Patient-friendly definition from the DentistsDirectory.org dental glossary.
A bitewing X-ray is a dental radiograph taken with a small sensor or film held in place by the patient biting down on a small tab (the "wing"). It captures both the upper and lower teeth in a single image from the crown down to just below the gum line. Because most adults have four bitewing films taken per appointment — two on each side — they provide a comprehensive view of all the back teeth simultaneously.
Bitewings are primarily used to detect interproximal cavities — decay that develops between teeth where a dental probe and mirror cannot see. These cavities are almost entirely invisible during a visual examination but show up clearly on bitewing films as dark shadows in the enamel or dentin. Bitewings also reveal the level of bone between the teeth, making them the primary tool for monitoring bone loss from gum disease. Early detection through bitewings is what allows a cavity to be treated with a small, inexpensive filling rather than a larger restoration later.
For most adults at average risk for cavities, bitewing X-rays are recommended once per year. Patients with a history of frequent decay or active gum disease may benefit from more frequent films. Low-risk adults with excellent oral health and no history of cavities for many years may only need them every 18–24 months. The American Dental Association recommends frequency be based on individual risk rather than a fixed schedule — ask your dentist what interval makes sense for your situation.