In order to conduct laboratory studies on composition and behavior of Claus-derived molten sulfur, the examined sulfur should contain dissolved H2S and H2Sx with a concentration of about 230-250ppmw. Here, by injecting hydrogen sulfide to sulfur, a method for synthesis of molten sulfur containing hydrogen sulfide and polysulfide as a proper sample for laboratory studies is developed.The molten sulfur as product was prepared by injecting the pressurized hydrogen sulfide on the surface of solid sulfur followed by further heat treatments during the time. According to the Iodometric Back Titration (IBT) analysis, final molten sulfur contained 500-1100ppmw of soluble hydrogen sulfide and polysulfide components based on the initial gas pressure.

In order to determine the effect of root canal sealer on microleakage of obturated root canals by lateral condensation technique (LCT)-with and without tug-back (TB), seventy extracted single root canal teeth were examined. After preparation of root canal with step-back technique, teeth were divided to six groups as follows: 5 teeth as positive control group that obturated by LCT with gutta-perch without sealer. 5 teeth as negative control group in which entire root surfaces and apical foramen coated with nail varnish, and four experimental groups (each group consisted of 15 teeth). Group I ZOE with TB, group II ZOE without TB, group III Roth sealer with TB, and group IV Roth sealer without TB. Then the teeth were immerssed in Pelikan ink for 72 hours and weparated in two peices through vertical long axis. Stereomicroscope observation showed that TB groups (I & III) have statistically less microleakage than non TB groups (II & IV) (P<0.0001). There were no significant differences between two TB groups. Results also showed no relationship between root canal sealer and apical leakage with and without TB in both type of sealers.

Introduction: The final objective of root canal therapy is to create a complete seal along the length of the root canal system from the coronal opening to the apical termination and to accomplish the best adaptation from obturation material with canal walls. The tug-back of the master cone is recommended to provide apical seal. The purpose of this study was to determine the influence of tug-back on the quality of the apical seal. Materials & Methods: In this experimental in vitro study, seventy single canal teeth were selected. The crowns were removed; the canals were prepared using a step-back instrumentation technique. Patency of the apical foramen was maintained and the teeth were divided into 2 experimental groups of 32. In the first group obtruration was achieved by tug-back in master cone and in the second group without tug-back using lateral condensation technique. Six teeth were used as control group, out of which three served as negative and three as positive controls. The teeth were placed in 100% humidity and 37°c for three days. The roots of the teeth were coated with two layers of nail varnish and one layer of stick wax except for the 2mm of apical end. Teeth were immersed in methylenblue 2% solution for one week and finally the teeth were sectioned vertically. The depth of maximum dye penetration for each tooth was recorded by two evaluators with stereomicroscope. All results were submitted for statistical analysis using Student’s t-test. Results: The mean linear dye penetration for experimental group with tug-back in master cone was 6.918±2.140 mm while this was 8.110±1.929mm in the group without tug-back. This difference was statistically significant (P=0.02).  Conclusion: The results of this study showed that the tug-back in master cone provided a significantly better apical seal.