On minor salivary gland secretion in children, adolescents and adults

The minor salivary glands are of great importance for maintenance of homeostasis in the oral cavity. These glands continuously secrete substances which lubricate and protect the oral tissues, contributing to comfort and health. The minor salivary glands contribute approximately 7-8 per cent of the total volume of saliva. Flow rate and composition seem to vary according to anatomical location. Current knowledge about the minor salivary glands is derived primarily from studies on adults. The overall aim of this thesis was to study age-related changes in minor gland saliva, from childhood to adulthood. By increasing the knowledge of minor gland secretion, we hopefully better understand how different mucosal locations are lubricated and protected in individuals of different ages and various health statuses. The project comprises four papers. In Paper I, the flow rate and numerical density of the labial and buccal minor glands of pre-school children, adolescents and adults were investigated. Saliva was collected on filter paper discs and the flow rate was measured by the Periotron-method. The numerical density was assessed by PAS-staining.

The flow rate of the buccal glands was significantly lower in children than in adults and the number of labial glands was significantly higher in children than in the other age-groups. In Paper II, the composition of minor gland saliva of the three age groups (Paper I) was analysed (by ELISA-technique), with reference to the mucins MUC5B and MUC7, representing some of the major components of innate salivary immunity.

Children did not differ from adolescents and adults with respect to MUC5B content in labial gland saliva, but had less MUC7 than the adults. In the buccal gland saliva, detectable amounts of the mucins were found in only a few of the participants. In Paper III, the content of the adaptive immune component (salivary IgA) in minor gland saliva of pre-school children, adolescents and adults was measured by the ELISA technique. The salivary IgA-concentration in whole saliva of the three age-groups was also estimated.

The IgA-concentration was significantly lower in the labial glands and the whole saliva of the children than in the adults. In Paper IV, age-dependent differences of other innate components were studied in pre-school children, adolescents and adults, by analysing the amount of glycoprotein 340 (gp-340) in minor gland and whole saliva, using the ELISA technique. The content of sialic acid, a common terminal structure of glycoproteins, was analysed using the ELLA technique.

With respect to minor gland saliva, no differences were disclosed among pre-school children, adolescents and adults. However, the gp-340 content of whole saliva was significantly higher in the children than in the adults. The above investigations of properties of minor salivary glands in children, adolescents and adults seems to be the first to present data on age-dependent variations in gland density and secretions from healthy individuals. The results show high gland density, mature innate immunity and an ongoing maturation of adaptive immunity in the saliva of children. The report provides a reference for further comparative studies on minor gland saliva of younger individuals in health and disease.