Miscellaneous: How to read an OPG and pathology presentation

Orthopantomogram (OPG), serves as a cornerstone in the identification of various anatomical structures and the diagnosis of conditions such as dental diseases, cysts, and traumatic injuries, thus facilitating a meticulous assessment of the hard tissues of the face.
The radiation exposure associated with this technique is notably low, typically around 0.014 mSv, significantly less than that encountered in a standard chest X-ray, which is about 0.02 mSv. This extra-oral radiograph proves invaluable, especially when patients encounter challenges related to mouth opening or exhibit a pronounced gag reflex, which may preclude the use of intra-oral films.
During the imaging process, the X-ray generator and detection unit orbit around the patient’s head, resulting in a focused image of the dental and mandibular regions. However, this dynamic movement can introduce artefacts due to potential patient motion. Notably, the mandible is captured in a protruded position, primarily achieved through the use of a ‘bite block’ for precise focal trough alignment. Consequently, this positioning leads to the anterior placement of the condylar head of the mandible relative to its rest position in the glenoid fossa. Additionally, the cervical spine’s superimposition may obscure the anterior aspects of the dentition, while the occipital bone can project over the rami of the mandible on the opposite side.
The systematic analysis of an OPG can simplify the interpretation of what initially appears to be a complex image. A structured approach involves:
Enumerating all present teeth and noting their respective positions, while highlighting any instances of missing or misaligned teeth.
Tracing the contours of the mandible, typically from the right (or the left side of the image) to the left. Paying attention to the condylar head’s size and shape, assessing the continuity of the external border of the ramus and body, and evaluating the uniformity of internal bone density. Additionally, it’s crucial to observe the path of the inferior alveolar neurovascular canal, culminating in the mental foramina.
Identifying the maxillary sinuses and meticulously recording any opacities or lucencies within them. Furthermore, meticulously following the cortical outlines to assess their continuity.
Scrutinising the image’s peripheries for potential cervical spine abnormalities, zygomatic structures, submandibular regions, or any anomalies associated with the hyoid bone.
While intra-oral radiographs offer finer details of tooth structure, OPGs are indispensable screening tools. Pathological conditions, such as tooth decay, manifest as demineralisation of enamel and dentin, primarily induced by the production of organic acids by oral bacteria. This demineralisation becomes visible within the tooth structure on an OPG. In cases of tooth pulp infection, often resulting in necrosis, abscesses may form within the underlying bone, manifesting as radiolucencies beneath the affected roots.
The removal of teeth can lead to atrophy of both the mandible and maxilla due to the loss of alveolar bone, which primarily supports teeth. Subsequently, basal bone loss may occur over time. In severe cases, pathological mandibular fractures may transpire, coupled with neurosensory alterations of the inferior alveolar nerve due to the loss of overlying bone.
OPGs can also reveal radiolucent lesions within the maxilla or mandible. These may encompass cysts associated with teeth, both of dental origin and odontogenic, or result from infective, developmental, or rarer pathological conditions, such as metastatic lesions or metabolic disorders. Odontogenic cysts, while benign, necessitate removal to prevent bone degradation and infection. Distinguishing locally aggressive benign neoplastic lesions, such as odontogenic keratocystic tumours (OKCTs) and ameloblastomas, from other lesions mandates biopsy of the linings or contents, often requiring referral.
In cases of facial trauma, patients commonly seek assessment in the emergency department. However, in scenarios involving undisplaced fractures or concurrent injuries, patients may present to their general practitioners for evaluation post-hospital discharge. OPGs prove valuable, particularly when mandibular involvement is suspected, for diagnosing fractures of the facial bones, albeit overlapping or angulated fractures may necessitate additional imaging through plain radiographs or computed tomography.
The assessment of OPGs follows a standardised screening protocol, with a specific emphasis on ensuring the cortical continuity of the mandible. Notably, the most prevalent site of mandibular fractures is the angle, accounting for approximately 32% of cases, with an additional 40% involving fractures at the parasymphysis. In instances where cortical overlap obscures clarity, a perpendicular view, such as a posteroanterior view, may be ordered. Traumatic dislocations, while clinically diagnosable, can be visually elucidated through OPGs.