0099-2399/88/1401-0007/$02.00/0 JOURNAL OF ENDODONTIC:S Copyr~ht �9 1988 by The American Association of Endodofltists

Printed in U.S.A. VOL. 14, NO. 1, JANUARY 1988

A Comparison of Three Methods of Cleaning and Shaping the Root Canal In Vitro

Melvin Goldman, DDS, Robert R. White, DMD, Charles Ray Moser, DMD, and Joseph I. Tenca, DDS, MA

The purpose of this study was to compare the rela- tive effectiveness of three methods of endodontic instrumentation in vitro: hand instrumentation with K and H files, the Burns unifile, and ultrasonic instru- mentation. Silicone models were used to evaluate the physical appearance of the prepared canals. Scanning electron microscopy was used to evaluate the thoroughness of debridement with each prepa- ration technique.

1. None of the three techniques delivered a clean canal. There was no statistical difference in the three methods.

2. The K file and Hedstrom prepared a smoother, tapered canal more consistently than did the unifile or ultrasonics. The unifile was slightly better than ultrasonics in apical preparation and taper.

Proper biomechanical preparation of the root canal space is considered to be essential for success in endodontic therapy. The objective is the total removal of vital tissue, necrotic debris, and microorganisms from within a root canal system. This goal is attempted using chemomechanical root canal preparation consisting of mechanical debridement and enlargement combined with thorough irrigation utilizing bactericidal solutions. These solutions are also capable of dissolving organic debris (1). The complex nature of the root canal system has been thoroughly documented (2, 3). The results of biomechanical preparation techniques have also been extensively researched.

Gutierrez and Garcia (4) showed many ramifications present within a canal that were consistently untouched using the usual instrumentation filing techniques. Ac- COrding to Davis et al. (5), the inherent anatomy of the root canal system makes present instruments and pro- cedures appear inadequate in reaching our goal, even in canals thought to be "thoroughly" prepared. Mizrahi et al. (6), Moodnik et al. (7), and Bolanos and Jensen (8) using the scanning electron microscope also found that present instruments and techniques are not capa- ble of producing a clean canal. McComb and co-work- ers in both an in vitro (9) and an in vivo (10) study

demonstrated that a completely clean canal was never achieved using existing techniques.

Irrigation studies by Goldman et al. (11-13), Yamada et al. (14), and Baker et al. (15) have demonstrated the importance of irrigation during biomechanical prepara- tion.

In summary, significant emphasis has been placed by many researchers' attempts to improve both our mechanical and chemical cleansing techniques.

Recently, a new technique for instrumentating root canal systems utilizing ultrasonics was introduced by Martin et al. (16). They reported that the dentin-remov- ing ability of the ultrasonic energized files was superior to hand instrumentation. This system is based upon the ultrasonic energizing of a file for mechanical canal preparation and debris removal as well as ultrasonic activation of an irrigant for enhanced penetration, sol- vent, and bacteriocidal action. Specifically, the goal of this system is claimed to be achieved by using a con- stant flow-through irrigation and aspiration with any volume desired up to 45 ml per min. This continuous high volume exchange of irrigating solution is thought to markedly enhance the ability to dissolve, flush, and remove debris. Additionally, ultrasonic energizing of the irrigant creates numerous physicomechanical and phys- icochemical effects that purportedly aid the debriding action of the endosonic file. Cunningham et al. (17) believe that the ultrasonic energy can force a solution in all dimensions. They further hypothesize that ultra- sound, with its cavitational, heating, stirring, agitation, and acoustic streaming, can dislodge debris from sur- faces unreached by mechanical instrumentation.

This study will compare the efficacy of three different techniques, including ultrasound, for instrumenting root canal systems to determine if one of these techniques will provide a more efficient chemomechanical cleaning and shaping of the root canal system.

MATERIALS AND METHODS

Sixty freshly extracted maxillary central incisors were randomly divided into three groups of 20 teeth each: group 1, hand instrumentation (K-type and Hedstrom

8 Goldman et al.

files); group 2, hand instrumentation with the Burn's unifile; and group 3, ultrasonic endodontic instrumen- tation. Standard access preparations were made in all teeth and a #10 file was passed through the apical foramen of each tooth to assure canal patency. The teeth were then luted with acrylic into the appropriate dentoform arch and all subsequent instrumentation was accomplished attempting to mimic a real clinical situa- tion.

