An in vitro study of the pathfinding ability of a new automated handpiece

An in vitro study of the pathfinding ability of a new automated handpiece

0099-2399/87/1309-0429/$02.00/0 JouRNAL OF ENDODONTICS Copyright 9 1987 by The American AssooatK~nof Endodontists Printed in U.S.A. VOL. 13, NO. 9, ...

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0099-2399/87/1309-0429/$02.00/0 JouRNAL OF ENDODONTICS Copyright 9 1987 by The American AssooatK~nof Endodontists

Printed in U.S.A.

VOL. 13, NO. 9, SEPrEM•ER 1987

SCIENTIFIC ARTICLES An In Vitro Study of the Pathfinding Ability of a New Automated Handpiece Melvin Goldman, DOS, Eriko Sakurai, DDS, Joseph Kronman, DDS, PhD, and Joseph I. Tenca, DOS,MA

The effect of a new automated handpiece on the original canal shape of curved root canals was compared with conventional hand instrumentation. Forty extracted molars with curved roots were randomly divided into two groups. They were mounted in resin boxes and instrumented. Two tracings made from magnified radiographs clearly indicated the extent of the discrepancy of the initial file and the final file. Regardless of the preparation procedures, the files did straighten canals. However, preparation with the new automated handpiece maintained the original canal pathway more closely than did hand instrumentation.

the other hand, a rotating motion which is generated by engine-driven instruments, such as the Giromatic handpiece, causes many obvious problems in curved canals (12-15). The purpose of this study was to compare a new engine-driven technique, which is geared to impart lengthwise vibratory motion to an endodontic file, with a conventional hand instrumentation technique. The Societe Endo Technic (Endo Technic Corp., Natick, MA) contra angle (Fig. 1) moves the file only in an up and down direction. There is no rotation. There is also a clutch action which allows the file to stop working when too great a resistance is met. This ensures that if the curve is not being negotiated, the file will not create its own canal. When it is used with a low-speed handpiece at 500 rpm, the amplitude of movement is 1 mm. At 2000 rpm and higher, the amplitude is 0.3 mm. When the resistance is too great, there is no movement at all. The instrument also has the property of moving in the direction of any force placed on the tip. Thus, the convex portion of the curve tends to move the instrument in the direction of the curve. This is called a helicoid motion and allows the instrument to automatically follow the canal path.

An improperly prepared canal would be difficult to seal with any canal-filling technique (1-4). When a finecurved canal is instrumented, every file in the canal, whether precurved or straight, tends to straighten within the canal (1). It may cause root perforation, a zipped apex, or ledge formation (1). Lim and Webber (5) have concluded that the incidence of obtaining an hourglass-shaped root canal preparation increased when root canals of greater curvature were prepared. This problem occurs due to the increasing stiffness of each larger size file. Regardless of the type and make of the file used, canal zipping increased significantly with the increase in file size, especially from 30 to 35 (6). Thus, when an operator endeavors to maintain the curve (1, 4) and to impart a relatively round shape to the canal in cross-section (7-10), it cannot be obtained. Weine et al. (1) stated that, in curved canals, an hourglass appearance always occurs with the various preparation techniques, including those that depended mainly on reaming and quarter-turn filing, rasping, or a Combination. When a canal was prepared past the foramen, the apical foramen portion was enlarged to produce a teardropped-shaped opening. In the extracted tooth, canal preparation would have easily resuited in overextension of the enlarging instruments because of the easy exit of the apical foramen (11). On

FIG 1. SET contra angle with file. 429

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Goldman et al.

MATERIALS AND METHODS

Forty extracted human molars with curved roots that had mature apices were utilized in this study. The straight roots of these teeth were resected away, and a curved root on each tooth was saved. Standard access cavities were made on these teeth, and the orifices of the 40 canals were located. They were then randomly divided into two groups with 20 teeth in each group. To determine the ability of the pathfinder, 20 canals of group A were penetrated to the foramen with # 8 or 10 K files by hand. The other 20 canals of group B were penetrated with # 8 or 10 pathfinder files in the Endo Technic contra angle, hereafter called SET angle. The teeth that had negotiable canals were selected for further study. The canal length was obtained by measuring the initial file length to the apical foramen, and the file was replaced in the canal. A small ball of soft wax was placed on the tip of the root, and the direction of root canal curvature was ascertained. These teeth were then mounted in clear resin boxes with self-curing acrylic resin, so that the teeth could be repeatedly radiographed in a plane perpendicular to that of the root canal curvature (Fig. 2). A guide file radiograph (control) was made at a standard distance and exposure at 90 degrees. In group A, the root canals were prepared using K-type files (Union Broach, Long Island City, NY) with a circumferential filing action. The apical instrumentation was started with 8 or 10 precurved K files and completed at a 25 precurved file. In group B, the root canals were prepared using the SET angle according to the manufacturer's directions. The sequences were 8 K then 8 H, 10 K then 10 H, 15 K

