Orthopantomography (OPG / Panoramic Radiography) is a specialized extraoral radiographic technique that produces a single continuous image of the maxilla, mandible, dentition, temporomandibular joints (TMJs), and maxillary sinuses.
It operates on the principle of curvilinear rotational tomography: the X-ray tubehead and the image receptor rotate simultaneously in opposite directions around the patient’s head, keeping a curved slice of anatomy—the focal trough (image layer)—in sharp focus while blurring out structures outside this zone.
1. Clinical Indications & Contraindications
Detailed Indications:
- General Dental & Maxillofacial Survey: Full evaluation of dentition, missing teeth, supernumerary teeth, and dental developmental anomalies.
- Third Molar (Wisdom Teeth) Assessment: Evaluating angulation (mesioangular, distoangular, vertical, horizontal) and the proximity of mandibular third molar roots to the inferior alveolar (mandibular) canal.
- Trauma & Fractures: Screening for bilateral mandibular fractures (symphysis, body, angle, ramus, condyle) and Le Fort maxillofacial fractures.
- Cysts, Tumors & Bone Pathologies: Detection and localization of Ameloblastoma, odontogenic keratocysts (OKC), dentigerous cysts, fibro-osseous lesions, and osteomyelitis.
- Periodontal Bone Loss: Broad assessment of generalized horizontal or vertical alveolar bone resorption.
- TMJ Screening: Gross morphological evaluation of condylar heads for flattening, osteophytes, erosion, or asymmetry.
- Implant Site Planning: Vertical height assessment of available bone between the alveolar crest and the mandibular canal or maxillary sinus floor.
Contraindications & Limitations:
- Fine Detail Limitations (Caries & Endodontics): Lower spatial resolution compared to intraoral periapical (IOPA) and bitewing radiographs; not indicated for early interproximal caries or fine endodontic canal anatomy.
- Severe Motion / Pediatric Inability to Stand: Patients who cannot remain completely still for the 12 to 20-second rotation cycle.
- Inherent Magnification: Unequal magnification (10 to 30) occurs across different segments of the focal trough.
2. Technical Factors & Operating Parameters
| Parameter | Standard Adult Setting | Radiographic Rationale |
| Patient Posture | Strictly Erect (Standing or Seated) | Spine must be fully extended to prevent spinal ghost artifacts |
| Image Receptor | Digital Sensor (CCD / CMOS) or PSP | Captures continuous panoramic sweep |
| SID | Fixed by Unit Geometry (approx 45 to 50 cm) | Standardized rotational radius |
| Beam Collimation | Narrow Vertical Slit (1 to 2 mm wide) | Minimizes scatter; builds image column-by-column |
| Tube Potential (kVp) | 65 – 85 kVp | Adjusted based on patient jaw size/bone density |
| Tube Current (mA) | 4 – 12 mA | Lower current balanced by rotational exposure time |
| Exposure Time | 12 – 20 seconds | Duration of one complete tubehead rotation |
| Beam Angulation | Fixed -4⁰ to -8⁰ (Slightly Upward) | Projects the skull base superiorly to open the palate |
3. Step-by-Step Patient Positioning & Alignment
[ Panoramic Rotational Path ]
│
/────────────┴────────────\
│ Frankfort Plane // Floor│ ◄── FHP Horizontal (Tragus to Infraorbital Rim)
[ Canine Beam ] ──►│ │ Bite-Block (Edge-to-Edge)
│ ▼ │
│ ─────── [ MSP ⟂ ] ─────── │ ◄── Mid-Sagittal Plane Perpendicular (No Turn/Tilt)
│ Tongue on Hard Palate │ ◄── Eliminates Palatoglossal Air Gap
\─────────────────────────/
│
[ Spine Fully Erect ] ◄── Eliminates Ghost Shadow of C-Spine
- Patient Preparation (Removal of Metallic Items): Remove all metallic and dense objects from the head and neck: earrings, necklaces, spectacles, hairpins, clips, hearing aids, tongue studs, removable dentures, and intraoral piercings.
- Protective Lead Apron Rule: Use a lead apron without a thyroid collar (a thyroid collar blocks the vertical slit beam and creates a large radiopaque “shark-fin” artifact).
Step-by-Step Alignment Protocol:
- Spine Straightening: Instruct the patient to step forward, grasp the handgrips firmly, and pull their feet forward slightly while standing upright with shoulders relaxed and down. This straightens the cervical spine.
- Bite-Block Engagement (Anterior-Posterior Alignment):
- Patient places their maxillary and mandibular central incisors into the notches of the bite-block in an edge-to-edge relationship.
- Purpose: Positions the anterior teeth precisely within the focal trough.
- Mid-Sagittal Plane (MSP): Align the vertical laser light beam with the midline of the face. The MSP must be strictly perpendicular to the floor (ensures zero rotation or tilt).
