Dental X-Ray Glossary — Terms for Students

A tooth is layered. Enamel wraps the crown, dentin fills most of the tooth, and the pulp sits at the core. The cementoenamel junction (CEJ) marks the neck — the landmark you measure bone loss and cervical burnout against.

The radiographs

The three radiographs you meet most in general practice, and the two words that describe everything on them.

A bitewing radiograph showing upper and lower back teeth in contact, with several radiopaque (white) fillings. — A real bitewing: upper and lower back teeth meet in the middle, bright fillings stand out, and the dark gaps between teeth are where caries hides.

Bitewing radiograph: An X-ray that shows the crowns of the upper and lower back teeth on one image, taken while the patient bites on a tab. On the radiograph: The go-to view for spotting caries between teeth and checking bone levels.
Periapical radiograph a.k.a. PA: An X-ray of one or two whole teeth, from the crown all the way to the root tip and the bone around it. On the radiograph: Used to check root tips, abscesses, and the bone at the apex.
Panoramic radiograph a.k.a. OPG / pano: A single wide image of both jaws, all the teeth, the sinuses, and the jaw joints. On the radiograph: Great for the big picture — wisdom teeth, cysts, fractures — but low on fine detail.
Radiolucent: Areas that look dark on a radiograph because they let more radiation through — soft or less-dense tissue. On the radiograph: Caries, the pulp chamber, and cysts read dark.
Radiopaque: Areas that look light or white because they block radiation — dense tissue or materials. On the radiograph: Enamel, bone, fillings, and crowns read bright white.

Tooth anatomy on a radiograph

A tooth is layered. Knowing where one layer ends and the next begins is what tells you how deep a lesion has gone.

Enamel: The hard outer shell of the crown — the most mineralized tissue in the body. On the radiograph: The brightest, most radiopaque outline of the crown.
Dentin: The softer, living layer under the enamel that makes up most of the tooth. On the radiograph: Slightly greyer than enamel. Caries speeds up once it reaches here.
Pulp a.k.a. nerve: The soft core of the tooth holding the nerves and blood vessels. On the radiograph: A radiolucent (dark) chamber in the middle of the crown, narrowing into the root canals.
Cementoenamel junction a.k.a. CEJ: The neck of the tooth where the enamel of the crown meets the root surface. On the radiograph: A key landmark for judging bone loss and where cervical burnout appears.

What you are hunting for

The findings that change a diagnosis — and the healthy landmarks you measure them against.

A bitewing radiograph with dark, radiolucent carious lesions on the proximal surfaces between molars. — Caries reads dark: look at the shadowy notches on the surfaces between the molars, below the contact points.

Dental caries a.k.a. cavity, decay: Tooth decay: a breakdown of tooth structure by acid from bacteria. On the radiograph: A dark, radiolucent notch or wedge, most often on the proximal surface just below the contact point.
Secondary caries a.k.a. recurrent caries: New decay that forms at the edge of an existing filling or crown. On the radiograph: A dark shadow hugging the margin of a bright restoration.
Calculus a.k.a. tartar: Hardened dental plaque stuck to the tooth, above or below the gumline. On the radiograph: Small radiopaque spurs or ledges on the proximal root surfaces.
Alveolar bone a.k.a. crestal bone: The jawbone that holds the tooth sockets. Its top edge is the bone crest. On the radiograph: Bone loss shows as the crest sitting lower, further from the CEJ.
Lamina dura: The thin, dense layer of bone lining a healthy tooth socket. On the radiograph: A crisp white line around the root. When it breaks up, something is wrong.
Periodontal ligament space a.k.a. PDL space: The tiny gap between the root and the socket bone, where the ligament sits. On the radiograph: A fine dark line hugging the root. Widening can signal infection or trauma.
Furcation: The point where the roots of a multi-rooted tooth split apart. On the radiograph: Bone loss reaching this split (a furcation involvement) is a serious perio sign.

Restorations & look-alikes

Dental work is easy to spot. The traps are the healthy shadows that look like disease.

A bitewing showing cervical burnout — a darker band near the necks of the teeth that mimics caries. — Cervical burnout: the grey band across the necks of these teeth is a normal optical effect, not decay.

Restoration a.k.a. filling, crown: Any material placed to repair a tooth — a filling, inlay, crown, or bridge. On the radiograph: Usually bright and radiopaque with sharp, man-made edges.
Overhang: Excess filling material sticking out past the edge of the tooth. On the radiograph: A radiopaque ledge under the contact point — a trap for plaque and future decay.
Interproximal surface a.k.a. proximal: The surface of a tooth that faces the tooth next to it. On the radiograph: The zone bitewings are built to show — and where most hidden caries starts.
Cervical burnout: A normal optical effect — not decay — where the tooth neck looks darker than the rest. On the radiograph: A grey band near the CEJ between the enamel and the bone. The classic caries look-alike.

Now read one for real.

Definitions stick when you use them. Try a real dental X-ray — make your call, then see a dentist's read.

Try a real X-ray

Radiographs from an open research dataset. Data were provided (in part) by Radboud University, Nijmegen, The Netherlands.