0099-2399/92/1801-0019/$03.00/0 JOURNAL OF ENDODONTICS Copyright © 1991 by The American Association of Endodontists

Printed in U.S.A. VOL. 18, NO, 1, JANUARY1992

A Radiographic Comparison of Two Root Canal Instrumentation Techniques Charles A. Backman, DDS, MSD, Robert J. Oswald, DDS, and David L. Pitts, DDS, MSD

merits used with clockwise and counterclockwise motions. To enhance the technique, the tips of standard K files are modified by grinding. The tips are nonend-cutting and are reported to provide better instrument control and to decrease the incidence of canal transportation (10). The purpose of this study was to compare the balanced force technique with the progressive enlargement technique, a type of step-back preparation taught at the University of Washington (11). The ability of the two instrumentation techniques to negotiate and enlarge small curved canals without producing deviation from the original apical root canal curvature was compared radiographically.

The ability of two instrumentation techniques to negotiate and enlarge small curved canals was corn, compared radiographically. Fifty canals in extracted human molar teeth were instrumented by the progressive enlargement (PE) technique, a form of step-back preparation using standard K files, or by the balanced force (BF) technique using K files whose tips had been specially modified. By using drawings and projected radiographic images of the files, the position of the largest file used in the apical preparation, #30 or #35 for the PE technique and #45 for the BF technique, was compared with the position of a small file placed in the canal before instrumentation. The PE and BF techniques were equally capable of instrumenting small curved canals to their respective largest apical preparation sizes. However, at sizes equivalent to the largest apical preparation sizes used in the PE technique, the BF technique produced significantly less deviation from the center of the original canal.

MATERIALS AND METHODS Sample The study used hydrated extracted human molar teeth. The buccal canals of maxillary molars and mesial canals of mandibular molars were instrumented. The experimental group for each instrumentation technique consisted of two canal types. Type A canals (n = 26) demonstrated unidirectional curvature in both clinical and proximal view radiographs, had a curvature of at least 15 degrees, and could be negotiated to the apical foramen with #10 files. Type B canals (n = 24) demonstrated unidirectional curvature in the clinical view and bidirectional or S-type curvature in the proximal view. Type B canals were acceptable regardless of the degree of curvature.

After endodontic instrumentation it is desirable that the original canal lie within the final root canal preparation (1). Schilder (2) stated that the objective of making the final root. preparation conform to the general shape and direction of the original canal may be one of the most neglected phases of endodontic instrumentation. Hence, the goal of root canal preparation is to maintain a three-dimensional relationship of the original canal to the final preparation while simultaneously satisfying the requirements of optimum canal debridement and ease of obturation. In small curved canals it is difficult to achieve these instrumentation goals (3, 4). Ledge formation, blockage of the apical foramen by dentin mud, transportation or zipping of the foramen, and root perforation may occur ( 1-3, 5). Currently, the most commonly advocated instrumentation technique is the flared or step-back preparation (1, 3, 6, 7). A notable departure from common variations of the stepback technique is the "balanced force" concept of instrumentation described by Roane (8) and others (9). They advocate instrumentation of small curved canals with straight instru-

Canal Curvature Determination

A modification of the system developed by Southard et al. (12) was used to ensure reproducible radiographic alignment of sample teeth. The teeth were mounted in clear acrylic blocks with holes machined through them. Flattened # 11 lead shot, placed into depressions cut into the mounting blocks, served as coronal and apical radiographic markers. These markers were set in the mesiodistal and buccolingual plane of the apical foramen to ensure that the appropriate markers and instrument tip images could be simultaneously focused when projecting the radiographs. A standard access preparation was made in each mounted tooth, the canal orifices located, and the chamber irrigated with 5 ml of 5.25% sodium 19

20

Journal of Endodontics

Backman et al.

