Hypothesis: all diseases are preceded by medical conditions, and all medical conditions have a period of reversibility.
Tooth decay is no exception: the reversible phase is the daily formation/removal of biofilms of bacteria and the daily reversible de-mineralization/re-mineralization of the enamel.
Under present technology, cavity formation is irreversible. Stem cells that can be coaxed into producing enamel may soon change that.
When biofilms form and are incompletely removed, the bacteria do two things:
1. Digesting starch and sugars, acidophilus bacteria digest the outer mineral surface of the tooth, using acid, a waste product of sugar/starch metabolism, as a catalyst.
2. When the protein core of the tooth is sufficiently exposed, protein digesting bacteria degrade the protein core of the tooth, forming a cavity.
1. must occur before 2. Acidophilus bacteria must do their job before the protein digesting bacteria.
Hypothesis: most food left between the teeth does not produce many cavities there because this food is generally of a high protein nature (example nuts and meat).
During the reversible phase of tooth decay, all of the following are useful: fluoride (fluoro-apatite is more resistant to acid hydrolysis than hydroxyapatite), abrasive pastes such as a paste of baking soda that can scrape off some of the biofilm, germ-killing mouthwashes (kills both acidophilus and protein-digesting bacteria), and the healthy saliva of a well nourished person, which is germ-killing, bacteriostatic, and mineral-rich (to re-mineralize teeth).
Once a cavity has formed, they are all of limited use, limited to preventing the growth of the cavity.
Hypothesis: the principal benefit to the animal that has amylase in his saliva is the digestion of the large starch molecules captured by acidophilus bacteria. As the saliva washes this digested starch away, this digestive action limits the bacterial food supply and reduces the rate of cavity formation. Salivary amylase has a very limiting role in our nutritional energy supply. Pancreatic amylase is the major enzyme in supplying our carbohydrate calories.
Note: there is no PURPOSE of salivary amylase. Teleology is not invoked. One can, however, speak of the benefits to a living creature vs. not having something.