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Apical extent of rotary canal instrumentation with an apexlocating handpiece in vitro
Apical extent of rotary canal instrumentation with an apexlocating handpiece in vitro D. Campbell, BSc, DDS, a S. Friedman, DMD, a H. Q. Nguyen, BA, DDS, a A. Kaufman, DMD, b and S. Keila, DMD, b Toronto, Canada, and Tel-Aviv, Israel UNIVERSITYOF TORONTOAND TEL-AVIVUNIVERSITY
Problem. The Tri Auto ZX (J. Morita Co., Kyoto, Japan) is a cordless endodontic handpiece with a built-in apex locator that is programmed to reverse the direction of rotation when the file reaches a predetermined apical level or when torque becomes excessive. Objective. The purpose of this investigation was to examine the apical extent of rotary canal instrumentation and the ability to maintain apical constriction with the Tri Auto ZX at different automated settings. Study design. In 60 extracted teeth, canals were measured to the apical constriction, first visually and then electronically with the Tri Auto ZX; then they were instrumented with nickel titanium rotary files. For the instrumentation, the automatic apical reverse mechanism of the handpiece was set to 1, 1.5, or 2; these settings correspond to different distances from the apical foramen. Instrumentation was carried out apically until rotation was reversed by the automatic apical reverse function; the instrumented length was then measured, and the canal was filled with gutta-percha and sealer. The integrity of the apical constriction was assessed by exposing the apical 4 mm of the canal and observing the dentin-cementum junction. Paired t-tests were used to compare the visually measured length, the electronically measured length, and the instrumented length for each tooth. Results. On average, the electronically measured length was 0.54 mm shorter than the visually measured length (p < 0.05). When the automatic apical reverse mechanism's setting was 1, the instrumented length was 0.1 mm shorter than the electronically measured length; when the setting was 1.5, the instrumented length was 0.36 mm shorter than the electronically measured length (p < 0.01). Results were inconsistent when the setting was 2. Conclusion. Instrumentation with the automatic apical reverse feature set at 1 consistently approximated the apical constriction; however, the constriction was frequently enlarged.
(Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1998;85:319-24)
Complete cleaning is fundamental to proper root canal therapy.1 Confinement of the cleaning procedure to the canal prevents irritation of the periapical tissues and possible overextension of the root filling. 20verinstrumentation is avoided by accurate location of the canal terminus 3 by means of radiographs, use of the tactile sense, and electronic measurement. Electronic apex locators, which were first introduced more than 20 years ago, have proved useful and continue to evolve. Because the canal is believed to terminate anatomically at the apical constriction, 4,5 the latest generation of apex locators is designed to identify the point of narrowest diameter of the canal and contact with the periodontal ligament. 6-8 A study performed in human cadavers confirmed the reliability of apex locators in identifying the apical constriction. 9 Apex locators have been recently proposed for the task of controlling the apical extent of root canal instruaDepartment of Endodontics, Faculty of Dentistry, University of Toronto. bSection of Endodontology, Maurice and Gabriela Goldshlagger School of Dental Medicine, Tel-AvivUniversity. Received for publication June 27, 1997; returned for revision Sept. 15, 1997; accepted for publication Nov. 5, 1997. Copyright © 1998 by Mosby, Inc. 1079-2104/98/$5.00 + 0 7/15/87634
mentation with rotary nickel titanium files. 1°,11 By the nature of their design, these files are driven apically when continuously rotated clockwise. Occasionally the file goes beyond the desired length, and overinstrumentation occurs. To minimize the possibility of such an occurrence, an apex locator can be connected to the file online and indicate when the apical constriction is reached; the file can then be withdrawn from the canal. 10 Recently, an innovative handpiece designed for rotary canal instrumentation, the Tri Auto ZX (J. Morita Co., Kyoto, Japan; Fig. 1), has been introduced. 11 Some of the features of this handpiece are a rechargeable battery, a rotation speed of 280 rpm, adjustable torque, and a built-in apex locator. The apex locator triggers reversal of rotation when the file reaches a predetermined level, referred to as the Auto Apical Reverse (AAR) level; the apical extent of the instrumentation can thus be controlled. The A A R settings are 0.5, 1, 1.5, and 2; accord~ ing to the manufacturer, the 0.5 setting corresponds to the apical constriction, whereas the other settings are arbitrary designations corresponding to increasing distances from the apical foramen, though not to particular millimetric values. 11 In addition, an Auto Torque Reverse (ATR) mechanism reverses the rotation if the
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Fig. 1. Tri Auto ZX and accessories. A, Handpiece, lip-clip electrode, and file holder. B, Control panel on body of handpiece. Top to bottom: Main switch and LEDs corresponding to low battery, manual mode, high and low mode, EMR, and eight AAR levels.
amount of torque on the file exceeds a preset level. The handpiece can also be operated in Manual Mode, without the ATR mechanism. The instrumentation lengths associated with the various A A R settings of the Tri Auto ZX have not been characterized. Therefore the objective of this in vitro study was to examine the apical extent of rotary canal instrumentation and the Tri Auto ZX's ability to maintain the apical constriction during instrumentation when the device is used at different A A R settings.
