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Analysis of Continuous-Wave Obturation Using a Single-cone and Hybrid Technique
JOURNAL OF ENDODONTICS Copyright © 2003 by The American Association of Endodontists
Printed in U.S.A. VOL. 29, NO. 8, AUGUST 2003
Analysis of Continuous-Wave Obturation Using a Single-cone and Hybrid Technique Garrett M. Guess, DDS, Kevin R. Edwards, DDS, Ming-Lung Yang, DDS, Mian K. Iqbal, BDS, MS, and Syngcuk Kim, PhD, DDS
ing from 70% to 98% have been reported for conventional root canal treatment where gutta-percha and sealer cement have been used to fill the canals (3). Most new techniques are introduced and tested against the standard obturation technique: lateral condensation. Lateral condensation has the advantage of providing a tight apical seal through the compaction of many gutta-percha points by a spreader in the apical region. The best quality of apical seal has been achieved when the spreader depth is within 1.0 mm of the working length (4). Canal curvature and anatomic intricacies often prevent this objective. Another major drawback of the lateral condensation obturation technique is the inability of the cold gutta-percha cones to adapt to the canal walls, especially in the presence of canal irregularities (5). Another obturation technique developed to overcome the shortcoming of lateral condensation is the warm vertical gutta-percha technique. Warm gutta-percha can adapt more effectively to canal irregularities, providing a better obturation result (1). One version of this approach is the continuous-wave technique of root canal obturation. Using a single master cone and a heat source, the root canal is obturated by the softened gutta-percha and sealer under pressure from the heated plugger (6). This technique effectively provides an adequate apical seal in addition to obturating lateral canals (7). The main criticism of this technique is that only a single, uncondensed cone is present in the apical region to seal the root canal apex. Unlike the lateral condensation technique, the plugger depth for the continuous-wave obturation technique is recommended to be within 3 to 5 mm of the working length (1, 6). Studies have shown that when the plugger is farther than 3 mm from the working length, no apical adaptation of the master cone occurs (5, 8). To overcome the possible negative effect of a single, uncondensed gutta-percha cone surrounded by sealer in the apical region (single-cone technique), this study tested a hybrid technique of root canal obturation, which uses an initial lateral condensation of cones followed by a continuous-wave down-pack with a System-B plugger. This technique was compared to the single-cone continuous-wave obturation technique by analyzing the ability of both techniques to adapt gutta-percha to the prepared root canal walls in the apical 1 mm and 3 mm of the root. In addition, this study analyzed the effect that various System-B heated plugger depths had on the adaptation of the gutta-percha to the root canal walls during continuous-wave obturation using both hybrid and singlecone techniques.
This study analyzed the adaptation of gutta-percha to prepared root canal walls using two obturation techniques and determined the influence of the System-B plugger depth on filling adaptation. Fiftysix extracted human mandibular molars were instrumented using Profile NiTi rotary instruments, stratified based on curvature, then randomly distributed into two groups. Group 1 was obturated using the single-cone continuous-wave technique. Group 2 was obturated with a hybrid technique: lateral condensation followed by a continuouswave down-pack. Based on System-B plugger penetration, teeth were divided into three subgroups: (a) < 3.5 mm, (b) 3.5 to 4.5 mm, and (c) > 4.5 mm. Roots were horizontally sectioned at 1 mm and 3 mm coronal to the apical foramen, stained, and photographed. Four evaluators scored the adaptation of gutta-percha to the prepared canal walls. In 100% (n ⴝ 56) of the samples, no statistically significant difference existed between the two obturation methods at 1-mm (x ⴝ 1.80, SD ⴞ 0.69) or 3-mm (x ⴝ 1.804, SD ⴞ 0.69) sections. Best results were obtained with a plugger depth 3.5 to 4.5 mm from the working length.
Obturation of the cleaned and shaped root canal system is vital in endodontic therapy to prevent the ingress of bacteria into the cleaned and disinfected root canal space, in addition to preventing the recolonization of bacteria present at the time of root filling. Providing a filling in the root canal capable of sealing the coronal, apical, and lateral openings is one of the main treatment objectives. Sealing the root canal system relies on the adequate adaptation of a filling material to obliterate the canal space and its intricacies: fins, deltas, isthmuses, and lateral canals (1). Providing an adequate seal allows for complete obturation to minimize the chance of endodontic failure (2). Obturation of the root canal space has been performed using various techniques, most of which have been largely successful when looking at historical prognostic studies. Success rates rang509
510
Guess et al.
