Saliva is a mixture of mucous and serous fluid, the term given to bodily fluids that are pale yellow, transparent, and benign in nature.  This mixture is formed by the salivary glands, whose structure and function are explained in more detail below.

Video 1. Saliva.
Saliva is the most important fluid that we have in relation to oral diseases. Saliva is not simply a fluid that keep the mouth moist. It is full of many components, including calcium, phosphate, some fluoride, proteins, anti-bacterials, lipids, and buffering agents. So saliva in terms of dental decay – first action is it buffers or neutralizes the acids as the bacteria are producing them or after that. Secondly, it provides calcium and phosphate to slow down the dissolving of the mineral and also to provide calcium and phosphate for remineralization and fluoride cannot work unless than calcium and phosphate is present. Secondly, it has a large number of antibacterial substances which slow down the action of the bacteria. Without that, decay would be rampant in all of us, as is seen when we have situations where the saliva flow is interrupted or stopped or slowed down. In that case, you can put as much fluoride as you like in, and it still will not be enough to balance the pathological effects from the bacteria.