The gnathic index (GI) can be used to describe the anterior edge of the maxilla relative to normal.
Synonym: alveolar index
Cephalometric landmarks in a lateral imaging study of the head:
(1) basion (lowest point on the anterior rim of the foramen magnum
(2) middle of the nasofrontal suture
(3) middle of the anterior edge of the maxilla
gnathic index =
= (distance from the basion to the middle of the upper front edge of the maxilla in cm) / (distance from the basion to the middle of the nasofrontal suture in cm) * 100
Ratio
Term
< 98
orthognathous
98 to 103
mesognathous
> 103
prognathous
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