Propagation of Light through Human Dental Enamel and Dentine

Abstract

Techniques based on transillumination of teeth with visible light will be a valuable aid in caries diagnosis, if a higher sensitivity than that of the present Foti method is achieved. Therefore, a better understanding of light propagation through teeth is required, and hence it is 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 illuminated using a fibre rod transporting the light from a HeNe laser (λ = 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 material 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 transmitted intensities in perpendicular and parallel direction was 0.86 ± 0.06 for enamel and 2.88 ± 0.43 for dentine. In addition, for enamel the asymmetry parameter, g, was estimated. The averaged value was g= 0.68 ± 0.09. It was concluded that for dentine the optical anisotropy as measured supports the idea that tubules are the predominant cause of scattering in dentine. For enamel the results indicate that the hydroxyapatite crystals contribute significantly to scattering and that the influence of the prism structure on the light propagation is small.

Correlation between light transmission and permeability of human dentin

“…Our results cannot be directly compared to those of previously cited authors [25,26], who irradiated dentin blocks obtained from the proximal region of the teeth or thicker dentin discs, in which the dentin tissue presented tubules with varied curvatures. Further research should investigate the transmission of LED light with different parameters through dentin discs of varied thicknesses obtained from different regions of the teeth.…”

“…As LED sources usually present a wide illumination area, it is likely that they have a different dosimetry from that used for lasers. In another study [26], horizontal and vertical sections of different regions of molar teeth were prepared and light transmission through the sections was examined varying the irradiation angle. Although the authors did not specify the type of light applied to the dental structures, the ability of light to propagate through dentin tubules with high refractive index was demonstrated.…”

“…Although the authors did not specify the type of light applied to the dental structures, the ability of light to propagate through dentin tubules with high refractive index was demonstrated. However, the authors [26] claim that, although possible, light transport along the tubule centers does not play an important role, and that light propagation in a dentin section is apparently based on the total internal reflection through the peritubular dentin. The optical properties of a tooth as a whole are determined by its architectonics, i.e., the tubules specifically distributed over the dentin.…”

“…Both Vaarkamp et al [25] and Zolortev et al [26] analyzed light transmission and its possible relationship with dentin tubules using various irradiation directions on different dentin regions. In the present study, two factors are important to justify the weak correlation between dentin permeability and light attenuation.…”

“…The dentin tubules are considered as the predominant cause of scattering in dentin. Studies investigating the optical properties of dentin [25,26] have shown that the transdentinal laser light transmission is related to the shape and arrangement of dentin tubules. Hence, it is possible to suggest the existence of a direct relationship between dentin permeability and light transmission through dentin.…”