MATERIAL AND METHODS
Fig. 2. Experimental model consists of tooth with reduced crown height embedded in alginate. Tooth is stabilized by means of an acrylic layer poured over alginate surface. Tri Auto ZX lip-clip electrode is inserted into alginate.
Sixty extracted human teeth with single roots and apparently mature apices were selected. All teeth were radiographically confirmed to have reasonably narrow canals with curvatures of less than 20 degrees. ~2 The teeth were stored in 10% buffered formalin at r o o m temperature, then thoroughly washed with water before use. Each tooth crown was cut horizontally at 3 m m coronal to the cemento-enamel junction, access to the
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l a n e I. Length measurements (mm) of canals instrumented with rotary nickel titanium files driven by Tri Auto ZX handpiece AAR 1
AAR 1.5
AAR 2
Specimen number*
AL
EL
IL
AL
EL
IL
AL
EL
IL
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
14.8 17.2 16.4 14.4 18.0 16.8 15.0 18.6 17.2 16.2 17.4 17.0 15.0 15.8 15.2 16.2 16.8 16.0 14.2 15.0
14.2 16.8 15.8 13,8 17.2 15.6 14.2 18.0 16.8 15.6 16.8 16.2 14.4 15.2 14.8 15.6 16.6 15.6 13.4 14.6
14.2 16.6 15.6 13.8 17.2 15,4 14,0 18,0 16,8 15,4 16,6 16,0 14,2 15.2 14.6 15.6 16.6 15.4 13.4 14.6
16.4 16.6 17.8 16.2 17.8 16.0 15.6 19.0 14.2 17.6 17.0 15.2 16,0 17.8 17.0 16.6 14.2 15.0 15.2 15.4
15.8 15.4 17.2 15,4 17.2 15.2 15.0 18.2 13.8 16.8 16.8 15.0 15.4 17.0 16.4 16.2 14.0 14.8 15.0 14.2
15.4 14.8 16.6 15.0 16.8 14.0 14.6 18.0 13.6 15.8 16.4 14.8 15.2 16.8 16.0 16.0 13.6 14.6 14.8 13.8
16.4 16.8 16.6 16.0 13.6 15.6 15.2 19.8 15.0 15.2 11.8 20.6 16.0 12.6 14.2 15.0 16,0 15.0 12.0 15,0
16.2 16.4 16.4 16.0 13.2 15.6 15.0 19.2 14.6 15.0 11.6 20.0 16.0 12.4 14.0 14,0 15.4 14.2 11.2 14.0
14.6 13.4 14.4 14.8 13.0 14.8 13.8 17.8 14.6 14.4 11,0 18.4 11,8 11.4 12.4 14.0 15.0 12.4 10.6 13.4
AL, Actual length, determined visually; EL, electronic length, determined by means of the Tri Auto ZX in its apex-locating (EMR) mode; IL, instrumentedlength, determined by means of the Tri Auto ZX's automatic apical reverse mechanism(AAR), which was set at 1, 1.5, or 2. *There were 20 different teeth for each AAR group.
canal was established, and the canal was negotiated to the major apical foramen with a size-1 Profile Series 29 hand file (Tulsa Dental Products, Tulsa, Okla.). With the help of magnifying telescopes, the file was retracted so that its tip remained visible in the minor apical foramen, then marked with a stopper at the reference point; its measurement from tip to stopper was recorded as the canal's visually determined actual length (AL). All lengths throughout the study were measured to the nearest 0.2 ram. Each tooth was embedded in an alginate mold (Geltrate Plus; Dentsply, Milford, Del.), 13 up to 2 mm short of the cemento-enamel junction, with the size-1 Profile hand file in place. The alginate was used as a conducting medium for the electronic apex locator. 13 A layer of self-curing acrylic was poured over the alginate surface to the level of the cemento-enamel junction of the teeth. A small hole was drilled in the acrylic, and the lip-clip electrode of the Tri Auto ZX was inserted into the alginate. The entire assembly (Fig. 2) was kept moist and refrigerated when not in use. Initially, the canal length was measured with the Tri Auto Z X in its electronic manual recording (EMR) mode. The canal was irrigated with 2.5% sodium hypochlorite; then, with the file holder connected, a size-1 Profile hand file was advanced apically until the
light-emitting diode (LED) marked "0.5" on the instrument panel began to glow; when lighted, this LED indicates that the file has reached the apical constriction, u The file was marked at the reference point, withdrawn from the canal, and its measurement from tip to stopper was recorded as the electronic length (EL). With the Tri Auto ZX in its Manual mode, the canals were flared Coronally with Gates-Glidden burs in descending sequence (sizes 4 through 2). Then the device's torque and rotation were adjusted tO the low mode, and the canal was instrumented in a modified crown-down sequence 14 with 0.04 Taper Series 29 nickel titanium rotary files (Tulsa Dental Products), the canal being intermittently irrigated with 2.5% sodium hypochlorite. AAR settings were selected according to the following random sequence: the setting marked "1" was used for the first 20 teeth, the setting marked "1.5" was used for the next 20 teeth, and the setting marked "2" was used for the last 20 teeth. The canal was enlarged apically to file size-7 (0.46 mm at the tip) until the preset AAR LED glowed and rotation reversal occurred. At this point rotation was stopped, the last file was marked at the reference point, and its measurement from tip to stopper was recorded as the instrumented length (IL). The files used for instrumentation were not changed
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Fig. 3. Exposed canals after instrumentation with rotary nickel titanium files driven by Tri Auto ZX and filling with vertically compacted gutta-percha and sealer (original magnification x25). A, Canal instrumented with AAR set at 1 shows relative constriction at cementum-dentin junction. B, Canal instrumented with AAR set at 1 shows loss of apical constriction.