Journal of Endodontics

then 15 H, and 20 H was the final file. Files used in the SET angle were never precurved. The files designated K were K files in which the corners of the blank were rounded before they were twisted into shape (Fig. 3). This made them true pathfinders, since they do not cut. The designation H meant a Hedstrom file. In both groups, the root canal lengths, which were measured before mounting in the resin boxes, were used as the working distances. During instrumentation, debris was removed by recapitulating and flushing between each instrument with 1 ml of 5.25% NaOCI. There was a final flush of 10 ml of 5.25% NaOCI. Flaring of the canal was done by circumferential filing. The radiograph of the final file in place was made at the same angle, exposure, and distance as the initial one. The radiographs were placed onto a magnifying viewer which magnified 7.8 times (Fig. 4). A tracing of the tooth and the guide file (control) was made in black on transparent plastic sheets. A tracing of the tooth and the final file was made in red on transparent graph paper. The two tracings were overlaid and clearly indicated the extent of discrepancy of the initial and final files (Fig. 5). By using the method of Schneider (10), the curvature of the initial file on the tracing picture was measured.

Usual cross section

Section of SET file with r o u n d e d a n g l e s FIG 3, Dia( ram of the SET file blank before twisting to final shape. Note rounded corners of file.

FiG 2. File in place in tooth mounted in a resin box so that the same angle was maintained for radiography.

FiG 4. Magnifying viewer.

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New Automated Handpiece

The root canal curvature was obtained by drawing one line parallel to the long axis of the file and a second line from the apical foramen to intersect the first line where the root canal leaves the axis of the root canal (Fig. 6). The data were analyzed with x 2 and Fisher's exact probability tests.

FIG 5. Composite overlay of guide file and final file, clearly indicating, any discrepancies.

FIG 6. Method for measuring angulationof the curved canal.

RESULTS Seventeen canals in the hand instrument group and 18 canals in the SET group were negotiable to the foramina with size 8 or 10 files (Table 1 ). These canal curvatures ranged from 19 to 53 degrees and most of the canals showed more than 25 degrees of curvature, which placed them in the severe curvature category (10).

FIG 7. Note the discrepancy of the two files and the marked straightening with the larger size file coronally.This occurred in both groups.

FIG8. Note the marked straighteningwith the largersize file apically-hand instrumentation.

TAmE 1. Incidence of deviation of apical instrumentation

Pathway of Guide File Maintained (n = 20)

Discrepancyfrom Guide File Pathway (n = 15)

Experimental Group

Sample Size

No Difference in Working Distance

Shortened* Working Distance

Ledge Formations

Zipped Apex

Hand instrument SET

17 18

5 5

0 10

2 2

10 1

* Finalfilewas1to 2 mmshortof thefocamenwithoutledgeformationor blockagebydetxis.

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TABLE 2. Relationship between root canal curvature and incidence of discrepancy at apex Hand Instrumentation Canal Curvature

SET

(degrees)

Sample Size (n = 17)

Discrepancy* (n = 12)

Sample Size (n = 18)

Discrepancy* (n = 3)

19-24 25-30 31-40 41-53

4 6 5 2

1 5 4 2

1 7 6 4

0 1 1 1

* Discrepancyat apexwas apparentledgeformationor zippedapex.

DISCUSSION FiG 9. The straightening with the larger size file is much less in this group--SET instrumentation.

FaG 10. The final file is short of the foramen with the SET angle.

Superimposed tracing pictures showed that the coronal half of the canal was straightened in all canals of the~hand instrumentation group (Fig. 7). Coronally, most of the files had moved to the outer aspect of the curve. The final files had moved to the inner aspect between the point where the root canal began to curve and the final 1.5 to 2 mm. Apically, 12 cases showed discrepancies (Fig. 8). There was ledge formation in two cases and zipped foramina in 10 cases. The other five cases in this group showed no discrepancy at the apex (Table 1). The canals were also straightened in the SET group; however, the amount was not as great (Fig. 9). Apically, three SET cases showed discrepancies. Two were ledge formations and one was a zipped foramen. In 10 SET cases, the final file was 1 to 2 mm short of the foramen (Fig. 10). However, the foramen was not blocked, since a smaller size file could be replaced to the working distance (Table 1). The incidence of apical discrepancies according to instrument group could be related with the degree of root canal curvature (Table 2). Chi-square analysis that compared the incidence of apical deviation~was 8.29, which was highly significant (p < 0.01). A further analysis using a Fisher's exact probability test was also highly significant (p < 0.001).

