0099-2399/92/1801-0010/$03.00/0 JOURNAL OF ENDODONTICS Copyright © 1991 by The American Association of Endodontists
Printed in U.S.A.
VOL. 18, NO. 1, JANUARY1992
Comparison of Conventional Root Canal Obturation Techniques with Thermafil Obturators Aida A. Chohayeb, DDS, MSD, FACD, FICD
This study compared microleakage of Thermafil Obturators to the single cone technique in Lexan blocks simulating root canals (n = 20) stained with Prussian blue dye. The microleakage of Thermafil and laterally condensed extracted human teeth was also investigated after the teeth were stained with India ink or Prussian blue dye over 1- or 2-wk dye immersion periods. In Lexan blocks there was no statistical difference in mean leakage between the single cone technique and Thermafil. Teeth, with Thermafil Obturators exhibited greater leakage than those with the lateral condensation. Greater leakage was also seen where India ink was used. Dye immersion time did not have a significant influence on leakage scores. The combination of India ink with Thermafil demonstrated the greatest average leakage. This study demonstrated that Lexan canal simulating blocks do not mimic extracted human teeth for evaluating microleakage.
condensed gutta-percha or the single cone techniques. Contradicting results were reported by Lares and E1Deeb (5), who stated that the lateral condensation technique had significantly less leakage than Thermafil. These conflicting conclusions prompted this current investigation. Different root canal sealers were used in the above studies evaluating Thermafil Obturators: Beatty et al. (4) used Roth Regular root canal sealer, while Lares and EIDeeb (5) used Tubli-Seal. Also, different dyes were used in those studies: Lares and E1Deeb (5) used India ink and Beatty et al. (4) used aqueous 1% methylene blue dye. A review of other microleakage studies identified variations in the experimental techniques, namely, the type of dye used for leakage measurement and the time period for dye immersion. The objectives of this study were (a) to compare the efficacy of Thermafil Obturators to the tingle cone obturation method in completely obturating the root canal(s), including accessory canals; (b) to compare the apical seal of the Thermafil Obturators to the lateral condensation and single cone obturation techniques as manifested by the degree of microleakage; (c) to establish whether different dyes used in leakage studies can elicit different degrees of microleakage and whether the time of immersion in the dye can contribute to the degree of microleakage seen; and (d) to compare the effectiveness of canal-simulating Lexan blocks to extracted human teeth in conducting leakage studies.
Total obturation of the root canal space is the ultimate objective of endodontic treatment procedures. Failures of endodontic treatment are attributed to incomplete obturation of the root canal system (1). Many root canal obturation techniques have been developed over the years with lateral condensation as the most widely used method of obturation. In 1978, Johnson (2) recommended "A simple, fast and efficient means of obturating canals." His method was to use a sealer, stainless steel files, and thermally plasticized guttapercha to obtain a three-dimensional obturation of the root canal system. This method of obturation was recently commercialized under the name Thermafil Endodontic Obturators (Tulsa Dental Products, Tulsa, OK) (3). The Obturator is a metal carrier coated with a-phase gutta-percha. When heated, the gutta-percha softens, and the carrier transports and compacts the gutta-percha to the working length of the canal. The advantages cited by the manufacturer of the Thermafil Obturators are that this technique completely fills the root canal system with a single insertion and maintains an excellent apical seal. A study by Beatty et al. (4) showed Thermafil to be more effective in restricting apical dye penetration than the laterally
MATERIALS AND METHODS
Before conducting the experiment, the author mastered the technique of obturation with the experimental Thermafil Obturators in both Lexan plastic simulated root canals and in extracted human teeth. Also, a pilot test was conducted to evaluate the reaction, if any, when the two dyes used in this study came in contact with the a-phase gutta-percha used with Thermafil Obturators. One Thermafil Obturator was placed in a vial containing India ink; another Obturator was placed in a vial containing Prussian blue dye. Evaluation of these Obturators over 1- and 2-wk periods revealed no change in the color of the a-phase gutta-percha. This suggested that there was no chemical interaction between the a-phase guttapercha and the dyes tested. 10
Vol. 18, No. 1, January 1992
Experiment l Twenty Lexan plastic blocks with simulated root canals, size 30, were used for obturation with the Thermafil Obturatots. Another 20 blocks were obturated by the single cone obturation technique. The root canal sealer used for both filling techniques was AH26 (De Trey; Dentsply, Zurich, Switzerland). The sealer was mixed and used according to the manufacturer's instructions. A fresh mix of the sealer was mixed for every two obturated blocks. After placement of the root canal filling materials, the treated blocks were placed at 37"C and 100% humidity for 24 h to ensure complete setting of the sealer (6). The treated blocks were placed for 1 wk in aqueous 5% Prussian blue drawing ink dye (Gunter Wagner, FRG). The blocks were then examined and evaluated in reference to (a) degree of microleakage in millimeters from the apical to coronal direction; (b) adaptation of the filling materials to the wall of the block determined with a stereomicroscope at x 10 magnification; and (c) under- or overfilling of the simulated root canal Lexan blocks with the sealer, the gutta-percha, or the Thermafil Obturator. The measurements were made by two independent examiners, and the means were calculated for each specimen.