MATERIALS AND METHODS Fifty-six human extracted mandibular molar mesiobuccal roots were used. One canal in each root was chosen to instrument. Instrumentation was performed using rotary instrumentation with electric Aseptico Motors (Dentsply Tulsa Dental, Tulsa, OK). Water as an irrigant and RC Prep as a lubricant were used liberally during the instrumentation process. The final shape obtained for all samples was a size 6 Series 29 Profile (Dentsply Tulsa Dental) 0.06 taper at a working length 0.5 mm from the end of the root. Curvatures of sample teeth were assessed and the samples were stratified, then randomly divided into two groups allowing an even distribution of curvature with a random overall distribution between the groups. Group 1 teeth were part of the single-cone continuous-wave obturation group, whereas Group 2 teeth were obturated using a hybrid technique: a combination of lateral condensation of a master cone with three accessory cones, followed by warm vertical compaction of the gutta-percha cone mass using the System-B (Analytic Endo) heat-source in one step. After instrumentation, roots in both groups were rinsed with water and dried with paper points. Each group 1 root was obturated by the same operator with a fine medium size gutta-percha point trimmed to size 40 using a GuttaGauge (Dentsply/Maillefer, Tulsa, OK) and razor blade. The point was fitted in a dry canal to assess proper tug-back and working-length measurement and trimmed accordingly. ZOE Roth’s Sealer (Patterson Dental Supply, Inc., St. Paul, MN) was delivered into the canals using a #20 ISO K-file, applied to the cone, and the cone firmly seated into place. A System-B heat-source was used in a single step at the 200°C setting in the manner outlined by Buchanan, 2000 (6). The coronal guttapercha was removed at the orifice and a 4-5 plugger used to condense and seat the master cone; a heated FM plugger on the System-B at 200°C advanced until just before reaching its premeasured binding point. The heat was released and a 10-s wait followed, during which time the stopper on the heated plugger was adjusted to allow measurement of the plugger insertion depth. A burst of heat was applied for 2 s and the plugger removed. After removal of the heat source, the remaining apical gutta-percha was compacted with a stainless steel #4-5 plugger. Depth of plugger penetration from the working length was recorded as a difference in the plugger depth from the root canal working length. Backfill was not performed. Group 2 teeth were obturated by fitting an ISO size 40 standardized gutta-percha cone to the working length. Tug back was confirmed before obturation. Sealer was applied in a similar manner as group 1. The master cone was inserted with sealer to the working length and condensation with a stainless steel D11T spreader was performed to within 1 to 2 mm of the working length if possible. Three FF size accessory cones followed lateral condensation with the spreader. Using the System-B heat source in a similar manner as in group 1, down-pack was performed in one step after the initial searing of the cones at the orifice level. After the down-pack to the point before binding, plugger depth was recorded in the same manner as group 1. Apical gutta-percha was compacted with the same stainless steel plugger as in group 1 after System-B plugger withdrawal. During the down-pack with the System-B in both groups, the depth of the plugger penetration from the working length was recorded in 0.5-mm increments and three subgroups were formed: (a) 2.5 to 3.5 mm; (b) 3.5 to 4.5 mm; and (c) 4.5 to 7mm from the apical extent of the working length.
Journal of Endodontics
For each tooth, two horizontal sections were performed: one at 1 mm from the root end; another at 3 mm from the root end. Teeth were sectioned using a slow-speed fine diamond disc (Brasseler USA, Savannah, GA) submerged under water. Each section’s apical surface was stained with methylene blue dye, rinsed with water, and dried by blotting on absorbent paper. Sections were photographed using a Nikon 990 digital camera attached to the beam splitter of an operating microscope at ⫻16 magnification. Images were taken at 1024⫻768 resolution and downloaded to an Apple PowerBook laptop computer (Apple Computer, Inc., Cupertino, CA). A panel of four dentists evaluated the images obtained (112 total): one board-certified endodontist, two first-yr endodontic residents, and one second-yr endodontic resident. The criteria for evaluation were established and sample evaluations were performed on 10 images to calibrate the evaluators. Images were projected from the laptop computer onto a screen for the amount of time needed to obtain a score by a majority vote. Images were scored using a three-point scoring system. A score of 1 was awarded for gutta-percha adaptation (contact) to all of the prepared root surface with minimal sealer; score of 2 for a section with gutta-percha adapting to 2⁄3 of the prepared root surface; and a score of 3 for adaptation of gutta-percha to less than 1⁄3 of the prepared root surface. Upon projection of a section image onto the screen, the group agreed on a score to assign the section. Evaluators were unaware of which technique, section depth, or pluggerdepth insertion for the image shown. Upon agreement of a score that the sample represented, the value was recorded. No scores were disputed or disagreed on. The results of the evaluation were subjected to statistical analysis using a Wilcoxon rank sum test. Depth of spreader penetration was reviewed and compared to the obturation adequacy scores.
