Inhibition of calcium phosphate precipitation by human salivary secretions

Although human saliva is supersaturated with respect to most basic calcium phosphate salts, it lacks the properties which are characteristic of metastable solutions. The purpose of this investigation was to elucidate the reasons for this anomaly. Saliva, salivary ultrafiltrates and the protein fraction of saliva were examined for their effect on the precipitation of calcium phosphate from supersaturated solutions. Salivary ultrafiltrates had little or no effect, but saliva and its macromolecular fraction strongly inhibited precipitation. Serum proteins were inactive, even at 50 times active salivary protein concentrations. The specific inhibitory activity, per unit of protein, of the parotid saliva from 15 subjects varied by a factor of three. Comparison of the unstimulated and stimulated parotid and submandibular secretions of one subject showed activity to be present in the unstimulated salivas and to increase substantially in the stimulated secretions.