JOURNAL OF ENDODONTICS Printed in U.S,A. Copyright © 1999 by The American Association of Endodontists VOL. 25, No. 11, NOVEMBER 1999

Comparison of the Cleaning Efficacy of Passive Sonic Activation and Passive Ultrasonic Activation After Hand Instrumentation in Molar Root Canals

Scott A. Jensen, DMD, MS, Thomas L. Walker, DDS, Jeffrey W. Hutter, DMD, MEd, and Brian K. Nicoll, DDS

The purpose of this study was to compare the cleaning efficacy of passive ultrasonic activation with that of passive sonic activation after hand instrumentation. Sixty curved molar canals were hand-instrumented to size 35 and divided into three groups. Group 1 received no further treat- ment. Group 2 received 3 rain of passive sonic activation. Group 3 received 3 rain of passive ultra- sonic activation. The roots were split and photomi- crographs (×20) were made of the apical 6 mm of canal. A transparent grid was placed over pro- jected images, and the total number of squares covering the apical 6 mm of canal space and the number of squares containing debris were counted. A debris score was calculated for each specimen by dividing the number of squares with debris by the total number of squares. The mean debris scores were 31.6% for hand instrumentation only, 15.1% for the sonic group, and 16.7% for the ultrasonic group. The debris scores for the sonic and ultrasonic activation groups were significantly lower than that for the hand instrumentation only group (p < 0.01); however, there was no significant difference between the sonic and ultrasonic acti- vation groups. Passive sonics after hand instru- mentation produces a cleaner canal than hand in- strumentation alone and is comparable with that of passive ultrasonics.

al. (6), in 1985, were the first to report on the use of a sonic instrument for endodontics.

When a file is ultrasonically activated and placed passively in a canal, a phenomenon called acoustic streaming is produced (7). Acoustic streaming is one of the purported mechanisms for supe- rior debridement. It produces shear stresses that are capable of disrupting biological cells and removing debris (8).

Several studies have shown that ultrasonically or sonically pre- pared teeth have significantly cleaner canals than teeth prepared by hand instrumentation (9-11). Other studies have failed to demon- strate the superiority of ultrasonics or sonics as a primary instru- mentation technique (12-16). This may be due in part to the fact that, when power-driven files are used to instrument a canal, they can bind or contact the canal walls in a way that restricts their vibratory motion and cleaning efficacy (17). This may be partic- ularly true for the fine, curved canals found in molars.

Perhaps a more effective technique for canal debridement would be to passively activate a file, sonically or ultrasonically, inside the canal as a final step in root canal preparation. Passive activation implies that no attempt is made to instrument, plane, or contact the canal walls with the file. This should allow for the maximum benefits from acoustic streaming. Archer et al. (18), in 1992, evaluated such a combination technique, using ultrasonics for 3 min after hand instrumentation, and found that it resulted in greater canal cleanliness than hand instrumentation alone.

Sonic instruments operate at lower frequencies and produce smaller shear stresses than ultrasonic instruments (7). The impact of this, however, on debris removal in root canal systems has not been reported. The purpose of this study was to compare the cleaning efficacy of passive ultrasonic activation with that of passive sonic activation after hand instrumentation in molar root canals.

Complete debridement of the root canal system is a critical com-

ponent of endodontic therapy ( l , 2). Ultrasonic and sonic activa- tion of endodontic instruments have been suggested as a means to improve canal debridement (3). Ultrasonic devices were intro-

duced for use in root canals in 1957 by Richman (4). A commercial ultrasonic unit, designed by Cunningham and Martin was reported on and made available for endodontic use in 1982 (5). Tronstadt et

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

Sixty extracted human molars were-used in this study. Canals were selected that had curvatures of 25i to 35 degrees, as deter- mined by Schneider 's method. Teeth were discarded if a #20 K-file did not bind short of the working length. The teeth were stored in saline at all times except during canal preparation. Access prepa- rations were made, and pa{ency was established by passing a #10

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736 Jensen et al.

