Novel Bioactive Low-shrinkage-stress Nanocomposite with Antibacterial and Remineralization Properties and Thermal-cycling and Aging Resistance.

Abstract

Dental composites continue to be the material of choice in daily dental practice for several reasons, including their good mechanical properties, conservative cavity design, and superior esthetics. However, the longevity of current resin composite restorations ranges only 5-10 years. Recurrent caries and tooth fracture are the most common types of failure during the first 6 years of clinical service. These failures are often caused by the polymerization shrinkage stress of the dental composite materials. Thus, there is an increased need to develop a new generation of bioactive dental composite with the ability to reduce polymerization shrinkage stress, long-term antibacterial, remineralization abilities, and excellent mechanical properties. Therefore, this dissertation aims to develop a new bioactive low-shrinkage-stress dental composite containing dimethylaminohexadecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP) which could be a promising approach to increase the chances of success of composite restorations and strengthen tooth structures. First, we found that the new bioactive low-shrinkage-stress resin composite significantly reduced the polymerization shrinkage stress, without compromising their mechanical properties. Increasing the DMAHDM mass fraction increased the antibacterial effect in a dose-dependent manner. Next, we investigated the low-shrinkage-stress composite mechanical stability and antibacterial durability in thermal cycling for 20,000 cycles, equivalent to two years of clinical life. We found that the 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. Lastly, we further examined the mechanical and antibacterial durability of a bioactive low-shrinkage-stress after 50,000 and 100,000 thermal cycles which corresponds to 5 and 10 years respectively of in vivo function. We found that the bioactive low-shrinkage-stress composite maintained its antibacterial potency after thermal cycling, indicating long-term antibacterial durability. In addition, it possessed good mechanical properties that were comparable to commercial composite both before and after thermal cycling. The triple benefits of antibacterial, remineralization, and lower shrinkage stress have a great potential to inhibit recurrent caries and increase restoration longevity.