Low shrinkage light curable nanocomposite for dental restorative material.

The aim of this study was to develop a low shrinkage visible light curable nanocomposite dental restorative material without sacrificing the other properties of conventional materials. This nanocomposite was developed by using an epoxy resin 3,4-epoxycyclohexylmethyl-(3,4-epoxy)cyclohexane carboxylate (ERL4221) matrix with 55% wt of 70-100 nm nanosilica fillers through ring-opening polymerization. GPS (gamma-glycidoxypropyl trimethoxysilane) was used to modify the surfaces of silica nanoparticles. The nanocomposite was shown to exhibit low polymerization shrinkage strain, which is only a quarter of currently used methacrylate-based composites. It also exhibited a low thermal expansion coefficient of 49.8 microm/m degrees C which is comparable to that of the methacrylate based composites (51.2 microm/m degrees C). The strong interfacial interactions between the resin and fillers at nanoscales were demonstrated by an observed high strength and high thermal stability of the nanocomposite. A microhardness of 62 KHN and a tensile strength of 47 MPa were reached. A high degree of conversion ( approximately 70%) can be obtained after less than 60 s of irradiation upon the nanocomposite. A transmission electron microscope (TEM) study of the nanocomposite showed no aggregation of fillers. Comparable results to the methacrylate based composites were obtained from the one day MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide) cytotoxicity test. The developed epoxy resin based nanocomposite demonstrated low shrinkage and high strength and is suitable for dental restorative material applications.