PROPAGATION OF LIGHT THROUGH HUMAN DENTAL ENAMEL AND DENTIN

Techniques based on transillumination of teeth with visible light will be a valuable aid in caries diagnosis, if a higher sensitivity than t hat of the present Foti method is achieved. Therefore, a better unders tanding of light propagation through teeth is required, and hence it i s useful to investigate the propagation of light through sound dental material. In this study the intensities emanating from the surfaces of enamel and dentine bars were measured when these bars were illuminate d using a fibre rod transporting the light from a HeNe laser (lambda = 633 nm) as a light source. From the measured intensities, the radiant fluxes emanating from the surfaces were calculated. To account for a directional dependence of these fluxes, optical anisotropy in dental m aterial was investigated by comparing the transmitted light intensity in a direction perpendicular and parallel to the approximal surface of the tooth from which the sample was cut. The mean ratio of the transm itted intensities in perpendicular and parallel direction was 0.86 +/- 0.06 for enamel and 2.88 +/- 0.43 for dentine. In addition, for ename l the asymmetry parameter, g, was estimated. The averaged value was g = 0.68 +/- 0.09. It was concluded that for dentine the optical anisotr opy as measured supports the idea that tubules are the predominant cau se of scattering in dentine. For enamel the results indicate that the hydroxyapatite crystals contribute significantly to scattering and tha t the influence of the prism structure on the light propagation is sma ll.