Optical properties of composite resins

Abstract

The translucency and colour of a composite resin are characterized by two wavelength-dependent parameters: the absorption coefficient, K and the scattering coefficient, S. These parameters were calculated according to the Kubelka-Munk (1931) equations for two commercial resins. The calculations were based on reflectance spectra of samples of different thicknesses which were placed on a black and a white background. Employing the values of these parameters, calculated spectra were obtained of samples on the same as well as different backgrounds. The difference between the experimental and the calculated spectra was evaluated in terms of Friele-MacAdam-Chickering (Hemmendinger, 1970) colour differences. The Munsell colour values, corresponding to the spectra were evaluated. It was found that the colour of a resin sample of a specified thickness which is placed on a particular background may be predicted to a fair degree of accuracy from calculations employing the K and S values of the resin and the reflectance spectrum of the background. It has been demonstrated that illuminating the sample at 45 degrees instead of using diffuse illumination, affected the results only to a small extent. The effect of internal reflections at the resin surface on the relfectivity on the sample is discussed. An expression has been derived for computing the reflectivity of a sample on any background from its transmittance and reflectivity on a completely absorbing background.

Changes on transmittance mode of different composite resins

“…Time Wavelength G1 G2 G3 G4 G5 G6 G7 G8 Initial 460 0, Masotti et al 13 (2008) define translucence as the partial passage of light through a certain structure. However, it should be noted that translucence is not synonymous with transparency.…”

“…An increase in the specimen's thickness causes its opacity to increase and the material's transmittance to decrease. 8,11,[19][20][21] This fact was considered when standardizing the thickness of the specimens in all the experimental groups evaluated in this study.…”

“…12 This study evaluated direct transmittance using a visible light spectrophotometer to record the transmittance of specimens at wavelengths ranging from 400 to 700 nm, which corresponds to the light spectrum visible to the human eye, according to the methodology described by Brodbelt et al 12 (1980) and Masotti et al 13 (2007). Several factors such as filler and polymeric matrix, refractive index, type of monomer and filler, and filler content 13,15,16 can influence the light transmittance and opacity of composite resins. These properties must be thoroughly evaluated in order to ensure the esthetic longevity of a restoration in terms of color stability.…”

“…Therefore, the presence of different degrees of translucency in composite resins is a determining factor for the quality of esthetic reproductions of lost portions of teeth. 13 Finely honed sensitivity and professional skills are required to perfectly mimic the transmittance of lost dental tissues, since these tissues have different indices of transmittance. Enamel has a higher transmittance than dentine, which in turn differs considerably from that of cementum, since these tissues have different compositions, and mineral and organic components of different amounts and qualities.…”

“…12,13 Transmittance was measured immediately after preparation of the specimens, i.e., before immersion in artificial saliva at 36° (±1°C). The second measurement was taken after 24 hours in saliva, and the last measurement 10 days after immersion in artificial saliva.…”