Some cavities are visible to the naked eye, while others are not.

Clinically, some cavities can be observed with the naked eye. Such cavities usually have damage that extends beyond the enamel, with obvious cavities and incomplete tooth structures visible. For example, cavities on the biting surfaces of molar teeth and on the adjacent surfaces of front teeth that are moderate to severe can be seen with the naked eye.

However, not all cavities can be observed with the naked eye. When the decay is confined within the enamel without obvious cavity formation, it cannot be seen with the naked eye, but it can be diagnosed by taking dental X-rays. Clinically, there are also some cavities on adjacent surfaces where the decay starts from hidden parts of the tooth; some of these might show ink-soaked-like dark brown discoloration on the biting surfaces, but they too require dental X-rays for diagnosis.