K-file beyond the apex. Working lengths were established by subtracting 1 mm from the length at which the file first appeared at the apical foramen. All canals were flared coronally with #2 to #4 Gates-Glidden drills. They were then instrumented to a #35 at the working length using Flex-R files (Union Broach Corp., Long Island, NY) and a balanced force technique. Step-back flaring was accomplished up to a #55 file by subtracting 0.5 mm increments

from each successively larger file size. One milliliter of 5.25% NaOC1 was used as an irrigant between

each file size, with a 5-ml rinse used at the completion of hand instrumentation. The irrigant was delivered in a 10-ml syringe, with a 27-gauge side-venting needle. The needle was placed as far as possible into the canal without binding, but never closer than 5 mm from the established working length. All canals were prepared by a single clinician familiar with the instrumentation technique. Upon completion of" instrumentation, the teeth were randomly divided into 3 groups of 20 canals each and treated in the following

manner.

Journal of Endodontics

Group 1: Hand Instrumentation Only

The chamber and canal were filled with 5.25% NaOCI, which remained in the canal for 3 min. No further treatment was per-

formed.

Group 2: Passive Sonic Activation

The canals were filled with 5.25% NaOCI. An MM1500 sonic handpiece with a #15 Ripsisonic file (Medidenta International, Inc., Woodside, NY) was placed 2 mm short of the working length and activated for 3 rain. No attempt was made to plane, shape, or

remove dentin from the canal walls.

Group 3: Passive Ultrasonic Activation

The canals were filled with 5.25% NaOC1. A Mini-Endo ultra- sonic unit with a #15 file (EIE/Analytic Technology, Orange, CA) was set at the manufacturer 's recommended power setting, placed 2 mm short of the working length, and activated for 3 min. As with the sonic group, activation was considered passive, with no attempt

made to contact the canal walls. Treatment was then completed for all three groups, with a final

2-ml rinse of NaOC1. The canals were dried with paper points, followed by placement of a cotton pellet and Cavit in the canal

orifice.

Sectioning the Roots

The anatomical crowns were removed with a separating disk. A shallow longitudinal groove was cut with a diamond separating disk on the buccal and lingual surfaces of the root. The roots were then split with a surgical chisel and mallet, resulting in a mesial and distal half for each canal. All intact halves were used for evalua-

tion.

FIG 1. Scoring debris. This photomicrograph has a superimposed grid that illustrates how debris was scored. Squares with debris were marked and then divided by the total number of squares to arrive at a debris percentage. (Original magnification ><:20.)

parencies were taken of the specimens using a stereomicroscope at ×20 magnification. The transparencies were then coded and ran- domized by an investigator not associated with tooth instrumen- tation or the photomicrography. The photomicrographs were pro- jected onto a screen to 24 times the original size to produce a 2 × 3 foot image. A transparent mylar grid was placed over the pro- jected images. Each square in the grid represented a 200 ~m × 200

/ ,m subdivision of the root. An evaluator, who was unaware of which specimen or group

was being scored, counted the total number of squares covering the apical 6 mm of canal space and the number of squares that contained debris (Fig. 1). Particles or chips of any structure on the surface of the root canal were judged as debris.

A debris percentage was calculated for each specimen by di- viding the number of debris containing squares by the total number of squares. A mean debris score was then calculated for each group. Differences among the treatment groups were determined using a one-way analysis of variance and Bonferonni post-hoc tests

(p < 0.05).

Measurement of Surface Debris

The root sections were mounted with the exposed canal system facing up on a calibrated grid. Photomicrograph ektachrome trans-

RESULTS

Canals treated by hand instrumentation alone had a mean debris score of 31.6%, whereas the mean debris scores for the passively

Vol. 25, No. 11, November 1999 Cleaning Efficacy of Sonics/Ultrasonics 737

FIG 2. Hand instrumentation. This photomicrograph from group 1 shows heavy debris in the apical half of the root. (Original magnifi- cation ×20.)

activated sonic and ultrasonic groups were 15.1% and 16.7%, respectively. The mean debris scores for the passive sonic and ultrasonic groups were significantly lower than the debris score for the hand instrumentation only group (p < 0.01). There was, how- ever, no significant difference in debris scores between the sonic and ultrasonic activation groups. Figures 2 to 4 are photomicro- graphs representative of the debris typically observed in each of the respective treatment groups.

