Effect of age on salivary flow obtained under feeding and non-feeding conditions

Age, health status and disease treatments are thought to influence salivary flow. In this study, age effect on salivation was compared in non-feeding (at rest and during parafilm chewing) and feeding (during meat chewing) conditions for two groups of healthy subjects, 25 young subjects (mean age 27.4 years) and 20 old subjects (mean age 71.2 years). In non-feeding conditions, parotid flow was assessed at rest (3 min) and during parafilm chewing (1 min) from the absorptive capacity of a cotton roll placed in front of the upper duct apertures. Remaining saliva emanating mainly from the submandibular/sublingual glands was determined at rest by a sublingual cotton roll. In order not to impede in the chewing process during parafilm chewing, no cotton roll was placed in the lower part of the mouth and the remaining saliva was simply spit out for evaluation. Assessments were made under feeding conditions during the mastication of meat of different textures. The saliva content of the bolus was evaluated at different stages of the chewing process by weighing the mouth contents after spitting. No direct age effect was found on the different salivary flow rates measured during different conditions of stimulation. However, a significant correlation was found between the salivary flow rates at rest and those obtained during meat chewing in the elderly group but not in the young group. In elderly adults, rest salivary flow rate appears as a good predictor of salivary flow during the consumption of food. Within each group, significant correlations were found between salivation elicited by meat and by parafilm chewing. These results confirm the lack of direct global age effect on salivary flow rate by chewing in the 3 min after the stimulation, although adaptations to the measurement conditions are different between both groups of subjects.