Effects of thermal cycling on mechanical and antibacterial durability of bioactive low-shrinkage-stress nanocomposite

Objectives: Recent studies developed low-shrinkage-stress composite with remineralizing and antibacterial properties to combat secondary caries and increase restoration longevity. However, their long-term durability in thermal cycling is unclear. The objectives of this study were to develop an antibacterial, remineralizing and low-shrinkage-stress composite, and to investigate its durability in thermal cycling for 20,000 cycles, equivalent to two years of clinical life. Methods: The resin consisted of urethane dimethacrylate (UDMA) and triethylene glycol divinylbenzyl ether (TEG-DVBE). Composites were made with 5% dimethylaminohexadecyl methacrylate (DMAHDM) and 20% of nanoparticles of amorphous calcium phosphate (NACP). Composites were thermal cycled at 5°C and 55°C for 20,000 cycles. A human salivary biofilm model was used to evaluate antibiofilm activity before and after thermal cycling. Results: After 20,000 cycles, the flexural strength of bioactive low-shrinkage-stress composite matched commercial control with no antibacterial activity (p > 0.05). Surface roughness was clinically acceptable at less than 0.2 μm. UV+NACP+DMAHDM composite reduced the total microorganisms, total streptococci, and mutans streptococci by 2-5 logs, compared to commercial composite. Biofilm lactic acid production was reduced by 11 folds. The antibacterial performance was maintained after thermal cycling, with no decrease after 20,000 cycles. Conclusions: Bioactive low-shrinkage-stress composite possessed good mechanical properties that matched commercial composite both before and after thermal cycling. The new composite had potent antibacterial activity, which was maintained and did not decrease after thermal cycling. Clinical significance: The new bioactive low-shrinkage-stress composite could reduce polymerization shrinkage stress and release calcium and phosphate ions, with good mechanical properties and strong antibacterial function that were durable after thermal cycling. These properties indicate great potential for inhibiting recurrent caries and increasing the restoration longevity.