Geometrical interpretation for abnormal facial behaviour with possible correction of angle S-N-A and S-N-B.

The orientation of the sella nasion (SN) line in lateral skull radiographs is important for accurate assessment of antero-posterior and vertical facial relationship. Lateral skull radiographs of a random sample were traced and digitized to produce a mean shape template of the sample, with the craniofacial centroid line (CFC) used as a base for superimposition of the sample. A geometrical triangle was formed using the sella nasion line, craniofacial centroid line and the mandibular plane as the sides of the triangle. Simple geometric calculations were done to re-orient both the mandibular plane and sella nasion line in cases with balanced clinical profiles, while the S-N-A and S-N-B measurements indicate otherwise.