Experiment 2 This experiment was designed to evaluate the effects and interactions of three factors on the leakage of the two root canal filling systems used in experiment 1. The responses being measured were the penetration distance of the dye from the apex and the length of over- or underextension of the filling material from the apex. A 2 3 factorial design was applied with four replicates of each combination of factors blocked into two sets of 16 samples per experimental run. The order of fabrication of each sample in the two runs was randomized over all three factors. This design was chosen to determine the primary effect of each of the three factors plus any interaction existing between the factors. Thirty-two freshly extracted, randomly selected, singlerooted human teeth were utilized for this study. The crowns of all teeth were removed at the level of the cementoenamel junction to obtain equal length of the roots. The canals were cleaned and shaped tO #25 at the apical one-third of the root and flared to #45 at the coronal two-thirds of the canal. After the completion of instrumentation with one size file, the canal was irrigated with 1.5 ml of 1% sodium hypochlorite solution and dried with paper points. Mixed AH26 sealer was inserted in the canal with the last size file used for instrumentation. The file was inserted and turned counterclockwise to coat the walls of the canal walls with the sealer. In the lateral condensation method, a master cone corresponding to the size of the last file used to instrument the canal was selected. The tip of a master cone was snipped until tugback was obtained at the recorded working length. The cone was then coated with the mixed sealer. A #2 finger spreader (Union Broach Corp., Health-Chem Corp., Long Island, NY) was inserted 1 to 2 mm shorter than the working length. The spreader was kept in the canal until a fine gutta-percha accessory cone was placed. The canal was considered to be adequately obturated when enough points were placed that the spreader could no longer penetrate beyond the coronal third of the canal. The
Comparison of Obturation Techniques
11
coronal third of the canal was then condensed with a #9 plugger. The access opening of each obturated root was sealed with Cavit-G temporary filling material (ESPE; Premier, Norristown, PA). The teeth of the Thermafil group were obturated as specified by the manufacturer. A Thermafil device of the same size as the apical size file was selected. The mixed sealer was placed in the canal by the same method used for the lateral condensation teeth. The gutta-percha portion of the Thermafil device was heated over an open flame by rotating uniformly until the gutta-percha began to expand and become plasticized. The device was then inserted into the canal to the working length. The Thermafil Obturator was left intact after obturation so as not to disturb the seal, and the excess gutta-percha was condensed around the handle. The obturated roots were stored for 24 h at 37°C and 100% humidity to allow complete setting of the sealer (6). Each tooth was coated with two layers of nail varnish except for the apical 2 to 3 mm of the root. The roots were suspended in a glass vial with only the apical 2 to 3 mm of the root submerged in one of the selected dyes for the designated experimental period (1 or 2 wk) (5). After the teeth were stained, they were rinsed and allowed to dry for 24 h. The dye on the external root surface was wiped off with 2- × 2-inch gauze soaked in alcohol. For study of the filling materials in the obturated roots, the teeth were decalcified and cleared by Robertson's clearing technique (7). The dye penetration in the transparent teeth was measured to the nearest 0.5 mm by two independent investigators. The scores of the two evaluators were statistically compared to assure correlation and then added and averaged. The extension of the filling material relative to the apex was also measured to the nearest 0.5 ram, with positive values being the length of overfilling through the apex and negative values being the length of unfilled canal short of the apex. The data were recorded by two independent examiners, and the mean was calculated for each specimen. RESULTS
Experiment I The mean leakage for the conventional and Thermafil materials was 0.1 mm (SD = 0.2 mm) and 0.1 mm (SD = 0.3 mm), respectively. A one-way analysis of variance and unpaired t test of the leakage data for both materials indicated no significant difference at p -< 0.05. The average over- or underfill of the filler beyond the apical opening was 1.0 mm (SD = 1.3 mm) for the single cone technique and 2.9 mm (SD = 1.4 mm) for the Thermafil technique. Analysis of variance and unpaired t tests (10) of this data indicated a greater degree of overfilling with the Thermafil technique at a significance level ofp -< 0.001.
