Diffraction and waveguide propagation of light in tooth enamel

The propagation of light in tooth enamel was studied using longitudinal meridional sections of extracted teeth. The propagation of light in enamel depends on the angle of incidence of the light beam relative to the direction of the enamel prisms. When the laser beam is incident on the enamel perpendicular to the plane of the thin section, one can observe an ordered pattern of diffraction at periodic inhomogeneities, which are represented by parallel external sections of enamel prisms. When a laser beam falls on the tooth surface in the section plane, the pattern of laser radiation propagation in the enamel can be explained by the waveguide propagation of light along enamel prisms. Based on the waveguide model, the conditions for the manifestation of the known optical effect in the form of Hunter–Schreger bands in reflected and transmitted light are explained. The presence or absence of a diffraction pattern corresponding to diffraction at periodic inhomogeneities of tooth enamel depends on the age of the tooth and the thickness of the section. The results enable the conclusion about the nature of the age-related mineralization of enamel during its maturation, which leads to an increase in the transparency of enamel and a decrease in the degree of its optical anisotropy.