Mineral Exchange in Teeth
The salts of teeth, like those of bone, are composed of hydroxyapatite with adsorbed carbonates and various cations bound together in a hard crystalline substance. Also, new salts are constantly being deposited while old salts are being reabsorbed from the teeth, as occurs in bone. Deposition and reabsorption occur mainly in the dentin and cementum and to a very limited extent in the enamel. In the enamel, these processes occur mostly by diffusional exchange of minerals with the saliva instead of with the fluids of the pulp cavity.
The rate of absorption and deposition of minerals in the cementum is about equal to that in the surround-ing bone of the jaw, whereas the rate of deposition and absorption of minerals in the dentin is only one third that of bone. The cementum has characteristics almost identical to those of usual bone, including the presence of osteoblasts and osteoclasts, whereas dentin does not have these characteristics, as explained earlier. This difference undoubtedly explains the different rates of mineral exchange.
In summary, continual mineral exchange occurs in the dentin and cementum of teeth, although the mech-anism of this exchange in dentin is unclear. However, enamel exhibits extremely slow mineral exchange, so that it maintains most of its original mineral comple-ment throughout life.