0099-2399/92/1811-0530/$03.00/0 JOURNAL OF ENDODONTICS Copyright © 1992 by The American Association of Endodontists

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VOL. 18, NO. 11, NOVEMBER1992

Histomorphometric Comparison of Canals Prepared by Four Techniques J. Craig Baumgartner, DDS, PhD, Howard Martin, DMD, Clyde L. Sabala, DDS, Edward J. Strittmatter, Jr., DDS, William L. Wildey, DDS, and Nicholas C. Quigley, DDS

MATERIALS AND METHODS

Numerous methods of root canal preparation have been recommended and used by clinicians. This study used histomorphometrics to determine the area of root canal preparations using four currently popular techniques. Clinicians that were highly skilled in each technique prepared curved canals in acrylic blocks. Each clinician described this technique and discussed the technique with regard to the use of acrylic blocks as compared with dentin. Analysis of the areas of the root canals after preparation revealed a significant difference among the groups. The mean areas after treatment were stepback technique, 17.33 mm2; Cavi-Endo technique, 15.87 mm2; Canal Master technique, 13.56 mm2; and balanced force technique, 17.31 mm 2. Photographs of the blocks used in the study were included for inspection by the reader.

Forty-eight ENDO-VU blocks (#001; Pecina & Assoc. Inc., Waukegan, IL) with artificial canals were marked with a number and divided into four groups of 12 blocks. The artificial canals used in this study had approximately a 30degree curve. Prior to canal preparation, a microscope (ZeissAxiphot, New York, NY) with appropriate software (QUIKLeica, Deerfield, IL) was used for histomorphometric analysis of each root canal. The area of each unprepared canal was determined by outlining the image of the artificial canal on the monitor (x20 magnification) from the top of the block to the top of the apical reservoir. The computer program was then used to determine the actual area in square millimeters of the canal. The working distance for this study was established at 17 mm and defined as that point to which it is desired to fill with gutta-percha. A photograph of each group of uninstrumented resin blocks was taken for use by the clinicians instead of an X-ray to evaluate the curvature of the artificial root canals. Each block was covered with white opaque tape (Professional Tape Co., Burr Ridge, IL) and the end of the tape sealed with fingernail polish (Noxell Corp., Baltimore, MD). Because of the nature of acrylic blocks the clinicians were allowed to use an unlimited amount of water for irrigation to prevent apical packing of particles of acrylic. Each of the four techniques studied was performed by clinical investigators ~ very skilled with the technique. Histomorphometric analysis was used to measure the area of each prepared canal. Photographs of each group of prepared resin blocks were again taken and are shown in composite photographs with the pretreatment photographs so that the reader may make visual comparisons of the four methods of root canal preparation (Fig. 1). In the following section, each clinical investigator described his method of canal preparation and discussed the technique of canal preparation with regard to the use of acrylic blocks for investigational purposes.

Clinicians generally agree that the most important aspect of nonsurgical root canal treatment is the preparation of the root canal. The goal of this cleansing and shaping process is the debridement of the root canal system and shaping of the root canals to allow the placement of a filling material. It is important to develop an overall taper to the canals that facilitates filling of the canal system. In addition, it is important to either maintain an apical constriction or develop an apical stop to prevent overextension of the filling. Several methods of root canal preparation have been popularized for the cleansing and shaping process. These include the stepback technique (1, 2), Cavi-Endo technique (3, 4), balanced force technique (5, 6), and Canal Master technique (7, 8). The design of this study was to use histomorphometric analysis to determine the amount of canal enlargement and to use composite photographs to examine the canal preparations in clear acrylic blocks. The descriptive nature of this study for the four cleansing and shaping techniques mentioned above should help students and clinicians better understand the rationale and capabilities of each of these techniques for the preparation of root canal systems.

Step-back Technique(Strittmatter) The step-back technique seems to be the most widely taught technique for root canal preparation (9). When using this technique, the size of the apical preparation will be related to Strittmatter, step-back technique; Martin, Cavi-Endo technique; Roane, balanced force technique; and Wildey, Canal Master technique.