hypochlorite. This and all subsequent irrigation was accomplished with a 5/s-inch 25-gauge needle placed as far into the canal as possible without binding. By using a stem-winding motion (one-eighth to one-fourth turn clockwise, one-eighth to one-fourth turn counterclockwise), the canals were negotiated to the apical foramina with small K files (Union Broach, York, PA). Radiographs were made with the first file to bind at the visually determined apical foramen in two views: (a) a clinical or buccolingual projection and (b) a proximal or mesiodistal projection. Radiographs of the smallest f'de were mounted in glass slide mounts (Gepe, BiWex, Gotene, Sweden) for projection. A Kodak Ektagraphic model E slide projector fitted with a 3inch f/3.5 Ektanar projection lens (Eastman Kodak, Rochester, NY) was bolted vertically to project onto a countertop. Radiographs were projected onto drawing paper secured to the countertop, resulting in an enlargement of approximately x7. The clinical and proximal angles for type A canals were determined from drawings made from these images. Similarly, for type B canals, the clinical, proximal apical and proximal coronal angles were determined (Fig. 1). The radius measurement for single curvatures was measured from the tip of the instrument at the apical foramen to where the canal deviated from the coronal axis. Two radius measurements were determined for double or S-type curvatures, the first from where the first curve began to the point at which the second curvature occurred. The second measurement was made from the tip of the instrument at the apical foramen to where the second curvature began. Thus, two radius measurements were obtained for each type A canal and three for each type B canal.

Determination of curvatures and radius measurements was carried out independently by two evaluators. Differences of 5 degrees or less in curvature measurements between evaluators were accepted and the mean of the evaluations was recorded as the angle of curvature. Differences larger than 5 degrees were resolved by a conference between evaluators to determine the reason for the discrepancy and to make a collaborative determination of the angle of curvature. The mean of the two evaluators" radius measurements was recorded as the radius value. The sample was divided into matched pairs so that canals of the same type and similar curvature were instrumented by both techniques. Pairing was performed by two evaluators. Angle measurements from the clinical view for each canal were ranked in order from greatest to least. The canals then were paired on the basis of the best match of clinical angles in conjunction with the angle measurements from the proximal view. Once matched pairs were formed, the canals in each pair were randomly assigned to an instrumentation technique. The operator then was provided with a list of numbered samples to be instrumented by each technique. It was postulated that in addition to canal curvature per se, the length of the canal segment over which a given curvature occurred may be an important factor affecting the ability of an instrument to negotiate the curvature. In order to test this, a value termed the "radius quotient" was calculated for each canal. This value was obtained by dividing a given angle by its "radius" measurement. Thus, the larger the value of the radius quotient, the greater the presumed "severity" of the curvature. In type A canals the radius quotient for the clinical angle was computed by dividing the clinical angle measurement by its radius measurement. The radius quotient for the proximal angle was computed in a similar fashion using the proximal angle and the proximal radius measurement. In type B canals the radius quotient for the clinical angle was computed as described above. In the proximal view two radius quotients were computed, one for the apical angle and one for the coronal angle. Radius quotient for the proximal apical angle was equivalent to the value of the proximal apical angle divided by its radius measurement and radius quotient for the proximal coronal angle was equivalent to the value of the proximal coronal angle divided by its radius measurements. The means of the radius quotients were subjected to unpaired t tests.

Instrumentation Procedures

BALANCED FORCE TECHNIQUE

FIG 1. Method of canal curvature measurement. A, Method for single curvature, a and b lines drawn on image of instrument; c, angle of canal curvature formed by intersection of lines a and b. B, Method for double curvature, a, b, and d lines drawn on image of instrument; c, angle of coronal canal curvature; e, angle of apical canal curvature.

All canals in this group (Fig. 2A) were prepared using the balanced force (BF) technique of instrumentation as described by Southard et al. (12) with the following modifications. The tips of the triangular stock files (Unitek, Monrovia, CA) were specially shaped by grinding using a process devised by Roane so that the file tips were rounded. Because of the instrument tip modification, all files from #20 to #45 were used to the same working length, which in this study was the apical foramen.

Comparison of InstrumentationTechniques

Vol. 18, No. 1, January 1992

I G.G. #6

G.G. #3

G.G. #5

GG. #2

-Size #50 Hedstrom G.G. #4

G.G. #3

/__~ Sizes #35-50

G.G. #2

Size #45 To apical foramen

/

Size #:313

J 314mm from foramen

A

B

FIG 2. Canal preparations. A, BF technique. B, PE technique.

