The effect of endosonic instrumentation in simulated curved root canals

0099-2399/87/1305-O215/$02 00/0 J(~LIRNAL OF ENDODON'rlCS Co0),~jh! 9 1987 by Fhe A.'~encan A.s.sooabonof Endodont]sts

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VOL 13. NO 5 MA't T987

The Effect of Endosonic Instrumentation in Simulated Curved Root Canals Laurence W. Kielt, DOS, and Steve Montgomery, DDS

to work on the inner wall of the curve between the orifice and the elbow and on the outer wall of the curve between the elbow and the tip of the preparation. The thin portion of the mid-root area, called the "danger zone," is vulnerable to "stripping"-type perforation (5). Ultrasonic and sonic endodontic instrumentation systems (endosonic systems) have been developed to simplify the cleansing and shaping of the root canal. Studies have demonstrated the ability of ultrasonics to rapidly debride (6, 7), disinfect (8, 9), and shape (10, 11) the root canal system. In a study of 51 curved canals, which were ultrasonically instrumented, straightening was observed in only 5.9% of the canals (12). In another study using simulated root canals, canal curvatures were maintained both with hand and sonic techniques (13). The purpose of this study was to measure the amount of root canal transportation after preparation using ultrasonic, sonic, and hand instrumentation techniques in simulated curved canals in resin blocks.

This study evaluated the effects of ultrasonic, sonic, and conventional instrumentation techniques on curved root canals. Fifty resin blocks with curved canals were divided into five groups. Each group was instrumented by one of the following techniques: conventional hand instrumentation, sonic instrumentation using the Medidenta MM3000 unit, sonic instrumentation using the Syntex Endostar 5 unit, ultrasonic instrumentation using the Caulk Cavi-Endo unit, and ultrasonic instrumentation using the Osada Enac OE-2 unit. All preparations were made to the size of a # 3 5 K-type file. Measurements of the amount of transportation of the canal were made at the apical and middle portions of the preparations. The results were significantly different based on statistical analysis of variance. A multiple comparison test revealed that the Medidenta and Caulk systems transported significantly less at the apex of the curved canals than the Syntex system and hand instrumentation techniques. The Medidenta, Syntex, and hand instrumentation transported significantly less in the middle portion of the curved canals than the Caulk and Osada systems.

MATERIALS AND METHODS Fifty clear resin blocks (R. W. Pecina Assoc., Waukegan, IL), each with a simulated root canal with curvature of approximately 30 degrees, were used in this study. The side of the block with the view of the canal curving to the left was called the facial view and the adjacent side with the canal apex was called the distal view. Preoperative procedures included: (a) removing the manufacturer's rubber stop at the apex of the canal with a discoid-cleoid carver to facilitate irrigation; (b) numbering the blocks from 1 to 50 on the facial and distal sides; (c) scoring these sides with three crosshatches to facilitate postoperative alignment of photomicrographs; (d) enlarging the canals by hand to the size of a #15 K-type file to allow the #15 endosonic files to reach the working length; (e) determination of working lengths using a #10 file measured from the top of the block to 05-mm short of the foramen; (f) photographing the facial and distal views of the canals using a 35-mm SLR camera (OM-2N; Olympus Co., Tokyo, Japan) and slide film (Ektachrome ASA 64;

Shaping of the root canal has long been recognized as an essential part of endodontic therapy (1, 2). Root canal instrumentation objectives include: (a) developing a continuously tapering conical form; (b) making the canal narrow apically with the narrowest cross-sectional diameter at its terminus; and (c)leaving the apical foramen in its original position spatially (3). Meeting these goals in teeth with curved canals is difficult and time consuming. Weine et al. (4) using simulated curved canals in resin blocks demonstrated the tendency of endodontic files to straighten out within the canal, thereby straightening and transporting the canal. When various conventional hand instrumentation techniques were used, this effect resulted in an "hourglass" preparation with the narrowest area called the "elbow" (Fig. 1). Weine et al. also described the enlarged apical foramen which produced a teardrop shaped opening as the "zip." The instruments tended 215

