15. Appendices
vatech A9 (Model name: PHT-30CSS) User Manual 183
English
Superior-Inferior (Up-Down) Positioning Error
Positioning the dental arches within the superior-inferior (up-down) dimension of the
focal trough can be challenging to achieve, especially with children whose smaller
size reduces the distance between the shoulders and the inferior border of the chin.
When the arches are positioned incorrectly in the superior-inferior direction, the
image exhibits multiple distortions, including increased overlap in the premolar
regions. When the arches are positioned too far up or down, the teeth will
simultaneously move into a position that is too far back or too far forward,
respectively, out of the focal trough.
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Positioning the arches too far superiorly produces a characteristic "frown" or flat,
downward-turned appearance to the occlusal plane (Figure 5). The condyles flare
out and off the edges of the image, and the palate appears as a widened, thick,
dense radiopacity. This positioning error results in a widened appearance of the
palate and obliterates the apical regions of the maxillary teeth, compromising the
images of the unerupted developing dentition. As the maxillary arch tips upward, the
anterior teeth tilt backward, producing the same widened appearance that results
from an incorrect anterior-posterior position. Positioning the arches too far inferior
produces a characteristic "smile" appearance or the upward curve of the occlusal
plane, with the condyles tilting inward toward the center of the image (Figure 6).
Depending on the severity of the downward position, the vertebrae may also curve
inward and appear superimposed over the condyles, and the hyoid bone may be
superimposed over the mandible blocking a clear view of the erupted and unerupted
mandibular teeth.
Correct positioning of the arches in the superior-inferior dimension requires that the
patient stands with erect posture while tucking the chin in and down slightly, a
direction that both adults and pediatric patients often find difficult to follow without
specific guidance. The result is often a slumped position with the patient hunching the
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