Comparative study between the SFS and LFS rotation as a possible morphogenic mechanism.

Cephalometric tracings of twenty-seven untreated adult Caucasians, selected on a clinical impression of reduced lower facial height were studied and compared with tracings of nine untreated adult Caucasians with increased lower facial height. Various linear and angular measurements for both groups were analyzed and compared. As has been previously described for the SFS, the LFS group can be subdivided into at least two subtypes. Subtype I is characterized by a long ramus, increased OP-PP, an increased SN:MP-angle, and excessive lower anterior facial height. These persons manifest the most typical clinical characteristics of the long face syndrome and have excessively long faces. In Subtype II, however, extreme backward and downward rotation of the mandible, combined with a short or extremely short ramus, is associated with an increase in lower anterior facial height. The increase in posterior maxillary height was not striking in this subtype. It was demonstrated that many of the characteristics of the LFS group and the SFS group can be explained by clockwise or counterclockwise rotation of the mandible "in concert" with the hyoid, tongue, pharynx, and cervical spine. The LFS group was characterized by a clockwise rotation of the mandible "in concert" with the hyoid, tongue, pharynx, and cervical spine. The mandible of the SFS group rotated similarly, but in the opposite counterclockwise direction. The vital need to maintain patency of the upper airway at the level of the base of the tongue may account for rotation in the LFS.