Extraoral Radiography
Dental Radiology · Extraoral Imaging
TL;DR
Extraoral radiography encompasses all dental imaging techniques where the receptor is placed outside the mouth — providing broad anatomical coverage of the jaws, skull, and facial skeleton that intraoral techniques cannot achieve alone.
- Extraoral radiography refers to techniques where the image receptor is positioned outside the patient’s mouth — including panoramic (OPG), cephalometric, cone beam CT (CBCT), skull projections, and temporomandibular joint (TMJ) radiographs
- The panoramic radiograph (OPG/OPT) is the most widely used extraoral view in dentistry — it provides a broad single-image survey of all teeth, jaws, TMJs, and sinuses but at lower resolution than intraoral radiographs
- Cephalometric radiographs (lateral skull) are used primarily in orthodontics for growth analysis, treatment planning, and outcome assessment using standardised cephalometric landmarks
- CBCT produces 3D volumetric data of the dentofacial complex and is indicated for implant planning, complex endodontics, impacted teeth, orthodontic assessment, and jaw pathology — but delivers significantly more radiation than 2D techniques
- Extraoral radiographs supplement but never replace intraoral radiographs for caries detection, periapical pathology, and fine root detail
Key Facts
What Is It?
Extraoral radiography encompasses all dental radiographic techniques in which the image receptor is positioned outside the patient’s mouth. Unlike intraoral techniques (periapical, bitewing, occlusal), extraoral methods provide broad anatomical coverage of the jaws, skull, temporomandibular joints, and facial skeleton — often in a single exposure.
Extraoral techniques range from the commonly used panoramic radiograph (a staple of most dental practices) to specialised projections including lateral skull (cephalometric), posteroanterior skull, Waters’ view (occipitomental), submentovertex, lateral oblique jaw, and the increasingly prevalent cone beam computed tomography (CBCT). Each technique has specific indications, advantages, limitations, and radiation dose considerations.
Why It Matters
No single radiographic technique can answer every clinical question. Extraoral radiography expands the diagnostic toolkit, providing field-of-view coverage that intraoral radiographs cannot deliver. From screening new patients to planning complex surgical procedures, extraoral imaging is central to contemporary dental practice.
Clinical Relevance
- Panoramic survey: new patient screening, third molar assessment, jaw pathology detection, implant planning overview, trauma, and cyst/tumour evaluation all benefit from the broad field of view of the OPG.
- Orthodontic planning: the lateral cephalometric radiograph is the cornerstone of orthodontic diagnosis and treatment planning — required for all comprehensive orthodontic cases.
- Surgical planning: CBCT is now standard for implant placement planning, complex impacted tooth removal, and orthognathic surgery — providing precise 3D measurements impossible with 2D imaging.
- Limitations: extraoral radiographs have lower spatial resolution than intraoral radiographs. A panoramic radiograph should never be used in place of periapical radiographs for endodontic diagnosis or caries detection.
Panoramic Radiography (OPG/OPT)
The panoramic radiograph — also called OPG (orthopantomogram) or OPT (orthopantomograph) — is the most commonly taken extraoral radiograph in general dental practice. In a single exposure it captures all teeth, both jaws, the TMJs, and the adjacent bony structures including the maxillary sinuses and anterior nasal spine.
Mechanism — Tomographic Principle & Positioning Errors
The panoramic unit uses a narrow slit X-ray beam and a rotating tube-receptor assembly that revolve simultaneously around the patient’s head in opposite directions. Only structures within a curved focal trough (image layer) are in focus; structures outside this trough are blurred. The patient must be positioned with the dental arches aligned within the focal trough — incorrect positioning is the leading cause of poor panoramic quality.
