Dental X-rays are black-and-white pictures of the hard tissues of the mouth such as teeth and bone. They are used as a diagnostic tool following clinical examination in order to detect hidden cavities, wisdom teeth as well as bone loss. Dental X-rays are generally safe with extremely low levels of radiation thus minimizing the harmful effects of radiation to a very minimal.
There are two types of dental x-rays

Intraoral – These show a few teeth, and help in detecting cavities as well as bone loss between teeth.

Extraoral 

These show a wider view of all the teeth as well as bone, temporomandibular joints, infections and impacted teeth.