Degradation of Resin-based Dental Composites Under Biologically Relevant Conditions

Dental restorative composites are widely used for their aesthetic appeal and biocompatibility. However, despite these advantages, composite restorations face issues such as recurrent caries and mechanical failures due to harsh oral conditions. This research delves into the degradation behavior of nano-filled and micro-hybrid composite specimens under simulated oral environments. Aging effects were explored via exposure to artificial saliva, volatile fatty acids, alcohols, and enzymes, alongside interactions with cariogenic and non-cariogenic oral bacteria. Mechanical properties (diametral tensile strength, flexure strength, fracture toughness, hardness, pushout strength) post-aging were evaluated. Fracture toughness emerged as a robust failure predictor due to its lower variability compared to other properties. Cyclic loading impact on composite strength was inconclusive, warranting more cycles for fatigue assessment. Enhanced confined compression test methods were recommended for accurate stress calculations. Growth of oral Streptococci, cariogenic and non-cariogenic, significantly deteriorated resin-based composites, partly due to fermentation metabolites. This highlights oral Streptococci's role in biodeterioration. Volatile fatty acids from glucose and sucrose fermentation equally contributed to acid decay. Composite degradation occurred irrespective of cariogenic potential, debunking its necessity for deterioration. Notably, surface roughness influenced biofilm formation, underscoring its impact on restoration performance. Adhesive application improved composite-to-tooth interfaces, minimizing flaws. In summary, this research comprehensively addresses dental composite deterioration: aging effects, methodologies, bacterial influence, glucose-sucrose roles, mastication impact, biofilm formation, and adhesive effects. These insights advance dental material science and inform the enhancement of restorative dental materials.