X-rays help dentist to detect problems that would be missed by just looking in your mouth, such as:

1) cavities between teeth or under fillings
2) trouble with teeth and jaw development in children and teens
3) bone loss from gum disease
4) jaw bone tumors
Sometimes x-rays are needed as part of your dental treatment for diagnosis if you have tooth ache or in case of tooth fracture.
Types of Dental X-rays
Common x-rays used in the dental office include bite-wing, periapical, and panoramic x-rays. Bite-wing x-rays help dentist check for tooth decay between the back teeth or under dental fillings. Periapical x-rays help dentist observe conditions below the gum line, showing the roots of the teeth and surrounding bone. Panoramic x-rays use a machine that rotates around the head. It produces a long film that shows the entire jaw and all of the teeth in one image.
Cone-beam computed technology is used to create a 3-dimensional image from a series of images. Because it relies on multiple images, the radiation exposure is higher than that of commonly used x-rays and is used for surgical treatments.
Are Dental X-rays Safe?
Because dental x-rays expose us to radiation, patients sometimes wonder if they are safe. Routinely we are exposed to radiation from a number of sources, even sunshine, air and soil around us.
To help limit the amount of radiation exposure to your thyroid gland when taking x-rays, your dentist may cover your throat with a special collar.
Source: The Journal of the American Dental Association (2019; 150: 636)