Susceptibility of RBC to various clinical relevant curing conditions: Effect of filler...

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Introduction: The study aims to quantify the impact of various curing conditions on the micro-mechanical properties of methacrylate and silorane resin-based composites (RBCs) in order to determine the threshold for sufficient polymerization. Methodology: The analyzed RBCs have either a similar filler volume amount (55%) but a different monomer matrix composition (methacrylate or silorane) or a similar monomer matrix but a different filler volume amount (63.3% vs. 55%). Twenty-four different curing conditions were simulated. A blue-violet LED curing unit was applied in different curing modes, exposure times and distances (0-mm and 7-mm). Measurements (Vickers hardness, HV, and Indentation modulus, E) were performed after 24 h of storage in distilled water at 37°C at the top and bottom of 2-mm thick specimens (360 specimens in total). One and multiple-way ANOVA and Tukey HSD post hoc-test (α =0.05) was used. A multivariate analysis (general linear model) assessed the effect strength of the parameters exposure time, location of measurement (top-bottom), incident irradiance, radiant exposure (ranging from 1.0 to 47.0 J/cm²) and exposure distance on HV and E. Results: In all materials, the highest effect on HV and E was exerted by the exposure time and location of measurement. Susceptibility to various curing conditions is material dependent, while less filled methacrylate-based as well as the silorane micro-hybrid are more robust to these variations. Fast polymerization (3s) with high irradiance is not recommended. Conclusions: The best micro-mechanical properties at the top and bottom of 2-mm thick specimens are generated with a curing time of at least 20s at moderate irradiance. Keywords: Resin-based composites; Hardness; Modulus of elasticity; Light curing unit; Radiant exposure.

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