Predicting infiltration of the surface layer of natural enamel caries

•Surface layer of enamel caries limits proper resin infiltration in natural lesions.•Enamel components predictive values of infiltration of SL by liquids are unknown.•Two Thoulet's solutions with different penetration coefficients were tested.•Thoulet's solutions infiltrated 3-30% of the pore volume of the surface layer.•αd (inversely proportional to organic volume) had the highest predictive value.

AimTo test the hypothesis that the water volume more easily available for diffusion (αd) is the best predictor among all major components of the proportion of pore volume infiltrated by a liquid in the surface layer of dry natural enamel caries (NEC).Materials and methodTwo aqueous solutions of mercuric and potassium iodide (Thoulet's solutions) with different refractive indexes (1.4 and 1.47) and penetration coefficients (3212 cm/s and 2297 cm/s) were tested at histological points (n = 63) of ground sections of NEC lesions. Component volumes were measured with microradiography and interpretation of birefringence. Real-time 2D mapping of capillary flow was performed with orientation-independent polarizing microscopy.Resultsαd was a good predictor for both liquids (T1.40: R2 = 0.413; T1.47: R2 = 0.505), but was similar to the water and air volumes for Thoulet's 1.47, and to the mineral and organic volumes for Thoulet's 1.40. From real-time 2D mapping, infiltration in ground sections occurred in two propagation directions, perpendicularly to the prism paths (at the centre of the lesion bodies) and axially to the prism paths (at all parts of the lesions), with two penetration rates, the faster related to prisms sheaths and the slower related to intraprismatic pores, affecting penetration length and air displacement.Conclusionsαd was a good predictor for both liquids, but was similar to the water and air volumes for T1.47 and to the mineral and organic volumes for T1.40. Both flow mechanics and component volumes are required to interpret infiltration of liquids into NEC.