Depth of cure and mechanical properties of nano-hybrid resin-based composites with novel and conventional matrix formulation

Abstract

This study's purpose was to evaluate the depth of cure (DOC) and the variation of mechanical properties with depth of two nano-hybrid resin-based composites (RBCs) containing a novel monomer composition based on dimer-acid derivatives (h-Da) or rather tricyclodecane-urethane structure (TCD-urethane) compared to three conventionally formulated nano-hybrid RBCs based on hardness-profile measurements. Specimens were produced through different layering techniques (bulk, incremental) and curing times (10, 20, and 40s). Mechanical properties (Vickers hardness (HV), modulus of elasticity (E)) were evaluated every 100μm longitudinally throughout the bisected samples using an automatic micro-hardness indenter. DOC was determined as the depth at which the 80% hardness cutoff value in relation to the surface hardness was reached. Results were compared using one- and multiple-way ANOVA, Tukey HSD post-hoc test (α = 0.05) and partial eta-squared statistic. Increasing curing time resulted in a significant increase in DOC. Generally, the novel-formulated materials showed higher DOC values. "Curing time" and "material" showed the strongest effect on DOC. Starting in 4mm depth, significantly higher HV and E was reached for incremental compared to bulk-curing technique. Values in 0.1 and 2mm depth (bulk, incremental) as well as in 4mm depth (incremental) were independent from curing time, while in greater depths, values generally increased with curing time. "Filling technique" and "material" performed the strongest influence on mechanical properties. Within the limits of this study, the novel-formulated RBCs showed better performance concerning DOC compared to conventional materials. For cavities deeper than 3mm, all tested materials should be placed incrementally to ensure adequate polymerization. In large cavities (≥6mm), the lowest increment should be cured at least 40s. The novel-formulated RBCs might be cured in comparatively bigger increments.