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Vol. 18, No. 11, November 1992

Comparison of Canal Preparations

531

C

A

"Canal Master" Technique (Before) "Step-Back" Technique (Before)

"Canal Master" Technique (Completed) "Step-Back" Technique (Completed)

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FIG 1. Composite photographs of each of the four types of root canal preparations showing the groups of acrylic blocks before preparation and following preparation. A, Step-back technique. B, Cavi-Endo technique. C, Canal Master technique. D, Balanced force technique. the degree of root curvature. The apical 1 to 2 m m should be enlarged by instrumenting only one or two sizes larger than the first file that binds at the working length. With the acrylic blocks, the first K-type file (Union Broach, Long Island, NY) to bind was #20 in eight of the canals and #15 in four of the canals. The apical portion of the root canal was enlarged from a #10 file to a #25 file by working each successive size of file until it was loose. The canals were then recapitulated with a smaller file before irrigating. In addition to copious irrigation with water in between instruments, R. C. Prep (Premier Dental Products Co., Norristown, PA) was used as a lubricant. Once the root canal was instrumented to a size #25, Gates Glidden burs (GG) (Union Broach) were used to open the canal orifice. Because the curve in the acrylic blocks, as seen in the photograph, begins near 9 mm from the orifice, the #2 G G was used to 8.0 mm, the #3 GG was used to 6.0 mm, and the #4 GG was used to 4 mm. The canal preparation was then stepped back to a #60 at 13 m m in 0.5-mm steps. After each larger file size, the #25 master apical file was used to return to the full working length. Circumferential filing was used to smooth out the steps in the preparation.

Cavi-Endo Technique (Martin) The Cavi-Endo technique utilizes ultrasonically energized filing with high volume irrigation (3, 4). The size of the artificial root canals at the working length was equivalent to a #20 K-type file. The criterion for the end point in preparation of the apical portion of the root canal was when a #30 K-type file would go to the full working distance of 17 mm. Initially a #30 K-type would penetrate about 11 m m into the canals. A # 15 Endosonic (ES) file was used in the Cavi-Endo P105 insert powdered by a Cavi-Endo unit (Dentsply International, York, PA). An ES #15 file that was fully energized (highest power setting) with continuous irrigation at the highest flow rate was used for the canal preparation. The precurved ES #15 was worked with a push-pull circumferential motion down the artificial canal to working length. Following 90 s of preparation to working length with the ES #15 file, the ES #25 diamond was used for 30 s to flare the coronal portion of the canal. This was then followed by recapitulation to the working length with the #15 ES file for an additional 30 s. The preparation was considered complete when a #30 K-type

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Journal of Endodontics TABLE 1. Histomorphometric analysis of artificial canals

Technique Group

Mean Area (mm2) before Treatment

SD*

Mean Area (mm2) of Canal Enlargement

SDI"

Mean Area (mm2) after Treatment

SD$

Coefficient of Variance§

Step-back Cavi-Endo Canal master Balanced force

10.407 10.478 10.399 10.675

1.011 1.110 0.961 0.987

6.920 5.388 3.164 6.638

1.472 1.117 0.821 1.135

17.327 15.866 13.563 17.312

1.362 0.953 0.525 0.928

7.86 6.01 3.87 5.36

* There was no significant difference in the mean areas or standard deviation of the mean areas before treatment. 1" Using the Fr~,= test, the difference among the standard deviations of the mean areas of canal enlargement was significant at p = 0.056, F = 3.214. :1:Using the F.~= test, there was a significant difference among the standard deviations of the mean areas after treatment at p = 0.0054, F = 6.725. § Standard deviation/mean x 100.

file could penetrate to the full working length with ease and the cervical area was opened to a #40.

