In vitro Study Comparing Fracture Resistance of Nanocomposites with and without Fiber Reinforcement with Different Cavity Designs Used for Obliquely Fractured Incisal Edge Restoration.

AIM: The aim of the study is to evaluate fracture resistance of nanocomposites with and without fiber reinforcement with different cavity designs used for obliquely fractured incisal edge restoration. MATERIALS AND METHODS: In the present study, 60 sound extracted maxillary central incisors were mounted on autopolymerizable acrylic resin up to the cementoenamel junction, out of which, 10 intact teeth were kept as control (group 1) and the remaining 50 samples were reduced incisally in an oblique manner up to 3 mm. All incisally reduced samples were divided into five groups (n = 10) based on the restoration techniques as follows: group 2 (conventional bevel), group 3 (single central palatal slot on the incisal edge), group 4 (single palatal slot with central 2 mm fiber), group 5 (two palatal slots on the incisal edge with a distance of 0.5 mm to 1 mm between them), and group 6 (two slots on the incisal edge with two 2 mm fibers). All samples were built incrementally with nanocomposites followed by finishing and polishing. All samples including control were then stored in distilled water before their fracture resistance was measured using a universal testing machine. Failure modes were visually examined and the results were subjected to statistical analysis. RESULTS: The mean fracture resistance among the experimental groups was observed, group 4 with single fiber in the central position had the highest (832.68 N) followed by group 3 (490.84 N), group 5 (446.175), and group 2 (270.1359), and the least in group 6 (223.443). The mean fracture resistance of group 4 is comparable to intact teeth, i.e., group 1 (1096.40). The mean of all samples was compared using the one-way Anova test, and it was found that there is statistically significant difference in fracture resistance among groups (p < 0.001**). CONCLUSION: Fibers certainly have the reinforcing effect and the position of fibers determines their reinforcing effects. A single central slot with fiber (Ribbond) showed maximum fracture resistance almost equivalent to natural teeth. Modifying conventional beveled cavity design with an additional slot in the center also increases the fractural strength of restoration. CLINICAL SIGNIFICANCE: Nanocomposites reinforced with single fiber in the central palatal slot used for restoring fractured incisors provide strength almost equivalent to natural teeth. In case when the fiber is not available for preparing a single palatal slot also, we can increase the fracture resistance.

Comparative evaluation of residual monomer content and polymerization shrinkage of a packable composite and an ormocer.

AIM: The aim of this study is to evaluate the residual monomer content and polymerization shrinkage of a packable composite (Surefil) and an ormocer (Admira). MATERIALS AND METHODS: The study was conducted in two parts. In Part I, 10 samples of each material were prepared in a standardized split brass mould, using incremental curing technique. The residual monomer content was measured by observing change in weight before and after Soxhlet Extraction procedure. In part II, the volumetric polymerization shrinkage was calculated by measuring the difference in specific gravities of 10 uncured and 10 cured samples of each material using a modified version of ASTM D-792 method. The data obtained was put to statistical analysis using student's 't' test. RESULTS: Part I - The percentage change in weight for Surefil was 0.525% while that for Admira was 0.374%, which was found to be statistically significant. Part II - The volumetric percentage shrinkage for Surefil ranged between 1.04-3.42% and that for Admira between 1.01-2.31%, which was not found to be significant statistically. CONCLUSION: Admira may be considered more biocompatible than Surefil due to the lower residual monomer content in the former; however, both are comparable with regards to their polymerization shrinkage.