Experiment 2 The data for the leakage response (Table 1) were analyzed for all primary and interactive effects between the three factors: flling system, dye type, and time of immersion in the dye (8). A box plot of the mean values of leakage is given in Fig. 1. A normal probability plot and analysis of variance of
12
Chohayeb
Journal of Endodontics TABLE 1. Leakage response Specimen Type
Leakage Scores
Lateral condensation/Prussion blue (1-wk dye time) Lateral condensation/Prussion blue (2-wk dye time) Thermafil/Prussion blue (1-wk dye time) Thermafil/Prussion blue (2-wk dye time) Lateral condensation/India ink (1-wk dye time) Lateral condensation/India ink (2-wk dye time) Thermafil/India ink (1-wk dye time) Thermafil/India ink (2-wk dye time)
1.7
0.8
Prussian Blue 0.0 D a
0.0 0.5 0.0 3.5 0.0 0.0 0.0 0.5
1.6 0,0
Two
--
I ~Time
/
Weeks
0,3
India Ink 0.2 FillingSystem 0.O One Week Lateral Condensation Thermafil FJG 1. Represents a box plot of the average values of each of the eight obturation/dye/immersion-timecombinations.
all the effects indicated that the type of filling material, type of dye, and the interaction between one filling material and dye had significant influence on the degree of leakage. The effect of the stain immersion time of 1 versus 2 wk showed no significant influence. The only significant interacting factor was the interaction between India ink and Thermafil. The combination of India ink with Thermafil demonstrated slightly greater leakage than all other combinations but at a significance level of p = 0.056. Data for the degree of overor underextension of the filling material were analyzed in the same manner. The only factor expected to demonstrate an influence on this response was the type of filling material. Analysis of variance of a model by use of this parameter resulted in a significance level of only p = 0.058. All other factors and interactions demonstrated much less significance.
0.0 1.0 3.0 0.3 0.0 0.0 0.0 0.7
0.0 1.0 3.0 0.0 0.7 0.0 0.0 0.0
0.0 0.5 0.5 3.0 0.0 0.0 0.0 0.0
Average
SD
0.0 0.7 1.6 1.7 0.2 0.0 0.0 0.3
0.0 0.3 1.6 1.8 0.4 0.0 0.0 0.4
plastic blocks are appropriate for the evaluation of root canal obturation techniques. More leakage was detected when the Thermafil Obturators were compared with the lateral condensation in extracted teeth. This could be due to the composition of the a-phase gutta-percha and its ability to tightly maintain adaptation to the canal wall. These results are in contrast to the findings of Beatty et al. (4). They showed Thermafil Obturators to be more effective in restricting apical dye penetration when compared with the laterally condensed gutta-percha or single cone techniques. Also, slightly more leakage was detected when the Thermafil obturated teeth were placed in the India ink dye than when the teeth were placed in the Prussian blue dye. This difference could be due to the dye particle size or the difference in surface activity of the dyes. Another hypothesis could be that a chemical reaction takes place once the Prussian blue contacts the a-phase gutta-percha, creating a compound that blocks further penetration of the dye. No definite explanation for this difference could be derived from this experiment, and further research should be conducted to examine this phenomenon. The results of this study also showed that the immersion time had no influence on the degree of microleakage. The author would like to thank Dr. Frederick Eichmiller, American Dental Association Health Foundation, Paffenbarger Research Center, National Institute of Standards and Technology, Gaithersburg, MD, for his assistance with data analysis, and Mrs. Margaret Chalkley, also of Paffenbarger Research Center, for editorial assistance. Dr. Chohayeb is professor, Howard University College of Dentistry, Washington, DC. Address requests for reprints to Dr. Aida Chohayeb, 15517 Grinnal Terrace, Rockville, MD 20855.
