Orthopantomography (OPG / Panoramic Radiography): Patient Positioning & Error Guide

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

OPG Positioning Diagram

Orthopantomography (OPG) Positioning Protocol

[ Panoramic Rotational Path ]

[ Canine Beam ] ──►

Frankfort Plane // Floor

│ Bite-Block (Edge-to-Edge)

─────── [ MSP ⟂ ] ───────

Tongue on Hard Palate

◄── FHP Horizontal: Tragus to Infraorbital Rim

◄── Mid-Sagittal Plane: Perpendicular (No Turn / Tilt)

◄── Palatoglossal Air Gap: Completely eliminated

[ Spine Fully Erect ]

◄── Eliminates ghost artifact of the cervical 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

Lateral Cephalometric Landmarks & Reference Planes

Orthodontic / Maxillofacial

Standard Craniofacial Triangulation & Tracing Mesh

Diagnostic Reference Planes

S-N Plane (Cranial Base) Sella ➔ Nasion

Frankfort Horizontal (FHP) Porion ➔ Orbitale

Palatal Plane (ANS-PNS) ANS ➔ PNS

Mandibular Plane (MP) Gonion ➔ Menton / Gn

Essential Skeletal Landmarks

S Sella: Center of sella turcica

N Nasion: Nasofrontal suture

A Point A: Maxillary sub-spinale

B Point B: Mandibular supra-mentale

Pog Pogonion: Anterior-most chin

Go Gonion: Mandibular angle apex

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.