Methods for sampling and analysis of the aqueous phase of human dental plaque

Abstract

The use of calcium and fluoride ion selective electrodes in whole plaque, the conditions for obtaining the aqueous phase in dental plaque and methods of storage of plaque were investigated. Calcium-ion activity measurements in whole plaque were unreliable. Fluoride-ion activity measurements in whole plaque, without the addition of buffer, were internally consistent provided successive samples did not differ widely in their expected concentrations. Electrode response time was slow and unstable. The optimum conditions for obtaining plaque fluid were obtained by pooling more than 20 mg of sample and centrifuging in a fixed-angle rotor at 5000 g for 15 min at 2 °C. Recovery of 50–70 per cent of estimated plaque fluid was obtained, depending on sample weight. Determinations of fluoride, calcium and inorganic phosphate concentrations in plaque fluid were unaffected by the methods of storage adopted (ice and liquid N 2). Potassium and magnesium concentrations were higher in liquid N 2-stored samples. A systematic study of the concentration of solutes present in the aqueous phase of plaque is possible with this method.