0099-2399/90/1605-0230/$02.00/0 JOURNAL OF ENDODONTICS Copyright 9 1990 by The American Association of Endodontists
Printed in U.S.A. VOL. 16, No. 5, MAY 1990
Comparison of Mechanical and Standard Hand Instrumentation Techniques in Curved Root Canals Juan M. Campos, DDS, and Carlos del Rio, DDS
when resistance is met, and produces a quarter turn rotation that guides the file in the path of the root canal. The system uses specially designed K files made out of square blanks in which the corners have been rounded. When twisted, a dull file is produced which is used as a pathfinder. Hedstrom files are used with the handpiece for cleaning and shaping the root canal. A study of the CFS in extracted human molars concluded that the CFS follows the curvature of the root canals closer than hand instrumentation. The investigators recommended that further investigation was necessary (13). In plastic blocks with simulated root canals, the CFS was efficient with no reported complications (14). A scanning electron microscopic evaluation of the CFS in curved root canals of extracted human premolars and molars showed that many of the curved canals were straightened. The inner wall of dentin was enlarged and there was frequent destruction of the apical constriction. There was no ledge formation (15). Investigators have used different methods to evaluate the cleaning and shaping of root canals. These methods include microscopic, plastic block, and pre- and postinstrumentation radiographic evaluations (5, 12, 16, 17). The previous microscopic methods only observed the postinstrumentation results, producing inaccurate evaluations based on the examiners' estimate of root canal preinstrumentation shape. The use of plastic blocks allows visualization of instruments working inside the canal, but failed to duplicate intricacies of the root canal system or dentin hardness. Radiographic evaluation methods gave pre- and postinstrumentation pictures of three-dimensional root canal systems in only two planes. A method has been introduced (18) and modified (19) in which root canals can be observed before and after instrumentation using extracted human teeth. The roots are encased in plastic blocks and crosscuts are made through the cervical, middle, and apical thirds. Preinstrumentation stereomicroscopic photographs are made of the root sections and the blocks are reassembled in their molds for instrumentation. After instrumentation, the blocks are disassembled and photographs are again made. The pre- and postinstrumentation photographs are then compared for changes in the position of the root canal in the root, changes in canal shape, and differences in the amount of dentin removed. This new methodology makes qualitative and statistical studies of the cleaning and shaping of the root canal possible. The purpose of this investigation was to compare the effects of the Canal Finder System with a standard hand instrumentation technique after instrumentation. The techniques were
The original and postinstrumentation shapes of the mesial root canal system of 12 mandibular molars were compared after being instrumented with a mechanical handpiece and a hand instrumentation technique. Area of dentin removed and amount and direction of transportation were evaluated in relation to degree of root canal curvature. Pre- and postinstrumentation measurements were taken of the root canal system in the cervical, middie, and apical thirds. The mechanical handpiece removed dentin and transported the root canal more than the hand instrumentation in the cervical and apical thirds. Both techniques transported to the distal in the cervical third and to the mesial in the apical third. In the middle third, the mechanical handpiece transported more to the mesial and the hand instrumentation more to the distal. Degree of root canal curvature had no influence on the amount of dentin removed or transportation of the root canal.
Many methods have been developed to solve the problem of zipping, transporting, or perforating the curved root canal system during cleaning and shaping (1-4). As the degree of curvature of the root canal increases, the incidence of zipping or making an hourglass preparation in the apical third of the canal increases. Sequential progression to larger instruments during cleaning and shaping procedures results in decreased flexibility and increased rigidity of instruments which increases zipping in the apical third of the root canal (5, 6). Originally, hand instruments like files, reamers, Hedstrom files, and broaches were designed for cleaning and shaping root canals. These instruments have been adapted to be used in automated handpieces like the Giromatic (Giro MicroMega S., Geneva, Switzerland), the W + H endodontic contraangle (Dentalwork Buermoos Salzburg, Austria), the Canal Finder System (Endo Technique Corp., Newton, MA), and sonic and ultrasonic handpieces (6-11). The adaption of these hand instruments to mechanical handpieces produced a more aggressive cutting instrument and increased the problems of transportation and perforation of the root canal (10-12). The Canal Finder System (CFS), a technique utilizing engine-driven instruments, has a special handpiece that produces an up and down motion of the file, disengages the file
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compared as to the alteration of the shape of the root canal, amount of dentin removed, and the amount and direction of transportation of the root canal. MATERIALS AND METHODS After hemisection, mesial roots of mature extracted mandibular first and second molars were radiographed. A smooth broach was inserted into each root canal to the apical foramen to delineate the root canal system. Twelve roots with two separate root canals (24 canals) and curvatures from 20 to 30 degrees were selected for the investigation. At the same time, working lengths 0.5 m m from the foramen were visually determined. Horizontal lines were drawn onto each root 1.5 m m coronally from the apical foramen, at the height of the root canal curvature, and 1.5 m m apically from the canal orifices. The root canal orifices and foramina of each root were sealed with sticky wax. The roots were embedded in clear casting resin (Chemco Resin Crafts, Dublin, CA) using brass molds (Fig. 1). The cervical surface of the roots was kept at the top surface of the plastic block for accessibility to the root canal orifices during instrumentation. After complete polymerization of the resin, the blocks were removed from the brass molds and cut perpendicular to the root canal at the three levels previously marked (Fig. 1). A diamond wafering blade 0.3-mm thick (Buehler Ltd., Lake Bluff, IL) in an Isomet low-speed saw (Buehler Ltd., Evanston, IL) was used. The cervical, height o f the curve, and apical resin sections of each root canal were encoded and marked with a red dot to identify the coronal side and the location of the mesiofacial canal. The root canals in each section were filled with blue inlay wax (Fig. 2A) (Sybron Kerr, Romulus, MI). A n impression of the apical side of each resin section was made with green stick compound and glued onto the center o f a microscopic glass slide (Fig. 1). The resin sections mounted in the impression were placed in a centering jig under a stereomicroscope with a camera (Zeiss, Oberkochen, West Germany). The sections were photographed at x3 with Kodak EPY-50 color slide film.