Group 1

The working length was established at the foramen in all specimens and then they were instrumented by hand using K-type files with a reaming action until an apical preparation was established three sizes larger than the first file which bound short of the working length. One milliliter of 5.25% NaOCI was used as irrigation after each change in file size. Upon completion of the apical preparation, the canals were flared using step-back filing with the next two larger sizes of Hed- strom files. All work was accomplished in a wet field. When the operator felt that the preparations were complete (ready to fill clinically), they were subjected to a final irrigation using 10.0 ml of 5.25% NaOCI delivered with a 23-gauge needle placed as far as possible into the preparation, without binding. The prepared canals were then dried using paper points and the teeth were stored at 100% humidity at 34~ until further process- ing.

Group 2

Twenty dentoform-mounted teeth were prepared in a similar manner using the standard sizes of the Burn's unifile. The working length was established at the for- amen and the unifile was used with a reaming action to establish an apical preparation three sizes larger than the first file to bind at the working length. The unifiles were then used in a step-back manner similar to the Hedstroms to circumferentially flare the preparation. Irrigation was identical to group 1 instrumentation, as was drying and storage.

Group 3

Ultrasonic instrumentation (Endo-Sonic; L. D. Caulk Co., Milford, DE) was performed on dentoform- mounted teeth according to the manufacturer's instruc- tions at the time this study was done. K files #10 and 15 were placed to the predetermined length and used with a reaming action, until the #15 file was loose in the canal. One milliliter of 5.25% NaOCI was used as irrigation between each change in size. Endosonic files #15, 20, 25, 1-mm short of the working length, were then used with a continuous NaOCI flush of 35 ml per min until the apical preparation was established. The next three sizes of endosonic diamond files (25, 35,

Journal of Endodontics

and 45) were used in a step-back manner to circumfer- entially flare the preparation, again using the same rate of continuous NaOCI flush. Upon completion of instru- mentation, these specimens were dried using paper points and stored as the others.

Each group was then randomly divided into two subgroups of 10 teeth each and all teeth were checked with a #10 file to ensure the patency of the apical foramen. Subgroup A was injected with a syringe-type impression material (Plastosil; J. Bosworth Co., Chi- cago, IL). After mixing according to the manufacturer's directions, the material was syringed into the prepared canal spaces until a slight excess was noted at the foramen. After the material had set, excess at each end was removed with a scalpel blade. These teeth were then decalcified in 5% nitric acid until radiographically complete, rinsed in water, and placed in 5.25% NaOCI until all remaining tooth structure had dissolved. These silicone models were recovered, rinsed, and stored in water until dissecting microscope examination.

Subgroup B was subjected to scanning electron microscopic examination. This processing involved placing shallow longitudinal grooves on the root and coronal aspects of the instrumented teeth, followed by splitting them with a mallet and chisel. Any tooth that showed evidence of groove penetration into the canal was discarded and replaced with another specimen. The paired halves of these teeth were kept together throughout the rest of the processing and examination. Specimen dessication was accomplished in a chamber containing anhydrous CaOS4. The specimens were then coated with approximately 200/~ of gold palladium and examined with a scanning electron microscope (SEM) (Fig. 1).

Evaluation of Silicone Models

For the silicone models, a predetermined scale of 1 (poor) to 4 (excellent) was used to evaluate and grade

FIG 1. Paired halves of tooth prepared for scanning electron micro- scopic viewing.

Vol. 14, No. 1, January 1988

the models when viewed blindly under the dissecting microscope. There were five categories set up and evaluated by the: (a) presence of a defined stop and roundness of the preparations, apical preparation; (b) absence of fins and small projections in the model, apical abberations; (c)lack of roughness or irregularities in the walls of the filling models, smoothness; (d) con- tinuous blending of the access cavity with the canal walls to the apical third, flow; and (e) conical shape of the canal model from the cervical zone to the apical third level, taper.

Five reviewers were carefully briefed as to the mean- ing of each description and then each reviewer evalu- ated all of the models. Efficacy was graded on the predetermined scale of 1 to 4. If a sample received a grade of 1 or 2, it was considered to have a poor/fair quality, whereas a sample that received a grade of 3 or 4 was considered to have a good/excellent quality. This was done to simplify the statistical analysis. A log linear analysis was done to determine differences between treatments and investigators.

