Sir, panoramic radiographs are a common imaging modality used in primary and secondary dental care. Being able to interpret panoramic radiographs is an important skill for all dental practitioners using these images as part of their practice. Understanding the technique of panoramic radiography as well as a good knowledge of anatomy is important for accurate diagnosis.1

A request was made for CBCT imaging of the lower left third molar to assess its relationship to the inferior alveolar canal. The panoramic radiograph (Fig. 1) suggested an intimate relationship. In addition, the panoramic radiograph showed a radiolucent outline overlying the inferior aspect of the body of the mandible. This is consistent with the submandibular gland fossa. We use the panoramic/CBCT combination to explain the cause of this appearance (Fig. 2).

Fig. 1
figure 1

Panoramic radiograph taken to assess the proximity of 38 to the inferior alveolar canal. A distinct line is seen, separating the radiopaque and radiolucent appearances of the body of the mandible

Fig. 2
figure 2

CBCT image and 3D reconstruction showing the varying bone thickness

An x-ray beam is variably attenuated depending on the structure it passes through, its thickness and density.2 In this case the mylohyoid ridge separates the crestal (thicker) mandible from the apical (thinner) submandibular gland fossa. As the beam travels through the mandible, less attenuation occurs in the submandibular gland fossa, resulting in a more radiolucent appearance.

Pawar and Makdissi highlighted that distinguishing artefacts from pathological conditions remains a challenge in panoramic radiography. This is the main limitation of the technique.3 In this case the submandibular gland fossa has given rise to a more radiolucent appearance which could have imitated the presence of pathological condition. The use of CBCT has helped in explaining its appearance.

These images demonstrate the thicker bone coronally which becomes narrower apically in the region of the submandibular gland fossa. This is responsible for the differing radiopacity of the body of the mandible seen on the panoramic radiograph. A good understanding of the technique and anatomy in panoramic radiography remains an essential skill for practitioners in order to establish good diagnostic ability.