The aim of this study was to evaluate the effectiveness of sealer placement in simulated root canal extensions. Forty resin blocks were attained from the Endo-training Bloc. In each block, the simulated root canal was made with #20, 08taper GT file. After each block was longitudinally split into two halves, a standardized groove was prepared on one canal wall of two halves to simulate the canal extensions with various irregularities. The two halves of each block were assembled and all simulated root canals were obturated by single cone method with AH26 sealer. Four different methods of sealer placement were used: group A, #20 K-file; group B, ultrasonic file; group C, lentulo spiral; group D, EZ-Fill bi-directional spiral. All obturated blocks were stored in 100% humidity at 37℃ for 1 week. Using a low speed saw, each block was sectioned horizontally. Images of the sections were taken using a stereomicroscope at × 30 magnification and a digital camera. The amount of the sealer in the groove was evaluated using a scoring system, a higher score indicated better sealing effectiveness. The data was statistically analysed by Fisher' s Exact Test.The sealing score was the lowest, specially at the middle area of canal extensions in group A, and that was statistically significant difference from other groups. In conclusion, the ultrasonic file, lentulo spiral and EZ-Fill bi-directional spiral were effective methods of sealer placement in simulated canal extensions. The K file was the least effective method, specially at the middle area of canal extensions.[J Kor Acad Cons Dent 30(1): [31][32][33][34][35][36][37] 2005]
Physical properties of composite resins such as strength, resistance to wear, discoloration, etc depend on the degree of conversion of the resin components. The purpose of this study was to evaluate the degree of conversion of the composite resins according to the thickness of tooth structure penetrated by light and applied light curing time. The coronal portions of extracted human teeth (one anterior tooth, three posterior tooth) was embedded by pink denture material. the mounted teeth were cut into three illumination sections (1mm thickness enamel section, 1mm thickness dentin section, 2mm thicknes dentin section) and one backing section with cutting wheel. Thin resin films were made by using 6kg pressure between slide glass during 5 minutes.Thin resin film was light cured on coupled illumination section during 40sec, 80sec and 120sec. each illumination section was coupled as follows; no tooth structure(X), ename section(E), enamel section + 1mm dentin section(ED1), enamel section + 2mm dentin section(ED2), enamel section + 1mm dentin section + 2mm dentin section(EDD). To simulate the clinical situation more closely, thin resin film was cured against a backing section of tooth structure. The degree of conversion of carbon double bonds to single bonds in the resin films were examined by means of Fourier Transform Infrared Spectrometer. The results were obtained as follows;1. As curing time was increased, conversion rate was increased and as tooth thickness which was penetrated by curing light was increased, conversion rate was decreased. 2. At all tooth thickness groups, conversion rate between 80sec and 120sec was not significantly increased(P>0.05). 3. At 40sec group and 80sec, conversion rate between no tooth structure(X) group and 1mm enamel section(E) group was not significantly decreased(P>0.05). 4. At 80sec group and 120sec, conversion rate between 1mm enamel section(E) group and 1mm enamel section + 1mm dentin section(ED1) group was not significantly decreased(P>0.05).ABSTRACT
The purpose of this study was to investigate the bonding of resin-based root canal sealer, AH26 when the sealer was applied as a thin layer between dentine and gutta-percha surface.In this study, forty non-caries extracted human molars and resin-based root canal sealer(AH 26, DeTrey/Dentsply, Germany) were used. Disks of gutta-percha, 6mm in diameter⋅6mm thick (Diadent/Dentsply, Korea) for thermoplastic obturation were used and dentin surfaces were treated with 2% NaOCl(Group 1) or 2%NaOCl+17% EDTA(Group 3). Disks of gutta-percha, 6mm in diameter⋅6mm thick (Diadent/Dentsply, Korea) for conventional obturation were used and dentin surface were treated with 2% NaOCl(Group 2) or 2%NaOCl+17% EDTA(Group 4). Enamel was removed by a horizontal section 1mm below the deepest portion of the central occlusal groove by using a water-cooled low speed diamond saw. A second horizontal section was done around cementoenamel junction. Exposed dentin surface was cut to approximately 8×8 mm rectangular shape and was ground against 320, 400, 600 grade silicon carbide abrasive paper serially. After grinding, the dentine surface were soaked in a solution of 2% NaOCl for 30 minutes and twenty of specimens were treated with 17% EDTA solution for 1 minute. The treated specimens were washed and dried. Root canal sealer, AH26 was prepared according to the manufacture's instructions. The Gutta-percha and dentin surface were coated with a thin layer of the freshly mixed sealer. The specimens were left overnight at room temperature. After their initial set, they were transferred to an incubator at 37。 C for 72 h. After 72 hours, resin blocks were made. The resin block was serially sectioned vertically into stick of 1⋅1mm. Twenty sticks were prepared from each group.After that, tensile bond strength for each stick was measured with Microtensile Tester. Failure patterns of the specimens at the interface between gutta-percha and dentin were observed under the SEM(×1000) and Stereomicroscope (LEICA M420, Meyer Inst., TX U.S.A) at 1.25 ×25 magnification. The results were statistically analysed by using a One-way ANOVA and Tukey's test.The results were as follows; 1. Tensile bond strengths(mean±SD) were expressed with ascending order as follows: Group 1, 3.09± 1.05MPa ; Group 2, 6.23±1.16MPa ; Group 3, 7.12±1.07MPa ; Group 4, 10.32±2.06MPa. 2. Tensile bond strengths of the group 2 and 4 used disks of gutta-percha for conventional obturation were significantly higher than that of the group 1 and 3 used for thermoplastic obturation. (p < 0.05) 3. Tensile bond strengths of the group 3 and 4 treated with 2% NaOCl+17% EDTA were significantly higher than that of the group 1 and 2 treated with 2% NaOCl. (p < 0.05) 4. In analysis of failure patterns at the interface between sealer and gutta-percha, there were observed 49 (61%)cases of adhesive failure patterns and 31(39%) cases of mixed failures patterns.ABSTRACT
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