RESULTS Results show that in 100% (n ⫽ 56) of the obturated teeth, no statistically significant difference existed between the two obturation methods when measured at 1 mm (x ⫽ 1.80, SD ⫾ 0.69) or 3 mm (x ⫽ 1.804, SD ⫾ 0.69) from the apical working length. The scores obtained were as follows: 37 sections received a score of 1; 54 received a score of 2; and 21 sections received a score of 3. During evaluation of the cases by the panel of four evaluators, no ties in the voting resulted. The panel was in agreement by a majority for each case evaluated. With regards to plugger depth of insertion for both obturation techniques, best results were obtained when plugger depth range was within 3.5 to 4.5 mm from the working length, with 46% of the sections at this plugger depth receiving a score of 1 and 46% receiving a score of 2 for this group. However, differences between the three subgroups had no statistically significant difference.
DISCUSSION We hypothesized that the cold lateral condensation of guttapercha cones followed by a continuous-wave down-pack would provide better gutta-percha adaptation and density in the apical third of the root canal compared with a single-cone continuouswave technique. Additionally, we hypothesized that the deepest penetration possible with the heated plugger would provide the best adaptation results.
Vol. 29, No. 8, August 2003
The hybrid method of obturation as described in this study seems to take advantage of the apical sealing and adaptive ability of lateral condensation. Additionally, this technique would take advantage of the greater adaptability of the heat-softened guttapercha formed during the heated down-pack. The data obtained for both groups of teeth show that there is no statistically significant difference between the adaptation of gutta-percha to the prepared root canal wall at 1- and 3-mm sections whether a single-cone or multiple-cone (hybrid) technique for obturation was used. This finding suggests that having a single cone with sealer in the apical region as in group 1 is as effective as several smaller cones laterally compacted together in filling the root canal space. This is in agreement with a similar finding concluded by Friedman et al. (9). For lateral condensation to be most effective, the spreader depth has to reach within 1 mm of the working length (4). Similar to the clinical practice using lateral condensation, the depth of D11T spreader penetration during the lateral condensation of a master and three accessory cones was not measured. During obturation of the cases, the spreader was taken into the canal space as far as reasonably possible, with a reasonable amount of force. This is the same course of action taken when obturating clinical cases; although deep penetration of the spreader is desired, it is not always obtainable. In addition, the depth of penetration of the accessory cones after spreader insertion was not measured. This may account for the lack of a significant difference between the single-cone and hybrid techniques. If the spreader does not penetrate to the correct depth, the accessory cones fail to reach into the space created by the spreader; the gain by laterally condensing numerous cones in the apical third may not be obtained. No increase in gutta-percha density or adaptation will occur without the cones or spreader reaching into the apical region, within millimeters of the working length. This may account for no difference between the two obturation groups. Heated plugger depth of penetration has been shown to be an important element for success in the warm-vertical obturation technique (1) and the continuous-wave technique (6). Recommendations for each technique suggest that the best results occur when the plugger is within 5 to 7 mm of the working length, with claims of heat traveling up to 3 mm through gutta-percha. Deeper penetration of the heated plugger in the root canal allows better heating of the gutta-percha, which facilitates closer adaptation of guttapercha to the root canal walls and their irregularities (5, 8). With regards to our findings, the System-B heated plugger depth, which extended within 3.5 to 4.5 mm of the working length, provided the best overall adaptation of gutta-percha to the prepared root canal walls. Our finding is not in accordance with our hypothesis or with the findings of Smith et al. (5). Smith et al. found that the closer the plugger gets to the working length the better the incorporation of canal irregularities in the gutta-percha filling, which resulted especially in the critical apical region. Our subgroup that represented the closest penetration of the plugger to the working length did not provide the best number of adaptation scores. The difference in our study may be caused by the extension of the plugger, in several cases, to a level that was below the sectioning depth. In some samples the plugger extended to 2.5 mm from the working length. A section at 3 mm would cut through a section of the root that is not filled, because a backfill of gutta-percha was not performed in either group. The resulting score from the evaluation would be poor, because little or no gutta-percha would be present on the prepared canal walls. An additional reason for the lack of difference between the two obturation techniques may be because of the inability of heat to be
