Stoichiometry and Thermodynamic Solubility Properties of Dentin Mineral of Human Permanent and Deciduous Teeth

Abstract

Acquisition of substantial amounts of CO32-, HPO42- and other impurities is universally encountered in bioapatites from mammals. To date, however, there is a paucity of information about the stoichiometry and, on that basis, solubility product of dentin mineral. In this report, we summarize our experimental approach toward the determination of the stoichiometry model and thermodynamic solubility products of human dentin apatites. Dentin samples were collected separately from the coronal portion of permanent premolars (extracted for orthodontic reasons) and exfoliated deciduous teeth. Both pooled materials were pulverized with an agate-mortar, and then plasma-ashed at approx. 60°C to remove the organic matter. The stoichiometry model selected for these crystals was (Ca) 5-x (Mg) q (Na) u (HPO4) v (CO3) w (PO4) 3-y (OH) 1-z. These stoichiometric coefficients were analytically determined by assessing separately the labile or surface pools of the ionic species on the crystal surface and their stable pools in the bulk crystal lattice. The dentin mineral was equilibrated in dilute phosphoric solutions (100mg/100ml) at 25°C for a maximum of 28 days under constant partial pressures of CO2. The results showed that there are appreciable differences in the crystal stoichiometry between the permanent and deciduous dentin mineral and that the solubility product constants (KDN) were 4.11×10-45 for permanent dentin and 1.74×10-43 for deciduous dentin, which were determined under 1.8% CO2/N2. Notably, the solubility properties of the dentin mineral remained relatively constant in the range of 1.0 through 3.3% CO2/N2, whereas the discrete solubility data were obtained below and above the corresponding partial pressure of CO2.