FiG 1. Brass mold (a) used to embed the root in clear casting resin to form a plastic block (b). Plastic block was cut into sections, marked to identify the coronal side and location of the mesiofacial canal (arrowhead), and mounted onto a microscopic slide (c).
FIG 2. Photomicrograph of preinstrumentation (A) and postinstrumentation (B) sections at height of curvature. Note size, shape, and location of the original root canals. Dashed line in A shows Xl, the preinstrumentation distance from the root canal to the closest border of the root after direction of transportation was determined. Dashed line in B shows X2, the postinstrumentation distance from the root canal to the closest border of the root. Arrowhead denotes mesiofacial surface. Mesiofacial canal instrumented with Canal Finder System. Mesiolingual canal instrumented with hand instrumentation (original magnification x3).
The blue inlay wax removed from each root canal with a smooth broach. Rubber base adhesive (L. D. Caulk, Milford, DE) was applied to the periphery of each resin section to prevent leakage of the irrigating solution and the blocks were reassembled in the corresponding brass molds. The 24 root canals were divided into two main groups according to the technique used: canals to be instrumented by the CFS (group 1) and canals to be instrumented by hand instrumentation (group 2). Each group had six facial and six lingual root canals and an equal representative selection of root canal curvatures. The buccal and lingual canals in each root were instrumented by a different technique. Teeth in group 1 were instrumented with the CFS following the directions provided by the manufacturer (8) and the personal instruction of Dr. Guy Levy, inventor of the CFS. The instrumentation was divided into pathfinding and enlargement of the canals. The pathfinding instrument was a K-
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type file (K) modified to be flexible and blunt, and the instrument for enlargement was a Hedstrom file (H), whose blades were set at an angle of 75 degrees which produced a more aggressive cutting instrument. The instrumentation sequence for curved canals was performed alternating the pathfinding K files and the Hedstrom files as follows: 8 K, 8 H; 1 0 K , 10 H; 15 K, 15 H ; 2 0 K, 20 H ; 2 5 H a n d 30 H to working length; 35 H and 40 H, 2 to 3 mm, respectively, from the working length; and 50 H to enlarge the middle and cervical third. The pathfinding was performed for 10 s with a down and up pumping motion, and the enlargement was for 45 s with an upward sweeping motion. Group 2 was instrumented with K-Iqex files (Sybron Kerr) using a standard hand instrumentation technique (20). Using circumferential filing, the apical segments were cleaned and shaped to #30 to the working length and sequential step-back instrumentation was performed to #45 in the body of the root canal. Irrigation was performed with 2 ml of 2.6% sodium hypochlorite after each file in both instrumentation techniques. All cleaning and shaping in both techniques were performed by one operator. After instrumentation was accomplished, the molds were disassembled and the root canals were filled with red wax (Fig. 2B) (Sybron Kerr). Postinstrumentation photographs were made in exactly the same manner as the preinstrumentation photographs. A Fixott-Everett grid (Union Broach, New York, NY) was photographed at the same microscopic magnification. Black and white (8 x 10 inch) prints were made from each preoperative (Fig. 2A) and postoperative (Fig. 2B) slide and the slide of the Fixott-Everett grid. The print of the Fixott-Everett grid was used to standardize all of the measurements. All area and distance measurements were obtained from the photographic prints of the root canal sections using a Sigma Scan Program (Jandel Scientific, Corte Madera, CA) in an IBM Personal Computer XT (Personal Computer; IBM Corp., Boca Raton, FL) with a digitized tablet. Two measurements for each area and distance were obtained by one observer and the average was used to minimize any visual error during measurement. Pre- and postinstrumentation root canal areas were measured in square millimeters in each section. The difference between them gave the area of dentin removed from the periphery of the root canal (Fig. 2). Comparison of the original shape of the canal with the postinstrumentation shape provided evaluation of the uniformity of the root canal following instrumentation (Fig. 2). The uneven enlargement or transportation was measured in millimeters. The point of the canal closest to a root border was marked as was the closest point to the canal on the border of the root. A measurement of the distance between the two points was made and recorded as X2 (dashed line, Fig. 2B). The same points were located and marked in the postinstrumentation print, and the distance between them was measured and recorded as X 1 (dashed line, Fig. 2A). The distance that the root canal was transported was the difference between X I (the preinstrumentation distance) and X2 (the postinstrumentation distance). A t test was used to compare the differences in area of dentin removed and amount of transportation between the two techniques. Since both techniques were performed in the same root, paired t tests were used to statistically analyze the data at each level the root was cut. The level of significance was p < 0.05.