from one canal to the other; however, any file that demonstrated distortion was replaced. The difference between the AL and EL measurements in all 60 canals was computed, as was the difference between the EL and IL measurements in the 20 canals instrumented with each A A R setting. Paired t-tests were used for statistical analysis; the level of significance was 5%. Finally, the canal was dried with paper points, and a fine-medium gutta-percha cone (Kerr, Romulus, Mich.) was fitted to the IL with "tug-back." Root canal sealer (Roth 801, Elite Grade; Roth International Ltd., Chicago, Ill.) was introduced, and the canal was filled with vertically compacted warm gutta-percha by means of Schilder pluggers (Caulk, York, Pa.) placed apically to within 5 m m of the IL. The remainder of the canal was back-filled with injectable gutta-percha (Obtura II; Obtura Corp., Fenton, Mo.). All teeth were removed from the alginate, and the apical 4 m m of the filled canal of each tooth was exposed by grinding with a water-cooled, high-speed diamond bur. Under a surgical microscope (x16; Global Surgical Corp., St. Louis, Mo.), the canal was observed for the presence or
absence of a relative constriction at the level of the cementum-dentin junction as an indication of a maintained apical constriction. The root filling was used to visually enhance the contour of the canal.
RESULTS All AL, EL, and IL measurements obtained are presented in Table I. The EL was shorter than the AL in all but three of the canals; the mean difference was 0.54 m m (_+ 0:26 mm; p < 0.05). In every canal the IL was either equal to or shorter than the EL (p < 0.01). These two measurements were most consistent when the A A R setting was 1. The mean differences were 0.1 mm (+ 0.10 ram) for A A R setting 1; 0.36 m m (_+ 0.20 ram) for setting 1.5; and 1.30 m m (_+ 1.04 ram) for setting 2. Microscopic examination after exposure of the filled canals disclosed the cementum-dentin junction in all of the roots. At this level, a relative constriction was evident in only 10 of the canals instrumented with the A A R set at 1, as opposed to 18 canals and 17 canals instrumented with the A A R set at 1.5 and 2, respectively (Fig. 3).
