The effect of microwave/laboratory light source postcuring technique and wet-aging on microhardness of composite resin

BACKGROUND Although composite restorations are really valuable for esthetic zones, they have shown less longevity rather than amalgam restorations. Since it may be related to the method used for curing the composite, postcuring could increase the degree of conversion and result in more long-lasting composite restorations. This study was planned to evaluate the effect of two different postcuring techniques on microhardness of indirect composite resin after wet-aging and comparing them with the direct type. MATERIALS AND METHODS In this experimental study, 99 composite disk-shaped (6.5 × 2.5 mm) specimens of composite (Gradia GC, Japan) were prepared in split mold. The indirect composite specimens were postcured by laboratory light source (Labolite LV-III GC Corp, Japan) or microwave unit (MC 2002 JR, LG, Korea). Then, the aging procedure was done for 24 h, 30 and 180 days in distilled water. The Vicker's Hardness test (VHN) on surface of specmens was measured by Wolpert microhardness tester and the data were analyzed by the two-way analysis of variance (ANOVA) and Tukey's post hoc tests. (P ≤ 0.05). RESULTS The statistical analysis revealed that surface microhardness of postcured composite by microwave and laboratory light source was more than that of direct composite (P = 0.0001) and postcuring by microwave was more effective than postcuring by laboratory light source (P = 0.004). The 30 days stored composite demonstrated significant decrease of VHN compared with the 24-h stored samples (P = 0.0001), with a more significant VHN decrease after 180 days of aging (P = 0.045). CONCLUSION Postcuring increased the surface microhardness and aging reduced the surface microhardness of indirect composite.