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Journal of Endodonl~.4

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Kodak Co., Rochester, NY) through a microscope (American Optical, Buffalo, NY); (g) masking the blocks with tape, leaving a hole at the foramen for irrigation flow; (h) distributing the blocks randomly into five equal groups; (i) scoring the bottom of the blocks with a code corresponding to its group; and (j) positioning each block in a vise (Panavise Products, Long Beach, CA) with the facial side facing the operator. While photographing, the blocks were placed into a positioning template to allow for exact alignment of pre- and postoperative slide films. A Fixott-Everett millimeter grid (University of Oregon, Eugene, OR) was incorporated into the positioner, so that the slides contained a known measured reference. Each group was instrumented by one of the following systems (Fig. 2): (a) Cavi-Endo ultrasonic (L. D. Caulk Co., Milford, DE) with Caulk Endosonic files; (b) Enac model OE-2 ultrasonic (Osada Electric Co., Tokyo, Japan) with recommended Zipperer K-type files (Dentalwerke KG, Munich, West Germany); (c) Endo Sonic Air MM3000 handpiece (Medidenta International, Inc., Woodside, NY) with Medidenta Tno-sonic files; (d) Endostar 5 sonic handpiece (Syntex Dental Products, Valley Forge, PA) with Endostar files; and (e) hand instrumentation with K-Flex files (Kerr, Romulus, MI) using circumferential filing as the control. All instrumentation was done by one operator and new files were used on each block. Operation of the ultrasonic and sonic systems were performed according to the manufacturer's manuals. Files were precurved to facilitate instrumentation and irrigation was accomplished with tap water through the endosonic systems or by needle and syringe in the hand instrumentation group. Apical preparations were started with #15 files and then serially increased 'until #35 K-type test files could be placed to the working lengths. Postoperative procedures included: (a) removing the

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FIG 2 Endosonic systems: a, Caulk Cavi-Endo; b. Osada Enac OE2; c, Medidontia MM 3000; d, Syntex Endostar 5.

masking tape; (b) drying the canal with an air syringe; (c) photographing the blocks using the same technique as done preoperatively; and (d) aligning the pre- and postoperative slides together exactly by the use of the cross-hatches. These superimposed slides were then projected so that a 1-mm square on the Everett-Fixott grid projected as a 5- x 5-cm square, thereby giving a 50-power magnification. The distance between the preand postoperative canal walls at the middle inner aspect and the apical outer aspect were measured with a millimeter ruler at 1- and 8-ram distances ~om the apical tip of the preparation (Fig. 3). These measurements were converted to actual size by dividing by 50. The

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Figure 4 shows a superimposed pre- and postoperative slide transparency. The amount of transportion of the prepared root canals in each of the five instrumentation groups is shown in Table 1 and Fig. 5. A completely randomized analysis of variance (p < 0.01) showed a significant difference between the groups at both of the measured areas in the facial views and at the 8-ram area ot the distal views. There was no significant differences in measurements of the 1-mm areas of the distal views. Duncan's multiple range test using the results from the analysis of variance revealed which pairs of group means were sigmficantly different from each other (Table 2). At the 1-mm level in the facial views, the transportation mean values of the Medidenta MM3000 and the Cauik Cavi-Endo were significantly !ess than those of the Syntex Endostar 5 or the controls. At 8 mm in the facial views, the MM3000, Endostar 5, and control group means were significantly less than the Cavi-Endo or Enac OE-2 groups. At 8 mm in the distal views, the MM3000 and the control were significantly less than the Cavi-Endo. No significant differences were seen at 1 mm in the distal views.