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DISCUSSION The in vitro model used in our study was adapted from a m o d e l used in previous studies. 1°,13 Rotary instruments used for the canal instrumentation of teeth mounted in alginate may bind and loosen the teeth. The acrylic resin poured over the alginate surface effectively prevented dislodgement of the teeth during the experimental procedures. In previous studies, researchers have avoided irrigating canals with sodium hypochlorite to prevent damage to the alginatel°'13; in the present study, the canals were irrigated with sodium hypochlorite to better simulate clinical conditions. This procedure did not appear to cause any deterioration of the alginate surrounding the roots. The EL measurements, obtained with the 0.5 LED of the Tri Auto Z X used as reference, were on average 0.54 m m shorter than the A L measurements. This result was consistent with the findings in a previous study, l° in which the 0.5 bar of the Root ZX apex locator (J. Morita Co.) was used as reference. The similar results in the two studies have confirmed that the 0.5 indicators of both devices are equivalent; indeed, the two devices have the same apex locator mechanism. 11 According to Kobayashi et al., 8,11 the 0.5 indicator corresponds to the location of the apical constriction. Morphometrically, the apical constriction was found to be 0.51 m m from the minor foramen, 5 which appears to validate the ability of the Tri Auto Z X to locate it with adequate accuracy. Although the IL was shorter than the EL at all three of the A A R settings, the results demonstrated a variation in consistency among the A A R settings. With the A A R set at 1, the IL was, at most, 0.2 m m shorter than the initial EL, known to correspond to the apical constriction. 11 With the A A R set at 1.5, the discrepancy ranged from 0.2 to 1.2 ram. A A R setting 2 proved to be the least consistent, with the discrepancy between EL and IL ranging from 0 to 4.2 mm; such an inconsistent apical extent of instrumentation would be clinically unacceptable. Both the Root Z X apex locator and the Tri Auto ZX handpiece operate on a ratio-method principle that is designed to locate the narrowest canal diameter, which normally coincides with the apical constriction. 8 From the differences in consistency between the three A A R settings, it appeared that the Tri Auto ZX could locate this point of narrowest diameter, or apical constriction, with greater accuracy than it could determine the distance from it. Our group has previously demonstrated that rotary canal instrumentation can be controlled by connecting an apex locator online. 1° To do so, however, the opera-
tor must constantly monitor the apex locator and withdraw the file from the canal when the desired apical extent is indicated. Although such a technique is possible, it is cumbersome and requires close attention. In contrast to the apex locator connected online, the Tri Auto ZX's A A R mechanism actively and automatically prevented accidental overinstrumentation. In addition, the ATR mechanism, as set for this study, resulted in frequent rotation reversal. It was noted during instrumentation of the 60 canals that although five files manifested distortion of their tips (three of them were size4 files and two were size-5 files), no files broke. Presumably the ATR mechanism prevented excessive torque on the files and thereby prevented file breakage. It was concluded that under the conditions of this study, the apical extent of rotary canal instrumentation with the Tri Auto ZX was most consistent at A A R setring 1, less consistent at A A R setting 1.5, and least consistent at A A R setting 2. These findings suggested that A A R setting 1 might be appropriate for clinical application, pending confirmation in a clinical trial. Such clinical assessment is currently being performed by our group. We thank Rita Bauer, Steve Burany, and Annemarie Polis for their invaluable assistance.
REFERENCES 1. Tronstad L. Prognosis of endodontic treatment. In: Clinical Endodontics. 1st ed. New York: Thieme Medical Publishers Inc.; 1991. 2. Ingle JI, Balkland LK, Peters DL, Buchanan S, Mullaney TR Endodontic cavity preparation. In: Ingle JI & Bakland LK, editors. Endodontics. 4th ed. Malvern, Pa.: Williams & Wilkins; 1994. p. 92-227. 3. West JD, Roane JB, Goerig AC. Cleaning and shaping the root canal system. In: Cohen S, Burns RC, editors. Pathways of the pulp. 6th ed. St. Louis: Mosby-Year Book, Inc.; 1994: p. 179218. 4. KutflerY. Microscopic investigation of root apexes. J Am Dent Assoc 1955;50:544-52. 5. Dummer PMH, McGinn JH, Rees DG. The position and topography of the apical canal constriction and apical foramen. International Endodontics Journal 1984;17:192-8. 6. Ushiyama J. New principle and method for measuring the root canal length. J Endod 1983;9:97-104. 7. Salto T, Yamashita Y. Electronic determination of root canal length by a newly developed measuring device: influences of the diameter of apical foramen, the size of K-file and root canal irrigants. Dentistry in Japan 1990;27:65-72. 8. Kobayashi C, Suda H. New electronic canal measuring device based on the ratio method. J Endod 1994;20:111-4. 9. Pratten DH, McDonald R. Comparison of radiographic and electronic working lengths. J Endod 1996;22:173-6. 10. Nguyen HQ, Kanfman AY, Komorowski RC, Friedman S. Electronic length measurement using small and large files in enlarged canals. Int Endod J 1997;29:359-64. l 1. Kobayashi C, Yoshioka T, Suda H. A new engine-driven canal preparation system with electronic canal measuring capability. J Endod 1997;23:751-4. 12. Schneider SW. A comparison of canal preparations in straight
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March 1998 and curved root canals. Oral Surg Oral Med Oral Pathol 1971;32:271-5. 13. Katz A, Mass E, Kaufman AY. Electronic apex locator: a useful tool for root canal treatment in the primary dentition. J Dent Child 1996;63:414-7. 14. Morgan LF, Montgomery S. An evaluation of the crown-down pressureless technique. J Endod 1984;10:491-8.
Reprint requests: Shimon Friedman, DMD Department of Endodontics Faculty of Dentistry, University of Toronto 124 Edward Street Toronto, Ontario, M5G 1G6 Canada
CALL FOR REVIEW ARTICLES The January 1993 issue of Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontics contained an Editorial by the Journal's Editor in Chief, Larry J. Peterson, that called for a Review Article to appear in each issue. These Review Articles should be designed to review the current status of matters that are important to the practitioner. These articles should contain current developments, changing trends, as well as reaffirmation of current techniques and policies. Please consider submitting your article to appear as a Review Article. Information for authors appears in each issue of Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology,
and Endodontics. We look forward to hearing from you.
