Low shrinkage light curable nanocomposite for dental restorative material

Objectives: 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-epoxycyctohexyLmethyt-(3,4-epoxy)cyclohexane carboxylate (ERL4221) matrix with 55% wt of 70-100 nm nanosilica filters through ring-opening polymerization. GPS (gamma-glycidoxypropyl trimethoxysilane) was used to modify the surfaces of silica nanoparticles. Results: 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 mu m/m degrees C which is comparable to that of the methacrylate based composites (51.2 mu m/m degrees C). The strong interfacial interactions between the resin and filters at nanoscales were demonstrated by an observed high strength and high thermal stability of the nanocomposite. A microhardness of 62KHN and a tensile strength of 47 MPa were reached. A high degree of conversion (similar to 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 filters. Comparable results to the methacrylate based composites were obtained from the one day MTT (3-(4,5dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide) cytotoxicity test. Significance: The developed epoxy resin based nanocomposite demonstrated low shrinkage and high strength and is suitable for dental restorative material applications. (c) 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.