Salivary glucose clearance, dry mouth and pH changes in dental plaque in man

The aim was to study the effect of different salivary secretion rates on glucose clearance in saliva and on pH changes in dental plaque in man. Eighteen dental students, 21-33 yr old, participated. Dry mouth was induced by injecting methylscopolamine-nitrate submucosally in the labial sulcus. When dry mouth was established, two variables were measured at 1 h intervals, while the salivary flow was recovering: (1) secretion rate of resting and paraffin wax-stimulated whole saliva, and (2) glucose clearance in saliva after ingestion of a glucose tablet. pH changes in dental plaque were studied in 9 of the 18 subjects after a mouth rinse with 10% glucose at two separate occasions, once before and once after an injection of methylscopolamine-nitrate. Higher glucose concentration levels in saliva were found at low than at normal salivary secretion rate. After logarithmic transformation of the salivary glucose concentration values, a biphasic elimination pattern could be seen, with a steeper initial phase followed by a slower one. A critical value for the secretion rate with respect to the salivary glucose clearance time was found to be 0.14 ml/min for resting and 0.62 ml/min for stimulated whole saliva (mean values). The pH changes in dental plaque after the mouth rinse with glucose at extremely low secretion rate were significantly more pronounced than at normal flow rate. Thus, salivary secretion rate affects both the glucose clearance in saliva and the pH changes in dental plaque in man.