A Monte Carlo simulation of the influence of sound enamel scattering coefficient on lesion visibility in light-induced fluorescence.

Quantitative light-induced fluorescence (QLF) is based on the dark appearance of a white spot in otherwise highly fluorescent enamel. This can be explained by the increased scattering coefficient in the white spot compared with that of sound enamel. The aim of this study was to estimate the effect of different sound enamel scattering coefficients (s(SE)) and enamel thickness d, caused by developmental enamel differences, on the fluorescence appearance of white-spot lesions. We ran a Monte Carlo simulation of a 4 x 4 mm(2) illuminated enamel slab on a highly fluorescent background. The slab had a 0.7 x 0.7 mm(2), 100-microm-deep, white spot in the center. Fluorescent and back-scattered photons re-emitted from the central 2 x 2 mm(2) were recorded. We found that the fluorescence photon excitance from the white spot (F(WS)) was less than that of sound enamel (F(SE)), with an optimum difference for S(SE) between 20 and 80/mm. For s(SE) <20/mm, both F(SE) and F(WS) decreased with d. We found no relation with d for s(SE) >20/mm. The results indicate that for small s(SE), we are suffering from edge losses, which explains why the optimum for lesion visibility is not found at s(SE) = 0/mm, as would be expected.