In vitro studies on the effect of sodium tripolyphosphate on the interactions of stain and salivary protein with hydroxyapatite

Objectives To study properties of sodium tripolyphosphate (STP) relevant to inhibition or removal of dental stain in vitro. Methods The effects of STP and other phosphates on adsorption of a dietary chromogen (black tea polyphenol) and salivary protein to hydroxyapatite (HA) powder were studied by analysing loss of protein or tea stain from solutions mixed with HA or HA pre-treated with the test agents. The effects on desorption of protein and stain from HA were studied by analysis of water or solutions of test agents mixed with HA or HA pre-treated with saliva or tea solution. Results At concentrations and pH representative of those likely to occur in the mouth, STP inhibited adsorption of salivary protein and black tea polyphenol to, and desorbed these substances from, HA surfaces. Adsorption and desorption of protein and stain were not influenced by pH of the STP solutions but adsorption varied with concentration. STP showed equivalent effectiveness with respect to salivary protein adsorption and desorption as a longer-chain condensed phosphate. The inhibitory activity of HA-bound STP on adsorption of salivary protein and stain resisted extensive washing. Conclusions STP is likely to be an effective agent for inhibiting and removing dental stain, whether bound directly to mineralised surfaces or indirectly via salivary pellicle.