976;93:813-7. 16. Council on Dental Materials. Instruments and Equipment, American Dental Association. Amedcan Dental Association revised ANSl/ADA specification number 28 for root canal files and reamers. J Am Dent Assoc 1982;104:506.

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