The buffer capacity of single-site, resting, human dental-plaque fluid.

A carbonate equilibration method was used to measure the buffer capacity of resting plaque fluid collected from single buccal or interproximal sites of upper and lower first molars or anterior teeth. The maximum buffer capacity was 26 m-equiv./l at pH 7.1. The buffer contribution from the measured concentrations of phosphate and carbonate was calculated for each sample. These values were compared with the buffering actually measured and with that expected from organic acids, proteins, and amino acids at average values, as taken from reports in the literature. Relative contributions of buffer species at the average pH of the samples (6.86) were: 35 per cent phosphate, 10 per cent carbonate, 10 per cent protein, 10 per cent organic acids, 2 per cent amino acids, 30 per cent unidentified. There were no significant differences in the buffer capacities of samples originating from sites that differ in their accessibility to saliva. Buffering in resting plaque fluid is more than twice that in saliva and did not show differences correlated with the intra-oral location of the samples.