Light scattering in human dentin

Understanding light propagation in human dentin is critical for dental diagnostics, including optical coherence tomography (OCT) and early caries detection. Dentin's heterogeneous microstructure-a dense network of cylindrical tubules ( $\approx 2\mu \text{m}$ diameter) embedded in an organic-inorganic matrix-induces both isotropic and anisotropic light propagation. Previous isotropic-only models cannot capture the pronounced angular dependence observed experimentally, leading to substantial errors in the estimation of optical parameters. We present a combined isotropic-anisotropic Monte Carlo model for light transport in dentin, incorporating directionally dependent propagation in tubules based on Maxwell's equations for infinitely extended cylinders. Optical parameters were determined from angular-resolved goniometric measurements on three human teeth across wavelengths from 400 nm to 700 nm, with controlled tubule orientations. Using particle swarm optimization to fit the model to experimental data, we quantitatively characterized both propagation regimes: the intertubular matrix ( ${\mu }_a\approx 0.5{\text{mm}}^{-1}$ , ${\mu }_s\approx 1.8{\text{mm}}^{-1}$ , g ≈ 0.85) and tubule geometry (diameter 2.25 µm, areal density 19 000 mm^-2 to 60 000 mm^-2). Comparison with an isotropic-only model revealed that neglecting anisotropic propagation introduces absorption errors exceeding 40 %, emphasizing the importance of the combined approach. This framework enables robust inverse problem solving for dental optics and can be extended to study other tissues exhibiting anisotropic light propagation, such as brain white matter, tendon, and muscle.