Objectives: Increasing demand for aesthetic restorations requires dental restorative materials to reproduce the translucency as well as the colour of natural teeth .The purpose of this study was to determine the translucency of dental composites and investigate the influence of thickness and standard illuminants. Methods: Three dental composites of different matrix chemistry (dimethacrylate, Ormocer and Silorane) were investigated in the form of discs (Φ20mm) of varying thickness (ranging from x=0.38mm to x=1.46mm) of each material. The translucency parameter (TP) was used to characterize the translucency of the materials and was calculated as the colour difference of the specimen over white and black backgrounds. The colour co-ordinates (L*, a*, b*) of samples of each material were measured (n=3) on white and black backgrounds according to the CIE Lab colour scale. The CIE Lab colour scale operated on the reflectance mode, with a two degree (2
o) observer and standard illuminants, D65 and A using an USB4000 fibre optic Spectrometer operated by Spectra Suite software. The translucency parameter changes and the changes of the colour co-ordinates were analyzed by One-way analysis of variance (Anova) combined with Tukey post-hoc multiple tests at a significance level of p=0.05 and regression analysis. Results: The translucency parameter (TP) decreased significantly (p<0.05) with an increase in thickness of the materials and varied according to the Lambert's Law with both standard illuminants D65 and A. Linear regression analysis of ln(TP) with thickness were obtained with r
2 values ranging from 0.91 to 1.00. Conclusions: The significant differences in translucency parameter between the thicknesses of the dental composites would affect their appearance and colour and hence an important optical property to be considered clinically during colour matching procedures.
Keywords: Resin-composites, Standard illuminant, Colour, Silorane, Ormocer, Translucency.