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OBJECTIVES: The objective is to evaluate the effect of collagen stabilizing agents-chitosan and proanthocyanidin (PA) on the shear bond strength to dentin and microleakage of resin composite at enamel and cemental walls. MATERIALS AND METHODS: Thirty premolars were decoronated 2 mm above cemento-enamel junction and restored with composite resin. Teeth were then randomly divided into three groups: Group I - Control, Group II - Pre-treatment with chitosan, and Group III - Pre-treatment with PA. Samples were then subjected to thermocycling for 500 cycles at 5°C and 55°C with the dwell time of 30 s and transfer time of 5-10 s. Then, the samples were subjected to shear bond strength evaluation on Universal testing machine. Shear load was applied until failure occurred. The load to failure was recorded individually and statistical analysis was done. Microleakage was determined by methylene blue dye penetration method and subjected to stereomicroscopic evaluation. Statistical analysis was carried out using Mann-Whitney test and Chi-square test. RESULTS: Group II specimens produced the highest median shear bond strength and group I showed the least. In addition, Group I, Group II, and Group III showed no statistically significant difference in microleakage. CONCLUSIONS: Application of Chitosan and PA improved the shear bond strength to dentin as compared to the control. However, no significant difference in shear bond strength and microleakage was found between them.
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BACKGROUND: Giving a time gap and distance during curing can decrease the polymerization shrinkage. AIM: To evaluate the effect of time gap and distance between the curing tip and restoration on the polymerization shrinkage, degree of monomer conversion (DOC), and microhardness of a nanohybrid composite. MATERIALS AND METHODS: A total of 50 standardized cylindrical specimens (Z350, 3M ESPE) were fabricated using a brass mould. The curing was done in contact with the sample surface for 20 seconds in the control group. In the four experimental groups, curing was initiated at 1-cm distance, followed by variation in the time gap and the curing cycle. The polymerization shrinkage, DOC, microhardness was calculated. STATISTICAL ANALYSIS: One-way analysis of variance (ANOVA) and post hoc-Dunnett test were used to analyze the data. RESULTS: Curing at 1-cm distance for 10 seconds with a gap of 10 seconds and finishing the curing cycle with 20 seconds at 0 cm proved to be an appropriate technique to reduce the polymerization shrinkage without significantly affecting the DOC and microhardness. CONCLUSION: A simple innovative modification of varying the distance of curing and a time gap in the curing cycle can decrease the polymerization shrinkage without affecting the DOC and microhardness.