What causes tooth decay?

Sugar: Bacteria in your mouth cling to your tooth & if fed by sugar they produce acids that erode your tooth & result in decay ( a cavity).

Certain Bacteria: You need the combination of of a few things. 1) bacteria in your mouth. The better you can control the bacteria count the less likey you are to get decay. 2) carbohydrate. The bacteria use and produce acid as a by-product. Sugar is worst 3) a susceptible tooth surface. Smooth sufaces and self cleansing areas of the mouth are less prone to cavities...Sealants can fill in groves and pits 4) time.

Combination: Tooth decay comes from a combination of food debris left on and in between teeth and bacteria that use the food debris and create acids that damage tooth enamel and dentin.

Bacteria and sugar: Decay is caused by bacteria which are naturally occurring in your mouth. When the bacteria are fed sugar, either simple like sweets or complex like bread or sugar, they produce acid which eats into the tooth.

A dry mouth and acid reflux can be accelerators of decay and harm to the dentition. Obesity increases reflux and many medications cause dry mouth - so these issues should also be considered.

Poor diet , poor oral hygiene, and not going for dental exams.