Effects of Diet on Salivary Secretion and Composition

The composition of saliva is potentially of great importance to the prevention of caries. Saliva contains buffers that tend to reduce the fall in pH that is associated with acid formation from carbohydrate by the dental plaque; it also contains urea, a substrate for base formation by dental plaque. Saliva contains at least one enzyme (amylase), which is involved in the first stages of the metabolism of starch, a component of many foods. In addition, saliva contains ions such as calcium, phosphate, and fluoride, the concentrations of which determine the pH at which tooth mineral will begin to dissolve. The main criticism that can be leveled against the majority of studies on the effects of diet on saliva is that the experimental design did not control the nondietary variables that can affect salivary flow rate or composition. These include the source of saliva, flow rate, degree of hydration of the subject, nature of the stimulus, duration of stimulation, plasma composition, the time of day at which samples are collected, and the serial dependency of saliva samples (the effect of previous stimulation on the composition of saliva collected subsequently). The importance of some of these factors has only recently been appreciated. In addition, the experimental design of previous studies rarely included a group of control subjects kept on a constant diet. The effect of nutrition on saliva was reviewed briefly by Krasse.1