Application of diffusion–reaction equations to model carious lesion progress

Nonlinear equations that describe the diffusion–reaction process with one static and one mobile substance are used to model a carious lesion process. The system under consideration consists of two initially separated substances A (an acid causing caries) and C (a static enamel mineral) which react chemically according to the formula A+C→0̸(inert). The so-called surface layer, which is formed in this process and in which chemical reactions can be neglected, is also included in this model. Changes in the substance concentrations are calculated approximately using the perturbation method. We show that the experimental data on the enamel mineral concentrations are well described by the analytical solutions of the diffusion–reaction equations.