| Error | Appearance on Image | Correction |
|---|---|---|
| Patient too far forward (teeth anterior to focal trough) | Anterior teeth blurred and narrow | Move patient posteriorly |
| Patient too far back (teeth posterior to focal trough) | Anterior teeth blurred and wide/magnified | Move patient anteriorly |
| Head tilted down (chin too low) | Occlusal plane curves upward; hard palate shadows upper roots; condyles cut off | Tilt chin upward to Frankfort plane horizontal |
| Head tilted up (chin too high) | Occlusal plane curves downward; reverse smile line; lower condyles elongated | Tilt chin down to Frankfort plane horizontal |
| Head tilted laterally | Asymmetric jaw sizes; unequal magnification left vs right | Ensure head is centred and upright |
| Patient moving during exposure | Ghost images and blurring | Instruct patient to remain still |
| Tongue not on palate | Dark radiolucent shadow over upper roots | Instruct patient to place tongue on palate during exposure |
| Lips not closed / teeth not in occlusion | Central incisor region difficult to interpret | Instruct patient to bite lightly on anterior positioning device |
Indications for Panoramic Radiography
- Third molar assessment (most common indication)
- New patient screening when comprehensive intraoral series not available
- Detection of jaw lesions (cysts, tumours, bone pathology)
- Trauma assessment (mandibular fractures, condylar fractures)
- Orthodontic assessment (tooth development, eruption sequence, impacted teeth)
- Implant screening (bone height and quality overview)
- Periodontal disease (broad-field bone level assessment)
- Salivary gland calculi (submandibular, parotid duct)
Limitations of Panoramic Radiography
- NOT suitable for caries detection — bitewing radiographs are required
- NOT suitable as sole periapical assessment — intraoral PAs required for endodontics
- Lower spatial resolution than intraoral radiographs
- Ghost images can mimic pathology (e.g., cervical spine, hyoid bone, earrings, tongue piercings)
- Significant magnification (mean ~25% horizontal, ~30% vertical in most units — varies by machine)
Cephalometric Radiography
The lateral cephalometric radiograph (lateral skull, “lat ceph”) is a standardised projection of the skull taken with the patient positioned in a cephalostat — a head-positioning device that maintains a fixed, reproducible relationship between the patient, X-ray source, and receptor. This standardised geometry allows sequential comparison of the same patient over time, and comparison between patients using established norms.
Primary use is orthodontic diagnosis, growth assessment, treatment planning, and outcome evaluation. It is also used for orthognathic surgery planning, sleep apnoea assessment (airway analysis), and craniofacial anomaly assessment.
Key Cephalometric Landmarks (High-Yield INBDE)
| Landmark | Abbreviation | Location | Clinical Use |
|---|---|---|---|
| Sella | S | Centre of sella turcica (pituitary fossa) | Reference point for cranial base |
| Nasion | N | Most anterior point of frontonasal suture | Reference point; defines facial profile |
| A-point | A | Deepest concavity of anterior maxilla | Maxillary position |
| B-point | B | Deepest concavity of anterior mandible | Mandibular position |
| Menton | Me | Most inferior point of mandibular symphysis | Vertical dimension |
| Pogonion | Pog | Most anterior point of mandibular symphysis | Chin prominence |
| Gonion | Go | Most posterior-inferior point of mandibular angle | Mandibular ramus assessment |
| Porion | Po | Most superior point of external auditory meatus | Frankfort plane |
Key Cephalometric Angles
- SNA angle (normal ~82°): angle at nasion between sella and A-point. Measures maxillary position relative to cranial base. Increased SNA = maxillary prognathism; decreased = retrognathism.
- SNB angle (normal ~80°): angle at nasion between sella and B-point. Measures mandibular position relative to cranial base. Increased SNB = mandibular prognathism.
- ANB angle (normal ~2°): SNA minus SNB. Measures the sagittal relationship between maxilla and mandible. ANB >4° = Class II skeletal; ANB <0° = Class III skeletal.
The posteroanterior (PA) cephalometric is a front-on projection of the skull used for facial asymmetry assessment, transverse skeletal discrepancies, and midline deviations. It complements the lateral ceph by providing frontal plane data.
CBCT & Other Extraoral Techniques
CBCT (Cone Beam Computed Tomography)
CBCT produces true 3D volumetric data of the dentofacial region using a cone-shaped X-ray beam that rotates around the patient. The data is reconstructed into axial, coronal, and sagittal planes; any cross-sectional view can be generated.