Canal Master Technique (Wildey) The Canal Master (CM) instrument and technique were introduced in 1989 (7, 8). The Canal Master Rotary (CMR) instrument has a noncutting pilot (tip), a short cutting head (blade), and a rigid shaft. The pilot was designed to guide the instrument apically and to advise the dentist when a curve in the canal was reached (a resistance is felt). The hand instrument has a variable length noncutting pilot (tip), a very short cutting head (blade), and a flexible shaft. For this study, the canals were checked for patency with a #15 file to the working length of 17 mm. The photograph of the blocks was measured to the canal curvature and a depth of approximately 9 mm (rotary length) was established for the use of engine-driven rotary instruments. This was determined from the photographs and not by feel because the rotary pilot will melt its way down the canal. All of the blocks were first instrumented to rotary length with the CMR #50. A step-back of 1 mm was then used for the CMR #60 followed by further stepping back with 1-mm increments for the #70, #80, and #90 to the final CMR #100. The canals were checked with a #15 file to make sure no blockage of the canals had developed following the use of each rotary instrument. The first CM hand instrument to bind in the artificial canals at the working length of 17 mm was a #32.5. These canals were instrumented using the recommended technique except that a clockwise-counterclockwise rotation of less than a quarter turn was used. The #35 was worked firmly against resistance, indicating that the canal was being adequately enlarged. For the step-back phase, 1 mm was subtracted from the working length of 17 mm and the canals were instrumented with a #37.5 followed by a #40 to a depth of 16 mm. Another 1-mm step-back was made and the canals were instrumented with a #42.5 followed by a #50 to a length of 15 mm. This completed the instrumentation of the plastic blocks. The canals in the plastic blocks were cleaned by using water and paper points. The step-back was used to fit the taper of a standard gutta-percha cone.

Balanced Force Technique (Sabala) Based on the principle that for every action there is an equal and opposite reaction, the balanced force concept for the instrumentation of curved canals was introduced (5, 6). Instrument placement is accomplished by clockwise rotation

of the instrumented that is limited to no more than 180 degrees to prevent overinsertion of the apical portion of the instrument. Each placement motion is followed by a counterclockwise rotation of 120 degrees or greater to produce the cutting. The files used in this study were the Flex-R file (Union Broach) and the Gates Glidden (GG) (Union Broach) drills both of which were stainless steel. Each canal in this study was prepared using tap water as a lubricant and irrigant. Patency was checked and each canal recapitulated to 19 mm with a #20 file. The canal was enlarged to a file #25 at the working distance of 17 ram. The #25 Flex-R file was the first file to bind in these canals at 17 mm. Sizes #30 and #35 files were used to instrument to 16.5 mm. The canals were enlarged through size #35 before a GG access preparation was created. This was made using the GG to the following penetration depths: #2 GG, 12 mm; #3 GG, 10 mm; #4 GG, 8 mm; #5 GG, 6 ram; and #6 GG, 4 mm. Irrigation with tap water was provided following the use of each file and each GG. For verification and debris removal, file #25 and #35 were placed to their respective depths before continuing the preparation. The canal was then enlarged to 16 mm using a #40 and a #45 file. Upon completion to size #45, the apex was recapitulated. The canal was then thoroughly irrigated and #25, #35, and #45 files were placed again to their respective depths. With all sizes and depths verified, the canals were again irrigated and the preparation considered complete. Approximately 5 ml of tap water were used to irrigate each canal during the cleaning and shaping procedure. A 25-gauge front delivery needle and syringe were used to irrigate. One block was damaged with a #2 GG. The blockage was bypassed and the preparation completed. An altered canal wall could still be felt and can be seen in the photograph. RESULTS The mean areas of the artificial canals before and after preparation are shown in Table 1. Analysis of the mean areas of the artificial canals before treatment showed that there was no evidence of differences among the groups. The areas of the untreated canals ranged from 8.46 mm 2 to 12.38 mm 2. Analysis of the mean areas of the prepared canals revealed significant differences among the groups. The mean areas of the final preparations ranged from 13.56 mm 2 for the Canal Master technique to 17.33 mm 2 for the step-back technique. Intermediate size areas for prepared canals were produced by the Cavi-Endo technique (15.87 mm z) and the balanced force technique (17.31 mm2). The Canal Master technique produced a prepared canal that was between 15 and 22% smaller

