Quantitative Study of Enamel Dissolution Under Conditions of Controlled Hydrodynamics

A rotating disk method has been used to study the dissolution of bovine enamel. A diffusion model adequately describes the reaction for a wide range of conditions, and the rate is also hydrogen ion dependent. The solubility product of bovine enamel, 5.9 ± 1.8 X 10-59 moles9 1-9 at 25 C is derived by a method that minimizes the possibility of phase changes. S;nce dental caries is a disease that involves the dissolution of dental enamel by bacterially produced acid, many studies have been made of the rates and mechanisms of the reaction.1-8 Because knowledge of the processes occurring in the mouth is the ultimate goal, a number of these studies have attempted to reproduce con-ditions found in the mouth.68 However, the complex nature of the fluid dynamics and coD-ditions of the oral environment makes the in-terpretation of suchi results difficult. In this study, conditions have been optimized for the measurement of dissolution rates accessible to treatment by fundamental theories of solution chemistry. Such rate laws may be used to in-terpret experiments designed to more exactly reproduce conditions found in nature or to quantitate the effects of natural or synthetic inhibitors. The exceptionally stable and repro-ducible mass transport conditions found at the surface of a rotating disk allow calculations of the hydrodynamic boundary layer dimen-sions to be made using the Levich theory9 for fluid flow at a rotating disk. In the present work, the dependence of the rate of dissolu-tion of bovine enamel on the concentrations of hydrogen, calcium, and phosphate ions has been studied under a variety of hydrodynamic conditions. Materials and Methods Analytical grade chemicals, water pre-paled by deionization followed by double dis-tillation tinder nitrogen, and Grade A glassware Received for publication January 12, 1976. Accepted for publication July 9, 1976