Estimates, from salivary analyses, of the turnover time of the oral mucosal epithelium in humans and the number of bacteria in an edentulous mouth

The objectives were to obtain rough estimates of the number of bacteria in an edentulous mouth and the mean turnover time of the oral mucosa and the conditions under which the salivary phase in the mouth might act as a bacterial continuous culture system. The premise was that at steady state in vivo, the rates of loss of bacteria and epithelial cells in saliva must be equal to their rates of proliferation. Drooled saliva was collected from 17 subjects and the number of epithelial cells per millilitre was determined in a Coulter Counter. The numbers of adherent bacteria per epithelial cell were counted on cells stained with Toluidine Blue. For 10 subjects, salivary bacterial counts were obtained after saliva had been diluted in Reduced Transport Fluid and grown anaerobically on Blood Agar for 5 days. From the known surface areas of the oral mucosa and individual epithelial cells and the rate of loss of epithelial cells into saliva, the surface layer of epithelial cells was calculated to be replaced every 2.7 h. From the calculated number of epithelial cells lining the oral mucosa, the number of bacteria per epithelial cell, and the rate of swallowing of the bacteria in saliva, the number of bacteria in an edentulous mouth was calculated to be about 1.58×109 and the mean time between bacterial cell divisions to be 1.38 h. Given a residual volume of 0.8 ml and a maximal bacterial division rate of 3 h−1, the salivary phase in the mouth could act as a continuous culture system for certain fast-growing bacteria only if the maximum flow rate were <0.04 ml/min.