PROGRESSIVE E N L A R G E M E N T TECHNIQUE All instrumentation (Fig. 2B) was carried out using K files and Hedstrom files (Union Broach). Sodium hypochlorite was used as an irrigant throughout instrumentation. A #8 or #10 K file was placed into the canal and worked apically using a stem-winding motion (one-eighth to one-fourth turn clockwise, one-eighth to one-fourth turn counterclockwise) with slight apical pressure. The file was worked until the tip was visible at the apical foramen. This length minus 3/4 m m was the working length. A #10 file was used to maintain patency of the foramen throughout instrumentation. The progressive enlargement (PE) technique consists of three phases: apical preparation, progressive filing, and coronal twothirds filing. New files were used in the apical preparation phase for each canal. Apical preparation began with the first K file to bind in the canal at the working length. If that instrument was larger than a #25 K file, the canal was excluded from the study. The final size of the apical preparation was 15 units larger than the size of the first instrument to bind at the working length. After using a # 15 file in the apical preparation, a #20 file was placed into the canal to at least one-half the working length, used with a filing motion (push-pull), and worked around the canal walls circumferentially. Then a #2 Gates Glidden drill was used to enlarge the canal 5 m m apical to the orifice or to a point where the canal curvature prevented penetration to this depth. After irrigation, the #3 Gates Glidden drill was used to enlarge the canal to a level approximately 3 m m apical to the orifice or to a point where the canal curvature prevented penetration to this depth. The canal was irrigated again, patency was reestablished with a #10 file, and apical preparation was continued with the #15 file. In the apical preparation, files were used in the following manner. To assure accuracy, all files were measured before precurving the working end. A curve was placed in the most apical portion of the file. The curved file was inserted into the canal and worked apically using a stem-winding motion and light apical pressure. Once the file reached working length, it was withdrawn several millimeters, then worked to length and withdrawn again. This sequence was repeated until the file

21

was able to slide easily to working length without using the stem-winding motion. Each sequentially larger K file was worked in a similar fashion. After each file used during apical preparation, the canal was irrigated with 1.0 ml of sodium hypochlorite. After the apical preparation, the progressive filing began with a K file one size larger than the largest file used in the apical preparation and progressed sequentially to 20 additional units. Beginning with the first file in the series, a stemwinding motion was used to work the instrument down the root canal to where it bound. The file_was withdrawn slightly and then worked using a filing motion (15 to 20 strokes). After irrigation a file one size smaller than the final size used for apical preparation was placed into the canal to working length to remove dentin filings from the apical portion of the canal. The next larger file was then worked into the root canal until it bound, was withdrawn slightly, and then worked using a filing motion. Each larger file was used in a similar manner. The following end point criteria were established for the progressive filing phase. The first file of the series had to slide easily to within 0.5 m m coronal to working length. The next larger file in the sequence had to be easily placed to 1.0, 1.5, and 2.0 mm, respectively, coronal to working length. After completion of progressive filing, the canal was irrigated, patency was reestablished, and the apical preparation was debrided with the largest file in the apical preparation series. The coronal two-thirds filing phase was accomplished with a Hedstrom file the same size as the largest K file used in the progressive filing series. The length was set 2.5 m m coronal to the working length. The file was flexed against the walls of the canal, worked with a filing motion, and was continued around the periphery of the canal until all of the walls felt smooth and clean dentinal filings appeared on the flutes of the file. After completion of coronal two-thirds filing, the canal was irrigated, patency was reestablished, and the apical preparation was cleansed of dentinal filings.

Radiographic Analysis of Instrument Deviation Radiographs of the mounted teeth were taken in a jig designed by Southard (12). All radiographs were taken in triplicate with #2 Kodak DF-58 periapical X-ray film (Eastman Kodak) at 65 kVp, 15 ma, and a target-to-film distance of 19 inches. Exposure times and processing were standardized. Twelve views were taken in triplicate for each BF canal (one for each of the six file sizes in the clinical view and the same for the proximal view). To standardize radiographic procedures, the clinical views were always made with the surface of the mounting block corresponding to the buccal surface of the tooth against the film. The proximal views were made by placing the block surface corresponding to the mesial tooth surface against the film. Each radiograph was mounted in a glass slide mount and labeled with the sample number, radiographic view (clinical or proximal), and instrument size. The triplicate radiographs of each file size were identified as a, b, and c. Eight views were taken in triplicate for each PE canal (one for each of the four apical preparation file sizes in the clinical view and the same for the proximal view). The radiographic position of a # 15 or #20 instrument in the canal in both the clinical and proximal views was assumed

22

Backman et al.