Problem. The Tri Auto ZX (J. Morita Co., Kyoto, Japan) is a cordless endodontic handpiece with a built-in apex locator that is programmed to reverse the direction of rotation when the file reaches a predetermined apical level or when torque becomes excessive. Objective. The purpose of this investigation was to examine the apical extent of rotary canal instrumentation and the ability to maintain apical constriction with the Tri Auto ZX at different automated settings. Study design. In 60 extracted teeth, canals were measured to the apical constriction, first visually and then electronically with the Tri Auto ZX; then they were instrumented with nickel titanium rotary files. For the instrumentation, the automatic apical reverse mechanism of the handpiece was set to 1, 1.5, or 2; these settings correspond to different distances from the apical foramen. Instrumentation was carried out apically until rotation was reversed by the automatic apical reverse function; the instrumented length was then measured, and the canal was filled with gutta-percha and sealer. The integrity of the apical constriction was assessed by exposing the apical 4 mm of the canal and observing the dentin-cementum junction. Paired t-tests were used to compare the visually measured length, the electronically measured length, and the instrumented length for each tooth. Results. On average, the electronically measured length was 0.54 mm shorter than the visually measured length (p < 0.05). When the automatic apical reverse mechanism's setting was 1, the instrumented length was 0.1 mm shorter than the electronically measured length; when the setting was 1.5, the instrumented length was 0.36 mm shorter than the electronically measured length (p < 0.01). Results were inconsistent when the setting was 2. Conclusion. Instrumentation with the automatic apical reverse feature set at 1 consistently approximated the apical constriction; however, the constriction was frequently enlarged.
(Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1998;85:319-24)
Complete cleaning is fundamental to proper root canal therapy.1 Confinement of the cleaning procedure to the canal prevents irritation of the periapical tissues and possible overextension of the root filling. 20verinstrumentation is avoided by accurate location of the canal terminus 3 by means of radiographs, use of the tactile sense, and electronic measurement. Electronic apex locators, which were first introduced more than 20 years ago, have proved useful and continue to evolve. Because the canal is believed to terminate anatomically at the apical constriction, 4,5 the latest generation of apex locators is designed to identify the point of narrowest diameter of the canal and contact with the periodontal ligament. 6-8 A study performed in human cadavers confirmed the reliability of apex locators in identifying the apical constriction. 9 Apex locators have been recently proposed for the task of controlling the apical extent of root canal instruaDepartment of Endodontics, Faculty of Dentistry, University of Toronto. bSection of Endodontology, Maurice and Gabriela Goldshlagger School of Dental Medicine, Tel-AvivUniversity. Received for publication June 27, 1997; returned for revision Sept. 15, 1997; accepted for publication Nov. 5, 1997. Copyright © 1998 by Mosby, Inc. 1079-2104/98/$5.00 + 0 7/15/87634
mentation with rotary nickel titanium files. 1°,11 By the nature of their design, these files are driven apically when continuously rotated clockwise. Occasionally the file goes beyond the desired length, and overinstrumentation occurs. To minimize the possibility of such an occurrence, an apex locator can be connected to the file online and indicate when the apical constriction is reached; the file can then be withdrawn from the canal. 10 Recently, an innovative handpiece designed for rotary canal instrumentation, the Tri Auto ZX (J. Morita Co., Kyoto, Japan; Fig. 1), has been introduced. 11 Some of the features of this handpiece are a rechargeable battery, a rotation speed of 280 rpm, adjustable torque, and a built-in apex locator. The apex locator triggers reversal of rotation when the file reaches a predetermined level, referred to as the Auto Apical Reverse (AAR) level; the apical extent of the instrumentation can thus be controlled. The A A R settings are 0.5, 1, 1.5, and 2; accord~ ing to the manufacturer, the 0.5 setting corresponds to the apical constriction, whereas the other settings are arbitrary designations corresponding to increasing distances from the apical foramen, though not to particular millimetric values. 11 In addition, an Auto Torque Reverse (ATR) mechanism reverses the rotation if the
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Fig. 1. Tri Auto ZX and accessories. A, Handpiece, lip-clip electrode, and file holder. B, Control panel on body of handpiece. Top to bottom: Main switch and LEDs corresponding to low battery, manual mode, high and low mode, EMR, and eight AAR levels.
amount of torque on the file exceeds a preset level. The handpiece can also be operated in Manual Mode, without the ATR mechanism. The instrumentation lengths associated with the various A A R settings of the Tri Auto ZX have not been characterized. Therefore the objective of this in vitro study was to examine the apical extent of rotary canal instrumentation and the Tri Auto ZX's ability to maintain the apical constriction during instrumentation when the device is used at different A A R settings.