DISCUSSION References
Lexan blocks were recommended for use for visualization of endodontic treatment procedures (9). In this study more leakage was observed in extracted human teeth than with the Lexan plastic blocks with the Thermafil Obturators. This may have been due to the fact that the plastic blocks are highly hydrophobic, not readily allowing water and stain permeation as in the more hydrophilic natural teeth. Significantly more overfi]ling or underfilling was seen in the plastic blocks when compared with the extracted teeth. This may be due to the fact that the blocks do not represent the actual anatomical configurations of the root canal system as seen in the extracted teeth, namely, the presence of a constricted foramen. The question is then raised whether the
1. Ingle Jl. Endodontics. 3rd ed. Philadelphia: Lea & Febiger, 1985:27-53. 2. Johnson WB. A new gutta-percha technique. J Endodon 1978;4:184-8. 3. Johnson WB. The Thermafil obturation instruction brochure. Tulsa, OK: Tulsa Dental Products, 1988. 4. Beatty RG, Baker PS, Haddix J, Hart F. The efficacy of four root canal obturation techniques in preventing apical dye penetration. J Am Dent Assoc 1989;119:633-7. 5. Lares C, ElDeeb ME. The sealing ability of the Thermafil obturation technique. J Endodon 1990;16:474-9. 6. EIDeeb ME. The sealing ability of injection-molded thermoplasticized gutta-percha. J Endodon 1985;11:84-6. 7. Ropertson D, Leeb IJ, McKee M, Brewer E. A clearing technique for the study of the root canal system. J Endodon 1980;1:421-4. 8. Box GEP, Hunter WG, Hunter JS. Statistics for expedmenters. New York: John Wiley and Sons, 1978:21-31. 9. Weine FS, Kelley RF, Lid PJ. The effect of preparation procedures on original canal shape and on apical foramen shape. J Endodon 1975;1:255-62.
Printed in U.S.A.
VOL. 18, NO. 1, JANUARY1992
Comparison of Conventional Root Canal Obturation Techniques with Thermafil Obturators Aida A. Chohayeb, DDS, MSD, FACD, FICD
This study compared microleakage of Thermafil Obturators to the single cone technique in Lexan blocks simulating root canals (n = 20) stained with Prussian blue dye. The microleakage of Thermafil and laterally condensed extracted human teeth was also investigated after the teeth were stained with India ink or Prussian blue dye over 1- or 2-wk dye immersion periods. In Lexan blocks there was no statistical difference in mean leakage between the single cone technique and Thermafil. Teeth, with Thermafil Obturators exhibited greater leakage than those with the lateral condensation. Greater leakage was also seen where India ink was used. Dye immersion time did not have a significant influence on leakage scores. The combination of India ink with Thermafil demonstrated the greatest average leakage. This study demonstrated that Lexan canal simulating blocks do not mimic extracted human teeth for evaluating microleakage.
condensed gutta-percha or the single cone techniques. Contradicting results were reported by Lares and E1Deeb (5), who stated that the lateral condensation technique had significantly less leakage than Thermafil. These conflicting conclusions prompted this current investigation. Different root canal sealers were used in the above studies evaluating Thermafil Obturators: Beatty et al. (4) used Roth Regular root canal sealer, while Lares and EIDeeb (5) used Tubli-Seal. Also, different dyes were used in those studies: Lares and E1Deeb (5) used India ink and Beatty et al. (4) used aqueous 1% methylene blue dye. A review of other microleakage studies identified variations in the experimental techniques, namely, the type of dye used for leakage measurement and the time period for dye immersion. The objectives of this study were (a) to compare the efficacy of Thermafil Obturators to the tingle cone obturation method in completely obturating the root canal(s), including accessory canals; (b) to compare the apical seal of the Thermafil Obturators to the lateral condensation and single cone obturation techniques as manifested by the degree of microleakage; (c) to establish whether different dyes used in leakage studies can elicit different degrees of microleakage and whether the time of immersion in the dye can contribute to the degree of microleakage seen; and (d) to compare the effectiveness of canal-simulating Lexan blocks to extracted human teeth in conducting leakage studies.