Vol. 18, No. 11, November 1992

in area than the other techniques in this study. The Canal Master technique achieved the greatest precision (smallest standard deviation) in producing the same size prepared canal (Table 1). Composite photographs of each of the techniques before and after treatment are included for the reader to inspect (Fig. 1). DISCUSSION The results showed that there was a significant difference in the amount of canal enlargement among the techniques of canal preparation evaluated in this study (Table 1). The Canal Master technique had the lowest standard deviation and produced the smallest amount of canal enlargement followed in order from smallest to largest by the Cavi-Endo technique, the balanced force technique, and the step-back technique. Photographs of the preparations are included so that the amount of flare and the amount of taper maintained through the 30-degree curve in these artificial canals may be evaluated. This information may help clinicians evaluate the techniques and determine which techniques are the most consistent with their treatment philosophy and rationale. A discussion of each technique by the investigator who uses it follows.

Step-back Technique (Strittmatter) The step-back technique is considered the standard for root canal preparation at many dental schools. It was described by Clem (1) and has been modified by others (2). Plastic blocks have been shown to be suitable for studying the cleansing and shaping process (10, 11). However, the nature of the plastic contributes to ledging and difficulty in instrumentation. The use of RC Prep with copious amounts of tap water for irrigation helped to lubricate and facilitate the instrumentation process. The pretreatment photograph of the group of blocks served as a two-dimensional guide for canal preparation similar to a radiograph. The curvature of the canal was inspected and the desired depth of the GG preparation could be determined. In the literature, the depth of G G penetration is often given as an arbitrary figure. It is difficult to put a numerical length on this portion of the technique because all canal curvatures are different. The method used in this study was to measure from the top of the canal to the point where the canal started to curve. One millimeter was subtracted from this length and used as the depth for initial G G penetration. Sequential use of the G G followed by recapitulation to the working length helps to reduce the chances for transportation, stripping, and ledging.

Cavi-Endo Technique (Martin) The artificial canals in acrylic slow down the ultrasonic vibrations as the acrylic softens and may clog the endosonic file/diamond while intracanal dentin will not. When the CaviEndo technique is used in a clinical situation, the root canal should be prepared to a #10 to #15 file by hand followed by the use of the ES # 15 for at least 1 to 2 min in a push-pull motion followed by circumferential action. Precurving of the ES #15 enhances the shape of the ultrasonically prepared

Comparison of Canal Preparations

533

canal. In addition, due to surface tension the irrigant flow will follow the curved ES #15 file to the tip of the file. This provides irrigation to the full working length. The ES #25 diamond should be used to flare the cervical and mid-portion of the canal for 30 to 60 s in an initial push-pull and circumferential action to taper the canal. A final irrigation with the ES # 15 should be done for 30 s. Recapitulation with a #20, #25, or #30 K-type file depends on the curvature and hardness of the root canal wall. Recapitulation with hand instruments should also be used to check the apex for final preparation of the apical step/matrix. All preparation of the root canal should be accompanied with Cavi-Endo ultrasonic irrigation for cleansing, debriding, and disinfection of the root canal system. The irrigant recommended for use in the Cavi-Endo is 1.3% sodium hypochlorite. This modified technique, which has been simplified and improved, uses only the ES # 15 file and ES #25 diamond.

Canal Master Technique (Wildey) A problem with engine-driven CMR occurs in plastic blocks. The plastic melts from the friction and does not give the dentist a feeling of resistance when a curve is encountered. Another problem with plastic blocks is the difficulty of plastic chip removal from the canal which causes bogging down of the instrument. This does not occur as readily in dentin. The bogging down of the instrument may result from the instrument actually threading instead of cutting the plastic. It is interesting to note that the first CM hand instrument to bind in these standardized artificial canals at the working length of 17 m m was a #32.5. This suggests that the CM can determine the original apical diameter while the standard instrument has a taper that binds at a level higher in the canal. This gives the dentist the impression that the instrument is binding at the apex when it is binding elsewhere. The cutting portion of the CM is approximately 4 mm in length. This limits the cutting to a small segment of the canal and makes it clear to the clinician where cutting is taking place. When the CM is pushed apically without rotation, a resistance to advancement indicates where the cutting head begins to engage the dentinal walls and where cutting will begin. The distance from this point to the working length is the remaining distance that the instrument must cut. Rotating the instrument starts the cutting process and the instrument advances apically. If the instrument seems to "run" toward the apex with minimum resistance, this suggests minimum dentin removal such as when the round instrument is cutting an oval canal. If the CM advances slowly with resistance, the blades are cutting a greater amount of dentin. It takes much less force to instrument a root canal with the short head on the CM instruments versus the long cutting segments on conventional instruments. To avoid fracture of instruments, less force should be used with a rotational motion compared with the force used with a filing motion.