Hybrid versus Single-cone Obturation
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transferred to the apical region. Smith et al. (5) and Weller et al. (8) demonstrated the importance of the plugger reaching a depth within several millimeters from the working length to obtain softened gutta-percha. Without enough heat reaching the apical third to soften the gutta-percha in the single-cone group, the result would be an unadapted single-cone in the apical region. This would make the two obturation methods essentially the same: a single, unheated cone in the apical third. The method for evaluation in our study was controlled in two ways. First, no evaluator knew which case corresponded to the obturation technique or extension of the heated plugger. Second, the images were projected in a backward manner in an automated slide show preventing any further knowledge of the case type. During evaluation no ties resulted during the assignment of adaptation scores, suggesting proper evaluator calibration. Although subjective in nature, the data groupings used allowed clear distinctions to be made between the different obturation adaptation qualities. During instrumentation of the roots, water was chosen as an irrigant. Water does not have the potent tissue dissolving abilities of sodium hypochlorite (10). This study looked at the instrumented canal space and the adaptation of gutta-percha to only the area touched by the file’s action. Therefore, the cleaning ability of the instrumentation technique was limited to the file only—not the irrigant. By not dissolving the surrounding tissue and debris, the evaluation of gutta-percha and its adaptation to the instrumented canal wall was facilitated by the sharp contrast between the filling material, sealer, dentin, and stained debris. Although the same root type was used from the same tooth type, canal configurations were extremely variable, as can be expected. The canal morphology was not controlled for in the selection of teeth for the two instrumentation groups, because clinically this cannot be measured. Degree of angulation was accounted for because groups contained an even representation of all degrees of curvature. This is important because canal curvature has been shown to influence both plugger penetration and spreader penetration depths (11). Because of the differing anatomical shapes of the root canals, different depths of penetration of the plugger can be expected, even though the teeth were instrumented to the same final instrument size. With regards to evaluation, only the instrumented canal space was evaluated. Therefore, a section displaying an isthmus would not be graded less for the inability of the gutta-percha to extend into this uninstrumented space. It does seem that the size and configuration of the root canal would have an effect on the obturation result. A larger canal would not allow the hydraulic “wave of obturation” to occur, as described by Buchanan (6), possibly decreasing the adaptive abilities of the continuouswave single-cone technique. Therefore, in a larger canal, an increased density of gutta-percha with better adaptation may result with the lateral condensation of numerous gutta-percha cones. Further investigation with regard to case outcome needs to be performed to see if there is any in vivo benefit to the findings obtained by this study. Prognostic studies to date have not been able to distinguish better outcomes based on different gutta-percha obturation techniques. Additionally, an objective analysis of the adaptation of the gutta-percha to the canal walls using CAD technology to measure the filled areas of the root canal space would strengthen our conclusions. The authors thank Kimberly Naugle for assistance with the statistical analysis. Drs. Guess, Edwards, and Yang are affiliated with the Department of Endodontics, Dr. Iqbal is director, and Dr. Kim is chairman, Department of
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Endodontics, University of Pennsylvania School of Dental Medicine, Philadelphia, PA. Address requests for reprints to Garrett M. Guess, DDS, University of Pennsylvania School of Dental Medicine, Department of Endodontics, 4001 Spruce Street, Philadelphia, PA 19104.
References 1. Schilder H. Filling root canals in three dimensions. Dent Clin North Am 1967;1:723– 44. 2. Dow PR, Ingle JI. Isotope determination of root canal failure. Oral Surg Oral Med Oral Pathol 1955;8:1100 – 4. 3. Sjogren U, Hagglund B, Sundqvist G, Wing K. Factors affecting the long-term results of endodontic treatment. J Endodon 1990;16:498 –504. 4. Allison DA, Michelich RJ, Walton RE. The influence of master cone adaptation on the quality of the apical seal. J Endodon 1981;7:61–5.
