Clinical Science

Abstract

A theoretical study of oral sugar clearance (Caries Res 17:321-334, 1983) suggested that the unstimulated salivary flow rate (UNSTFR) and the volume of saliva present in the mouth before swallowing (VMAX) can greatly affect the rate of sugar clearance. The object of this study was to determine whether variations in UNSTFR, by water infusion into the mouth, and in VMAX, which can be altered by varying the swallowing frequency, would influence sugar clearance and whether changes in VMAX would affect the extent of the pH fall produced by S. mitior in vivo after sucrose consumption. In three experiments on each of ten adult subjects, UNSTFR was measured initially (mean value = 0.55 mllmin), and a swallowing schedule was calculated so that the volumes swallowed were either 0.3 ml or 1.0 ml. After a 10-second rinse with 20 ml of a 10% sucrose solution, the subjects maintained a swallowing frequency such that the volumes swallowed were either 0.3 ml or 1.0 ml at normal UNSTFR or were 0.3 ml when UNSTFR was increased by infusing water at 0.5 mllmin. In all subjects, clearance of sugar was faster at the higher swallowing frequency and at the higher flow rate, as predicted by the theoretical model. Small acrylic splints were made to fit over the lower incisors of ten subjects and to hold in the floor of the mouth an antimony microelectrode covered by a 0.5-mm layer of S. mitior, which was held in place by a dialysis membrane. On two occasions, and in random order, the subjects rinsed with a 25% sucrose solution for 10 sec. Then, with the bacteria-covered electrode in the floor of the mouth, pH changes were followed for 30 min while the subjects swallowed either once each 15 sec or once each 120 sec. In all subjects, the pH fall from an initial mean value of 6.6 was less at all time points at the high swallowing frequency (min. mean pH = 6.05) than at the low (min. mean pH = 5.56). The results confirm the predictions of the theoretical model that, with larger values of UNSTFR and smaller values of VMAX, less time is required for sugar clearance. In addition, they show that, with larger values of VMAX, a greater pH fall is produced by oral bacteria. Thus, VMAX may be an important determinant of caries susceptibility.