The SET angle seems to show a great deal of promise in maintaining a curve and not making its own path. The pathfinder K file does not cut, since the sharp corners of the blank are rounded off before it is twisted. It is, as its name states, a pathfinder. The H file or Hedstrom file is the cutting instrument and is guided within the canal by the helicoid motion, moving away from the convex portion of the canal. In addition, if too much resistance is encountered, the amplitude of motion drops almost to zero and, thus, there is no cutting action. If this occurs, one simply drops back one size and works the H file a little longer. Then one returns to the next larger size. This maintains the shape of the canal and that of the foramen. The mechanical movement and the circumferential movement of the file by the operator allows the canal to be enlarged sufficiently to accomplish the cleaning and shaping goals with smaller sized, more flexible H files. Since the H file cuts mostly on withdrawal, it cannot, in most cases, push debris ahead of itself. This, plus copious irrigation during the instrumentation, keeps the canal from being blocked. Tables 1 and 2 illustrate clearly that the hand instrument makes its own pathway while the SET file does not when the canal preparation was done to the full length of the root canal. The manufacturer states that, in the curved canal, the largest size instrument should be the 20 H, since circumferential filing with the handpiece is more efficient than when done by hand. Thus, even though the hand instrument group went to #25, the same cleansing can be accomplished by #20 H in the SET angle. Suprisingly, there were other discrepancies noted in the enlarging procedure. Generally, it has been assumed that the discrepancies in a curved canal occurred only at the foramen. A number of cases in this study were seen where the canal was not followed even 5 or 6 mm from the apex at the beginning of the curve (Fig. 11). This indicates that even this portion of the canal may not be cleaned as thoroughly as we would like it to be. There were very large differences as the coronal orifices, which could also mean that coronal areas of the canal are not instrumented. This

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This study was supported by a grant from Endo Technic Corp. (Natick, MA). Dr. Goldman is a clinical professor in endodontics, Tufts University School of Dental Medicine, Boston, MA. Dr. Sakural is a visiting assistant professor in endodontics, Tufts University School of Dental Medicine, and assistant professor in endodontics, Tokyo Dental College, Tokyo, Japan. Dr. Kronman is a professor in orthodontics and gross anatomy, Tufts University School of Dental Medick'~. Dr. Tenca is a professor and chairman in endoclontics, Tufts University School of Dental Medicine.

References

FgG 11. A and B, Note the discrepancies in these cases in the middle one third o f the canal. This is also clear in Figs. 7, 8, and 10.

1. Welne FS, K ~ y RF, Lio PJ. The effect of preparation procedures on original canal shape and on apical foramen shape. J Endodon 1975;1:255-62. 2. Brown BD, Kafrawy AH, Patterson SS. Studies of Sargenti technique of eododontics-autoradiograp~ic and scanning electron microscope studies. J Endodon 1979;5:14-9. 3. AMison DA, Weber CR, Walton RE. The influence of the method of canal preparation on the quality of apical and coronal obturation. J Endodon 1979;5:298-304. 4. Welne FS, Healey HJ, Gersteln H, Evanson L. Pre-curved files and incremental instrumentation for root canal enlargement. J Can Dent Assoc

1970;36:155-7.

leads us to believe that more of the canal than we realized may be left uninstrumented. SUMMARY AND CONCLUSIONS Mechanical instrumentation with the SET angle followed the path of curved canals far more closely than did hand instrumentation with rotated K files. When a guide file radiograph (control) and a final file radiograph were superimposed, these differences were clearly seen. In addition, other portions of the canal may not be instrumented as thoroughly as we formerly believed. Further investigations are presently being conducted with the scanning electron microscope and silicone models.

5. Lira KC, Webber J. The effect of root canal preparation on the shape of the curved root canal. Int Endodon J 1985;18:233-9. 6. Eldeeb ME, Boraas JC. The effect of different files on the preparation shape of severely curved canals. Int Endodon J 1985;18:1-7. 7. Jungmann CL, Uchin RA, Bucher JF. Effect of instrumentation on the shape of the root canal. J Endodon 1975;1:66-9. 8. Vessey RA. The effect of filing versus roaming on the shape of the prepared root canal. Oral Surg 1969;27:543-7. 9. Walton RE. Histo/ogic evaluation of different methods of enlarging the pulp canal space. J Endodon 1976;2:304-11. 10. Schneider SW. A comparison of canal preparations in straight and curved root canals. Oral Surg 1971 ;32:271-5. 11. Palmer MJ, Weine FS, Healey HJ. Position of the apical foramen in relation to endodontic therapy. J Can Dent Assoc 1971;37:305-8. 12. Harry FJ, Stock CJR. The giromatic system compared with hand instrumentation in endodontics. Br Dent J 1974;137:239-44. 13. O'Connelt DT, Brayton SM. Evaluation of root canal preparation with two automated eododontic handpieces. Oral Surg 1975;39:298-303. 14. Weine FS, Kelly RF, Bray KE. Effect of preparation with endodontic handpieces on original canal shape. J Endodon 1976;2:298-303. 15. Frank AL. An evaluation of the Giromatic endodontic handpiece. Oral Surg 1967;24:419-21.