  We develop a theoretical model of the carious lesion progress caused by acids
diffusing into the tooth enamel from the dental plaque. The acids react with
static hydroxyapatite, which leads to demineralization of the enamel, and
consequently to the development of the carious lesion. The model utilizes the
diffusion-reaction equations with one static and one mobile reactant where the
reaction term is proportional to the product of concentrations of acids and of
mineral. The changes of concentrations are calculated approximately by means of
a perturbation method. The analytical approximate solutions are compared with
the numerical ones and experimental data.
