The effect of fluorhydroxyapatite in experimental human dental plaque on its pH, acid production and soluble calcium, phosphate and fluoride levels following glucose challenge.

Plaque grown on terylene gauze in the mouths of 5 volunteers was treated with a mineralizing solution intermittently for 4 days to deposit fluorhydroxyapatite. Control plaque grown simultaneously was not treated. Sixteen hours after the last treatment, plaque gauzes were incubated in 0.28 M glucose under N2 at 37 degrees C. The mean pH, reached by the 5 mineralized plaques after 30 min, (4.78) was significantly higher than the mean pH reached by control plaques (4.13), a difference that was due neither to unequal microbial mass nor to unequal acid concentrations. Acid neutralization following the dissolution of apatite was probably mainly responsible for the pH differences although a small antiglycolytic effect from leached F could not be ruled out. Mineralized plaque lost on average 24 per cent of its Ca, 25 per cent of its P and 16 per cent of its F, resulting in 0.868 mM Ca, 0.676 mM P and 0.075 mM F in the supernatant. Test plaque fluid was saturated with respect to fluorapatite and only moderately undersaturated with respect to hydroxyapatite at the end of the incubation period; this could explain the pronounced caries-protective effect of plaque fluorhydroxyapatite shown previously.