The aim of this study was to evaluate the optical characteristics such as color and translucency changes before and after light curing, to quantify the CQ and to measure refractive indices of body and opaque shade of resin composites materials.

Resin composites used in this study were A2 body and A2 opaque shade of Esthet-X, Filtek supreme, Gradia Direct, Clearfil Majesty and Beautifil II Color and translucency changes before and after light curing were evaluated by colorimeter, the CQ was quantified by GC-MS and refractive index changes were measured by spectroscopic ellipsometer.

Translucency parameter (TP) was significantly increased after curing. The CQ content of body shades are higher than that of opaque shades in all resin composites. Refractive index increased after polymerization in all materials and significant difference in Δrefractive index was found between body and opaque shade (significance level 0.05).

For an accurate shade match, direct shade matching of resin composite should be performed by using the cured material.

This study evaluated microtensile bond strength (µTBS) and short-rod fracture toughness to explain fractural behavior of repaired composite restorations according to different surface treatments.

Thirty composite blocks for µTBS test and sixty short-rod specimens for fracture toughness test were fabricated and were allocated to 3 groups according to the combination of surface treatment (none-treated, sand blasting, bur roughening). Each group was repaired immediately and 2 weeks later. Twenty-four hours later from repair, µTBS and fracture toughness test were conducted. Mean values analyzed with two-way ANOVA / Tukey's B test (α = 0.05) and correlation analysis was done between µTBS and fracture toughness. FE-SEM was employed on fractured surface to examine the crack propagation.

The fresh composite resin showed higher µTBS than the aged composite resin (p < 0.001). Mechanically treated groups showed higher bond strength than non-mechanically treated groups except none-treated fresh group in µTBS (p < 0.05). The fracture toughness value of mechanically treated surface was higher than that of non-mechanically treated surface (p < 0.05). There was no correlation between fracture toughness and microtensile bond strength values. Specimens having high K_IC showed toughening mechanism including crack deviation, microcracks and crack bridging in FE-SEM.

Surface treatment by mechanical interlock is more important for effective composite repair, and the fracture toughness test could be used as an appropriate tool to examine the fractural behavior of the repaired composite with microtensile bond strength.