Journal of Endodontics
Analysis of variance was used to predict the dependability of the area of dentin removed and amount of transportation in relation to the angulation of the root canal.
RESULTS Direction of Transportation CERVICAL LEVEL The results showed that the CFS transported to the distal in 12 canals (100%); the hand instrumentation transported to the distal in 11 canals (91.7%) and to the facial in 1 canal (8.3%) (Table 1). H E I G H T OF C U R V A T U R E LEVEL The CFS transported seven canals to the mesial (58.3%), four canals to the distal (33.3%), and one canal remained centered (8.3%); the hand instrumentation transported four canals to the mesial (33.3%), seven canals to the distal (58.3%), and one canal remained centered (8.3%) (Table 1). APICAL LEVEL The CFS transported eight canals (66.7%) to the mesial, one canal to the distal (8.3%), and three canals remained centered (25%); the hand instrumentation had seven canals (58.3%) transported to the mesial and five canals remained centered (41.7%) (Table 1). There was only one instance of canal perforation at the apical level. This was with the CFS.
Area of Dentin Removed CERVICAL LEVEL The mean area of dentin removed by the CFS was 0.72 mm 2. This was significantly greater than the mean area of dentin removed by the hand instrumentation which was 0.47 m m 2 (p -- 0.008) (Fig. 3). H E I G H T O F CURVE LEVEL The mean values were not significantly different (Fig. 3).
TJUBLE 1. Direction of transportation
CFS
Hand Instrumentation
Level 12 Root Canals
12 Root Canals
Cervical
Distal, 12 (100%)
Height of the curve
Mesial, 7 (58.3%) Distal, 4 (33.3%) Center, 1 (8.3%) Mesial, 8 (66.7%) Distal, t (8.3%) Center, 3 (25%)
Distal, 11 (91.7%) Facial, 1 (8.3%) Mesial, 4 (33.3%) Distal, 7 (58.3%) Center, 1 (8.3%) Mesial, 7 (58.3%) Center, 5 (41.7%)
Apical
Hand and Mechanical Instrumentation
/ol. 16, No. 5, May 1990 I-
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233
I"
I~'~CFS
0.9-
0.9-
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0.8-
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E 0.5-
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~
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0.3C3 0.2-
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0. ICervical
*
Height
***
Apical
of
Curvature * d f - l l , t-value=3.23,
p.O.OOB * * df =11, t -value= 0.31, p-0.761 * * * d f = II, l-value = ;).41, p= 0.035
:lG 3. Graph of area of dentin removed for the CFS and hand nstrumentation (HI) techniques at cervical, height of curvature, and tpical levels.
e~PICAL LEVEL The mean area of dentin removed in the apical level by the ~FS was 0. I 1 mm 2. This was significantly greater than the mean area of dentin removed by the hand instrumentation ~r was 0.06 m m 2 (p = 0.035) (Fig. 3).
Distance Transported CERVICAL LEVEl. The mean transportation by the CFS was 0.42 mm. This r162 significantly greater than the mean transportation by the aand instrumentation which was 0.28 m m (p = 0.038) (Fig. 0. HEIGHT O F THE CURVE LEVEL The mean values were not significantly different (Fig. 4). e~PICAL LEVEL The mean transportation by the CFS was 0.42 mm. This 0vas significantly greater than the mean transportation by the aand instrumentation which was 0.17 mm (p = 0.019) (Fig. ~). The average curvature of the root canals instrumented with -he CFS was 23.83 degrees and 23.25 degrees with hand nstrumentation. The results of the analysis of variance did not show a relationship between the area of dentin removed 3r amount of transportation and the angulation of root canal -urvature. DISCUSSION Although plastic models have their limitations, they appear :o give a reliable picture of the way instruments work in the
"7
0 *
Cervical
** Height
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***Apical
Curvature * d f , l l , t-value,2.36, p , 0 . 0 3 8 * * d f ' l l , t-volue- I.ST, p , 0 . 1 4 4 * * * d f = l l , t-value, Z.80, p,O.OI9
FiG 4. Graph of amount of transportation performed by the CFS and hand instrumentation (HI) techniques at cervical, height of curvature, and apical levels.
