Dental X-Ray Glossary

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

The radiographs

The three radiographs you meet most in general practice, the two words that describe everything on them, and the 3D examination they get compared to.

A bitewing radiograph showing the maxillary and mandibular posterior crowns in occlusion, with several radiopaque restorations. — A bitewing: the maxillary and mandibular posterior teeth on one radiograph, with the contact points open to view. Fillings read radiopaque, and caries hides in the dark gaps between the teeth.

Bitewing radiograph: A bitewing radiograph shows the crowns of the maxillary and mandibular posterior teeth on one receptor. On the radiograph: The interproximal surfaces and the alveolar crest are the structures this projection records best. Full entry
Periapical radiograph a.k.a. PA: A periapical radiograph shows one or two whole teeth, from the crown to the apex and the surrounding bone. On the radiograph: The apex, the lamina dura and the periapical bone are visible on this projection. Full entry
Panoramic radiograph a.k.a. OPG, pano: A panoramic radiograph is a single image of both jaws, the full dentition, the maxillary sinuses and the temporomandibular joints. On the radiograph: Third molars, cysts and fractures are shown across both jaws, at lower resolution than an intraoral projection.
Cone-beam computed tomography a.k.a. CBCT: A three-dimensional radiographic examination that reconstructs a volume from a single rotation of a cone-shaped beam.
Radiolucent: Radiolucent describes a structure or region that permits the passage of the X-ray beam, so more radiation reaches the receptor. On the radiograph: Caries, the pulp chamber and cysts are radiolucent relative to the surrounding tooth structure and bone. Full entry
Radiopaque: Radiopaque describes a structure or material that resists the passage of the X-ray beam, so less radiation reaches the receptor. On the radiograph: Enamel, bone, amalgam restorations and crowns are the most radiopaque structures on a bitewing. Full entry

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: Enamel is the mineralised outer layer of the crown and the most highly mineralised tissue in the body. On the radiograph: Enamel is the most radiopaque tissue of the tooth and outlines the crown.
Dentin: Dentin is the mineralised tissue beneath the enamel that forms the bulk of the tooth. On the radiograph: Dentin is more radiolucent than enamel and more radiopaque than the pulp chamber.
Pulp a.k.a. nerve: The pulp is the soft tissue at the centre of the tooth, containing its vessels and nerves. On the radiograph: The pulp chamber is radiolucent, lying centrally within the crown and narrowing into the root canals.
Cementoenamel junction a.k.a. CEJ: The cementoenamel junction is the line at the neck of the tooth where the enamel of the crown meets the cementum of the root. On the radiograph: The CEJ is the landmark against which the alveolar crest is measured, and the level at which cervical burnout appears.
Dentinoenamel junction a.k.a. DEJ: The dentinoenamel junction is the interface within the crown where the enamel meets the underlying dentin. On the radiograph: The DEJ is the interface at which enamel gives way to the more radiolucent dentin, and a Mach band may arise along it.

What you are hunting for

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

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

Dental caries a.k.a. cavity, decay: Dental caries is the bacterial disease that demineralises tooth tissue, and the lesion that results from it. On the radiograph: Proximal caries appears as a radiolucency on the proximal surface, apical to the contact and often triangular. Full entry
Secondary caries a.k.a. recurrent caries, recurrent: Secondary caries is a carious lesion at the margin of an existing restoration. On the radiograph: Secondary caries appears as a radiolucency along the margin of a radiopaque restoration. Full entry
Calculus a.k.a. tartar: Calculus is mineralised dental plaque adherent to the tooth surface, above or below the gingival margin. On the radiograph: Calculus appears as small radiopaque projections on the proximal surfaces at or below the alveolar crest.
Alveolar bone: Alveolar bone is the bone of the jaws that forms and supports the tooth sockets. On the radiograph: Loss of alveolar bone appears as a crest lying further apical to the CEJ.
Lamina dura: The lamina dura is the thin layer of cortical bone that lines the tooth socket. On the radiograph: The lamina dura appears as a continuous radiopaque line following the outline of the root.
Periodontal ligament space a.k.a. PDL, PDL space: The periodontal ligament space is the narrow space between the root surface and the lamina dura, occupied by the periodontal ligament. On the radiograph: The periodontal ligament space appears as a fine radiolucent line following the root. Widening of the space may be suggestive of inflammation or trauma.
Furcation: The furcation is the region where the roots of a multi-rooted tooth diverge. On the radiograph: Alveolar bone loss reaching the furcation is described as a furcation involvement.

Restorations & look-alikes

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

A bitewing radiograph showing cervical burnout as a radiolucent band at the necks of the teeth. — Cervical burnout: the grey band across the necks of these teeth comes from the thinner tooth at the cervical margin.

Restoration: A restoration is any material placed to restore the form and function of a tooth. On the radiograph: Most restorations are radiopaque, with regular margins that follow the preparation. Full entry
Overhang: An overhang is restorative material extending beyond the margin of the preparation. On the radiograph: An overhang appears as a radiopaque ledge apical to the contact, projecting beyond the tooth outline. Full entry
Interproximal surface: An interproximal surface is a tooth surface that faces the adjacent tooth across the contact. On the radiograph: The interproximal surfaces are the region a bitewing is taken to record, and the commonest site of proximal caries. Full entry
Cervical burnout: Cervical burnout is a radiographic effect in which the cervical region of a tooth appears radiolucent. On the radiograph: Cervical burnout appears as a diffuse radiolucent band at the neck of the tooth, between the enamel and the alveolar crest. Full entry

Errors & artifacts

Marks the exposure leaves on the radiograph. Each one hides something you were trying to see.

Cone cut a.k.a. cone cutting: A cone cut is an unexposed region of the radiograph where the beam did not cover the receptor. On the radiograph: A cone cut appears as a sharp curved border crossing teeth and bone alike, and the region beyond it was not recorded. Full entry
Elongation: Elongation is the projection of teeth longer than they are, caused by insufficient vertical angulation of the beam. On the radiograph: Elongated roots appear at normal crown width, and the alveolar crest reads further from the CEJ than it is. Full entry
Foreshortening: Foreshortening is the projection of teeth shorter than they are, caused by excessive vertical angulation of the beam. On the radiograph: Shortened roots appear at normal crown width, which is the projection error opposite to elongation. Full entry
Ghost image: A ghost image is a second, false image of a real structure, produced by the rotating beam of a panoramic machine. On the radiograph: A ghost image appears blurred, on the contralateral side and superior to the structure that produced it. Full entry

Judging the image

Whether a radiograph is good enough to read, and what that judgement costs.

As low as reasonably achievable a.k.a. ALARA: A radiation-protection principle: an exposure is justified by its benefit, and a necessary exposure is kept as low as reasonably achievable. Full entry
As low as diagnostically acceptable a.k.a. ALADA: Dose is lowered only as far as the radiograph still answers the question it was taken for. Full entry
Reject analysis: An audit of the radiographs that were never presented for diagnosis, counted as a share of those taken. Full entry

Read a real radiograph.

The reading test is three bitewings, and it takes two minutes. Mark what you find, then compare your read with the expert labels.

Start the reading test

Every finding above is covered in depth in the reference library.

Data were provided (in part) by Radboud University, Nijmegen, The Netherlands.