Features of an Ideal Panoramic Radiograph

Before we learn how to correct for poor technique, we should first be able to recognize the features that make for a good panoramic radiograph. There are two general features that distinguish this panoramic from a poor one – they are adequate exposure and correct anatomic representation.

Figure 65.
fig65
Example of an excellent edentulous panoramic radiograph
with adequate exposure and correct anatomic representation.
  • Adequate exposure – An assessment of adequate exposure implies that there is adequate density and contrast to recognize anatomic features.
    • Density – The ideal density should be such that structures are not obstructed by areas of darkness i.e. areas of “burn out” or areas that are too light i.e. areas of “white out”. Visually this can be assessed by looking at the mandibular parasymphyseal area and region associated with the apices of the maxillary teeth. In the maxilla this is most evident when the tongue is not held in position during panoramic exposure. Excessive or inadequate density can lead to failure to detect features such as unerupted and impacted teeth or even pathology.
Figure 66.
fig66
Regions on a panoramic radiograph
to look at to determine adequate density.
Figure 67.
fig67
Example of an overexposed panoramic radiograph.
Example of an overexposed panoramic radiograph:
Figure 68.
fig68
Figure 69.
fig69
Images demonstrating how excessive exposure can lead to failure to detect pathologic features. The image on the right is a digitally enhanced version of the left overexposed panoramic radiograph and clearly demonstrates the appearance of a radiolucent region causing expansion and thinning of the inferior cortex of the right mandible – features that were not evident on the original.
Example of an underexposed panoramic radiograph:
Figure 70.
fig70
Figure 71.
fig71
Images demonstrating how inadequate exposure can lead to failure to detect pathologic features. This image on the right is a digitally enhanced version and clearly demonstrates the appearance of an impacted mandibular right third molar that was not readily apparent on the original (left). This enhancement also clearly demonstrates a large pericoronal pathology that seems to involve the right second mandibular molar.
  • Contrast – The second element of adequate exposure assessment is contrast. This can best be assessed by determining if the interface between the enamel and the dentine can be seen, usually in the molar region. This is particularly important in areas where there are multiple overlapping structures. Inadequate contrast can lead to failure to detect features such as unerupted and impacted teeth.
  • Figure 72.
    fig72
    Assessment of contrast in panoramic radiograph.
    • Anatomically representative – A panoramic should be a good representation of the maxillofacial structures that it images. This means that there is adequate coverage of the osseous structures and that they are represented with some degree of accuracy. To determine correct anatomic representation, a visual assessment of the panoramic radiograph should be performed for accuracy of both anatomic structures and the dentition.
      • Anatomic assessment – A number of features can be used to determine anatomic accuracy including:
        • The condyles are on film – Usually in the upper outer sextant and at same level.
        • Palate and ghost images of palate should be above the apices of the maxillary teeth, running through the lower portion of the maxillary sinus.
        • Ramus width should be very similar on both left and right sides.
    Figure 73.
    fig73
    Anatomic features to be compared in the
    assessment of panoramic anatomic accuracy.
  • Panoramic anatomy – A reference for anatomic structures commonly observed on panoramic radiographs appears below. Many of these structures are mentioned in the prior text and in the subsequent discussion of common errors.
  • Figure 74.
    fig74
    1. Mandibular Condyle 12. Cervical Vertabra 23. Genial Tubercles
    2. Coronoid Process 13. Zygomatic Process 24. Nasal Concha
    3. Nasopharyngeal Airway 14. Incisive Foramen 25. External Oblique Ridge
    4. Oropharyngeal Airway 15. Mandibular Foramen 26. Angle of the Mandible
    5. Styloid Process 16. Mandibular Canal Space 27. Zygomatic Bone
    6. Lateral Pterygoid Plate 17. Soft Palate 28. Glenoid Fossa
    7. Zygomatic Arch 18. Hyoid Bone 29. Inferior Border Mandible
    8. Articular Eminence 19. Hard Palate 30. Rim of the Orbit
    9. Anterior Nasal Spine 20. Nasal Septum 31. Infraorbital Foramen
    10. Mental Foramen 21. Maxillary Sinus Floor 32. Maxillary Tuberosity
    11. Infraorbital Canal 22. Nasal Fossa 33. Medial Pterygoid Plate – Hamulus
  • Features of the Dentition – A number of visual features of the dentition can be used to assess whether the teeth, particularly the anterior teeth are positioned correctly within the focal trough:
    • No or slight upward curve of teeth
    • No tooth size discrepancy on left or right side
    • Anterior teeth in focus (see pulp canal clearly)
    • Anterior teeth shape “normal”
    • Not too narrow or too wide
    • Premolars will always overlap due to inherent x-ray beam projection to the arch of the teeth in this region.
    Figure 75.
    fig75
    Features of the dentition to be compared in the assessment of panoramic anatomic accuracy.