FIG4 Exarnl~eof superimposedslides.A. Facial.B, D=staJwew DISCUSSION

This study reflects the mechanical portion of the biomechanical preparation of the root canal. Lim and Webber (14)in their study comparing extracted teeth and simulated root canals in clear plastic blocks concluded that the simulated canals are a valid experimentar model for studying the shape of the prepared root canaJ. In this study, all of the endosonic systems and the hand instrumentation technique removed more canal wall on the inner aspect of the curve in the middle portion of the canal and on the outer aspect of the curve in the apical portion of the canal. This is the same pattern demonstrated by Weine et al. (4). In a clinical

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Joumal of Endodontics

and the ultrasonic systems range from 18,000 to 30,000 cycles per s. There are disadvantages and advantages with each of the endosonic systems. Some of the disadvantages of the Cavi-Endo system include a lack of a depth gauge and a cumbersome ultrasonic unit with separate wiring and plumbing connections. Advantages of the Cavi-Endo inc_.Jude a reservoir for irrigation solutions, irrigation through the handpiece and alongside the file, and convertibility to an ultrasonic periodontic scaler. The Enac system also is an ultrasonic unit with separate wiring and plumbing connections, which can convert to an ultrasonic scaler. Additionally, it has a vibratory t=p and a power setting for removing cast restorations. Advantages of the Endostar 5 and MM3000 sonic systems include the abilities to attach directly to the high-speed air line of a dental unit and to be completely sterilized. Overall the Medidenta unit was superior to the other endosonic systems and to the hand technique (control).

situation, a curved root is more likely be perforated in the mid-root danger zone area and in the apical zip area. The incidence of these untoward effects increases as the curvature of the canal increases (15). Since the simulated root canal is more or less straight in the distal view, this explains the relative lack of significance in this view. This does not simulate clinical conditions. Curved roots, especially in molars, often curve in both planes. The results obtained indicate that some endosonic systems shaped the canal preparation more evenly than other systems. Some systems transported more, some less than the hand controls. The statistical differences between the groups may be due to the files used. Each group of recommended endosonic files had slightly differently shaped flutes (Fig. 6). The Cavi-Endo and MM3000 systems have additional files for shaptng the root canal (not evaluated in this study). Diamond files, #35 and #45, are available for the Cavi-Endo and two additional types of files, the Risl~-Sonic and ShaperSonr are available for the MM3000. The oscillation frequency is also different between each group. The sonic systems range from 1,500 to 6,500 cycles per s

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TABLE 1. Transportation means Position of View

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0214• 0.708• 0.073 • 0.04 0 262 • 0 07

0.248:1:0.09 0.420• 0.050 • 0.02 0.267 • 0.01

0.262_+010 0.412 +- 0 15 0.089 • 0.04 0 189 • 0.06

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It enlarged 1he canal to the same size as the other techniques with less transportation of the canal. CONCLUSIONS Statistical analysis indicated a significant difference in transportation between the groups. The Medidenta MM3000 transported the canal the least amount in both areas. Both the Medidentia and Caulk systems transported significantly less than the Endostar 5 system or the hand technique in the apical portion of the curve. The Medidentia system, the Syntex system, and the hand technique transported significantly less than the Caulk or Osada systems in the middle portion of the curve. Overall the Medidenta unit was superior to the other endosonic systems and to the hand control technique. It enlarged the canal to the same size as the other techniques with less transportation of the canal. The o~n~ons exl~essed here,n are those of the authors and are not to be constnJed as reflecbng the views of the United States Air Force or the Department of Defense We thank Drs. George McWalter and Carlos E del Rio for their suggeshons and advice We also thank ~ John Doran and Malor Wilham Sctllndler for ~et" ass=stance Dr Kr is a restorer, Department of EndodontJcs. Wilford Hall USAF Medc_.al Center. Lac~kland A,r Force Base. T X Dr Montgomery ,s associate professor, Department of Endodontcs. Un,ver~b/ot Texas Health Science Center at San /~qton~o. San Anton,o. T X

Effect of Endowonic I n s t r u m e n t a b o n

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Referencee

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