MORPHOMETRIC ANALYSIS OF THE DEPOSITION AND MINERALIZATION OF ENAMEL AND DENTIN FROM RAT INCISOR DURING THE RECOVERY PHASE FOLLOWING A LOW-CALCIUM REGIMEN

The administration of a low-calcium diet to pups nursed by a mother on the same diet has been shown to induce a slowing of growth. A reducti on of the apposition rate of dentine, which was normally mineralized, and a dramatic reduction of the extent of mineralization of enamel, wh ose organic matrix was otherwise produced in an almost normal amount, was observed in the incisors of these animals. Modifications of the mi neral apposition rate of dentine, measured after administration of tet racycline (10 mg/kg), and the thickness and the microhardness of the t wo tissues, the latter being an expression of the degree of mineraliza tion, were now investigated when hypocalcic pups were restored to a no rmal-calcium diet for 10 or 60 days. Enamel microhardness was increase d by more than 60% after only 10 days of restored diet and had become the same as in the control tissue after 60 days, without any significa nt increase in thickness. Dentine thickness and mineral apposition rat e increased significantly, to become similar to those of the controls after 60 days of restored diet. In dentine there was no significant va riation of microhardness between experimental pups and controls, eithe r during the low-calcium diet or the restorative period. These results indicate that the deposition of the organic matrix of enamel is a pro cess independent from that of its mineralization, and that the mineral ization of the organic matrix happens by its replacement even a long t ime after its deposition. In contrast, the deposition and mineralizati on of dentine are strictly interdependent processes, at least in these experimental conditions. The modifications of the incisor tissues ind uced by this diet can be reversed by the administration of a correct d iet, at least in continuously growing teeth.