root canal system. Plastic models with simulated root canals have been used for the study of the CFS. Tronstad and Niemczyk (14) concluded that the CFS did not straighten curved canals nor cause zipping of the apical foramen. Their results are completely different from those in our study. This may be because simulated canals in plastic models do not completely represent the natural anatomy of the root canal and the plastic material used was harder than dentin. In natural teeth with the modified Bramante's technique (19), a three-dimensional view of the canals at different levels can be observed and measured pre- and postinstrumentation. Therefore, in our study, the CFS showed transportation of the canals with zipping most of the root sections. Radiographic studies in natural teeth can only evaluate one view of the root canal system, usually the faciolingual. This limitation may be the reason why reported results of transportation and zipping are so low in some studies. Goldman et at. (13) reported only 3 of 18 teeth (16.66%) with transportation when the CFS was used in comparison to 100% with our study. Furthermore, a 20 H instrument was the largest instrument they used to the working length. On the other hand, we used a 30 H to the working length in our study for three reasons: it was more clinically acceptable in order to accomplish a better obturalion, the curvature of the canals was between 20 and 30 degrees, and the same size was used as with hand instrumentation. The area of dentin removed by the CFS, using the sequence of instrumentation in this study, may jeopardize the integrity of the canal system in most of the roots. This may be critical in the cervical level of the root canal where more root structure was removed toward the furca and in the apical level where transportation and zipping was evident. A scanning electron microscopic study performed by Haikel and Allemann (15) showed that many of the curved canals instrumented with the CFS were straightened and that the inner wall of dentin was enlarged with destruction of the apical constriction. Our study corroborated their observations that transportation (canal straightened and inner wall enlarged) and zipping (destruction of the apical constriction)
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Campos and del Rio
were seen with the CFS. With their methods there were no true controls since they were not able to observe the root canal system before instrumentation. Our study used the photographic records of the root canal system before instrumentation as controls and compared them with postinstrumentation photographs. The hand instrumentation technique transported the original shape of the root canal system in most of the teeth. This finding corroborated several studies performed with hand instrumentation (5, 6, 12). The tendency of a stainless steel file to straighten during filing motion tends to transport the root canal in the cervical level toward the mesial, in the middle level toward the distal, and in the apical level toward the mesial. This study showed a tendency for both techniques to transport in the cervical level to the distal and in the apical level toward the mesial. At the height of the curve, the CFS tended to transport more mesiaUy (seven canals) than distally (four canals) whereas the hand instrumentation tended to do the opposite, more distally (seven canals) than mesially (four canals). The distal transportation in the cervical level can be explained by the tendency of the operator to remove the instrument by forcing it toward the distal. In the apical level transportation followed the straightening forces of the instrument, but in the middle level it appears that no rule was followed and transportation occurred either mesially or distally. The analysis of variance test showed no relationship between the area of dentin removed or the amount of transportation and the angulation of the root canals. This may be due to the low angulations of the root canals or to the small size of the sample. The authors wish to thank Mr. Robert Wood and Mr. Lea Pasquali for the statistical and computer analysis (Computing Resources) and Dr. Steve Montgomery for his interest and help in the elaboration of this article. Dr. Campos is an endodontic postdoctoral student, Department of Endodontics, University of Texas Health Science Center Dental School at San
Journal of Endodontics Antonio, San Antonio, TX. Dr. del Rio is professor and chairman, Department of Endodontics, University of Texas Health Science Center Dental School at San Antonio.
References 1. Abou-Rass M, Frank AL, Glick DH. The anticurvature filing method to prepare the curved root canal. J Am Dent Assoc 1980; 101:792-4. 2. Goerig AC, Michelich RJ, Schultz HH. Instrumentation of root canals in molars using the step-down technique. J Endoden 1982;8:550-4. 3. Mullaney TP. Instrumentation of finely curved canals. Dent Clin North Am 1979;23:575-92. 4. Roane JB, Sabala CL, Duncanson MG. The "balanced force" concept for instrumentation of curved canals. J Endodon 1985;11:203-11. 5. Welne FS, Kelly RF, LIO PJ. The effect of preparation procedures on original canal shape and on apical foramen shape. J Endodon 1975;1:255-62. 6. EIDeeb ME, Boraas JC. The effect of different files on the preparation shape of severely curved canals. Int Endod J 1985;18:1-7. 7. Cohen S, Bums RC. Pathways of the pulp. 4th ed. St. Louis: CV Mosby, 1987:170-8. 8. Canal Finder System, Directions for use. Endo Technic Corp., Natick, MA. 9. O'Connell DT, Brayton SM. Evaluation of root canal preparation with two automated endodontic handpieces. Oral Surg 1975;39:298-303. 10. Weine FS, Kelly RF, Bray KE. Effect of preparation with endodontic handpieces on original canal shape. J Endodon 1976;2:298-303. 11. Frank AL. An evaluation of the Giromatic endodontic handpiece. Oral Surg 1967;24:419-21. 12. Walker TL, del Rio CE. Histotogic evaluation of ultrasonic and sonic instrumentation of curved root canals. J Endodon 1989;15:49-59. 13. C-,-,-,-,-,-,-,-,~man M, Sakurai E, Kronman J, Tence Jl. An in vitro study of the pathfinding ability of a new automated handpi~7,e. J Endodon 1987;13:42933. 14. Tronstad L, Niemczyk SP. Efficacy and safety tests of six automated devices for root canal instrumentation. Endod Dent Traumato11986;2:270-6. 15. Haikel Y, Allemann C. Effectiveness of four methods for preparing root canals: a scanning electron microscopic evaluation. J Endodon 1988;14:3405. 16. Cimis GM, Boyer TJ, Pelleu GB. Effect of three file types on the apical preparations of moderately curved canals. J Endodon 1988;14:441-4. 17. Powetl SE, Simon JH, Maxe BB. A comparison of the effect of modified and nonmodified instrument tips on apical canal configuration. J Endodon 1986;12:293-300. 18. Bramante CM, Berbert A, Borges AP. A methodology for evaluation of root canal instrumentation. J Endodon 1987; 13:243-5. 19. Calhoun G, Montgomery S. The effect of four instrumentation techniques on root canal shape. J Endodon 1988;14:273-7. 20. Grossman LI, Oliet S, del Rio, CE. Endodontic practice. 11th ed. Philadelphia: Lea & Febiger, 1988:206-8.
