Objectives: An artificial saliva (AS) of defined composition is necessary for testing the performance of materials that serve in the mouth as natural saliva is too variable. The chemistry involved is critically important. Many AS recipes can be found in the literature, but the stability of tooth material, i.e. hydroxyapatite (HAP), in most of these has not been addressed. In fact, few contain all major ionic components with concentrations in the physiological range. The aim of the present study was (a) to review reported AS formulae from their inception in 1931 to date, (b) to compare the stability of HAP in various reported AS, and (c) to investigate the individual effects of ionic components present in the reported formulae on the stability of HAP.
Methods: A computer algorithm, RAMESES, for solving multiple equilibrium equations, was employed for all calculations.
Results: There was a marked difference between two groups, i.e. those with and without the presence of Ca; those with Ca were supersaturated with respect to HAP in the physiological pH range, the saturation pH ranging from about 4.5 to 6.0. There was also an approximately 180-fold range in solubility at pH 7, due to the individual effects of components such as phosphate, carbonate and citrate. Acetate, lactate and sulphate showed smaller effects, others have no appreciable effect.
Conclusions: All components and equilibria of relevance to saliva must be included in the system for detailed models. Continued systematic development of a standardized AS is essential.