Objective: An unstimulated whole saliva flow rate (UWSFR) of less than 0.1 mL/min is often related to symptoms of dry mouth. It is also used as a diagnostic criterion for Sjogren's syndrome, and for assessment of hyposalivation as a caries risk factor. The main hypothesis was that the circadian rhythm of salivary flow affects this diagnosis if saliva is collected at different morning time-points.
Design: UWSFR was tested at 7:30 and 11:30 a.m. in 108 individuals, age 15-46 years (mean 33+/-9). The participants were allocated to one of three groups (very low< or =0. 1/min, low 0.1-0.2 mL/min and normal>0.2 mL/min) based on the UWSFR at 7:30 a.m. Different aspects of the perception of oral dryness were rated using Visual Analog Scales.
Results: All three groups displayed a statistically significant increase in UWSFR at 11:30 a.m. compared with 7:30 a.m., all of similar magnitude (0.08-0.09 mL/min). In the group with very low UWSFR, 70% at 11:30 a.m. exceeded the 0.1 mL/min limit. There were significant difference in perception of oral dryness between the normal group and both the low and the very low groups. Only the subjects in the groups with a low or very low UWSFR perceived an increase in oral wetness at 11:30 a.m.
Conclusions: It was concluded that the time of measurement strongly influences the diagnosis of hyposalivation. To control the influence of variations in the time of saliva collection, we suggest that unstimulated whole saliva tests are performed at a fixed time-point or in a limited time interval early in the morning.