Balanced Force Technique (Sabala) It is evident when using the balanced force technique that the plastic blocks instrument somewhat differently than do teeth. The main difference is that if the Gates Glidden burs are used too vigorously the plastic becomes deformed and can

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hinder instrumentation. Debris can also be more of a problem in the plastic blocks. If debris is allowed to accumulate or block the canal in the plastic blocks, more rapid transportation of the apical portion of the canal occurs than in a tooth. Instrumenting with balanced forces, a nonaggressive cutting tip on the instrument, and a minimum predetermined or predefined preparation are easily demonstrated using the plastic blocks. If the canal in the plastic block is not masked, the rotated instrument motion can be viewed and studied. The physics involved in using balanced forces may be demonstrated by comparing rotation and filing techniques. A minimum predetermined preparation allows for verification of depth and size of the final preparation at any level. The minimum predetermined preparation also eliminates many of the clinical decisions necessary to complete the preparation. The preparation as described, with the exception of the initial patency check, is the predetermined #45 preparation that is recommended for small roots. Dr. Baumgartner is affiliated with Oregon Health Sciences University, Portland, OR. Dr. Martin is in practice in Silver Spring, MD. Dr. Sabala is affiliated with the University of Oklahoma, Edmond, OK. Dr. Stdttmatter is a member of U.S. Army Dental Activities, Walter Reed Army Medical Center, Washington, DC. Dr. Wildey is in practice in Hurst, TX. Dr. Quigley is a member of U.S. Army Institute of Dental Research, Walter Reed Army Medical Center, Wash-

Journal of Endodontics ington, DC. Address requests for reprints to Dr. J. Craig Baumgartner, School of Dentistry, Oregon Health Sciences University, 611 S.W. Campus Drive, Portland, OR 97201.

References 1. Clem WH. Endodontics in the adolescent patient. Dent Clin North Am 1969;13:483-7. 2. Mullaney TP. Instrumentation of finely curved canals. Dent Clin North Am 1979;23:195-222. 3. Martin H. Ultrasonic disinfection of the root canal. Oral Surg 1976;42:929. 4. Cunningham WT, Martin H. A scanning electron microscopic evaluation of root canal debridement with the endosonic ultrasonic synergistic system. Oral Surg 1982;53:527-31. 5. Roane JB, Sabala CL, Duncanson MG. The "Balanced Force" concept for instrumentation of curved canals. J Endondon 1985;11:203-11. 6. Sabala CL, Biggs JT. A standard predetermined endedontic preparation concept. Compend Contin Educ Dent 1991 ;12:656-63. 7. Wildey LW, Senia ES. A new root canal instrument and instrumentation technique: a preliminary report. Oral Surg 1989;67:198-207. 8. Leseberg DA, Montgomery S. The effects of Canal Master, Flex-R, and K-Flex instrumentation on root canal configuration. J Endodon 1991 ;17:59-65. 9. Walton RE, Torabinejad M. Principles and practice of endodontics. Philadelphia: WB Saunders, 1989. 10. Ahmad M. The validity of using simulated root canals as models for ultrasonic instrumentation. J Endodon 1989;15:544-7. 11. Lira KC, Webber J. The validity of simulated root canals for the investigation of the prepared root canal shape. Int Endod J 1985;18:240-6.

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Histomorphometric comparison of canals prepared by four techniques.

Numerous methods of root canal preparation have been recommended and used by clinicians. This study used histomorphometrics to determine the area of r...
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