hardness and depth of cure of conventional and bulk-fill composite resins in class ii restorations with transparent and metal matrix strips

Objectives: hardness is relevant to the degree of conversion (dc) and depth of cure (doc). the aim of this study was to determine the micro-hardness and doc of conventional and bulk-fill composite resins in class ii restorations using metal and clear matrix bands.materials and methods: twelve specimens of each of the two composite resins, i.e., filtek z350 xt bulk-fill and gradia posterior conventional composite, were prepared in the form of a class ii cavity in a tooth mold, using a clear or metal matrix band. all specimens were cured and stored at 37°c for 24 hours. vickers hardness was measured as a function of doc at 2mm intervals. data were analyzed by two-way anova (alpha=0.05).results: the bulk-fill composite exhibited significantly higher hardness levels than the conventional composite in all tested surfaces (p<0.001). however, while the metal matrix band had a significant impact on the bottom surface (p=0.059) and also on the furthest surface from the matrix and light source (p=0.04), it did not have a consistent effect across all tested surfaces. the simultaneous interaction of the composites and matrix band types in all surfaces, did not show significant differences in hardness values. the highest bottom-to-top surface hardness ratio (73%) was observed in the conventional composite near the metal matrix band.conclusion: in deep class ii cavities, the bottom-to-top surface hardness ratio did not reach the maximum of 80%, neither for bulk-fill nor conventional posterior composites. therefore, in such cavities extended light-curing and more incremental composite placement is needed.