Objectives: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. Materials and Methods: Resin composites used in this study were A2 body and A2 opaque shade of Esthet-X, Filtek supreme, Gradia Direct, Clearfil Majesty and BeautifilⅡ. 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. Results: 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). Conclusions: For an accurate shade match, direct shade matching of resin composite should be performed by using the cured material. [J Kor Acad Cons Dent 2011;36(3) properties such as color and translucency of the resin composites do not change before and after light curing, direct shade matching can be performed without light curing, resulting in spending less time. Therefore, stability in color and translucency before and after light curing would be an important property in esthetic restorative materials.Resin composite restorations may provide relatively poor color matches, specially a grayish shade is often seen after restoration, which is caused by a projection of the darkness in the oral cavity. From this point of view, the translucency of resin composites must be considered as a critical property just like the color of the material itself. 10,11 The translucency parameter (TP) is the color difference of a material having uniform thickness black and white backings, and corresponds directly to common visual assessments of translucency. 12The composite curing features are strongly influenced by the type and amount of photoinitiators inside.13 Camphorquinone (CQ) is the photosensitizing agent used in most of the brands available on the market. The increase in CQ amount in resin composites leads to a higher level of monomer conversion, improving mechanical and biological properties of these materials.14,15 Studies have shown that there is a limit for the increase of CQ concentration. 16,17 Above this limit the increase in photoinitiator does not benefit the final grade conversion. CQ has the aspect of an intense-yellow-colored powder. Additionally, it has poor photobleaching, which means the yellow color remains the same after light irradiation. Thus, CQ addition turns the material yellowish, making it difficult to be incorporated when lighter shades are desired. 16,18 Most of the organic molecules present in the matrix phase of dental composites and fillers do not effectively transmit visible light. As a result, scattering of light might be considered as...

Objectives: This study evaluated microtensile bond strength (μ TBS) and short-rod fracture toughness to explain fractural behavior of repaired composite restorations according to different surface treatments. Materials and Methods: Thirty composite blocks for μ TBS 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, μ TBS 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 μ TBS and fracture toughness. FE-SEM was employed on fractured surface to examine the crack propagation. Results: The fresh composite resin showed higher μ TBS 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 μ TBS (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 KIC showed toughening mechanism including crack deviation, microcracks and crack bridging in FE-SEM. Conclusions: 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.