The Influence Of Water Aging On Surface Hardness Of Low Shrinkage Light-cured Composite Resins

Objectives:Light-cured composite resins have been widely used since they were introduced into dentistry, but there are still many deficiencies. They have a degree of hydrolysis-. incomplete monomer polymerization and polymerization shrinkage when cured. Reduced the polymerization shrinkage rate is the most significant advantage of low shrinkage composite resins. This experiment discuss the changes of low shrinkage composite resin performance during long-term arfificial aging process.Method:Set up 2 energy levels (12J/cm2 and 16J/cm2),3 kinds of light intensity (500mW/cm2,700mW/cm2 and 900mW/cm2) to make the 6 kinds of light-cured composite resins (2 kinds of universal composite resins:FiltekTM Z250, Solitaire2; 4 kinds of low shrinkage composite resins:Clearfil Majesty Posterior, Kalore GC, FiltekTM LS and Admira) into circular samples (6mm diameter and 2mm height) before water aging process begins. Immersed in distilled water for 1 year, using microhardness tester to measure Vickers hardness of the composites’surface and subface at the fixed time. In order to investigate the change rules of light-cured composite resin hardness in the long-term aging process.Results:The Vickers hardness of Clearfil Majesty Posterior, FiltekTM Z250 and Solitaire2 continued to decline during the process of 1 year aging (P< 0.05), and slow down or being stable at last (P>0.05). The Vickers hardness values of Kalore GC, Admira and FiltekTM LS have been rising early and falling at last, the final hardness values of Kalore GC and Admira are still higher than the maximum initial hardness of 24h (P< 0.05), the final hardness value of FiltekTM LS is similar to the initial hardness of 24h (P>0.05).Conclusion:The hardness values of 6 kinds of commercial composite resins in this experi-ment present falling trend or basically stable after long-term water aging process. Among them, the kinds of prepolymerized, organically modified ceramics and silorane-based composites in low shrinkage composite resins have better aging resistance. The hardness of two universal composite resins are falling during water aging process, but they are not declined too much. Their total hardness retention can be up to 90%.