MATERIAL AND METHODS
Fig. 2. Experimental model consists of tooth with reduced crown height embedded in alginate. Tooth is stabilized by means of an acrylic layer poured over alginate surface. Tri Auto ZX lip-clip electrode is inserted into alginate.
Sixty extracted human teeth with single roots and apparently mature apices were selected. All teeth were radiographically confirmed to have reasonably narrow canals with curvatures of less than 20 degrees. ~2 The teeth were stored in 10% buffered formalin at r o o m temperature, then thoroughly washed with water before use. Each tooth crown was cut horizontally at 3 m m coronal to the cemento-enamel junction, access to the
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l a n e I. Length measurements (mm) of canals instrumented with rotary nickel titanium files driven by Tri Auto ZX handpiece AAR 1
AAR 1.5
AAR 2
Specimen number*
AL
EL
IL
AL
EL
IL
AL
EL
IL
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
14.8 17.2 16.4 14.4 18.0 16.8 15.0 18.6 17.2 16.2 17.4 17.0 15.0 15.8 15.2 16.2 16.8 16.0 14.2 15.0
14.2 16.8 15.8 13,8 17.2 15.6 14.2 18.0 16.8 15.6 16.8 16.2 14.4 15.2 14.8 15.6 16.6 15.6 13.4 14.6
14.2 16.6 15.6 13.8 17.2 15,4 14,0 18,0 16,8 15,4 16,6 16,0 14,2 15.2 14.6 15.6 16.6 15.4 13.4 14.6
16.4 16.6 17.8 16.2 17.8 16.0 15.6 19.0 14.2 17.6 17.0 15.2 16,0 17.8 17.0 16.6 14.2 15.0 15.2 15.4
15.8 15.4 17.2 15,4 17.2 15.2 15.0 18.2 13.8 16.8 16.8 15.0 15.4 17.0 16.4 16.2 14.0 14.8 15.0 14.2
15.4 14.8 16.6 15.0 16.8 14.0 14.6 18.0 13.6 15.8 16.4 14.8 15.2 16.8 16.0 16.0 13.6 14.6 14.8 13.8
16.4 16.8 16.6 16.0 13.6 15.6 15.2 19.8 15.0 15.2 11.8 20.6 16.0 12.6 14.2 15.0 16,0 15.0 12.0 15,0
16.2 16.4 16.4 16.0 13.2 15.6 15.0 19.2 14.6 15.0 11.6 20.0 16.0 12.4 14.0 14,0 15.4 14.2 11.2 14.0
14.6 13.4 14.4 14.8 13.0 14.8 13.8 17.8 14.6 14.4 11,0 18.4 11,8 11.4 12.4 14.0 15.0 12.4 10.6 13.4
AL, Actual length, determined visually; EL, electronic length, determined by means of the Tri Auto ZX in its apex-locating (EMR) mode; IL, instrumentedlength, determined by means of the Tri Auto ZX's automatic apical reverse mechanism(AAR), which was set at 1, 1.5, or 2. *There were 20 different teeth for each AAR group.
canal was established, and the canal was negotiated to the major apical foramen with a size-1 Profile Series 29 hand file (Tulsa Dental Products, Tulsa, Okla.). With the help of magnifying telescopes, the file was retracted so that its tip remained visible in the minor apical foramen, then marked with a stopper at the reference point; its measurement from tip to stopper was recorded as the canal's visually determined actual length (AL). All lengths throughout the study were measured to the nearest 0.2 ram. Each tooth was embedded in an alginate mold (Geltrate Plus; Dentsply, Milford, Del.), 13 up to 2 mm short of the cemento-enamel junction, with the size-1 Profile hand file in place. The alginate was used as a conducting medium for the electronic apex locator. 13 A layer of self-curing acrylic was poured over the alginate surface to the level of the cemento-enamel junction of the teeth. A small hole was drilled in the acrylic, and the lip-clip electrode of the Tri Auto ZX was inserted into the alginate. The entire assembly (Fig. 2) was kept moist and refrigerated when not in use. Initially, the canal length was measured with the Tri Auto Z X in its electronic manual recording (EMR) mode. The canal was irrigated with 2.5% sodium hypochlorite; then, with the file holder connected, a size-1 Profile hand file was advanced apically until the
light-emitting diode (LED) marked "0.5" on the instrument panel began to glow; when lighted, this LED indicates that the file has reached the apical constriction, u The file was marked at the reference point, withdrawn from the canal, and its measurement from tip to stopper was recorded as the electronic length (EL). With the Tri Auto ZX in its Manual mode, the canals were flared Coronally with Gates-Glidden burs in descending sequence (sizes 4 through 2). Then the device's torque and rotation were adjusted tO the low mode, and the canal was instrumented in a modified crown-down sequence 14 with 0.04 Taper Series 29 nickel titanium rotary files (Tulsa Dental Products), the canal being intermittently irrigated with 2.5% sodium hypochlorite. AAR settings were selected according to the following random sequence: the setting marked "1" was used for the first 20 teeth, the setting marked "1.5" was used for the next 20 teeth, and the setting marked "2" was used for the last 20 teeth. The canal was enlarged apically to file size-7 (0.46 mm at the tip) until the preset AAR LED glowed and rotation reversal occurred. At this point rotation was stopped, the last file was marked at the reference point, and its measurement from tip to stopper was recorded as the instrumented length (IL). The files used for instrumentation were not changed
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Fig. 3. Exposed canals after instrumentation with rotary nickel titanium files driven by Tri Auto ZX and filling with vertically compacted gutta-percha and sealer (original magnification x25). A, Canal instrumented with AAR set at 1 shows relative constriction at cementum-dentin junction. B, Canal instrumented with AAR set at 1 shows loss of apical constriction.
