Natural enamel caries in quinoline: Volumetric data and the pattern of infiltration

This study aimed to test the hypotheses that (i) a parameter related to permeability, α_d (ratio of squared water volume by the nonmineral volume) is, among all major component volumes (mineral, water, and organic volumes) the best predictor of quinoline infiltration in natural enamel caries (NEC), and (ii) the pore volume fraction infiltrated by quinoline (V_qui ) in NEC is much lower than previous estimates that neglected water and organic enamel volumes. Mineral and nonmineral volumes and α_d were measured at 341 histological points (from 20 approximal NEC lesions), and transport of quinoline was tracked by orientation-independent polarizing microscopy. R² values of V_qui were 0.596 (α_d ), 0.033 (mineral volume), 0.474 (water volume), and 0.011 (organic volume). V_qui values were 23% (body of the lesion), 7% (dark zone), and 9% (translucent zone), lower than previous estimates (with high effect size). Transport of quinoline occurred both parallelly and perpendicularly to prism paths, and dark zones were seen where only transport parallel to prisms occurred. In conclusion, α_d was the main predictor of quinoline infiltration, but it differed from the water volume with a small effect size, and the pore volume fraction with quinoline was much lower than previous estimates.