chapter  50
28 Pages

Optical Methods for Caries Detection, Diagnosis, and Therapeutic Intervention

Dental enamel is an ordered array of rods of inorganic apatite-like crystals surrounded by a protein/lipid/ water matrix. The crystals are approximately 30 to 40 nm in diameter and can be as long as 10 µm. The crystals are clustered together in 4-µm-diameter rods (or prisms), which are roughly perpendicular to

the tooth surface. Dentin is honeycombed with dentinal tubules of 1 to 3 µm in diameter. Each of these tubules is surrounded by a matrix of needle-shaped, hydroxyapatite (HAP)-like crystals in a protein matrix composed largely of collagen. Because of the complex nature of these materials, the scattering distributions are generally anisotropic and depend on tissue orientation relative to the irradiating light source

in addition to the polarization of the incident light. The optical properties of biological tissue can be quantitatively described by defining the optical

constants — the absorption (µ

) and scattering coefficients (µ

) — that represent the probability that the incident photons will be absorbed or scattered, as well as the scattering phase function

Φ

(cos

θ

), which is a mathematical function that describes the directional nature of scattering.