Total obturation of the root canal space is the ultimate objective of endodontic treatment procedures. Failures of endodontic treatment are attributed to incomplete obturation of the root canal system (1). Many root canal obturation techniques have been developed over the years with lateral condensation as the most widely used method of obturation. In 1978, Johnson (2) recommended "A simple, fast and efficient means of obturating canals." His method was to use a sealer, stainless steel files, and thermally plasticized guttapercha to obtain a three-dimensional obturation of the root canal system. This method of obturation was recently commercialized under the name Thermafil Endodontic Obturators (Tulsa Dental Products, Tulsa, OK) (3). The Obturator is a metal carrier coated with a-phase gutta-percha. When heated, the gutta-percha softens, and the carrier transports and compacts the gutta-percha to the working length of the canal. The advantages cited by the manufacturer of the Thermafil Obturators are that this technique completely fills the root canal system with a single insertion and maintains an excellent apical seal. A study by Beatty et al. (4) showed Thermafil to be more effective in restricting apical dye penetration than the laterally
MATERIALS AND METHODS
Before conducting the experiment, the author mastered the technique of obturation with the experimental Thermafil Obturators in both Lexan plastic simulated root canals and in extracted human teeth. Also, a pilot test was conducted to evaluate the reaction, if any, when the two dyes used in this study came in contact with the a-phase gutta-percha used with Thermafil Obturators. One Thermafil Obturator was placed in a vial containing India ink; another Obturator was placed in a vial containing Prussian blue dye. Evaluation of these Obturators over 1- and 2-wk periods revealed no change in the color of the a-phase gutta-percha. This suggested that there was no chemical interaction between the a-phase guttapercha and the dyes tested. 10
Vol. 18, No. 1, January 1992
Experiment l Twenty Lexan plastic blocks with simulated root canals, size 30, were used for obturation with the Thermafil Obturatots. Another 20 blocks were obturated by the single cone obturation technique. The root canal sealer used for both filling techniques was AH26 (De Trey; Dentsply, Zurich, Switzerland). The sealer was mixed and used according to the manufacturer's instructions. A fresh mix of the sealer was mixed for every two obturated blocks. After placement of the root canal filling materials, the treated blocks were placed at 37"C and 100% humidity for 24 h to ensure complete setting of the sealer (6). The treated blocks were placed for 1 wk in aqueous 5% Prussian blue drawing ink dye (Gunter Wagner, FRG). The blocks were then examined and evaluated in reference to (a) degree of microleakage in millimeters from the apical to coronal direction; (b) adaptation of the filling materials to the wall of the block determined with a stereomicroscope at x 10 magnification; and (c) under- or overfilling of the simulated root canal Lexan blocks with the sealer, the gutta-percha, or the Thermafil Obturator. The measurements were made by two independent examiners, and the means were calculated for each specimen.