Printed in U.S.A. VOL. 16, No. 5, MAY 1990
Comparison of Mechanical and Standard Hand Instrumentation Techniques in Curved Root Canals Juan M. Campos, DDS, and Carlos del Rio, DDS
when resistance is met, and produces a quarter turn rotation that guides the file in the path of the root canal. The system uses specially designed K files made out of square blanks in which the corners have been rounded. When twisted, a dull file is produced which is used as a pathfinder. Hedstrom files are used with the handpiece for cleaning and shaping the root canal. A study of the CFS in extracted human molars concluded that the CFS follows the curvature of the root canals closer than hand instrumentation. The investigators recommended that further investigation was necessary (13). In plastic blocks with simulated root canals, the CFS was efficient with no reported complications (14). A scanning electron microscopic evaluation of the CFS in curved root canals of extracted human premolars and molars showed that many of the curved canals were straightened. The inner wall of dentin was enlarged and there was frequent destruction of the apical constriction. There was no ledge formation (15). Investigators have used different methods to evaluate the cleaning and shaping of root canals. These methods include microscopic, plastic block, and pre- and postinstrumentation radiographic evaluations (5, 12, 16, 17). The previous microscopic methods only observed the postinstrumentation results, producing inaccurate evaluations based on the examiners' estimate of root canal preinstrumentation shape. The use of plastic blocks allows visualization of instruments working inside the canal, but failed to duplicate intricacies of the root canal system or dentin hardness. Radiographic evaluation methods gave pre- and postinstrumentation pictures of three-dimensional root canal systems in only two planes. A method has been introduced (18) and modified (19) in which root canals can be observed before and after instrumentation using extracted human teeth. The roots are encased in plastic blocks and crosscuts are made through the cervical, middle, and apical thirds. Preinstrumentation stereomicroscopic photographs are made of the root sections and the blocks are reassembled in their molds for instrumentation. After instrumentation, the blocks are disassembled and photographs are again made. The pre- and postinstrumentation photographs are then compared for changes in the position of the root canal in the root, changes in canal shape, and differences in the amount of dentin removed. This new methodology makes qualitative and statistical studies of the cleaning and shaping of the root canal possible. The purpose of this investigation was to compare the effects of the Canal Finder System with a standard hand instrumentation technique after instrumentation. The techniques were
The original and postinstrumentation shapes of the mesial root canal system of 12 mandibular molars were compared after being instrumented with a mechanical handpiece and a hand instrumentation technique. Area of dentin removed and amount and direction of transportation were evaluated in relation to degree of root canal curvature. Pre- and postinstrumentation measurements were taken of the root canal system in the cervical, middie, and apical thirds. The mechanical handpiece removed dentin and transported the root canal more than the hand instrumentation in the cervical and apical thirds. Both techniques transported to the distal in the cervical third and to the mesial in the apical third. In the middle third, the mechanical handpiece transported more to the mesial and the hand instrumentation more to the distal. Degree of root canal curvature had no influence on the amount of dentin removed or transportation of the root canal.
Many methods have been developed to solve the problem of zipping, transporting, or perforating the curved root canal system during cleaning and shaping (1-4). As the degree of curvature of the root canal increases, the incidence of zipping or making an hourglass preparation in the apical third of the canal increases. Sequential progression to larger instruments during cleaning and shaping procedures results in decreased flexibility and increased rigidity of instruments which increases zipping in the apical third of the root canal (5, 6). Originally, hand instruments like files, reamers, Hedstrom files, and broaches were designed for cleaning and shaping root canals. These instruments have been adapted to be used in automated handpieces like the Giromatic (Giro MicroMega S., Geneva, Switzerland), the W + H endodontic contraangle (Dentalwork Buermoos Salzburg, Austria), the Canal Finder System (Endo Technique Corp., Newton, MA), and sonic and ultrasonic handpieces (6-11). The adaption of these hand instruments to mechanical handpieces produced a more aggressive cutting instrument and increased the problems of transportation and perforation of the root canal (10-12). The Canal Finder System (CFS), a technique utilizing engine-driven instruments, has a special handpiece that produces an up and down motion of the file, disengages the file
230
Vol. 16, No. 5, May 1990
Hand and Mechanical Instrumentation
231
compared as to the alteration of the shape of the root canal, amount of dentin removed, and the amount and direction of transportation of the root canal. MATERIALS AND METHODS After hemisection, mesial roots of mature extracted mandibular first and second molars were radiographed. A smooth broach was inserted into each root canal to the apical foramen to delineate the root canal system. Twelve roots with two separate root canals (24 canals) and curvatures from 20 to 30 degrees were selected for the investigation. At the same time, working lengths 0.5 m m from the foramen were visually determined. Horizontal lines were drawn onto each root 1.5 m m coronally from the apical foramen, at the height of the root canal curvature, and 1.5 m m apically from the canal orifices. The root canal orifices and foramina of each root were sealed with sticky wax. The roots were embedded in clear casting resin (Chemco Resin Crafts, Dublin, CA) using brass molds (Fig. 1). The cervical surface of the roots was kept at the top surface of the plastic block for accessibility to the root canal orifices during instrumentation. After complete polymerization of the resin, the blocks were removed from the brass molds and cut perpendicular to the root canal at the three levels previously marked (Fig. 1). A diamond wafering blade 0.3-mm thick (Buehler Ltd., Lake Bluff, IL) in an Isomet low-speed saw (Buehler Ltd., Evanston, IL) was used. The cervical, height o f the curve, and apical resin sections of each root canal were encoded and marked with a red dot to identify the coronal side and the location of the mesiofacial canal. The root canals in each section were filled with blue inlay wax (Fig. 2A) (Sybron Kerr, Romulus, MI). A n impression of the apical side of each resin section was made with green stick compound and glued onto the center o f a microscopic glass slide (Fig. 1). The resin sections mounted in the impression were placed in a centering jig under a stereomicroscope with a camera (Zeiss, Oberkochen, West Germany). The sections were photographed at x3 with Kodak EPY-50 color slide film.
