Why do I need a filling if I’m not in any pain?

Decay in its early stages usually isn’t painful. It is once the decay has extended past the tooth's protective enamel layer into the dentin and beyond that things become sensitive and tender. As decay progresses closer to the nerves of a tooth, the pain begins to intensify and, if left untreated, can turn into a raging toothache. Once it reaches this point, a simple filling may no longer be possible. Attending to a cavity as soon as possible is always encouraged and recommended.