Nasion true vertical: a proposed method for testing the clinical validity of cephalometric measurements applied to a new cephalometric reference line.

A method is proposed to test a true vertical reference line through nasion and also other, more traditional, cephalometric variables on their ability to discriminate between clinical profiles. Twenty-seven women with Class I occlusion and normal overbite and overjet were divided clinically into three horizontal profile types (retrognathic, orthognathic, and prognathic) by five judges. A t test, discriminant analysis, and graphic plot interpretation were performed on the data of the orthognathic and retrognathic groups. The anteroposterior position of the maxilla was found to be irrelevant to the profile classification of the subjects investigated. For the variables describing mandibular position, only SNB performed well (P less than .01). The best discriminators were those variables that related one jaw to the other. The effective horizontal discrepancy between mandible and maxilla (AB distance) showed superior performance as an indicator of profile type (P = .001). Orthodontic and surgical treatment toward a value within the orthognathic AB range may provide a skeletal framework contributing to profile harmony.