FiG 1. Brass mold (a) used to embed the root in clear casting resin to form a plastic block (b). Plastic block was cut into sections, marked to identify the coronal side and location of the mesiofacial canal (arrowhead), and mounted onto a microscopic slide (c).
FIG 2. Photomicrograph of preinstrumentation (A) and postinstrumentation (B) sections at height of curvature. Note size, shape, and location of the original root canals. Dashed line in A shows Xl, the preinstrumentation distance from the root canal to the closest border of the root after direction of transportation was determined. Dashed line in B shows X2, the postinstrumentation distance from the root canal to the closest border of the root. Arrowhead denotes mesiofacial surface. Mesiofacial canal instrumented with Canal Finder System. Mesiolingual canal instrumented with hand instrumentation (original magnification x3).
The blue inlay wax removed from each root canal with a smooth broach. Rubber base adhesive (L. D. Caulk, Milford, DE) was applied to the periphery of each resin section to prevent leakage of the irrigating solution and the blocks were reassembled in the corresponding brass molds. The 24 root canals were divided into two main groups according to the technique used: canals to be instrumented by the CFS (group 1) and canals to be instrumented by hand instrumentation (group 2). Each group had six facial and six lingual root canals and an equal representative selection of root canal curvatures. The buccal and lingual canals in each root were instrumented by a different technique. Teeth in group 1 were instrumented with the CFS following the directions provided by the manufacturer (8) and the personal instruction of Dr. Guy Levy, inventor of the CFS. The instrumentation was divided into pathfinding and enlargement of the canals. The pathfinding instrument was a K-
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Campos and del Rio
type file (K) modified to be flexible and blunt, and the instrument for enlargement was a Hedstrom file (H), whose blades were set at an angle of 75 degrees which produced a more aggressive cutting instrument. The instrumentation sequence for curved canals was performed alternating the pathfinding K files and the Hedstrom files as follows: 8 K, 8 H; 1 0 K , 10 H; 15 K, 15 H ; 2 0 K, 20 H ; 2 5 H a n d 30 H to working length; 35 H and 40 H, 2 to 3 mm, respectively, from the working length; and 50 H to enlarge the middle and cervical third. The pathfinding was performed for 10 s with a down and up pumping motion, and the enlargement was for 45 s with an upward sweeping motion. Group 2 was instrumented with K-Iqex files (Sybron Kerr) using a standard hand instrumentation technique (20). Using circumferential filing, the apical segments were cleaned and shaped to #30 to the working length and sequential step-back instrumentation was performed to #45 in the body of the root canal. Irrigation was performed with 2 ml of 2.6% sodium hypochlorite after each file in both instrumentation techniques. All cleaning and shaping in both techniques were performed by one operator. After instrumentation was accomplished, the molds were disassembled and the root canals were filled with red wax (Fig. 2B) (Sybron Kerr). Postinstrumentation photographs were made in exactly the same manner as the preinstrumentation photographs. A Fixott-Everett grid (Union Broach, New York, NY) was photographed at the same microscopic magnification. Black and white (8 x 10 inch) prints were made from each preoperative (Fig. 2A) and postoperative (Fig. 2B) slide and the slide of the Fixott-Everett grid. The print of the Fixott-Everett grid was used to standardize all of the measurements. All area and distance measurements were obtained from the photographic prints of the root canal sections using a Sigma Scan Program (Jandel Scientific, Corte Madera, CA) in an IBM Personal Computer XT (Personal Computer; IBM Corp., Boca Raton, FL) with a digitized tablet. Two measurements for each area and distance were obtained by one observer and the average was used to minimize any visual error during measurement. Pre- and postinstrumentation root canal areas were measured in square millimeters in each section. The difference between them gave the area of dentin removed from the periphery of the root canal (Fig. 2). Comparison of the original shape of the canal with the postinstrumentation shape provided evaluation of the uniformity of the root canal following instrumentation (Fig. 2). The uneven enlargement or transportation was measured in millimeters. The point of the canal closest to a root border was marked as was the closest point to the canal on the border of the root. A measurement of the distance between the two points was made and recorded as X2 (dashed line, Fig. 2B). The same points were located and marked in the postinstrumentation print, and the distance between them was measured and recorded as X 1 (dashed line, Fig. 2A). The distance that the root canal was transported was the difference between X I (the preinstrumentation distance) and X2 (the postinstrumentation distance). A t test was used to compare the differences in area of dentin removed and amount of transportation between the two techniques. Since both techniques were performed in the same root, paired t tests were used to statistically analyze the data at each level the root was cut. The level of significance was p < 0.05.
