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Enamel demineralization is slowed by salivary proteins that inhibit calcium hydroxyapatite (HA) demineralization. Statherin (StN43), a 43-residue phosphorylated salivary protein with primary sequence similarities to osteopontin and caseins, binds calcium and HA. The aim of this study was to identify the minimum length of the functional domain of the statherin molecule required for cariostatic function by measuring the efficacy of peptides of progressively shorter length (i.e. containing only the N-terminal 21 (StN21), 15 (StN15), 10 (StN10), or 5 (StN5) residues) to reduce HA demineralization rates (RD(HA) ). Porous HA blocks were used as enamel analogues, and were exposed to 0.1 M acetic acid at pH 4 for 120 h, rinsed, and treated with StN21, StN15, StN10, or StN5 peptides (1.88 × 10(-5) M) for 24 h, then demineralized for a further 120 h. The RD(HA) was measured, before and after peptide treatment, using scanning microradiography. Hydroxyapatite blocks treated with StN21 and StN15 demonstrated a 50-60% reduction in the RD(HA) . However, no reduction in the RD(HA) was observed following treatment with either StN10, StN5, or buffer only. The mechanism by which statherin-like peptides reduce RD(HA) may be associated with their binding to HA surfaces. Comparisons with previously published binding energies of statherin to HA also suggest that statherin-like peptides containing 15 N-terminal residues or more, are required for binding, suggesting a link between binding and demineralization reduction.

Salivary proteins influence the biomineralization of hydroxyapatite (HAp) within enamel. Their effect on the crystal growth has been extensively studied, but, their effect on demineralization kinetics is less well investigated. In this study bovine serum albumin (BSA) was used as a model protein to measure its effect on demineralization kinetics of hydroxyapatite aggregates using scanning microradiography (SMR). HAp aggregates (8 and 20% porous) were cut into 5 x 5 x 2 mm blocks. SMR cells were prepared containing hydroxyapatite blocks. BSA was added to demineralising solutions (0.1 mol L(-1) acetic acid, buffered to pH 4.0; degree of saturation zero and 0.062 respectively) at a concentration range 0.76-75.8 micromol L(-1). Demineralising solution without added BSA was used as a control. The demineralising solutions were circulated past the samples at 0.4 mL min(-1). SMR was used to measure the rate of mineral loss (RML(HAp)) at 14 points in each sample repeatedly for 3 weeks. The results show that BSA increases or decreases the RML(HAp) depending on; BSA concentration, HAp porosity, and the degree of saturation of the demineralising solution. It is suggested that BSA influences demineralization kinetics of HAp either by modifying solution properties, or, by affecting the surface energy of hydroxyapatite.