Radiographic Imaging in Orthodontics: Indications, Interpretation and Dose Optimization

The radiological protocol in orthodontics is one of the clinical aspects most subject to inter-clinician variability and least guided by solid evidence, with practices ranging from routinely ordering a panoramic X-ray + cephalogram for every new patient regardless of age and clinical presentation, to selective protocols based on specific clinical indication. The ALARA principle (As Low As Reasonably Achievable) — the ethical and regulatory foundation of diagnostic imaging with ionizing radiation, established by the ICRP (International Commission on Radiological Protection) and implemented in European legislation (Directive 2013/59/EURATOM) — requires that every radiological exam be clinically justified, with expected diagnostic benefit exceeding the biological risk of radiation, and that dose be optimized to the minimum value consistent with the diagnostic information needed.

The panoramic X-ray (OPT, Orthopantomogram) remains the first-level exam in orthodontics thanks to its ability to provide an overview of the entire dental and bone complex at a relatively low dose (3-10 µSv with digital phosphor plate or flat panel technology). Its specific indications in orthodontics include: assessing erupting dentition (position and developmental stage of permanent teeth in mixed-dentition patients), identifying impacted or ectopic teeth (impacted canines, third molars), assessing tooth roots before major movements (pre-existing apical resorption, root anomalies such as taurodontism or dens in dente), and assessing bone level in patients with suspected periodontitis. OPT's limitations are significant and well known: intrinsic geometric distortion produces non-metric images (linear measurements on the OPT don't match actual dimensions), structural overlap in the anterior incisor area reduces resolution in this critical zone, and the two-dimensional projection doesn't allow buccal-palatal localization of impactions.

The lateral cephalogram (Lat Ceph) is the exam allowing standardized cephalometric analysis. Its main indication is planning cases with significant sagittal or vertical skeletal discrepancies — skeletal Class II, Class III, open bite, hyperdivergence — where the cephalometric diagnosis changes treatment planning. The exam is less indicated in cases of simple mild-moderate crowding in skeletal Class I with no vertical anomalies, where cephalometry adds limited information beyond clinical analysis. The dose of a digital Lat Ceph is 2-5 µSv — comparable to or lower than OPT — and isn't a significant dosimetric contribution if correctly indicated. Routinely using the Lat Ceph for every orthodontic patient, regardless of clinical indication, isn't supported by evidence of improved treatment outcome and violates the ALARA principle.

CBCT in orthodontics has specific indications, different from routine use. The European Academy of Dentomaxillofacial Radiology (EADMFR) 2013 document, updated in 2019, identifies evidence-based orthodontic CBCT indications: impacted upper canines when two-dimensional radiography (OPT + periapical) doesn't provide safe localization (particularly for palatal vs. buccal impactions), assessing the midpalatal suture for staging ahead of palatal expansion (Angelieri classification), orthognathic surgery planning, assessing severe root resorption, and inserting TADs in anatomically critical areas. CBCT's effective dose ranges from 40 to 600 µSv depending on FOV and protocol — significantly higher than OPT and Lat Ceph — making rigorous clinical justification mandatory.

Periapical radiography — with the bisecting-angle or paralleling technique (Long Cone Technique, LCT) — has specific indications in orthodontics for detailed assessment that the OPT doesn't provide: assessing the periapical area of the upper incisors before intrusion or torque movements (to rule out pre-existing resorption), periodic monitoring of root resorption induced during treatment (every 6-9 months in the upper incisors of high-risk patients), assessing TAD anchor teeth (periapical to check the root-mini-screw relationship), and confirming the position of impactions in anterior areas. LCT with a digital sensor provides images with minimal geometric distortion (<5% with a standardized positioner and long cone), usable for root length measurements with ±0.3 mm accuracy.

Radiological documentation in orthodontics must be supplemented by standardized clinical photo documentation: extraoral photos (frontal, frontal with smile, right lateral, left lateral, 3/4 right) and intraoral photos (frontal, right lateral, left lateral, upper occlusal, lower occlusal) taken with a standardized distance and lighting protocol. The complete orthodontic chart — including OPT, Lat Ceph, any CBCT, clinical photos, digital study models (STL from IOS or plaster model scans), cephalometric analysis, model analysis, and a documented treatment plan — is the professional file the clinician must retain for at least 10 years under European health data management regulations, and constitutes the primary documentation in case of a clinical-legal dispute.