to be centered in the original canal. The radiographic position of the tip of each larger instrument was compared with that of the #15 or #20 instrument to determine if the larger instrument had deviated from the center of the original canal. The first of the triplicate radiographs of the smallest file used was projected onto drawing paper. The image was focused to achieve maximum sharpness and a drawing of the tooth outline, the coronal markers, the apical markers, and the apical third of the file was made. Before analyzing instrumentation in each sample, a test was made to ensure the reliability of the radiographic projection-alignment system. To accept the sample, precise superimposition of the images of the remaining two radiographs of the triplicate set onto the drawing of the first radiographic image had to be demonstrated in both the clinical and proximal views. Only for samples in which projection reliability was established was evaluation of instrument deviation performed. The drawing of the smallest file was again positioned on the countertop. The first mounted radiograph from the triplicate set of radiographs showing the largest file used in apical preparation was projected and focused. A mask was placed over the file portion of the drawing so that it was not possible for the evaluator to use the image of the projected file to aid in alignment. The drawing and the projected image were superimposed by moving the drawing. Once the root and crown outline and markers were aligned, the mask was removed and the relative positions of the small file in the drawing and the projected image of the larger file were compared. In instances where the tooth and marker outlines of the projected image of the first film could not be superimposed on those of the masked drawing, superimposition was attempted with the remaining two films. Evaluation was performed only on those samples for which one of the three films could be accurately superimposed. If none of the files could be superimposed, the sample was rejected from the study. These evaluations were made with the clinical and proximal view radiographs of each file size used in the apical preparation. Instrumentation was evaluated by first making a gross comparison of the relative positions of all instruments used for each technique with the position of the first instrument in each canal from which the drawing was made; and, second, by measuring the amount of deviation of each file from the center of the original canal (as represented by the center of the instrument in the drawing of the smallest file used in apical preparation). For the first evaluation, "in" and "out" categories were established for each file used in the apical preparation in both the clinical and proximal views (Fig. 3). Files were categorized "in" if the drawing of the small file was completely within the projected image of the larger file. This category included those specimens in which the small file drawing was centered with respect to the projected image of larger files as well as samples in which the large files had deviated to the extent that the inner edge of the large file was superimposed over the inner edge of the small instrument. Files were categorized as "out" in instances where any portion of the small instrument in the drawing was outside the image of the larger file. For each canal, the largest file categorized as "in" was recorded for both clinical (INC) and proximal (INP) views. If none of the files in the sequence was "in," a zero was recorded. For each canal,

Journal of Endodontics

an overall "in" values was determined by the smallest of the INC or INP values. In the second type of evaluation, deviation was measured more precisely. Deviation was measured from the center of the larger file to the center of the small file drawing. The overall deviation equaled the sum of the clinical and proximal view measurements. The apical level of the large file tip dictated the level at which the measurements were made. Distance between the center of the drawing of the small file and the center of the projected image of the larger file was measured at the level where the ground tip of the large file gave way to its more parallel sides (Fig. 4). Deviation measurements were reported in millimeters taken from the x7 magnified images. Thus, measured values are approximately x7 actual. The evaluations were carried out independently by the two evaluators for both clinical and proximal views of each canal. In cases of disagreement, either in category designation or deviation measurements that differed by more than 0.25 mm, the two evaluators jointly repeated all necessary evaluation steps and arrived at a consensus. Results of the evaluation were not revealed to the operator until all samples had been evaluated and any differences had been resolved. Descriptive, sample mean, and bivariat correlation analyses of the data were performed on a CDC mainframe computer

x

/ IN

1 OUT

FIG 3. File position categories.

FiG 4. File deviation measurement. Measured in millimeters from center of small file drawing to center of the projected image of larger file (shaded).

Comparison of Instrumentation Techniques

Vol. 18, No. 1, January 1992

10-

with the Condescriptive, t test, and scattergram subprograms, respectively, of the SPSS System (13).

23

[ ] Progressive filing: Type A canals • Balanced fomes: Type A canals [ ] Progressive filing: Type B canals Balanced forces: Type B canals

RESULTS Twenty-six canals had type A curvature whereas 24 had type B curvature. This allowed the formation of 25 matched pairs including 13 type A pairs and 12 type B pairs.

(n (.tJ

"6 Analysis of Canal Curvatures For type A canals, the mean clinical angle and the mean proximal angle were 26.6 and 17.6 degrees, respectively. For type B canals, mean values for the clinical, proximal apical, and proximal coronal angles were 27.3, 15.1, and 17.3 degrees, respectively. The sample was subjected to unpaired t tests to determine if the teeth in the matched pair groups were similar in severity of canal curvature. In type A canals, statistical analysis was performed on the mean values of clinical, proximal, and the overall greatest angle in each canal. In type B canals, separate analyses were performed on the mean values of clinical, proximal apical, proximal coronal, overall largest proximal angle, and overall largest angle regardless of view. No significant differences were found in either type of canal (p < 0.05). The analysis of the means of radius quotients demonstrated that there were no significant differences in radius quotients between samples instrumented by each technique (p < 0.05).

