The maxillary-mandibular planes angle (MM degrees) bisector: a new reference plane for anteroposterior measurement of the dental bases.

A new plane, geometrically derived from the dental base planes, has been tested as an occlusal plane substitute for the measurement of anteroposterior jaw relationships. It lies close to but at an angle and inferior to the traditional occlusal planes and is highly reproducible at all times. Lateral cephalograms of 36 young adults (25 men and 11 women) and 43 10- to 12-year-old children (24 girls and 19 boys) were selected and the Wits technique of anteroposterior measurement was used to compare A-B values measured to the new plane with those measured to the functional occlusal plane (FOP) and to the traditional or bisecting occlusal plane (BOP). Because of the downward cant of the bisector anteriorly, B is projected onto it ahead of A in normal occlusion and coincides with A in skeletal (2) malocclusion. Mean values for normal occlusion were found to be approximately -4 mm for the children (-4.2 mm girls and -4.0 mm boys) and -4.5 mm for the adults (-4 mm women and -4.7 mm men).