Composition Adjusting Of Inorganic Fillers And Re-Mineralization/Self-Healing Properties Of Dental Restorative Resin Composites

Owing to a few decades of development, resin composites have already become the most popular dental restorative materials, instead of amalgam alloys. Compared with amalgam alloys, resin composites have better esthetics, biocompatibility, curing behavior as well as convenience in clinical practice and desirable mechanical properties. However, service life of resin composites normally can reach3-5years, much shorter than that of amalgam alloys. Many researches have been done to improve resin composites" mechanical properties and prolong the service life. The application of dental resin composites has been extended from anterior restorations to posterior restorations, making restoration leakage a main challenge, which may lead to secondary caries and even clinical repair failure. Although composites are generally satisfactory for small restorations, they are not recommended for large, stress bearing restorations. Secondary caries refers to the recurrence of tooth decay after the initial restoration, and is cited as the most frequent reason for the replacement of existing restorations. To solve the restoration leakage problem and make a further improvement of mechanical properties, the composition of fillers was adjusted in this dissertation. Because of its re-mineralization property, hydroxyapatite (HAP) was chosen to eliminate restoration leakage in oral environment.Ethoxylated bisphenol A dimethacrylate (EBPADMA,70wt%)/triethylene glycol dimethacrylate (TEGDMA,30wt%) system was chosen as the matrix of the resin composites. To solve the leakage problem, monodisperse SiO2microsphere and HAP were used as co-fillers to fabricate resin composites. After light cure, the prepared composites were immersed in simulated body fluid (SBF) at37℃to simulate the oral service environment in vitro. The excellent re-mineralization and self-healing properties of composites have been proven. When filler content was59.14wt%, the mass ratio of SiO2and HAP was4:1, HAP was unsilanized, the composite exhibited flexural strength(89.59±5.01MPa), compression strength (195.42±12.8MPa), depth of cure (4.05±0.17mm). After20d of immersion, it had the lowest decrease rate (21.4%) of flexural strength (70.41±8.14MPa).To improve mechanical properties of resin composites, diatomite was a good choice for its abundant reserve, low cost, easy silanization as well as its porous structure which reinforce the combination between inorganic and organic parts. Diatomite was grinded to sub-micron level to increase its filling amount for further enhancement of mechanical properties. However, the color of diatomite is still yellow after purification. Thus, diatomite encapsulated with rutile TiO2(Dia@TiO2) were synthesized by hydrolysis in oil bath. Whereas, sub-micron level diatomite has quite high light scattering rate and rutile TiO2on the surface made light scattering rate even higher. All these factors make it very hard to reach enough cure depth of composites to test their mechanical properties.