- Voxel size (3D pixel) determines resolution. Small FOV CBCT: voxel 0.08–0.2 mm (high resolution). Large FOV: voxel 0.3–0.4 mm.
- Field of view (FOV): small (single tooth/quadrant), medium (one or both jaws), large (full skull + cervical spine). Larger FOV = more dose.
- Dose: 20–600 μSv depending on FOV and unit — substantially more than 2D techniques.
- Indications: implant planning, complex impacted teeth (proximity to IAN), complex endodontics (extra canals, resorption, CBCT-guided surgery), orthodontic impaction assessment, jaw cysts/tumours, TMJ assessment, trauma, airway analysis.
Skull Projections
- Waters’ view (occipitomental): patient tilted with chin up to project maxillary sinuses below the petrous ridges. Best single view for assessing maxillary sinuses (sinusitis, fractures, masses).
- Submentovertex (SMV): beam directed from below chin upward through the skull. Shows zygomatic arches, base of skull, sphenoid sinuses. Used for zygomatic arch fractures.
- Posteroanterior skull (PA skull): frontal projection used in trauma, asymmetry, and bony lesions.
- Lateral skull (plain): general skull view — distinct from ceph because no cephalostat is used. Not standardised; cannot be used for cephalometric measurements.
TMJ Radiography
- Transcranial projection: lateral oblique projection of TMJ showing condylar head in lateral closed and open positions. Gives broad joint overview.
- Transpharyngeal (transorbital): different beam angle for medial condylar pole assessment.
- CBCT and MRI: now considered gold standard for detailed TMJ assessment — CBCT for bony changes (erosion, flattening, osteophytes, condylar hyperplasia); MRI for disc position and soft tissues.
| Technique | Primary Indication | Dose | Limitation |
|---|---|---|---|
| Panoramic (OPG) | Broad screening, 3rd molars, pathology | ~14–24 μSv | Low resolution; not for caries/endo |
| Lateral cephalometric | Orthodontic diagnosis and planning | ~5–6 μSv | 2D only; requires cephalostat |
| PA cephalometric | Facial asymmetry, transverse assessment | ~3–5 μSv | Frontal plane only |
| CBCT (small FOV) | Implant, endo, impacted tooth | ~20–100 μSv | Dose; must be justified |
| CBCT (large FOV) | Orthognathic, complex pathology | ~100–600 μSv | High dose; reserved for specific cases |
| Waters’ view | Maxillary sinus assessment | ~10–15 μSv | Poor for teeth; sinus-specific |
| Submentovertex | Zygomatic arch fractures | ~15–20 μSv | Limited to specific trauma applications |
Clinical Considerations
- Ghost images on panoramic: radiopaque structures outside the focal trough (but on the contralateral side of the head) produce a blurred, magnified ghost image. Common ghost images include the hyoid bone, mandibular angle, cervical spine, dental restorations, earrings, tongue piercings, and nose rings. Instruct patients to remove jewellery before panoramic exposure.
- Panoramic vs intraoral: panoramic radiographs are screening tools. Any suspicious finding on a panoramic (periapical pathology, possible caries, bone lesion) must be investigated with intraoral radiographs or CBCT for definitive assessment.
- CBCT justification: CBCT must only be prescribed when the 3D information will meaningfully change diagnosis or treatment. Dose is substantially higher than 2D imaging. Routine CBCT for all cases is not ALARA-compliant.
- Cephalostat use: the reproducible geometry provided by the cephalostat is what makes serial cephalometric comparison valid. A lateral skull taken without a cephalostat cannot be used for cephalometric analysis.
Common Mistakes & Misconceptions
-
Misconception: “A panoramic radiograph can replace a full-mouth periapical series for caries detection and endodontic diagnosis.”
Correction: The panoramic radiograph has insufficient resolution for reliable caries detection or detailed periapical assessment. Bitewing radiographs and periapical films are required for these purposes — panoramic radiographs are screening tools only. -
Misconception: “Ghost images on a panoramic are signs of pathology.”
