Restorative dentistry is the process of removing unhealthy tooth structure or teeth and restoring the form and function of the mouth. The most common destructive forces that adversely effect teeth include decay, trauma, and periodontal disease. Tooth decay is referred to as dental caries. It is the biological process of bacteria sitting on a tooth and eating what bacteria eat, and excreting acid by- products which over time eat away at tooth structure. The sole purpose of brushing and dental flossing your teeth is to remove all the bacteria from your teeth so that it can not produce acid to eat away at your tooth structure. The normal progression of tooth decay is a slow process because the protective enamel covering your teeth is usually hard enough to slow the effects of bacteria produced acid. Problems arise when the bacteria sits in the same place for prolonged periods of time and eventually dissolve the hard enamel and bacteria gets into the softer dentin inside your tooth. Once this happens the progression of “cavities” dramatically increases.
The most common places that caries or "cavities", occur are between teeth and in the deep grooves on the tops of your teeth. Think about the area between your teeth. It is usually a very tight fit from tooth to tooth. Your toothbrush is very good at cleaning the sides of your teeth but is never going to reach in between your teeth. The only thing that will is dental floss. When floss snaps through the contact between teeth it can remove the microscopic bacteria that has set up shop producing destructive acid.
Another place where a lot of tooth decay takes place is in the occlusal grooves on the tops of teeth. Bacteria hide in the base of these grooves and produce their destructive acid. Even though the top of your teeth are easy to brush, if bacteria hide deep in the groove the brush passes right over the top of them and they remain undisturbed.
In both these cases, once the bacteria eats through the outer enamel on your tooth it can hide in the hole or "cavity", it has excavated and continues its progress with little chance of being removed. Actually, even if you do remove it, more bacteria will move into that cavity as soon as it can. It is a fact of nature that the bacteria will do what it can to survive. It is also a fact of nature that once caries have made it to the softer dentin the decay will continue to grow and destroy more and more tooth structure as the cavity increases.