CBCT vs OPG X-ray UK

What does an OPG show in orthodontic assessment?

An OPG (orthopantomogram or dental panoramic tomogram) is a 2D curved-plane X-ray that images the entire dentition, jaws, and surrounding structures in a single exposure. For orthodontic purposes it shows the number, position, and stage of development of all teeth including unerupted and impacted teeth; root length and shape; bone levels; the temporomandibular joints; wisdom teeth; and any pathology such as cysts or root resorption. It is the most common radiograph taken as part of orthodontic records and is routinely justified before any comprehensive course of orthodontic treatment. The radiation dose from a modern digital OPG is approximately 2 to 4 microsieverts — equivalent to a few hours of background radiation or a short domestic flight.

What does a lateral cephalometric radiograph show?

A lateral cephalogram (lateral ceph) is a standardised 2D profile X-ray taken at a fixed distance with the head in a reproducible position using a cephalostat. It allows precise measurement of jaw relationships, incisor inclination, facial proportions, and skeletal pattern. Cephalometric analysis quantifies the angle of the upper and lower jaw relative to the cranial base, the degree of overjet, the inclination of the upper and lower incisors, and the vertical facial height. This information is essential for planning extraction cases, overjet correction, jaw surgery assessment, and growth modification. A lateral ceph is not always required — it is most clinically valuable when a skeletal discrepancy is suspected or when jaw surgery is being considered. The dose is approximately 3 to 6 microsieverts.

When is CBCT (cone beam CT) needed in orthodontics?

CBCT provides three-dimensional information about the dentofacial structures that two-dimensional radiographs cannot. It is clinically justified in specific scenarios: precise localisation of impacted canines or other impacted teeth where the relationship to adjacent root surfaces is unclear from a 2D image; assessment of root resorption during or after treatment; evaluation of supernumerary teeth or odontomes in complex positions; airway assessment for sleep apnoea planning; pre-surgical assessment of the temporomandibular joints; and assessment of bone volume and anatomy before miniscrew or implant placement. CBCT should not be used as a routine imaging modality in place of 2D radiographs when 2D imaging would adequately answer the clinical question. UK and European guidelines (SEDENTEXCT, FGDP) are explicit that CBCT is only appropriate when the clinical benefit justifies the higher radiation dose, which ranges from approximately 20 to 200 microsieverts depending on field of view.

What is the ALARA principle and why does it matter for orthodontic imaging?

ALARA stands for As Low As Reasonably Achievable. In UK dental and orthodontic practice, it is the guiding principle for radiation protection and is enshrined in the Ionising Radiation (Medical Exposure) Regulations 2017. It means that each radiograph should be clinically justified — the benefit must outweigh the risk — and that the lowest dose technique sufficient to answer the clinical question should be selected. In orthodontic practice this means: preferring digital OPG and lateral ceph over film-based equivalents (lower dose); using the smallest CBCT field of view that covers the area of interest rather than a full dentofacial scan; and not taking radiographs at routine intervals simply by protocol when there is no specific clinical indication. Patients are entitled to ask why a radiograph has been recommended and what information it will provide that affects their treatment plan. Orthodontists operating within a defined population, such as children, have additional responsibilities to minimise cumulative exposure.

How do orthodontic images compare in radiation dose?

To contextualise orthodontic radiation: a single bitewing X-ray delivers approximately 1 microsievert; a periapical film 1 to 3 microsieverts; a digital OPG 2 to 4 microsieverts; a digital lateral ceph 3 to 6 microsieverts; a small field-of-view CBCT approximately 20 to 50 microsieverts; and a large field-of-view CBCT up to 200 microsieverts. Annual background radiation in the UK from natural sources is approximately 2,700 microsieverts. The combined OPG and lateral ceph taken at the start of a comprehensive orthodontic course represents a very small fraction of annual background exposure. CBCT at a small field of view is still within a manageable dose range when clinically justified but should not be used routinely. These figures are approximate and vary by equipment, technique, and patient anatomy.

What other imaging might be used during orthodontic treatment?

Beyond OPG, lateral ceph, and CBCT, orthodontists occasionally use intraoral periapical radiographs to assess specific teeth in more detail than an OPG permits — commonly to monitor root resorption around specific incisors, to assess the eruption path of impacted teeth, or to evaluate the apical area of a tooth of concern. An anterior occlusal radiograph provides a 2D view of the upper or lower front region and is sometimes used for upper canine localisation as an alternative to periapicals. Digital dental models (intraoral scans) have largely replaced plaster study models at progressive practices and provide 3D tooth measurements without any radiation exposure. Photography is a non-ionising part of orthodontic records that documents soft tissue profile, smile, and dental occlusion.

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This guide is for general information only. It is not a diagnosis, treatment plan, or substitute for advice from a registered dentist or orthodontist.