Experiment 2 This experiment was designed to evaluate the effects and interactions of three factors on the leakage of the two root canal filling systems used in experiment 1. The responses being measured were the penetration distance of the dye from the apex and the length of over- or underextension of the filling material from the apex. A 2 3 factorial design was applied with four replicates of each combination of factors blocked into two sets of 16 samples per experimental run. The order of fabrication of each sample in the two runs was randomized over all three factors. This design was chosen to determine the primary effect of each of the three factors plus any interaction existing between the factors. Thirty-two freshly extracted, randomly selected, singlerooted human teeth were utilized for this study. The crowns of all teeth were removed at the level of the cementoenamel junction to obtain equal length of the roots. The canals were cleaned and shaped tO #25 at the apical one-third of the root and flared to #45 at the coronal two-thirds of the canal. After the completion of instrumentation with one size file, the canal was irrigated with 1.5 ml of 1% sodium hypochlorite solution and dried with paper points. Mixed AH26 sealer was inserted in the canal with the last size file used for instrumentation. The file was inserted and turned counterclockwise to coat the walls of the canal walls with the sealer. In the lateral condensation method, a master cone corresponding to the size of the last file used to instrument the canal was selected. The tip of a master cone was snipped until tugback was obtained at the recorded working length. The cone was then coated with the mixed sealer. A #2 finger spreader (Union Broach Corp., Health-Chem Corp., Long Island, NY) was inserted 1 to 2 mm shorter than the working length. The spreader was kept in the canal until a fine gutta-percha accessory cone was placed. The canal was considered to be adequately obturated when enough points were placed that the spreader could no longer penetrate beyond the coronal third of the canal. The
Comparison of Obturation Techniques
11
coronal third of the canal was then condensed with a #9 plugger. The access opening of each obturated root was sealed with Cavit-G temporary filling material (ESPE; Premier, Norristown, PA). The teeth of the Thermafil group were obturated as specified by the manufacturer. A Thermafil device of the same size as the apical size file was selected. The mixed sealer was placed in the canal by the same method used for the lateral condensation teeth. The gutta-percha portion of the Thermafil device was heated over an open flame by rotating uniformly until the gutta-percha began to expand and become plasticized. The device was then inserted into the canal to the working length. The Thermafil Obturator was left intact after obturation so as not to disturb the seal, and the excess gutta-percha was condensed around the handle. The obturated roots were stored for 24 h at 37°C and 100% humidity to allow complete setting of the sealer (6). Each tooth was coated with two layers of nail varnish except for the apical 2 to 3 mm of the root. The roots were suspended in a glass vial with only the apical 2 to 3 mm of the root submerged in one of the selected dyes for the designated experimental period (1 or 2 wk) (5). After the teeth were stained, they were rinsed and allowed to dry for 24 h. The dye on the external root surface was wiped off with 2- × 2-inch gauze soaked in alcohol. For study of the filling materials in the obturated roots, the teeth were decalcified and cleared by Robertson's clearing technique (7). The dye penetration in the transparent teeth was measured to the nearest 0.5 mm by two independent investigators. The scores of the two evaluators were statistically compared to assure correlation and then added and averaged. The extension of the filling material relative to the apex was also measured to the nearest 0.5 ram, with positive values being the length of overfilling through the apex and negative values being the length of unfilled canal short of the apex. The data were recorded by two independent examiners, and the mean was calculated for each specimen. RESULTS
Experiment I The mean leakage for the conventional and Thermafil materials was 0.1 mm (SD = 0.2 mm) and 0.1 mm (SD = 0.3 mm), respectively. A one-way analysis of variance and unpaired t test of the leakage data for both materials indicated no significant difference at p -< 0.05. The average over- or underfill of the filler beyond the apical opening was 1.0 mm (SD = 1.3 mm) for the single cone technique and 2.9 mm (SD = 1.4 mm) for the Thermafil technique. Analysis of variance and unpaired t tests (10) of this data indicated a greater degree of overfilling with the Thermafil technique at a significance level ofp -< 0.001.
Experiment 2 The data for the leakage response (Table 1) were analyzed for all primary and interactive effects between the three factors: flling system, dye type, and time of immersion in the dye (8). A box plot of the mean values of leakage is given in Fig. 1. A normal probability plot and analysis of variance of
12
Chohayeb
Journal of Endodontics TABLE 1. Leakage response Specimen Type
Leakage Scores
Lateral condensation/Prussion blue (1-wk dye time) Lateral condensation/Prussion blue (2-wk dye time) Thermafil/Prussion blue (1-wk dye time) Thermafil/Prussion blue (2-wk dye time) Lateral condensation/India ink (1-wk dye time) Lateral condensation/India ink (2-wk dye time) Thermafil/India ink (1-wk dye time) Thermafil/India ink (2-wk dye time)
1.7
0.8
Prussian Blue 0.0 D a
0.0 0.5 0.0 3.5 0.0 0.0 0.0 0.5
1.6 0,0
Two
--
I ~Time
/
Weeks
0,3
India Ink 0.2 FillingSystem 0.O One Week Lateral Condensation Thermafil FJG 1. Represents a box plot of the average values of each of the eight obturation/dye/immersion-timecombinations.
all the effects indicated that the type of filling material, type of dye, and the interaction between one filling material and dye had significant influence on the degree of leakage. The effect of the stain immersion time of 1 versus 2 wk showed no significant influence. The only significant interacting factor was the interaction between India ink and Thermafil. The combination of India ink with Thermafil demonstrated slightly greater leakage than all other combinations but at a significance level of p = 0.056. Data for the degree of overor underextension of the filling material were analyzed in the same manner. The only factor expected to demonstrate an influence on this response was the type of filling material. Analysis of variance of a model by use of this parameter resulted in a significance level of only p = 0.058. All other factors and interactions demonstrated much less significance.
