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[The influence of accelerated aging on color and microstructure of light-curing composite resin].

OBJECTIVE
The aim of this investigation was to examine the changes of the color stability, surface microstructure and chemical constitution of light-curing composite resin after accelerated aging, and the relations between them.


METHODS
Four light-curing composite resin were aged in an accelerated aging instrument. The color was measured by CIE L*a*b* with a spectrophotometer after treatment for 24 h and 96 h. And the color differences were calculated. Environmental scanning electron microscopy (ESEM) and Fourier transform infrared spectroscopy (FTIR) spectrometer were used to examine the microstructure and chemical composition of the specimens before and after accelerated aging. The color differences were analyzed statistically by repeated-measures two-way analysis of variance and t-test after aging for 24 h and 96 h. The level of significance was defined as alpha=0.05.


RESULTS
The materials demonstrated statistically significant differences in color after aging between the 24 h and 96 h (P<0.05). There were significant influences on the microstructure and the chemical composition after aging. The matrix appeared some concaves and pores, the filler particles exposed after aging. The energy of chemical bonds were weaken or broken under the aging, and the unsaturated polymer reacted again.


CONCLUSION
The color differences of the composite resin increase with the aging time and irradiation dose. The hybrid filled composites have the best color stability.