The second category of technical errors in panoramic radiography are tissue projection errors or those due to tissue superimposition. There are two errors possible:
Hard Tissue Projection Errors
Panoramic radiograph (schematic on right) showing the effect of the spine on the anterior of the image with slumping of the patient.
Panoramic radiograph (schematic on right) showing the effect patient movement on the image. Note the discontinuity of the left lower border of the mandible and distortion of dentition and palate immediately superiorly.
In this image (cropped and zoomed on right) notice that in the midline anterior region, tooth # 8 in the maxilla is extremely narrow and suggests that the patient may have a central incisor that is a microdont. On further examination it can be see that tooth # 26 in the mandibular arc, directly below # 8 is also a microdont. Further clues to this appearance being due to a motion artifact are revealed by comparing the anatomy above and below the teeth with the opposite side. This is especially apparent in the relative width of the ala or soft tissue shadow of the nose.
Soft Tissue Projection Errors
Panoramic radiograph (schematic on right) showing the effect of not placing the tongue on the roof of the mouth on the image.
This image demonstrates the effect that a relaxation in tongue position during panoramic exposure can produce. Notice that in the maxillary midline there appears to be a radiolucent, cyst-like radiolucency that has expanded inferiorly below the alveolar bone. Closer examination reveals that the uppermost part of this lesion is shaped in a gradual curve – this curve represents the top of the palate and is the tell tail sign that this "lesion" has been created because the patient’s tongue dropped during the exposure.
Panoramic radiograph demonstrating the effect that occurs when the lips are not closed during exposure resulting in an area of increased radiodensity in anterior crown regions.