Scanning Electron Microscopic Evaluation All halves were thoroughly examined at various mag-

nifications and photomicrographs were made of each half at x150 magnification from the coronal, middle, and apical one-thirds. The location for photography was chosen by calculating the number of turns for the stage shift control to cover the entire tooth length, dividing by three and thus arbitrarily locating a coronal, middle, or apical third location. Once this locus was identified, lateral shift was used only to center the photograph and the data were recorded on Polaroid 665 film.

These photographs were coded and evaluated blindly, in terms of remaining surface debris (Figs. 2 to

Cleaning and Shaping Root Canals 9

FIG 3. Typical example of a canal with a moderate amount of debris (original magnification x150).

FIG 2. Typical example of a canal with a great deal of debris (original magnification •

FIG 4. Typical example of a canal with a small amount of debris (original magnification x150).

4). A standard grid of 100 squares was placed over each original 23/4 x 33/4 print (Fig. 5). The number of squares in which surface debris (hard or soft tissue, smeared layer excepted) filled most of the square were counted independently by two investigators and ex- pressed as a percentage of the total area. A square that demonstrated more than 20% of its surface without noticeable debris of any kind was considered to be clean and was not counted. The scores of the two investigators were then averaged to derive a mean percentage of the area covered for the coronal, middle, and apical one-thirds of each specimen half. All subse- quent calculations were done after arc-sine transfor-

10 Goldman et al.

FIG 5. Photograph of scanning electron microscopic photograph with transparent grid overlay in place.

mation of data to establish homogenicity of variance. A one-way analysis of variance was used to test differ- ences in debris content between canal thirds and be- tween groups.

RESULTS

Silicone Models

The results of the five evaluators in determining the differences between the three different techniques are listed in Table 1. There was a difference between the three instrumentation techniques, p <0.01.

In Table 2, the differences between investigators when evaluating the silicone specimens are listed. It was found that p >0.05 and there were no significant differences between evaluators.

Table 3 represents the percentage of teeth having good quality, i.e. having a rating of 3 or 4, as determined by the mean standard error. The results indicate that in all categories, the K- and H-type files with hand instru- mentation were the best when compared with the endosonic and the Burns U file techniques (Figs. 6 to 8). t When comparing endosonics with the Burns unifile, statistical analysis (Table 3) showed that in aberration removal, smoothness, and flow, there was no signifi- cance (p >0.05), but in the apical preparation and taper, the unifile was significantly better (p <0.01).

Results of Scanning Electron Microscopic Evaluation

A one-way analysis of variance was used to test differences in debris in the coronal, middle, and apical regions of the canals in each group. In Table 4, one can see that there were no significant differences in the various regions of the canals. Since all methods showed no differences between the coronal, middle, and apical

All the teeth used in this study had straight canals. By mistake, the models were placed in individual small test tubes and this caused the models to curve. Thus, the curve is artifact and should be disregarded.

Journal of Endodontics

TABLE 1. Si l icone models: difference between three techniques

Category x 2 p

Apical preparation x 2 =55.22 <0.01 Apical abberation x 2 =36.88 <0,01 Smoothness x 2 =36.87 <0.01 Flow x 2 =16.99 <0.01 Taper x 2 =69.24 <0,01

TABLE 2. Silicone models: difference between investigators

Category x 2 p

Apical preparation =0.31 >0.05 Apical abberation =2.40 >0.05 Smoothness =6.42 >0.05 Flow =7.12 >0.05 Taper =19.26 >0.01

regions of the canal, the values were combined to test for differences between the three methods (Table 5). A one-way analysis of variance was used to test for percentage of surface cleaned using the three methods. The results were not significant, F = 0.622.

DISCUSSION

The search for a better means of accomplishing our goal is endless. The three methods used in this study are not markedly different in preparing a clean canal and thus ultrasonics does not seem to be of any great value when compared with hand instrumentation using either K files or the Burns file.

The second reason for preparing the canal is to establish a shape which lends itself most readily to being filled thoroughly and completely. A smooth, con- tinuously tapering preparation with a round apical prep- aration seems to be the most desirable. The K file approaches this ideal form more closely than the other two methods. The unifile is better than the ultrasonic in two of five categories and thus ultrasonics comes in last. Again, this information must be considered care- fully, for it is by no means totally clear that a definite predetermined shape lends itself to a better filling.

