[Disintegration of visible light-cured composite resins caused by long-term water immersion]

The purpose of this study is to clarify a cause of disintegration of composite resins by long-term immersion in distilled water. Three kinds of visible light-cured composite resins (Heliosit, Plurafil Super and Visio Dispers) and one conventional composite resin (Clearfil F II) were prepared as the specimens with a 20 mm diameter and 1 mm thickness. These specimens were immersed in distilled water at 37 +/- 1 degree C for 3 years. These specimens were analysed and observed by a comprehensive multi analyzer and scanning electron microscope. The other hand residues in distilled water were analysed by infrared (IR) and nuclear magnetic resonance (NMR) spectrometers. The surface layer of all four composite resins showed signs of disintegration. The composite resins with abundant dissolved substances had disintegrated markedly, and such disintegration occurred deep inside the specimens. In IR and 1H-NMR spectra of dissolved substances, two visible light-cured composite resins (Heliosit and Plurafil Super) could be detected unreacted monomers, but one visible light-cured composite resin (Visio Dispers) and one conventional composite resin (Clearfil F II) could not be detected them. In 1H-NMR spectra of dissolved substances of all four composite resins, new signals not composed originally were observed. The progress of disintegration were demonstrated clearly. The dissolved substances were shown as the disintegrated substance between resin matrixs and silane coupling agents. It is suggested that the disintegration of composite resins by long-term water immersion is derived from hydrolysis.