5. Smith RS, Weller RN, Loushine RJ, Kimbrough WF. Effect of varying the depth of heat application on the adaptability of gutta-percha during warm vertical compaction. J Endodon 2000;26:668 –72. 6. Buchanan LS. Continuous wave of condensation technique. Endod Prac 1998;1:7–10, 13– 6, 18. 7. DuLac KA, Nielsen CJ, Tomazic TJ, Ferrillo PJ Jr, Hatton JF. Comparison of the obturation of lateral canals by six techniques. J Endodon 1999; 25:376 – 80. 8. Weller RN, Kimbrough WF, Anderson RW. A comparison of thermoplastic obturation techniques: adaptation to the canal walls. J Endodon 1997; 23:703– 6. 9. Friedman S, Lost C, Zarrabian M, Trope M. Evaluation of success and failure after endodontic therapy using a glass ionomer cement sealer. J Endodon 1995;21:384 –90. 10. Senia ES, Marshall FJ, Rosen S. The solvent action of sodium hypochlorite on pulp tissue of extracted teeth. Oral Surg Oral Med Oral Pathol 1971;31:96 –103. 11. Berry KA, Loushine RJ, Primack PD, Runyan DA. Nickel-titanium versus stainless-steel finger spreaders in curved canals. J Endodon 1998;24: 752– 4.
Printed in U.S.A. VOL. 29, NO. 8, AUGUST 2003
Analysis of Continuous-Wave Obturation Using a Single-cone and Hybrid Technique Garrett M. Guess, DDS, Kevin R. Edwards, DDS, Ming-Lung Yang, DDS, Mian K. Iqbal, BDS, MS, and Syngcuk Kim, PhD, DDS
ing from 70% to 98% have been reported for conventional root canal treatment where gutta-percha and sealer cement have been used to fill the canals (3). Most new techniques are introduced and tested against the standard obturation technique: lateral condensation. Lateral condensation has the advantage of providing a tight apical seal through the compaction of many gutta-percha points by a spreader in the apical region. The best quality of apical seal has been achieved when the spreader depth is within 1.0 mm of the working length (4). Canal curvature and anatomic intricacies often prevent this objective. Another major drawback of the lateral condensation obturation technique is the inability of the cold gutta-percha cones to adapt to the canal walls, especially in the presence of canal irregularities (5). Another obturation technique developed to overcome the shortcoming of lateral condensation is the warm vertical gutta-percha technique. Warm gutta-percha can adapt more effectively to canal irregularities, providing a better obturation result (1). One version of this approach is the continuous-wave technique of root canal obturation. Using a single master cone and a heat source, the root canal is obturated by the softened gutta-percha and sealer under pressure from the heated plugger (6). This technique effectively provides an adequate apical seal in addition to obturating lateral canals (7). The main criticism of this technique is that only a single, uncondensed cone is present in the apical region to seal the root canal apex. Unlike the lateral condensation technique, the plugger depth for the continuous-wave obturation technique is recommended to be within 3 to 5 mm of the working length (1, 6). Studies have shown that when the plugger is farther than 3 mm from the working length, no apical adaptation of the master cone occurs (5, 8). To overcome the possible negative effect of a single, uncondensed gutta-percha cone surrounded by sealer in the apical region (single-cone technique), this study tested a hybrid technique of root canal obturation, which uses an initial lateral condensation of cones followed by a continuous-wave down-pack with a System-B plugger. This technique was compared to the single-cone continuous-wave obturation technique by analyzing the ability of both techniques to adapt gutta-percha to the prepared root canal walls in the apical 1 mm and 3 mm of the root. In addition, this study analyzed the effect that various System-B heated plugger depths had on the adaptation of the gutta-percha to the root canal walls during continuous-wave obturation using both hybrid and singlecone techniques.
This study analyzed the adaptation of gutta-percha to prepared root canal walls using two obturation techniques and determined the influence of the System-B plugger depth on filling adaptation. Fiftysix extracted human mandibular molars were instrumented using Profile NiTi rotary instruments, stratified based on curvature, then randomly distributed into two groups. Group 1 was obturated using the single-cone continuous-wave technique. Group 2 was obturated with a hybrid technique: lateral condensation followed by a continuouswave down-pack. Based on System-B plugger penetration, teeth were divided into three subgroups: (a) < 3.5 mm, (b) 3.5 to 4.5 mm, and (c) > 4.5 mm. Roots were horizontally sectioned at 1 mm and 3 mm coronal to the apical foramen, stained, and photographed. Four evaluators scored the adaptation of gutta-percha to the prepared canal walls. In 100% (n ⴝ 56) of the samples, no statistically significant difference existed between the two obturation methods at 1-mm (x ⴝ 1.80, SD ⴞ 0.69) or 3-mm (x ⴝ 1.804, SD ⴞ 0.69) sections. Best results were obtained with a plugger depth 3.5 to 4.5 mm from the working length.
