Orthopantomography

The orthopantomogram (also known as an orthopantomograph, panotomogram or an OPG) is a panoramic single image radiograph of the mandible, maxilla and teeth. It is often encountered in dental practice and occasionally in the emergency department; providing a convenient, inexpensive and rapid way to evaluate the gross anatomy of the jaws and related pathology. 

Indications

There are multiple indications for this type of radiograph including yet not limited to:

• general dental health evaluation for caries or pulp origin disease
• trauma assessment for tooth or jaw fractures 
• infection evaluation of sinusitis, periodontitis or periapical abscesses 
• tumor or radicular cyst evaluation  
• temporomandibular joint assessment for disease, fractures or dislocations 
• facial bone disease evaluation
• foreign body localization
• salivary stone identification (sialolithiasis)
• growth and development monitoring of pediatric teeth for location, shape, angle, supernumerary tooth presence and tooth germ absence to prevent or prepare for future aesthetic issues 
• initial and progressive evaluation of orthodontic treatment (note an OPG alone is not usually sufficient for preoperative inspection or prosthesis measurement)

Patient position

During an OPG the patient remains in a stationary position (seated or standing) while both the x-ray source and film rotate in combination around the patient. The x-ray source rotates from one side of the jaw, around the front of the patient, and then to the other side of the jaw. The film rotates opposite to the x-ray source behind the patient. It takes a few seconds during which the patient must remain completely still. 

Technical factors

• panoramic projection
• paused respiration (departmentally dependent)
• centring point
  • Frankfort's horizontal line is perpendicular to the floor 
  • laser lights will be vendor specific however 
    • central laser light in the midsaggital plane 
    • axial laser light at the IOML
    • lateral laser light at the lateral incisor 
• orientation  
  • lanscape
• detector size
  • OPG specific detector 
• exposure
  • 70-80 kVp
  • 8-15 mA over a number of seconds
• grid
  • yes

Image technical evaluation

• radiolucency over maxillary teeth
  • tongue not against the hard palate
• hard palate superimposed on roots, flat occlusal plane, condyles at the edge
  • chin too high 
•  the mandible is V-shaped, too much smile line
  • chin too low 
• unequal condyles, slanted mandible, distorted nasal structures
  • head tilted to side 
• teeth wide on one side and narrow on the other, condyle size asymmetry
  • head turned to side 
•  anterior teeth blurry small and narrow, large amount of spine visible on edges
  • too far forwards
• anterior teeth blurry and wide, ghosting of mandible and spine, condyles close to the edge
  • too far backwards
• blurred image
  • movement
• artefact
  • earrings, hearing aids, piercing  

Practical points

All jewelry, dentures, hearing aids and glasses should be removed. The patient should be positioned: 

1. sitting/standing completely upright
2. head immobilized and on a chin rest
3. bitting down on a radiolucent bite block
4. tongue against the hard palate 

Correct positioning is empirical for a sharp, accurate and undistorted image. OPG positioning errors are common affecting 60-96% of radiographs; rendering 5-33% uninterpretable. The most common error is tongue not against the hard palate. For interpretation purposes, it is important to be aware of common errors and how they affect image quality.

Technique

This technique creates a panoramic image the should include the lower limits of the mandible, the upper limits of the maxillary sinuses, and the mandibular condyles and temporomandibular joints laterally. Panoramic image limitations include inherent anatomy distortion, double images, ghost images and do not provide a spatial relationship between structures.