My tooth does not hurt, so why do I need treatment?

A cavity is best treated while it does not hurt - that is when the least amount of tooth has to be removed and treatment is simplest. By the time you feel pain, the decay has often already progressed close to the nerve, so root canal treatment and a crown may become necessary. In terms of scale, 1) an early cavity is one visit for a resin filling, while 2) decay that has reached near the nerve grows into 2 to 4 root canal visits plus a crown. Finding it early at a check-up is the way to save both money and tooth structure.