Obturation of the cleaned and shaped root canal system is vital in endodontic therapy to prevent the ingress of bacteria into the cleaned and disinfected root canal space, in addition to preventing the recolonization of bacteria present at the time of root filling. Providing a filling in the root canal capable of sealing the coronal, apical, and lateral openings is one of the main treatment objectives. Sealing the root canal system relies on the adequate adaptation of a filling material to obliterate the canal space and its intricacies: fins, deltas, isthmuses, and lateral canals (1). Providing an adequate seal allows for complete obturation to minimize the chance of endodontic failure (2). Obturation of the root canal space has been performed using various techniques, most of which have been largely successful when looking at historical prognostic studies. Success rates rang509
510
Guess et al.
MATERIALS AND METHODS Fifty-six human extracted mandibular molar mesiobuccal roots were used. One canal in each root was chosen to instrument. Instrumentation was performed using rotary instrumentation with electric Aseptico Motors (Dentsply Tulsa Dental, Tulsa, OK). Water as an irrigant and RC Prep as a lubricant were used liberally during the instrumentation process. The final shape obtained for all samples was a size 6 Series 29 Profile (Dentsply Tulsa Dental) 0.06 taper at a working length 0.5 mm from the end of the root. Curvatures of sample teeth were assessed and the samples were stratified, then randomly divided into two groups allowing an even distribution of curvature with a random overall distribution between the groups. Group 1 teeth were part of the single-cone continuous-wave obturation group, whereas Group 2 teeth were obturated using a hybrid technique: a combination of lateral condensation of a master cone with three accessory cones, followed by warm vertical compaction of the gutta-percha cone mass using the System-B (Analytic Endo) heat-source in one step. After instrumentation, roots in both groups were rinsed with water and dried with paper points. Each group 1 root was obturated by the same operator with a fine medium size gutta-percha point trimmed to size 40 using a GuttaGauge (Dentsply/Maillefer, Tulsa, OK) and razor blade. The point was fitted in a dry canal to assess proper tug-back and working-length measurement and trimmed accordingly. ZOE Roth’s Sealer (Patterson Dental Supply, Inc., St. Paul, MN) was delivered into the canals using a #20 ISO K-file, applied to the cone, and the cone firmly seated into place. A System-B heat-source was used in a single step at the 200°C setting in the manner outlined by Buchanan, 2000 (6). The coronal guttapercha was removed at the orifice and a 4-5 plugger used to condense and seat the master cone; a heated FM plugger on the System-B at 200°C advanced until just before reaching its premeasured binding point. The heat was released and a 10-s wait followed, during which time the stopper on the heated plugger was adjusted to allow measurement of the plugger insertion depth. A burst of heat was applied for 2 s and the plugger removed. After removal of the heat source, the remaining apical gutta-percha was compacted with a stainless steel #4-5 plugger. Depth of plugger penetration from the working length was recorded as a difference in the plugger depth from the root canal working length. Backfill was not performed. Group 2 teeth were obturated by fitting an ISO size 40 standardized gutta-percha cone to the working length. Tug back was confirmed before obturation. Sealer was applied in a similar manner as group 1. The master cone was inserted with sealer to the working length and condensation with a stainless steel D11T spreader was performed to within 1 to 2 mm of the working length if possible. Three FF size accessory cones followed lateral condensation with the spreader. Using the System-B heat source in a similar manner as in group 1, down-pack was performed in one step after the initial searing of the cones at the orifice level. After the down-pack to the point before binding, plugger depth was recorded in the same manner as group 1. Apical gutta-percha was compacted with the same stainless steel plugger as in group 1 after System-B plugger withdrawal. During the down-pack with the System-B in both groups, the depth of the plugger penetration from the working length was recorded in 0.5-mm increments and three subgroups were formed: (a) 2.5 to 3.5 mm; (b) 3.5 to 4.5 mm; and (c) 4.5 to 7mm from the apical extent of the working length.