However, the present criteria are the best we have at this time. Judged by these criteria, K files and Hed- stroms are better at obtaining a final desired shape than either the unifile or ultrasonics. None of the three methods delivered a totally clean canal. If one accepts the axiom that "what is taken out of the canal is more important than what is put into it," it becomes obvious that since the techniques for cleaning the canal are not very efficient, the axiom is not being fulfilled. The pres- ent study, utilizing a relatively objective means of de- termining cleanliness, indicates that there is little differ- ence in the three techniques. They all leave behind a residue of debris. Using the SEM, it is difficult some- times to distinguish between hard and soft tissue de- bris. If the debris is, indeed, small chips of dentin removed during the filing process, then perhaps this of

VoL 14, No. 1, January 1988 Cleaning and Shaping Root Canals

TABLE 3. Percentage of teeth having good quality as determined by the mean standard error

11

Group 1 : Group 2: Group 3: K and H Files U File Ultrasonic

Apical preparation 72.00 • 2.00 31.42 • 1.15 6.00 • 2.45 Apical abberation 90.00 • 4.47 44.44 _ 10,55 38.00 • 19.24 Smoothness 90.00 • 3.16 51.12 _+ 12.48 36.00 • 5.10 Flow 76.00 - 5.10 42.29 • 13.34 42.00 • 7.35 Taper 76.00 - 12.88 35.59 • 12.87 4.00 • 2,45

F~G 6. Typical silicone model of canal prepared by endosonics. Note the bulge at the junction of middle and al~cal one-third No stop at apex.

t

,

FIG 8. Typical silicone model of canal prepared with K and H files. Note fairly smooth taper and apical stop.

TASTE 4. Scanning electron microscopic differences in debds in the coronal, middle, and apical regions for each group using

one-way analysis of variance

Group Technique F p

1 K and H files =0.306 Not significant 2 U files =0.340 Not significant 3 Ultrasonic =0.941 Not significant

FIG 7, Typical silw_x)ne model of canal prepared by unifile. Note large bulge in middle one-third and no evidence of stop at apex. (It warped after tooth structure had dissolved.)

small import. The key word is perhaps, for it is not known whether this debris can be harmful; perhaps it is, perhaps it is not. There have been no publications to date that have attempted to assess this parameter. It is assumed that cleanliness and the absence of debris is highly desirable.

If the debris contains soft tissue, then there is another aspect that must be considered. Soft tissue can be- come necrotic and can thus be a snug harbor for microorganisms. It is fairly certain that the presence of microorganisms is not desirable and despite one's best efforts they may not be removed entirely.

TABLE 5. A compadson of the relative appearance of the root canals

Ultrasonic K and H Burns Unifile Instrument Instrument Instrument

Mean Mean Mean Group Score Group Score Group Score

1 58.3 1 60.2 1 59.7 2 50.3 2 51.25 2 64.5 3 49.3 3 52.1 3 57.3

F = 0.622 Not significant

The present results agree with both Langeland et al. (18) and Cymerman et al. (19). Both groups determined that ultrasonics does not seem to clean canals any more efficiently than hand instrumentation.

CONCLUSIONS

Instrumentation with a K file and Hedstrom, the Burns unifile, and endosonics were compared using silicone models and the SEM.

12 Goldman et al.

Silicone Models

1. Under the conditions of this study, the difference between the instrumentation techniques were all signif- icant, in that the K-type file was found to be the best when compared with the endosonic and Burn's unifile.

2. When comparing the endosonic with the Burn's unifile, it was found that the Burn's unifile was signifi- cantly better when evaluating the apical preparation and taper, but when evaluating the apical aberration, smoothness, and flow, there was no significant differ- ence.

Scanning Electron Microscopic Examination

In this study, it appears that a simple objective method of evaluation for debris removal from prepared canals has been devised. Instrumentation with all three techniques resulted in remaining surface debris. There was no significant difference between the three tech- niques.

This study was supported by a grant from L. D. Caulk, Milford, DE.

Dr. Goldman is a clinical professor in endodontics and director of postgrad- uate endodontics, Tufts University School of Dental Medicine, Boston, MA. Dr. White is an assistant professor in endodontics, Tufts University School of Dental Medicine. Dr. Moser is a former postgraduate endodontic student, Tufts University School of Dental Medicine. Dr. Tenca is professor and chairman of endodontics, Tufts University School of Dental Medicine,

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Journal of Endodontics

2. Barker BC. Anatomy of the root canals. Aust Dent J 1974;19:408-13, 3. Hess W. The anatomy of the root canals of the permanent dentition.

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