Edgewise therapy with cervical and intermaxillary traction--influence on the position of the bony chin

Comparison of treatment and control samples was intended to reveal those factors which, during Class II correction using Tweed Edgewise technique in conjunction with intermaxillary traction and low cervical traction to upper molars, may lead to undesirable posterior rotation of the mandible. Both samples exhibited similar condyle growth rates. Increased variability of the parameters tested was found within the treatment group. No significant difference was found in the vertical movement of the upper molars, while anterior movement of the upper molars was significantly inhibited in the treatment sample. The treatment sample displayed increased vertical and decreased anterior movement of pogonion, accompanied by posterior rotation of the mandible. Close and similar correlations were found in both samples between the anterior movements of the upper molars and pogonion, between the angles of upper molar and pogonion displacement in relation to Frankfort Horizontal, and between both of the upper molar parameters and changes of mandibular rotation. In the treated sample it was inhibition of anterior movement of the upper first molars, not enhancement of vertical movement that appeared to cause posteroinferior rotation of the mandible and displacement of pogonion through a geometric interdependence. The direction of upper molar movement and condyle growth rate both exert important influences on changes in position of the growing mandible and thus on the nature of profile changes in Class II correction.