A New Model for Nanoscale Enamel Dissolution

Objectives: The aim of this work was to quantify the dissolution kinetics of enamel and study surface structure during dissolution under simulated caries-forming physiological conditions. Methods: The dissolution kinetics of human tooth enamel surfaces was investigated using nanomolar- sensitive constant composition (CC) and in situ atomic force microscopy (AFM) under simulated caries formation conditions (relative undersaturation=0.90, pH=4.5). The resulting etched enamel surfaces were also examined by high resolution scanning electron microscopy (SEM). Results: AFM and SEM results showed that deminerzalization was initiated at core/wall interfaces of rods and developed anisotropically along c-axes. Following the more rapid removal of surface polishing artifacts, the dissolution rate decreased slightly from 3.3+/-0.1 to 3.0+/-0.1x10E-10 mol mm-2 min-1 as the reaction proceeded in accordance with our new crystal dissolution model, resulting in hollow cores in the enamel and nanosized remaining crystallites, resistant to further dissolution. Generally, dissolution of minerals is regarded as a spontaneous reaction in which all the solid phase can be dissolved in undersaturated solutions. However, the dissolution of biominerals may be suppressed when the crystallites approach nanometer sizes. Conclusions: This study shows that enamel demineralization in acidic medium by CC constitutes a new model that can be used to mimic carious lesion formation. The dissolution of enamel crystallites at the nanoscale can exercise a degree of self-preservation in the fluctuating physiological milieu. (Supported by NIDCR, DE03223).