15. Appendices
184 vatech A9 (Model name: PHT-30CSS) User Manual
neck and shoulders over to place the chin on the chin rest. The vertebrae collapse
causing attenuation of the x-ray beam that produces a triangular radiopacity
superimposed over the mandible, and if severe, over the anterior maxillary regions as
well.
Depending on the manufacturer, panoramic x-ray machines direct the operator to
position the Frankfort or the canthomeatal plane parallel to the floor, or the ala-tragus
line 5° down toward the floor. This is achieved by raising or lowering the chin rest so
that the appropriate landmark lines up with indicators on the machine (Figure 2). The
patient should be directed to stand in front of the panoramic x-ray machine allowing
the operator to place the chin rest in a position that is slightly higher than the patient's
chin. The patient is then requested to move into the overhead assembly of the
machine and remain standing tall. If further adjustment is needed, it is usually to a
lowered chin position. Once the patient's chin is resting on the chin rest, it is easier to
move to a lower position than to a higher one. To assist with placing the chin on the
chin rest while maintaining an erect posture, the pediatric patient can be directed to
stand like a soldier. Most children are familiar with the straight back, chest forward
tucked chin position demonstrated by military persons, and can readily mimic this
stance.
Further Recommendations
Before beginning the exposure, the patient should be directed to close the lips around
the bite block and to place the tongue against the palate. Leaving the lips open will
create a soft tissue shadow across the teeth that can be mistaken for caries.
7
Leaving
the tongue at rest during the exposure allows the radiation to easily penetrate the
space of the oral cavity between the dorsal surface of the tongue and the palate,
producing a radiolucent shadow that diminishes the diagnostic quality of the
radiograph (Figure 3).
"Filling in" this space with the soft tissue of the tongue can increase the quality of the
image by diminishing this radiolucent shadow. When directed to place the tongue on
the roof of the mouth, the pediatric patient is likely to press only the tip of the tongue
against the palate. While an adult patient can usually understand what is required
when directed to swallow and note the position of the tongue, a child may be directed
to suck in the cheeks, which results in pushing the tongue into a position flat against
the palate.
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