Changes in polymerization stress of self-adhesive resin composites during water storage

BackgroundResin composite restorations exhibit dimensional changes in the oral environment due to polymerization reaction and/or water sorption, which generates stresses in the surrounding tooth structures. The state of stress may differ between self-adhesive resin composites (SARCs) and conventional resin composites because only SARCs contain hydrophilic monomers.ObjectiveThe objective of this study was to evaluate the influence of water sorption on polymerization stresses of SARCs.MethodsCracks were introduced near a cylindrical hole in a glass disk, and their lengths were measured. The hole was filled with the composites. The crack lengths were repeatedly measured during 1-week water storage 37°C. Stresses at the composite-glass interface were calculated from the crack lengths and fracture toughness of the glass. Flexural moduli, water sorption and solubility of composites were also measured.ResultsPolymerization stresses of SARCs were equivalent to or less than that of a conventional composite generating relatively little stress. Significant reduction of stress occurred between 1-h and 1-day water storage in all composites. This reduction tended to be more noticeable with a larger decrease in modulus and/or larger water sorption.ConclusionsQuicker and/or larger stress reduction were considered to be beneficial for the longevity of SARC restorations.