from one canal to the other; however, any file that demonstrated distortion was replaced. The difference between the AL and EL measurements in all 60 canals was computed, as was the difference between the EL and IL measurements in the 20 canals instrumented with each A A R setting. Paired t-tests were used for statistical analysis; the level of significance was 5%. Finally, the canal was dried with paper points, and a fine-medium gutta-percha cone (Kerr, Romulus, Mich.) was fitted to the IL with "tug-back." Root canal sealer (Roth 801, Elite Grade; Roth International Ltd., Chicago, Ill.) was introduced, and the canal was filled with vertically compacted warm gutta-percha by means of Schilder pluggers (Caulk, York, Pa.) placed apically to within 5 m m of the IL. The remainder of the canal was back-filled with injectable gutta-percha (Obtura II; Obtura Corp., Fenton, Mo.). All teeth were removed from the alginate, and the apical 4 m m of the filled canal of each tooth was exposed by grinding with a water-cooled, high-speed diamond bur. Under a surgical microscope (x16; Global Surgical Corp., St. Louis, Mo.), the canal was observed for the presence or
absence of a relative constriction at the level of the cementum-dentin junction as an indication of a maintained apical constriction. The root filling was used to visually enhance the contour of the canal.
RESULTS All AL, EL, and IL measurements obtained are presented in Table I. The EL was shorter than the AL in all but three of the canals; the mean difference was 0.54 m m (_+ 0:26 mm; p < 0.05). In every canal the IL was either equal to or shorter than the EL (p < 0.01). These two measurements were most consistent when the A A R setting was 1. The mean differences were 0.1 mm (+ 0.10 ram) for A A R setting 1; 0.36 m m (_+ 0.20 ram) for setting 1.5; and 1.30 m m (_+ 1.04 ram) for setting 2. Microscopic examination after exposure of the filled canals disclosed the cementum-dentin junction in all of the roots. At this level, a relative constriction was evident in only 10 of the canals instrumented with the A A R set at 1, as opposed to 18 canals and 17 canals instrumented with the A A R set at 1.5 and 2, respectively (Fig. 3).
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DISCUSSION The in vitro model used in our study was adapted from a m o d e l used in previous studies. 1°,13 Rotary instruments used for the canal instrumentation of teeth mounted in alginate may bind and loosen the teeth. The acrylic resin poured over the alginate surface effectively prevented dislodgement of the teeth during the experimental procedures. In previous studies, researchers have avoided irrigating canals with sodium hypochlorite to prevent damage to the alginatel°'13; in the present study, the canals were irrigated with sodium hypochlorite to better simulate clinical conditions. This procedure did not appear to cause any deterioration of the alginate surrounding the roots. The EL measurements, obtained with the 0.5 LED of the Tri Auto Z X used as reference, were on average 0.54 m m shorter than the A L measurements. This result was consistent with the findings in a previous study, l° in which the 0.5 bar of the Root ZX apex locator (J. Morita Co.) was used as reference. The similar results in the two studies have confirmed that the 0.5 indicators of both devices are equivalent; indeed, the two devices have the same apex locator mechanism. 11 According to Kobayashi et al., 8,11 the 0.5 indicator corresponds to the location of the apical constriction. Morphometrically, the apical constriction was found to be 0.51 m m from the minor foramen, 5 which appears to validate the ability of the Tri Auto Z X to locate it with adequate accuracy. Although the IL was shorter than the EL at all three of the A A R settings, the results demonstrated a variation in consistency among the A A R settings. With the A A R set at 1, the IL was, at most, 0.2 m m shorter than the initial EL, known to correspond to the apical constriction. 11 With the A A R set at 1.5, the discrepancy ranged from 0.2 to 1.2 ram. A A R setting 2 proved to be the least consistent, with the discrepancy between EL and IL ranging from 0 to 4.2 mm; such an inconsistent apical extent of instrumentation would be clinically unacceptable. Both the Root Z X apex locator and the Tri Auto ZX handpiece operate on a ratio-method principle that is designed to locate the narrowest canal diameter, which normally coincides with the apical constriction. 8 From the differences in consistency between the three A A R settings, it appeared that the Tri Auto ZX could locate this point of narrowest diameter, or apical constriction, with greater accuracy than it could determine the distance from it. Our group has previously demonstrated that rotary canal instrumentation can be controlled by connecting an apex locator online. 1° To do so, however, the opera-
