The reason why cavities don't hurt is because the outer layer of the enamel don't have any nerve endings. This is why a lot of patients that show up in our office are very surprised that they have multiple cavities.
There are three layers in the tooth. The outer layer is the enamel. The middle layer is the dentin. The deepest layer is the pulp and nerves. Sensitivity and discomfort usually starts when the cavity gets inside the deeper middle layer of the dentin. Severe pain and swelling starts when the decay reaches the nerve.
Cavities can be prevented by keeping up with biannual checkup with x rays.
We can help prevent cavities by educating you about the proper technique of brushing and healthy diet.