This x-ray was taken by a dentist, showing two wisdom teeth (white arrows) positioned below the gum line. Most people have three permanent sets of molars: the first set usually appears at around the age of 6, and then the 2nd set appears at around the age of 12. The third set are called wisdom teeth because you are older (and presumably wiser) when these teeth appear.
Also shown on the x-ray is a branch of the trigeminal nerve (orange arrow) as it passes under the jaw. This nerve is usually numbed for a tooth extraction, but because branches also supply the lip and face, you may also experience numbness in those areas.