Model and Evaluator Reliability No canals were disqualified due to alignment discrepancies. Angle measurements by individual evaluators were within _45 degrees in 125 of 129 (97%) of the cases. Evaluators agreed on the "in" versus "out" categories in 43 of 50 (86%) canals; negotiation was required in 7 of 50 (14%) canals. The evaluators were within the acceptable deviation range of 0.25 mm in 204 of 208 (98%) of the deviation measurements.

Instrumentation Results In eight matched pairs both techniques achieved their respective apical preparation sizes without deviating from the original canal space. In eight other matched pairs, the PE technique was successful whereas the BF technique was not. In another eight pairs, the BF technique was successful and the PE technique was not. In the remaining pair neither technique was successful in attaining the desired apical preparation size. Comparison of instrumentation based on the "in"-"out" designation of the largest instrument used in apical preparation revealed that in type A canals both techniques had 9 of 13 (69.2%) instruments "in". In type B canals both techniques had 7 of 12 (58.3%) of their largest instruments "in" (Fig. 5). In four canals instrumented with the BF technique no file greater than #20 was designated as "in" from either the clinical (INC) or proximal (INP) views. One canal instrumented by the PE technique resulted in no file being "in". Both techniques demonstrated a greater number of the largest files used

.£1

E z

4

IN

OUT

FIG 5. Instrument position results classified according to "in"-"out."

in the apical preparation as "in" in the proximal view than in the clinical view. With the BF technique, 17 of 25 (68%) of the largest files used in apical preparation were "in" in the clinical view whereas in 21 of 25 (84%) canals the largest file was "in" in the proximal view. For the PE technique the largest file was "in" in 17 of 25 (68%) canals in the clinical view and was "in" in 22 of 25 (88%), canals in the proximal view. Statistical analysis (unpaired t test of the three-dimensional or overall deviation of the largest file used in apical preparation in both type A and type B canals revealed no significant difference between the techniques (p < 0.005). Deviation produced by the two instrumeritation techniques was also compared at a common file size or end point. These deviation values were termed equivalent deviations. In other words, the largest file used in apical preparation of the PE technique canal determined the file size at which the deviation for the BF technique canal in the matched pair was measured. Statistical analysis (unpaired t test) revealed the mean equivalent deviation for the PE technique to be significantly greater than that of the BF technique (p < 0.05) for both type A and type B canals. The mean value of equivalent deviation observed with the PE technique was 1.5 to 2.0 times that demonstrate with the BF technique. Bivariat correlation analysis revealed significant linear correlation between the raw clinical view radius measurements and both "in" (positive) and deviation (negative) for type A canals instrumented by the BF technique (p < 0.03). The Pearson's product-moment correlation coefficient squared (r 2) range was 0.4 to 0.52. Furthermore, for type B canals instrumented by the BF technique, significant correlation was found between the raw clinical radius measurements and "in" (positive p < 0.03, r 2 = 0.42) and between the clinical radius quotient and "in" (negative p < 0.01, r 2 = 0 . 5 0 ) . DISCUSSION In this study the BF technique and the PE technique were comparable in their ability to prepare root canals to their

24

Journal of Endodontics

Backman et al.

respective apical preparation sizes. There were no significant differences in deviation or in the number of largest files designated as "in" between the two techniques. However, it should be emphasized that for the BF technique apical preparation was taken to #45 compared with either #30 or #35 for the PE technique. In an attempt to determine whether the "in" classification data from the clinical view (usual clinical radiographic projection) could be used to predict the technique's performance in the proximal view (not available clinically), INC and INP were compared. The results suggest that if an instrument does not deviate from the original canal as seen in a clinical view, then in a majority of the cases the instrument does not deviate in the proximal view. The radius measurements of curves were found to influence the ability of instruments to stay within the canals instrumented by the BF technique. In type A canals, as the clinical radius measurement increased, the "in" file size increased and deviation decreased. In type B canals, as the length of the clinical radius measurement increased, the "in" file size increased. Similarly, as the radius quotient of the clinical angle (clinical angle/clinical radius measurement) decreased, the "in" file size increased. These findings indicate that the BF technique is most successful in achieving final apical size of #45 without deviation when the length of the canal segment over which a curve occurs is relatively long. In type A canals that were successfully instrumented ("in"), both clinical and proximal radius measurements means were approximately twice as large as the respective means in the canals in which instrumentation was not successful ("out"). In successfully instrumented type B canals, the mean radius measurement in the clinical view was approximately one and one-half times that demonstrated in the unsuccessful canals. Roane (8) states that it is the internally directed force applied by the canal wall toward the center of a file during rotation which offsets a smaller restoring force within the file itself and allows canal enlargement through its original axis. The data suggest that at a certain point the severity of canal curvature could result in a restoring force in the file which is larger than the internally directed force applied by the canal wall, resulting in deviation from the original canal axis. The fact that no correlation was found between canal characteristics and the ability to successfully instrument canals with the PE technique may be due to the use of precurved instruments and the manner in which they were manipulated. The procedures used to divide the sample canals between the two instrumentation techniques were worthwhile. With respect to severity of curvature, the use of matched pairs allowed a more equal distribution of the sample between techniques than could be expected from a totally random assignment. Certain aspects of the BF technique are worth mentioning. Because every file is taken to working length, the need to