Journal of Endodontics
Analysis of variance was used to predict the dependability of the area of dentin removed and amount of transportation in relation to the angulation of the root canal.
RESULTS Direction of Transportation CERVICAL LEVEL The results showed that the CFS transported to the distal in 12 canals (100%); the hand instrumentation transported to the distal in 11 canals (91.7%) and to the facial in 1 canal (8.3%) (Table 1). H E I G H T OF C U R V A T U R E LEVEL The CFS transported seven canals to the mesial (58.3%), four canals to the distal (33.3%), and one canal remained centered (8.3%); the hand instrumentation transported four canals to the mesial (33.3%), seven canals to the distal (58.3%), and one canal remained centered (8.3%) (Table 1). APICAL LEVEL The CFS transported eight canals (66.7%) to the mesial, one canal to the distal (8.3%), and three canals remained centered (25%); the hand instrumentation had seven canals (58.3%) transported to the mesial and five canals remained centered (41.7%) (Table 1). There was only one instance of canal perforation at the apical level. This was with the CFS.
Area of Dentin Removed CERVICAL LEVEL The mean area of dentin removed by the CFS was 0.72 mm 2. This was significantly greater than the mean area of dentin removed by the hand instrumentation which was 0.47 m m 2 (p -- 0.008) (Fig. 3). H E I G H T O F CURVE LEVEL The mean values were not significantly different (Fig. 3).
TJUBLE 1. Direction of transportation
CFS
Hand Instrumentation
Level 12 Root Canals
12 Root Canals
Cervical
Distal, 12 (100%)
Height of the curve
Mesial, 7 (58.3%) Distal, 4 (33.3%) Center, 1 (8.3%) Mesial, 8 (66.7%) Distal, t (8.3%) Center, 3 (25%)
Distal, 11 (91.7%) Facial, 1 (8.3%) Mesial, 4 (33.3%) Distal, 7 (58.3%) Center, 1 (8.3%) Mesial, 7 (58.3%) Center, 5 (41.7%)
Apical
Hand and Mechanical Instrumentation
/ol. 16, No. 5, May 1990 I-
T
233
I"
I~'~CFS
0.9-
0.9-
~'ACFS F-IHI
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~
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0.3C3 0.2-
0.3-
~- o.2-
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0. ICervical
*
Height
***
Apical
of
Curvature * d f - l l , t-value=3.23,
p.O.OOB * * df =11, t -value= 0.31, p-0.761 * * * d f = II, l-value = ;).41, p= 0.035
:lG 3. Graph of area of dentin removed for the CFS and hand nstrumentation (HI) techniques at cervical, height of curvature, and tpical levels.
e~PICAL LEVEL The mean area of dentin removed in the apical level by the ~FS was 0. I 1 mm 2. This was significantly greater than the mean area of dentin removed by the hand instrumentation ~r was 0.06 m m 2 (p = 0.035) (Fig. 3).
Distance Transported CERVICAL LEVEl. The mean transportation by the CFS was 0.42 mm. This r162 significantly greater than the mean transportation by the aand instrumentation which was 0.28 m m (p = 0.038) (Fig. 0. HEIGHT O F THE CURVE LEVEL The mean values were not significantly different (Fig. 4). e~PICAL LEVEL The mean transportation by the CFS was 0.42 mm. This 0vas significantly greater than the mean transportation by the aand instrumentation which was 0.17 mm (p = 0.019) (Fig. ~). The average curvature of the root canals instrumented with -he CFS was 23.83 degrees and 23.25 degrees with hand nstrumentation. The results of the analysis of variance did not show a relationship between the area of dentin removed 3r amount of transportation and the angulation of root canal -urvature. DISCUSSION Although plastic models have their limitations, they appear :o give a reliable picture of the way instruments work in the
"7
0 *
Cervical
** Height
of
***Apical
Curvature * d f , l l , t-value,2.36, p , 0 . 0 3 8 * * d f ' l l , t-volue- I.ST, p , 0 . 1 4 4 * * * d f = l l , t-value, Z.80, p,O.OI9
FiG 4. Graph of amount of transportation performed by the CFS and hand instrumentation (HI) techniques at cervical, height of curvature, and apical levels.