- Frankfort Horizontal Plane (FHP – Pitch Alignment): Adjust the unit height until the horizontal laser light connects the upper border of the external auditory meatus (Porion) to the lower border of the orbital rim (Orbitale) parallel to the floor. (Alternatively, align the ala-tragus line 5⁰ downward).
- Canine / Cuspid Laser: Position the canine positioning laser over the contact point between the maxillary lateral incisor and canine to center the focal trough curvature.
- Tongue & Lip Protocol (Critical Final Step): Instruct the patient to:
- Swallow and press the entire tongue flat against the roof of the mouth (hard palate) for the entire exposure.
- Keep lips closed tightly around the bite-block.
- Keep eyes closed and remain completely still until the machine stops rotating.
4. Anatomy of Artifacts: Real, Double, and Ghost Images
Panoramic imaging creates three distinct categories of anatomical projections:
| Image Type | Formation Mechanism | Anatomical Examples |
| Real Images | Structures situated between the rotational center and the image receptor within the focal trough. | Teeth, mandibular body, inferior alveolar canal, maxillary sinuses. |
| Double Images | Midline structures intercepted twice by the rotating beam (once during each lateral sweep). | Hard palate, soft palate, uvula, epiglottis, hyoid bone. |
| Ghost Images | Dense objects situated between the X-ray source and the rotational center; projected on the opposite side, higher up, and blurred/magnified. | Contralateral mandibular angle (gonion), cervical spine, earring artifacts, lead apron collars. |
5. Common Positioning Errors & Radiographic Signs
| Positioning Error | Radiographic Sign on Film | Clinical Impact | How to Correct |
| Patient Positioned Too Far Forward | Anterior teeth appear narrow, blurry, and “pencil-thin”; severe cervical spine superimposition. | Obscures anterior roots and crowns. | Move patient back until incisors rest in bite-block grooves. |
| Patient Positioned Too Far Backward | Anterior teeth appear fat, widened, and out of focus; condyles project off lateral edges. | Loss of incisor root detail. | Move patient forward into bite-block grooves. |
| Chin Tilted Too Low (FHP Angled Down) | Exaggerated “Joker Smile”; mandibular incisors foreshortened; condyles pushed off top of image. | Distorts occlusion curve; obscures mandibular symphysis. | Raise machine to level the Frankfort Plane parallel to floor. |
| Chin Tilted Too High (FHP Angled Up) | “Flat / Reverse Smile line” (Frown); hard palate superimposes over maxillary apices. | Maxillary apices completely obscured. | Lower machine to level the Frankfort Plane parallel to floor. |
| Head Rotated (MSP not 90°) | Teeth and ramus on one side appear widened, while contralateral side appears narrowed. | Creates false asymmetry in jaw size and condyles. | Realign vertical MSP laser directly on facial midline. |
| Tongue Not on Hard Palate | Large dark radiolucent band (palatoglossal air space) over the roots of maxillary teeth. | Masks periapical lesions and root tips of upper teeth. | Instruct patient to press tongue flat against roof of mouth. |
| Slumped Spine (Neck Kyphosis) | Dense triangular radiopaque shadow projected over the lower midline of the mandible. | Completely obscures the mandibular symphysis. | Instruct patient to stand tall and extend the neck. |
6. Radiographic Anatomy & Quality Evaluation Criteria
+───────────────────────────────────────────────────────────────────────────+
| [TMJ Condyle] [TMJ Condyle] |
| \ [ MAXILLARY SINUS ] [ MAXILLARY SINUS ] / |
| \─── (· · · · · · · · ·) (· · · · · · · · ·) ───/ |
| ══════════ Hard Palate Line ══════════ |
| |
| [#] [#] [#] [#] [#] [#] [#] [#] [#] [#] [#] [#] |
| [#] [#] [#] [#] [#] [#] [#] [#] [#] [#] [#] [#] ◄── Dentition|
| \─── Gentle Upward Curve of Spee (Smile Line) ───/ |
| |
| [ Mandibular ] [ Mandibular ] |
| [ Ramus ] (====== Mandibular Canal ======) [ Ramus ] |
| \ / |
| \────────────── [ Mandibular Base ] ──────────────────/ |
| (Mentum) |
+───────────────────────────────────────────────────────────────────────────+
- Gentle Upward Occlusal Curvature: The occlusal plane forms a gentle, natural upward smile line (Curve of Spee).
- Symmetrical Proportions: Mandibular rami, condyles, and tooth sizes are equal in width and height bilaterally.
- Full Anatomical Coverage: Visualizes both TMJ condyles superiorly, the lower border of the mandible inferiorly, and both maxillary sinuses.
- Clear Maxillary Apices: Absence of the dark palatoglossal airway shadow over the maxillary roots (confirming correct tongue placement).
- Minimal Cervical Ghosting: Mandibular symphysis is clear of dense cervical spine radiopacity.