Treatment Changes of Chin Position in Class-II Division 1 Patients - A Cephalometric Study

Abstract

The present study is designed to evaluate the changes of chin position in class-II division 1 growing patients, treated with Activator-headgear (ActHg) and Herbst appliance and attempt is made to ascertain the most important determinants of AP (anteroposterior) chin position.

Sample of 28 growing individuals with skeletal and dental Class II was divided in to three groups, (Activator headgear (ActHg) group 10, Herbst group 10 and a control group of 8 patients). Pre (T1) and post (T2) growth modulation/observation standardized lateral cephalograms were traced, horizontal and vertical movements of selected landmarks were described based on Reference grid, a rectangular coordinates (X, Y). Condylar growth and true rotation of the mandible were calculated by mandibular superimpositions.

Reduction in ANB was mainly due to mandibular growth with no significant change in SNA value. Schudy's pogonion formula was not supported by the results. The most important determinant of anterior chin movements during growth and treatment was true rotation.

Methods commonly used to correct Class II skeletal malocclusions produce no significant improvements in anteroposterior chin position. Skeletal Class II correction in growing adolescents results primarily from mandibular growth.

Anteroposterior changes in chin position cannot be accurately predicted by Schudy's pogonin formula, instead approximately 70% of the variability in anteroposterior movement of the chin can be explained by true rotation, horizontal and vertical condylar growth, and remodeling of the glenoid fossa