Dr Andrew Bolas
BDS FFDRCSI FDSRCS(Ed) MSc
Oral surgeon
Part-time lecturer in dental radiology
Dublin Dental Hospital

Address for correspondence:
Dr Andrew Bolas
HSE West Dental Department
Markievicz House,
Sligo

Poor-quality radiographs make diagnosis difficult or sometimes impossible. Rather than try and formulate a diagnosis or treatment plan from a poor radiograph, a decision should be made at an early stage to assess whether the exposure needs to be repeated or not. Panoramic radiographs have
a number of inherent faults due to the mechanism by which the image is created, they are also hugely reliant on the positioning of the patient.

STAGE 1: Assess the quality of the radiograph
Figure 1 shows a number of indicators that can help in assessing the image quality of a radiograph. The red line indicates the occlusal plane, this should follow a shallow arc, too flat and the patients’ chin is too high; and too deep (or “smiley”) and the patients’ chin is down on their chest. The blue arrows indicate the widths of the right and left ascending rami, these should be approximately the same size; a difference may indicate the patient is rotated in the machine, causing more magnification on one side. The third indicator is the ghost shadows of the angles of the mandible, again these should be at approximately the same level. In this example the line on the left is higher that the line on the right, indicting that the head is tilted to the left. Finally, the green highlighted area shows an area of the image that is much darker than its surroundings; this is an air space shadow caused by air between the hard palate and the dorsum of the tongue.

As can be seen, this often lies over the apical area of the maxillary teeth, making diagnosis difficult. By getting the patient to push their tongue against the roof of their mouth during exposure, this shadow can be reduced or eliminated. Exposure factors should be assessed, and be such that the contrast levels allow enamel. Dentine and bone should be distinguishable.

FIGURE 1: Indicators for assessing image quality.

FIGURE 1: Indicators for assessing image quality.

STAGE 2: Assess the whole radiograph in a logical fashion
One approach to assessing the radiograph is what could be described as the ‘windscreen wiper’ method, whereby the clinician casts their eyes from left to right and right to left, in an attempt to cover all the detail. A preferred method, as illustrated in Figure 2, is to assess the radiograph in an ‘ever-decreasing spiral’. Starting at the right condyle, the assessment progresses along the lower border of the mandible, right round to the left condyle. From here, the assessment crosses the maxilla taking in the maxillary antra and the hard palate. The next sweep starts at the right sigmoid notch and carries around the mandible again, this time assessing the periapical tissues and the alveolar bone. From the left sigmoid notch, the eye is then cast across the peri-apical tissues of the maxillary teeth back to the starting point. The final sweep involves looking at each of the teeth and the alveolar bone.

FIGURE 2: Assess the radiograph in an ‘ever-decreasing’ spiral.

FIGURE 2: Assess the radiograph in an ‘ever-decreasing’ spiral.

STAGE 3: Remember the normal anatomy
Figures 3 and 4 (cropped panoramic images) show some of the normal anatomy seen on a panoramic radiograph. There are also a number of soft tissue shadows that appear on the image, and also a number of ‘ghost shadows’ that appear as a result of how the panoramic image is captured.

FIGURE 3: Normal anatomy seen on a panoramic radiograph (1-15).

FIGURE 3: Normal anatomy seen on a panoramic radiograph (1-15).

1. Shadow of the hard palate
2. Lacrimal duct
3. Inferior orbital margin
4. Pterygopalatine fissure
5. Lateral pterygoid plate antrum
6. Hard palate
7. Zygomatic buttress
8. Zygomatic arch
9. Soft palate
10. Styloid process
11. Dorsum of the tongue
12. Inferior dental canal
13. Mental foramen
14. Body of the hyoid
15. Greater wing of hyoid

FIGURE 4: Normal anatomy seen on a panoramic radiograph (16-30).

FIGURE 4: Normal anatomy seen on a panoramic radiograph (16-30).

16. Nasal septum
17. Inferior concha
18. Anterior nasal spine
19. Shadow of nasal cartilage
20. Medial wall of the
21. Floor of the antrum
22. Posterior antral wall
23. Hamulus
24. Coronoid process
25. Maxillary tuberosity
26. Articular eminence
27. Condylar head
28. Mandibular foramen
29. Earlobe
30. Shadow of the angle of the mandible

Conclusion
One of the main problems with panoramic radiographs is that often normal anatomy or one of these ‘ghost shadows’ can look like pathology. By assessing the quality of the radiograph, reading the radiograph in a logical fashion and remembering the normal anatomical images, it is possible to get the most from the radiograph.