[Deterioration of Bis GMA-EDMA copolymers caused by exposure of UV and visible light]

Recently, the dimethacrylates, such as Bis.GMA and Triethylene glycol dimethacrylate (Tri.EDMA), have been used increasingly as a base material of composite restorative resins. The mechanical deterioration of these monomer-based resin may cause the unfavorable actions in clinical application. The purpose of this investigation was to examine the effects of photodeterioration on viscoelastic properties of the base materials (copolymers) for the composite restorative materials and to determine the monomer ratios of copolymers which have a superior light stability. Two lamps of visible light (VL) and ultraviolet (UV) were used for deterioration. In the case of polyethylene glycol dimethacrylate (Di.EDMA, Tri.EDMA and Tetra.EDMA), the degree of photodeterioration enlarged for UV than for VL and increased markedly according to an increase of repeated number of (-CH2-CH2-O-). The addition of Bis.GMA to EDMA improved extremely the light stability. This phenomenon may relate with the amount of benzene ring included in copolymer. Furthermore, in the case of an experimental composite resin, it was seen that the photodeterioration of the material proceeded from a relatively early stage after polymerization.