Discussion - References.
A modification of the lateral condensation method with a Thermafil backfilling technique was presented and evaluated in this study. The new technique can be regarded as a combination of the lateral condensation and the Thermafil techniques with the goal being to add the ease of use of the TF technique to the successful control of the length of the root filling in the master cone/LC technique.
Extrusion of gutta-percha and/or sealer is frequently seen in vivo in connection with TF. In the present study, all TF fillings produced overfilling with both sealer and gutta-percha. However, these in vitro observations in the plastic canals cannot be regarded as directly representative of the clinical situation. Apical patency with size15 K-le was established after the canal preparation, whereas in the clinical situation, apical patency cannot always be obtained. Moreover, resistance by the periapical tissues and tissue pressure in the in vivo situation may reduce the occurrence/extent of overfilling, although the exact effect of these variables is difficult to determine. In preliminary experiments with extracted teeth, less overfilling with the Thermafil technique was observed than in the present study with standardized simulated canals (data not shown). Similarly, pilot experiments to the present study, where apical patency was not established with the small K-les, showed that overfilling with TF seldom occurred. This can be explained through the packing of plastic chips at the apical foramen during preparation. Packing of dentine chips has been suggested in vivo for better control of overfilling when using the TF technique (Scott & Vire 1992). However, dentine chips may contain infectious or antigenic material, and therefore, apical packing of dentine chips should be considered only in vital cases.
The present study showed clearly that under the experimental conditions employed, the possibility of overfilling was greatly reduced with the backfilling technique and was similar to lateral condensation. Although the warm gutta-percha from the TF points seamlessly united with the gutta-percha of the master point as seen in the sections studied under the microscope, the heat capacity of the intruding warm gutta-percha was not high enough to cause melting of the master cone in the apical portion, which could have resulted in extrusion of the filling material. Moreover, no sealer was extruded from the canal during filling.
Radiographic analysis of the root fillings demonstrated good adaptation of the TF fillings to the canal walls in all parts of the canal. However, visual observations made during filling emphasized the importance of vertical compaction. Vertical condensation had a clear effect on the root filling down to the apical part of the canal, but did not, in any case, cause more extrusion of the root filling.
Small voids were detected in both LC and BF fillings. The total number of voids was 42 in 40 canals, 0-2voids per canal. However, the size of the voids was small, and their average total length per canal was less than 1mm. It seems that voids were created as a result of air being trapped in the filling after the apical opening was sealed with the master cone in the LC and BF techniques. The voids in the sealer were typically trapped between the gutta-percha and the canal wall. However, also in such areas, a thin and continuous layer of sealer was seen covering the canal wall resin.
In order to measure the volume of the voids, pilot experiments were completed using a micro CT-scan technique. However, the resolution and sensitivity of the method was not sufficient to detect the voids that were seen on radiographs and verified by stereo microscopy of thin sections.
The BF technique was easy to use and the filling was completed quickly. In the TF technique, the sealer was introduced into the canal with a paper point, whereas in the BF technique, the master gutta-percha point was used. The only additional step in the BF technique compared to TF alone was the condensation of the master gutta-percha point with the spreader before introducing the Thermafil point. In the model used in the present study, BF gave full control of overfilling and was an acceptable alternative to TF technique. The present study was completed in standardized plastic canals with round cross-sections; further studies are required to determine the suitability of the BF technique in natural root canals.
Bhambhani SM, SprechmanK(1994) Microleakage comparison of Thermafil versus vertical condensation using two different sealers. Oral Surgery, Oral Medicine and Oral Pathology 78, 105-8.
Clark DS, El Deeb ME (1993) Apical sealing ability of metal versus plastic carrier Thermafil obturators. Journal of Endodontics 19, 4-9.
Cohen BI, Pagnillo MK, Musikant BL, Deutsch AS (1999) The evaluation of apical leakage for three endodontic fill systems. General Dentistry 46, 618-23.
Dalat DM, Spangberg LS (1994) Comparison of apical leakage in root canals obturated with various gutta-percha techniques using a dye vacuum tracing method. Journal of Endodontics 20, 315-9.
Dummer PM, Kelly T, Meghji A, Sheikn I, Vanitchai JT (1993) An in vitro study of the quality of root fillings in teeth obturated by lateral condensation of gutta-percha or Thermafil obturators. International Endodontic Journal 26, 99-105.
Dummer PM, Lyle L, Rawle J, Kennedy JK (1994) A laboratory study of root fillings in teeth obturated by lateral condensation of gutta-percha or Thermafil obturators. International Endodontic Journal 27, 32-8.
Gencoglu N, Samani S, GundayM (1993a) Evaluation of sealing properties of Thermafil and Ultrafil techniques in the absence or presence of smear layer. Journal of Endodontics19,599-603.
GencogluN, Samani S, Gunday M (1993b) Dentinal wall adaptation of thermoplasticized gutta-percha in the absence or presence of smear layer: a scanning electron microscopic study. Journal of Endodontics19,558-62.
Gulabivala K, Holt R, Long B (1998) An in vitro comparison of thermoplasticized gutta-percha obturation techniques with cold lateral condensation. Endodontics and Dental Traumatology 14, 262-9.
Gutmann JL, Saunders WP, Saunders EM, Nguyen L (1993a) An assessment of the plastic Thermafil obturation technique. Part 2. Material adaptation and sealability. International Endodontic Journal 26,179-83.
Gutmann JL, Saunders WP, Saunders WP, Nguyen L (1993b) An assessment of the plastic Thermafil obturation technique. Part1. Radiographic evaluation of adaptation and placement. International Endodontic Journal 26,173-8.
Hata G, Kawazoe S, Toda T, Weine FS (1995) Sealing ability of thermoplasticized gutta-percha fill techniques as assessed by a new method of determining apical leakage. Journal of Endodontics 21,167-72.
Kytridou V, Gutmann JL, Nunn MH (1999) Adaptation and sealability of two contemporary obturation techniques in the absence of the dentinal smear layer. International Endodontic Journal 32, 464-74.
Lares C, elDeeb ME (1990) The sealing ability of Thermafil obturation technique. Journal of Endodontics 16, 474-9.
Lee CQ, Cobb CM, Robinson SJ, Lamartina T, VoT (1998) In vitro evaluation of the Thermafil technique with and without gutta-percha coating. General Dentistry 46,378-81.
Leung SF, Gulabivala K (1994) An in vitro evaluation of the influence of canal curvature on the sealing ability of Thermafil. International Endodontic Journal 27, 190-6.
Scott AC, Vire DE (1992) An evaluation of the ability of a dentin plug to control extrusion of thermoplasticized gutta-percha. Journal of Endodontics 18,52-57.
Taylor JK, Jeansonne BG, Lemon RR (1997) Coronal leakage: effects of smear layer, obturation technique, and sealer. Journal of Endodontics 23, 508-12.
Weller RN, Kimbrough WF, Anderson RW (1997) A comparison of thermoplastic obturation techniques: adaptation to the canal walls. Journal of Endodontics 23, 703-6.