Journal of Endodontics
For each tooth, two horizontal sections were performed: one at 1 mm from the root end; another at 3 mm from the root end. Teeth were sectioned using a slow-speed fine diamond disc (Brasseler USA, Savannah, GA) submerged under water. Each section’s apical surface was stained with methylene blue dye, rinsed with water, and dried by blotting on absorbent paper. Sections were photographed using a Nikon 990 digital camera attached to the beam splitter of an operating microscope at ⫻16 magnification. Images were taken at 1024⫻768 resolution and downloaded to an Apple PowerBook laptop computer (Apple Computer, Inc., Cupertino, CA). A panel of four dentists evaluated the images obtained (112 total): one board-certified endodontist, two first-yr endodontic residents, and one second-yr endodontic resident. The criteria for evaluation were established and sample evaluations were performed on 10 images to calibrate the evaluators. Images were projected from the laptop computer onto a screen for the amount of time needed to obtain a score by a majority vote. Images were scored using a three-point scoring system. A score of 1 was awarded for gutta-percha adaptation (contact) to all of the prepared root surface with minimal sealer; score of 2 for a section with gutta-percha adapting to 2⁄3 of the prepared root surface; and a score of 3 for adaptation of gutta-percha to less than 1⁄3 of the prepared root surface. Upon projection of a section image onto the screen, the group agreed on a score to assign the section. Evaluators were unaware of which technique, section depth, or pluggerdepth insertion for the image shown. Upon agreement of a score that the sample represented, the value was recorded. No scores were disputed or disagreed on. The results of the evaluation were subjected to statistical analysis using a Wilcoxon rank sum test. Depth of spreader penetration was reviewed and compared to the obturation adequacy scores.
RESULTS Results show that in 100% (n ⫽ 56) of the obturated teeth, no statistically significant difference existed between the two obturation methods when measured at 1 mm (x ⫽ 1.80, SD ⫾ 0.69) or 3 mm (x ⫽ 1.804, SD ⫾ 0.69) from the apical working length. The scores obtained were as follows: 37 sections received a score of 1; 54 received a score of 2; and 21 sections received a score of 3. During evaluation of the cases by the panel of four evaluators, no ties in the voting resulted. The panel was in agreement by a majority for each case evaluated. With regards to plugger depth of insertion for both obturation techniques, best results were obtained when plugger depth range was within 3.5 to 4.5 mm from the working length, with 46% of the sections at this plugger depth receiving a score of 1 and 46% receiving a score of 2 for this group. However, differences between the three subgroups had no statistically significant difference.
DISCUSSION We hypothesized that the cold lateral condensation of guttapercha cones followed by a continuous-wave down-pack would provide better gutta-percha adaptation and density in the apical third of the root canal compared with a single-cone continuouswave technique. Additionally, we hypothesized that the deepest penetration possible with the heated plugger would provide the best adaptation results.
Vol. 29, No. 8, August 2003
The hybrid method of obturation as described in this study seems to take advantage of the apical sealing and adaptive ability of lateral condensation. Additionally, this technique would take advantage of the greater adaptability of the heat-softened guttapercha formed during the heated down-pack. The data obtained for both groups of teeth show that there is no statistically significant difference between the adaptation of gutta-percha to the prepared root canal wall at 1- and 3-mm sections whether a single-cone or multiple-cone (hybrid) technique for obturation was used. This finding suggests that having a single cone with sealer in the apical region as in group 1 is as effective as several smaller cones laterally compacted together in filling the root canal space. This is in agreement with a similar finding concluded by Friedman et al. (9). For lateral condensation to be most effective, the spreader depth has to reach within 1 mm of the working length (4). Similar to the clinical practice using lateral condensation, the depth of D11T spreader penetration during the lateral condensation of a master and three accessory cones was not measured. During obturation of the cases, the spreader was taken into the canal space as far as reasonably possible, with a reasonable amount of force. This is the same course of action taken when obturating clinical cases; although deep penetration of the spreader is desired, it is not always obtainable. In addition, the depth of penetration of the accessory cones after spreader insertion was not measured. This may account for the lack of a significant difference between the single-cone and hybrid techniques. If the spreader does not penetrate to the correct depth, the accessory cones fail to reach into the space created by the spreader; the gain by laterally condensing numerous cones in the apical third may not be obtained. No increase in gutta-percha density or adaptation will occur without the cones or spreader reaching into the apical region, within millimeters of the working length. This may account for no difference between the two obturation groups. Heated plugger depth of penetration has been shown to be an important element for success in the warm-vertical obturation technique (1) and the continuous-wave technique (6). Recommendations for each technique suggest that the best results occur when the plugger is within 5 to 7 mm of the working length, with claims of heat traveling up to 3 mm