The structure of immature enamel and dentin in particular, allows the ready diffusion of acids and ions through channels and pores. Removal of the acquired dental (enamel) pellicle and exposure of open dentin tubules aids this diffusion, and the movements of tubule fluids may cause dentin hypersensitivity. Saliva is essential for maintaining the protection and normal functioning of the masticatory system. A ‘dry mouth’ or xerostomia resulting from a perceived reduction in salivary flow may lead to numerous signs and symptoms of oral dysfunction. The quality of life for affected people may be poor. Many of these persons are taking multiple medications that cause a reduced salivary flow, and the number of people taking such drugs can be expected to increase. The ingestion of softer cariogenic foods, and acidic foods and beverages in attempts to stimulate an increased saliva flow, is disastrous for the teeth. Even with a normal saliva flow, frequent acid assaults can overwhelm the protective buffering and remineralization capacity of the saliva and plaque fluid, leading to tooth erosion.