A cavity is a hole in your tooth that is filled with bacteria. Early on, a cavity may appear as a white spot that might be repaired. It will turn into a brown or black patch over time. Cavities can be small or large in size. Cavities can appear anywhere on your teeth, but they are most common on the crowns of your teeth where you bite and between your teeth where food gets caught. Cavities that are left untreated can lead to sensitivity, pain, infections, and even tooth loss. Preventing cavities is the best approach to keep your teeth and keep them healthy.