through gutta-percha. Deeper penetration of the heated plugger in the root canal allows better heating of the gutta-percha, which facilitates closer adaptation of guttapercha to the root canal walls and their irregularities (5, 8). With regards to our findings, the System-B heated plugger depth, which extended within 3.5 to 4.5 mm of the working length, provided the best overall adaptation of gutta-percha to the prepared root canal walls. Our finding is not in accordance with our hypothesis or with the findings of Smith et al. (5). Smith et al. found that the closer the plugger gets to the working length the better the incorporation of canal irregularities in the gutta-percha filling, which resulted especially in the critical apical region. Our subgroup that represented the closest penetration of the plugger to the working length did not provide the best number of adaptation scores. The difference in our study may be caused by the extension of the plugger, in several cases, to a level that was below the sectioning depth. In some samples the plugger extended to 2.5 mm from the working length. A section at 3 mm would cut through a section of the root that is not filled, because a backfill of gutta-percha was not performed in either group. The resulting score from the evaluation would be poor, because little or no gutta-percha would be present on the prepared canal walls. An additional reason for the lack of difference between the two obturation techniques may be because of the inability of heat to be
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transferred to the apical region. Smith et al. (5) and Weller et al. (8) demonstrated the importance of the plugger reaching a depth within several millimeters from the working length to obtain softened gutta-percha. Without enough heat reaching the apical third to soften the gutta-percha in the single-cone group, the result would be an unadapted single-cone in the apical region. This would make the two obturation methods essentially the same: a single, unheated cone in the apical third. The method for evaluation in our study was controlled in two ways. First, no evaluator knew which case corresponded to the obturation technique or extension of the heated plugger. Second, the images were projected in a backward manner in an automated slide show preventing any further knowledge of the case type. During evaluation no ties resulted during the assignment of adaptation scores, suggesting proper evaluator calibration. Although subjective in nature, the data groupings used allowed clear distinctions to be made between the different obturation adaptation qualities. During instrumentation of the roots, water was chosen as an irrigant. Water does not have the potent tissue dissolving abilities of sodium hypochlorite (10). This study looked at the instrumented canal space and the adaptation of gutta-percha to only the area touched by the file’s action. Therefore, the cleaning ability of the instrumentation technique was limited to the file only—not the irrigant. By not dissolving the surrounding tissue and debris, the evaluation of gutta-percha and its adaptation to the instrumented canal wall was facilitated by the sharp contrast between the filling material, sealer, dentin, and stained debris. Although the same root type was used from the same tooth type, canal configurations were extremely variable, as can be expected. The canal morphology was not controlled for in the selection of teeth for the two instrumentation groups, because clinically this cannot be measured. Degree of angulation was accounted for because groups contained an even representation of all degrees of curvature. This is important because canal curvature has been shown to influence both plugger penetration and spreader penetration depths (11). Because of the differing anatomical shapes of the root canals, different depths of penetration of the plugger can be expected, even though the teeth were instrumented to the same final instrument size. With regards to evaluation, only the instrumented canal space was evaluated. Therefore, a section displaying an isthmus would not be graded less for the inability of the gutta-percha to extend into this uninstrumented space. It does seem that the size and configuration of the root canal would have an effect on the obturation result. A larger canal would not allow the hydraulic “wave of obturation” to occur, as described by Buchanan (6), possibly decreasing the adaptive abilities of the continuouswave single-cone technique. Therefore, in a larger canal, an increased density of gutta-percha with better adaptation may result with the lateral condensation of numerous gutta-percha cones. Further investigation with regard to case outcome needs to be performed to see if there is any in vivo benefit to the findings obtained by this study. Prognostic studies to date have not been able to distinguish better outcomes based on different gutta-percha obturation techniques. Additionally, an objective analysis of the adaptation of the gutta-percha to the canal walls using CAD technology to measure the filled areas of the root canal space would strengthen our conclusions. The authors thank Kimberly Naugle for assistance with the statistical analysis. Drs. Guess, Edwards, and Yang are affiliated with the Department of Endodontics, Dr. Iqbal is director, and Dr. Kim is chairman, Department of
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Journal of Endodontics
Endodontics, University of Pennsylvania School of Dental Medicine, Philadelphia, PA. Address requests for reprints to Garrett M. Guess, DDS, University of Pennsylvania School of Dental Medicine, Department of Endodontics, 4001 Spruce Street, Philadelphia, PA 19104.
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