root canal system. Plastic models with simulated root canals have been used for the study of the CFS. Tronstad and Niemczyk (14) concluded that the CFS did not straighten curved canals nor cause zipping of the apical foramen. Their results are completely different from those in our study. This may be because simulated canals in plastic models do not completely represent the natural anatomy of the root canal and the plastic material used was harder than dentin. In natural teeth with the modified Bramante's technique (19), a three-dimensional view of the canals at different levels can be observed and measured pre- and postinstrumentation. Therefore, in our study, the CFS showed transportation of the canals with zipping most of the root sections. Radiographic studies in natural teeth can only evaluate one view of the root canal system, usually the faciolingual. This limitation may be the reason why reported results of transportation and zipping are so low in some studies. Goldman et at. (13) reported only 3 of 18 teeth (16.66%) with transportation when the CFS was used in comparison to 100% with our study. Furthermore, a 20 H instrument was the largest instrument they used to the working length. On the other hand, we used a 30 H to the working length in our study for three reasons: it was more clinically acceptable in order to accomplish a better obturalion, the curvature of the canals was between 20 and 30 degrees, and the same size was used as with hand instrumentation. The area of dentin removed by the CFS, using the sequence of instrumentation in this study, may jeopardize the integrity of the canal system in most of the roots. This may be critical in the cervical level of the root canal where more root structure was removed toward the furca and in the apical level where transportation and zipping was evident. A scanning electron microscopic study performed by Haikel and Allemann (15) showed that many of the curved canals instrumented with the CFS were straightened and that the inner wall of dentin was enlarged with destruction of the apical constriction. Our study corroborated their observations that transportation (canal straightened and inner wall enlarged) and zipping (destruction of the apical constriction)
234
Campos and del Rio
were seen with the CFS. With their methods there were no true controls since they were not able to observe the root canal system before instrumentation. Our study used the photographic records of the root canal system before instrumentation as controls and compared them with postinstrumentation photographs. The hand instrumentation technique transported the original shape of the root canal system in most of the teeth. This finding corroborated several studies performed with hand instrumentation (5, 6, 12). The tendency of a stainless steel file to straighten during filing motion tends to transport the root canal in the cervical level toward the mesial, in the middle level toward the distal, and in the apical level toward the mesial. This study showed a tendency for both techniques to transport in the cervical level to the distal and in the apical level toward the mesial. At the height of the curve, the CFS tended to transport more mesiaUy (seven canals) than distally (four canals) whereas the hand instrumentation tended to do the opposite, more distally (seven canals) than mesially (four canals). The distal transportation in the cervical level can be explained by the tendency of the operator to remove the instrument by forcing it toward the distal. In the apical level transportation followed the straightening forces of the instrument, but in the middle level it appears that no rule was followed and transportation occurred either mesially or distally. The analysis of variance test showed no relationship between the area of dentin removed or the amount of transportation and the angulation of the root canals. This may be due to the low angulations of the root canals or to the small size of the sample. The authors wish to thank Mr. Robert Wood and Mr. Lea Pasquali for the statistical and computer analysis (Computing Resources) and Dr. Steve Montgomery for his interest and help in the elaboration of this article. Dr. Campos is an endodontic postdoctoral student, Department of Endodontics, University of Texas Health Science Center Dental School at San
Journal of Endodontics Antonio, San Antonio, TX. Dr. del Rio is professor and chairman, Department of Endodontics, University of Texas Health Science Center Dental School at San Antonio.
References 1. Abou-Rass M, Frank AL, Glick DH. The anticurvature filing method to prepare the curved root canal. J Am Dent Assoc 1980; 101:792-4. 2. Goerig AC, Michelich RJ, Schultz HH. Instrumentation of root canals in molars using the step-down technique. J Endoden 1982;8:550-4. 3. Mullaney TP. Instrumentation of finely curved canals. Dent Clin North Am 1979;23:575-92. 4. Roane JB, Sabala CL, Duncanson MG. The "balanced force" concept for instrumentation of curved canals. J Endodon 1985;11:203-11. 5. Welne FS, Kelly RF, LIO PJ. The effect of preparation procedures on original canal shape and on apical foramen shape. J Endodon 1975;1:255-62. 6. EIDeeb ME, Boraas JC. The effect of different files on the preparation shape of severely curved canals. Int Endod J 1985;18:1-7. 7. Cohen S, Bums RC. Pathways of the pulp. 4th ed. St. Louis: CV Mosby, 1987:170-8. 8. Canal Finder System, Directions for use. Endo Technic Corp., Natick, MA. 9. O'Connell DT, Brayton SM. Evaluation of root canal preparation with two automated endodontic handpieces. Oral Surg 1975;39:298-303. 10. Weine FS, Kelly RF, Bray KE. Effect of preparation with endodontic handpieces on original canal shape. J Endodon 1976;2:298-303. 11. Frank AL. An evaluation of the Giromatic endodontic handpiece. Oral Surg 1967;24:419-21. 12. Walker TL, del Rio CE. Histotogic evaluation of ultrasonic and sonic instrumentation of curved root canals. J Endodon 1989;15:49-59. 13. C-,-,-,-,-,-,-,-,~man M, Sakurai E, Kronman J, Tence Jl. An in vitro study of the pathfinding ability of a new automated handpi~7,e. J Endodon 1987;13:42933. 14. Tronstad L, Niemczyk SP. Efficacy and safety tests of six automated devices for root canal instrumentation. Endod Dent Traumato11986;2:270-6. 15. Haikel Y, Allemann C. Effectiveness of four methods for preparing root canals: a scanning electron microscopic evaluation. J Endodon 1988;14:3405. 16. Cimis GM, Boyer TJ, Pelleu GB. Effect of three file types on the apical preparations of moderately curved canals. J Endodon 1988;14:441-4. 17. Powetl SE, Simon JH, Maxe BB. A comparison of the effect of modified and nonmodified instrument tips on apical canal configuration. J Endodon 1986;12:293-300. 18. Bramante CM, Berbert A, Borges AP. A methodology for evaluation of root canal instrumentation. J Endodon 1987; 13:243-5. 19. Calhoun G, Montgomery S. The effect of four instrumentation techniques on root canal shape. J Endodon 1988;14:273-7. 20. Grossman LI, Oliet S, del Rio, CE. Endodontic practice. 11th ed. Philadelphia: Lea & Febiger, 1988:206-8.
