Normal daily secretion of saliva is approximately á 1L to 1,5 L per day (i.e. 0,5
mL/min -1 mL/min) although flow rate varies depending on diurnal variation,
hydration, food intake and many other factors. Large variability in salivary flow
rates within and between individuals has been reported, which has impaired the
establishment of standard values. In a study of Ghezzi et al. [25] among 36 healthy
males and females (18 young, ages 20-38; 18 older, ages 60-77) salivary flow rates
varied 27-44% during a 6 hour period, suggesting that a 45% range in salivary flow
rates could be considered normal salivary variation, and values below 45% of normal
levels could be used to define salivary hypofunction. Salivary flow rate of unstimulated
saliva less than 0.1 mL/min (measured for 5 to 15 minutes) and less than
0.5 mL/min for the stimulated salivary flow respectively, is indicative for salivary
hyposecretion or hypofunction