DISCUSSION

Although passive activation of sonics and ultrasonics after hand instrumentation produced cleaner canals than hand instrumentation alone, no technique was able to debride the canal system con> pletely. Debris was observed at all levels of the canal system, but tended to be concentrated in the apical 1 to 3 mm. Whereas hand instrumentation alone tended to produce twice the mean debris of hand instrumentation combined with passive activation, the clini- cal significance of this difference was not tested in the present study.

A difficult variable to control in this type of study is the wide variation in canal morphology. The size of a canal may influence the incidence of binding of the ultrasonic or sonic file and thereby effect the debridement efficacy of the instruments. Despite selec- tion criteria designed to obtain canals of similar morphology, there was considerable variation in the final canal size, which ranged from 75 to 178 squares. Regardless of the variation within groups, the mean canal size was similar among the three groups (Table 1).

FIG 3. Passive ultrasonics. This photomicrograph from group 3 re- veals a much cleaner canal with debris present in only the apical 1/2 mm. (Original magnification x20.)

A unique feature of this study was the debris scoring method. Several previous studies have evaluated canals using the subjective assessment of an examiner grading debris and collecting nominal or ordinal data according to an index ranging from no debris to heavy debris. The method selected for this study was similar to that used by Wu and Wesselink (19), and was chosen in an effort to more accurately quantify debris and potentially permit the use of more sensitive parametric statistical analysis.

Passive activation of files using the sonic and ultrasonic hand- pieces was relatively simple and required minimal effort, although there were differences in handling characteristics. The ripsisonic file in the sonic handpiece would occasionally (one to two times a minute) bind to the canal walls, and continuous small repositioning movements were necessary to keep it from binding the canal wall. The ultrasonic file was less often felt binding or contacting the canal walls. This may be due to the greater horizontal amplitude of the file tip generated by the sonic handpiece. The occasional binding, however, did not seem to be detrimental to the cleaning efficacy of the sonics. The ultrasonic handpiece was also judged quieter in operation than the sonic handpiece. At this time, how- ever, the cost of the ultrasonic unit is approximately three times that of the sonic handpiece, and the sonic handpiece is air-driven and has the advantage of being hooked directly to the dental unit.

Operators may find it somewhat tedious to hold these hand- pieces steady and passive for 3 rain in the root canal, which would add 9 min or more to the preparation time of an average molar. Future studies should evaluate the cleaning efficacy of these in- struments when activated passively for shorter time intervals.

738 Jensen et al.

FJG 4. Passive sonics. This photomicrograph from group 2 shows a very clean canal with minimal debris. (Original magnification ×20.)

TABLE 1. Range of canal size and mean canal size for each group expressed in total grid squares

Group 1 Group 2 Group 3

Range 77-178 88-147 75-140 Mean (SD) 110.4 (26.1) 112.7 (16.7) 109.4 (16.8)

No statistically significant difference among groups.

In conclusion, when a file is passively activated in a canal by sonics or ultrasonics for 3 rain after hand instrumentation, it results in a significantly cleaner canal than that for hand instrumentation alone. There is no significant difference in cleaning efficacy be- tween sonically and ultrasonically activated files.

The opinions or assertions contained herein are those of the authors and are not to be construed as official or as reflecting the views of the Department of the Navy.

Journal of Endodontics

Dr. Jensen is a former resident of the Naval Dental School, Bethesda, MD, and is a staff endodontist at Great Lakes Naval Training Center, Great Lakes, IL. Dr. Walker is a former associate professor, Endodontics Department, Naval Dental School, Bethesda, MD, and is in private practice in Lynchburg, VA. Dr. Hutter is director, Advanced Specialty Education Program in Endodontics, Goldman School of Dental Medicine, Boston University, Boston, MA. He is a former chairman, Endodontics Department, and director, Advanced Specialty Education Program in Endodontics, Naval Dental School, Bethesda, MD. Dr. Nicoll is chair, Research Department, Naval Dental School, Bethesda, MD. Address requests for reprints to Librarian, Naval Dental School, National Naval Dental Center, 8901 Wisconsin Avenue, Bethesda, MD 20889-5602.

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