The diagnostic criteria for a panoramic image are outlined in Table 4.
Table 4. Panoramic Diagnostic Criteria.
- Entire maxilla and temporomandibular joints recorded.
- Symmetrical display of the structures right to left.
- Slight smile or downward curve of the occlusal plane.
- Good representation of the teeth with minimal under or over magnification.
- Tongue in place against the palate with the lips closed.
- Minimal or no cervical spine shadow visible.
- Overlapping of posterior teeth, particularly the premoloars, is expected.
- Acceptable image density and contrast.
- Free of patient preparation, technical and exposure errors.
An ideal panoramic radiograph should be free from errors related to patient preparation, technique or exposure.
Figure 27. Ideal Panoramic Radiograph.
In reality, many panoramic images are not ideal and present minor but acceptable errors.
Figure 28. Panoramic with acceptable errors.
Patient’s head is positioned slightly downward and a thin palatoglossal airspace is present. These errors do not interfere with the overall diagnostic acceptability and the image does not require a retake.
However, there are certain specific critical errors that result in images that fail to fulfill the criteria for an acceptable panoramic image. These errors are critical because they usually necessitate re-exposure of the patient.
The principle technical criterion for acceptance of a panoramic radiographic image is that it should adequately image all the structures of the maxillofacial region. If any of the structures are not present, either because it is not covered or obscured, then it should be retaken. It should be remembered that the patient pays for the interpretation and subsequent diagnosis generated from the panoramic image and not the procedure itself.
Specific exclusionary criteria include the inability to visualize any of the following either due to the structure not being imaged on the receptor or obstruction of the structure from view:
Condyle of the TMJ
Mandibular/maxillary anterior region
Figure 29 demonstrates three of the most common reasons for retakes – neither the condyle of the TMJ, the mandibular anterior region nor the mandibular ramus are visualized on this radiographic image. In this particular case it is because the patient’s head is tilted too far down during exposure.
Figure 30 demonstrates three further reasons for retakes; poor visualization of the maxillary anterior region, coverage of structures due to the presence of ghost images and/or labels. In this particular case the patient is positioned too far backward and has their head tilted too far up (as evidenced by the reverse or frown occlusal plane). These positioning errors place the maxillary anterior region out of the focal trough and produces excessive ghosting of the amalgam restorations of the opposite side.