calculate step-back file lengths as one progresses to larger instruments is eliminated. Once a file is able to be freely rotated in a counterclockwise direction at the working length, it is rotated in a clockwise direction and slowly withdrawn from the canal. After this step, it was common to find the apical 3 to 4 mm of the flutes packed with debris. By using a 360-degree rotation with the BF technique, instrument breakage may be more likely; however, no instrument separation occurred with either technique during the study. The results of this study suggest that both the BF technique and the PE technique can successfully instrument small curved canals. The BF technique instruments these canals to larger apical sizes than is traditionally advocated. The determinant of what constitutes an optimal size of an apical preparation and the relative debridement capabilities of the two techniques require further investigation. This study was supported by the Graduate Endodontics Fund, University of Washington, School of Dentistry, Seattle, WA. The authors wish to acknowledge the assistance of Ms. Maxine Woodall in preparation of the manuscript. Dr. Backman is clinical associate professor, Department of Endodontics, University of Washington, School of Dentistry, Seattle, WA and is presently in private endodontic practice in Seattle. Dr. Oswald is associate professor, Department of Endodontics, University of Washington, School of Dentistry. Dr. Pitts is associate professor and chairman, Department of Endodontics, University of Washington, School of Dentistry. Address requests for reprints to Dr. Charles Backman, Department of Endodontics, SM-48, University of Washington, School of Dentistry, Seattle, WA 98195.

References 1. Weine FS. Endodontic therapy. 3rd ed. St. Louis: CV Mosby Co., 1982:256-317. 2. Schilder H. Cleaning and shaping the root canal. Dent Clin North Am 1974;18:269-96. 3. Mullaney TP. instrumentation of finely curved canals. Dent Clin North Am 1979;23:575-92. 4. Schneider SW. A comparison of canal preparations in straight and curved root canals. Oral Surg 1971;2:271-5. 5. Oswald RJ. Procedural accidents and their repair. Dent Clin North Am 1979;23:593-616. 6. Ingle JI, Taintor JF. Endodontics. 3rd ed. Philadelphia: Lea & Febiger, 1985:195-8. 7. Schilder H, Yee FS. Canal debddement and disinfection. In: Cohen S, Burns RC, eds. Pathways of the pulp. 3rd ed. St. Louis: CV Mosby Co., 1984:175-96. 8. Roane JB. Endodontics in a single visit; teaching syllabus. Oklahoma City: University of Oklahoma Press, 1979:30-41. 9. Roane JB, Sabala CL, Duncanson MG. The "balanced force" concept for instrumentation of curved canals. J Endodon 1985;11:203-11. 10. Powell SE, Simon JHS, Maze BB. A cempadson of the effect of modified and nonmodified instrument tips on apical canal configuration. J Endodon 1986;12:293-300. 11. Oswald RJ, Harrington GW, Natkin E, Pitts DL. A course in endodontic technique. Syllabus. Seattle: University of Washington, School of Dentistry, 1987:81-8, 200-12. 12. Southard DW, Oswald RJ, Natkin E. Instrumentation of curved molar root canals with the Roane technique. J Endodon 1987;13:479-89. 13. Nie NH, Hull CH, Jenkins JG, Steinbrenner K, Bent DH. Statistical package for the social sciences. 2nd ed. New York: McGraw-Hill, 1975.

A radiographic comparison of two root canal instrumentation techniques.

The ability of two instrumentation techniques to negotiate and enlarge small curved canals was com-compared radiographically. Fifty canals in extracte...
1MB Sizes 0 Downloads 0 Views