0.0 1.0 3.0 0.3 0.0 0.0 0.0 0.7
0.0 1.0 3.0 0.0 0.7 0.0 0.0 0.0
0.0 0.5 0.5 3.0 0.0 0.0 0.0 0.0
Average
SD
0.0 0.7 1.6 1.7 0.2 0.0 0.0 0.3
0.0 0.3 1.6 1.8 0.4 0.0 0.0 0.4
plastic blocks are appropriate for the evaluation of root canal obturation techniques. More leakage was detected when the Thermafil Obturators were compared with the lateral condensation in extracted teeth. This could be due to the composition of the a-phase gutta-percha and its ability to tightly maintain adaptation to the canal wall. These results are in contrast to the findings of Beatty et al. (4). They showed Thermafil Obturators to be more effective in restricting apical dye penetration when compared with the laterally condensed gutta-percha or single cone techniques. Also, slightly more leakage was detected when the Thermafil obturated teeth were placed in the India ink dye than when the teeth were placed in the Prussian blue dye. This difference could be due to the dye particle size or the difference in surface activity of the dyes. Another hypothesis could be that a chemical reaction takes place once the Prussian blue contacts the a-phase gutta-percha, creating a compound that blocks further penetration of the dye. No definite explanation for this difference could be derived from this experiment, and further research should be conducted to examine this phenomenon. The results of this study also showed that the immersion time had no influence on the degree of microleakage. The author would like to thank Dr. Frederick Eichmiller, American Dental Association Health Foundation, Paffenbarger Research Center, National Institute of Standards and Technology, Gaithersburg, MD, for his assistance with data analysis, and Mrs. Margaret Chalkley, also of Paffenbarger Research Center, for editorial assistance. Dr. Chohayeb is professor, Howard University College of Dentistry, Washington, DC. Address requests for reprints to Dr. Aida Chohayeb, 15517 Grinnal Terrace, Rockville, MD 20855.
DISCUSSION References
Lexan blocks were recommended for use for visualization of endodontic treatment procedures (9). In this study more leakage was observed in extracted human teeth than with the Lexan plastic blocks with the Thermafil Obturators. This may have been due to the fact that the plastic blocks are highly hydrophobic, not readily allowing water and stain permeation as in the more hydrophilic natural teeth. Significantly more overfi]ling or underfilling was seen in the plastic blocks when compared with the extracted teeth. This may be due to the fact that the blocks do not represent the actual anatomical configurations of the root canal system as seen in the extracted teeth, namely, the presence of a constricted foramen. The question is then raised whether the
1. Ingle Jl. Endodontics. 3rd ed. Philadelphia: Lea & Febiger, 1985:27-53. 2. Johnson WB. A new gutta-percha technique. J Endodon 1978;4:184-8. 3. Johnson WB. The Thermafil obturation instruction brochure. Tulsa, OK: Tulsa Dental Products, 1988. 4. Beatty RG, Baker PS, Haddix J, Hart F. The efficacy of four root canal obturation techniques in preventing apical dye penetration. J Am Dent Assoc 1989;119:633-7. 5. Lares C, ElDeeb ME. The sealing ability of the Thermafil obturation technique. J Endodon 1990;16:474-9. 6. EIDeeb ME. The sealing ability of injection-molded thermoplasticized gutta-percha. J Endodon 1985;11:84-6. 7. Ropertson D, Leeb IJ, McKee M, Brewer E. A clearing technique for the study of the root canal system. J Endodon 1980;1:421-4. 8. Box GEP, Hunter WG, Hunter JS. Statistics for expedmenters. New York: John Wiley and Sons, 1978:21-31. 9. Weine FS, Kelley RF, Lid PJ. The effect of preparation procedures on original canal shape and on apical foramen shape. J Endodon 1975;1:255-62.