tor must constantly monitor the apex locator and withdraw the file from the canal when the desired apical extent is indicated. Although such a technique is possible, it is cumbersome and requires close attention. In contrast to the apex locator connected online, the Tri Auto ZX's A A R mechanism actively and automatically prevented accidental overinstrumentation. In addition, the ATR mechanism, as set for this study, resulted in frequent rotation reversal. It was noted during instrumentation of the 60 canals that although five files manifested distortion of their tips (three of them were size4 files and two were size-5 files), no files broke. Presumably the ATR mechanism prevented excessive torque on the files and thereby prevented file breakage. It was concluded that under the conditions of this study, the apical extent of rotary canal instrumentation with the Tri Auto ZX was most consistent at A A R setring 1, less consistent at A A R setting 1.5, and least consistent at A A R setting 2. These findings suggested that A A R setting 1 might be appropriate for clinical application, pending confirmation in a clinical trial. Such clinical assessment is currently being performed by our group. We thank Rita Bauer, Steve Burany, and Annemarie Polis for their invaluable assistance.
REFERENCES 1. Tronstad L. Prognosis of endodontic treatment. In: Clinical Endodontics. 1st ed. New York: Thieme Medical Publishers Inc.; 1991. 2. Ingle JI, Balkland LK, Peters DL, Buchanan S, Mullaney TR Endodontic cavity preparation. In: Ingle JI & Bakland LK, editors. Endodontics. 4th ed. Malvern, Pa.: Williams & Wilkins; 1994. p. 92-227. 3. West JD, Roane JB, Goerig AC. Cleaning and shaping the root canal system. In: Cohen S, Burns RC, editors. Pathways of the pulp. 6th ed. St. Louis: Mosby-Year Book, Inc.; 1994: p. 179218. 4. KutflerY. Microscopic investigation of root apexes. J Am Dent Assoc 1955;50:544-52. 5. Dummer PMH, McGinn JH, Rees DG. The position and topography of the apical canal constriction and apical foramen. International Endodontics Journal 1984;17:192-8. 6. Ushiyama J. New principle and method for measuring the root canal length. J Endod 1983;9:97-104. 7. Salto T, Yamashita Y. Electronic determination of root canal length by a newly developed measuring device: influences of the diameter of apical foramen, the size of K-file and root canal irrigants. Dentistry in Japan 1990;27:65-72. 8. Kobayashi C, Suda H. New electronic canal measuring device based on the ratio method. J Endod 1994;20:111-4. 9. Pratten DH, McDonald R. Comparison of radiographic and electronic working lengths. J Endod 1996;22:173-6. 10. Nguyen HQ, Kanfman AY, Komorowski RC, Friedman S. Electronic length measurement using small and large files in enlarged canals. Int Endod J 1997;29:359-64. l 1. Kobayashi C, Yoshioka T, Suda H. A new engine-driven canal preparation system with electronic canal measuring capability. J Endod 1997;23:751-4. 12. Schneider SW. A comparison of canal preparations in straight
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March 1998 and curved root canals. Oral Surg Oral Med Oral Pathol 1971;32:271-5. 13. Katz A, Mass E, Kaufman AY. Electronic apex locator: a useful tool for root canal treatment in the primary dentition. J Dent Child 1996;63:414-7. 14. Morgan LF, Montgomery S. An evaluation of the crown-down pressureless technique. J Endod 1984;10:491-8.
Reprint requests: Shimon Friedman, DMD Department of Endodontics Faculty of Dentistry, University of Toronto 124 Edward Street Toronto, Ontario, M5G 1G6 Canada
CALL FOR REVIEW ARTICLES The January 1993 issue of Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontics contained an Editorial by the Journal's Editor in Chief, Larry J. Peterson, that called for a Review Article to appear in each issue. These Review Articles should be designed to review the current status of matters that are important to the practitioner. These articles should contain current developments, changing trends, as well as reaffirmation of current techniques and policies. Please consider submitting your article to appear as a Review Article. Information for authors appears in each issue of Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology,
and Endodontics. We look forward to hearing from you.