The kinetics of inorganic phosphate in human dental plaque and saliva

Abstract

The kinetics of inorganic phosphate (P i), Na and K in plaque fluid and changes in the composition of the residual 24 h human dental plaque was studied following rinsing with water, 20 per cent sucrose, 0.12 M and 0.5 M phosphate. Rinsing with sucrose solution reduced plaque P i to a greater extent than water, and the effect was demonstrable 10 min later. The main effect of both on plaque P i was due to the exposure of plaque to a P i-free solution. Rinsing with P i elevated plaque fluid P i but the effect was short-lived and not detectable 15 min later irrespective of the concentration used. Changes in the Na and K concentrations in plaque fluid after sucrose could not be related to the effects of bacterial metabolism. Phosphate added to sucrose and ingested simultaneously was cleared from the saliva at a time when substantial amounts of carbohydrate remained. The effect of sucrose in lowering plaque fluid P i was prevented by 0.12 M P i introduced separately after the sucrose and was reversed by 0.5 M P i. It was concluded that the local effect of raising plaque P i would not contribute significantly to inhibition of acid production, desorption of protein from enamel hydroxyapatite or buffering and that when P i was introduced into plaque separately from, and after, sucrose the elevated plaque fluid P i could exert a short-lived local effect, by mass action, on the dissolution and remineralization of enamel.