Correction: Ghost images are blurred, magnified shadows of contralateral radiopaque structures (hyoid, cervical spine, restorations, jewellery) that fall outside the focal trough. They are artefacts, not pathology. Instruct patients to remove jewellery; be aware of normal ghost anatomy. -
Misconception: “An ANB angle of 0° means the patient has a normal skeletal relationship.”
Correction: Normal ANB is approximately 2° (Class I). ANB of 0° is at the lower limit of normal and trends toward Class III skeletal. ANB >4° = Class II; ANB <0° = Class III. -
Misconception: “CBCT should be used routinely for all implant placements.”
Correction: Simple single-tooth implants in the maxillary anterior with adequate bone may be planned with 2D imaging and clinical examination. CBCT is indicated when proximity to anatomical structures, bone quality concerns, or complex anatomy require 3D assessment — it should not be used routinely for all implants under ALARA principles. -
Misconception: “The panoramic radiograph reliably shows all teeth in focus.”
Correction: Only structures within the curved focal trough are in focus on a panoramic. Teeth outside this layer (often anterior teeth if the patient is positioned too far back) will be blurred. Anterior teeth, in particular, are often less clearly defined than posterior teeth on panoramic views.
Related Topics
Extraoral radiography connects with intraoral technique, radiation physics, and clinical imaging interpretation across dental specialties.
References & Sources
The following foundational texts and peer-reviewed sources inform this article.
- White SC & Pharoah MJ, 2014. Oral Radiology: Principles and Interpretation. 7th ed. Elsevier Mosby.
- Whaites E & Drage N, 2013. Essentials of Dental Radiography and Radiology. 5th ed. Churchill Livingstone.
- Ludlow JB & Ivanovic M, 2008. Comparative dosimetry of dental CBCT devices and 64-slice CT for oral and maxillofacial radiology. Oral Surgery, Oral Medicine, Oral Pathology, 106(1):106–114.
- Patel S, Durack C, Abella F et al., 2015. European Society of Endodontology position statement: The use of CBCT in endodontics. International Endodontic Journal, 47(6):502–504.
- Jacobson A & Jacobson RL (eds), 2006. Radiographic Cephalometry: From Basics to 3-D Imaging. 2nd ed. Quintessence Publishing.
- American Academy of Oral and Maxillofacial Radiology, 2013. Clinical recommendations regarding use of cone beam computed tomography in orthodontics. Oral Surgery, Oral Medicine, Oral Pathology, 116(2):238–257.
Summary
Extraoral radiography represents a spectrum of imaging tools — from the broad-field panoramic survey to the standardised cephalometric projection to the 3D precision of CBCT — each serving distinct diagnostic purposes. The panoramic radiograph excels as a screening tool for third molars, jaw pathology, and new patient assessment, but cannot substitute for intraoral radiographs where resolution matters. The lateral cephalometric radiograph, made valid by the cephalostat, remains the cornerstone of orthodontic diagnosis and longitudinal growth assessment. CBCT delivers unmatched 3D anatomical information for implant planning, complex impacted teeth, and surgical cases, but carries a significantly higher radiation dose that requires careful justification under ALARA principles. Skull projections including Waters’ view and submentovertex serve specific roles in sinus and trauma assessment. Across all techniques, a common theme holds: extraoral radiographs supplement — never replace — intraoral imaging, and every radiograph must be justified by clinical need.
Key Takeaways
- Panoramic as screening tool: The OPG is essential for third molar assessment, jaw pathology, and new patient surveys — but cannot replace intraoral radiographs for caries detection or periapical diagnosis.
- Cephalometric is the orthodontic standard: Standardised by the cephalostat for serial comparison. ANB angle — Class I ~2°, Class II >4°, Class III <0°.
- CBCT for 3D data: Indicated for implant planning, complex endo, and impacted teeth — but delivers significantly more dose than 2D techniques and must be justified under ALARA.
- Ghost images are artefacts: Blurred shadows from contralateral structures (hyoid, cervical spine, jewellery) — not pathology. Patient preparation and proper positioning minimise them.
- Extraoral supplements, never replaces, intraoral: Suspicious findings on a panoramic always require follow-up with high-resolution intraoral or CBCT imaging.
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