The effects of chin cup therapy on the mandible: a longitudinal study.

This study was conducted to evaluate the effects of chin cup therapy on the mandible and its dentition in persons with skeletal Class III malocclusion. The patients selected for this study were Japanese females treated with the extraoral chin cup appliance. Both the control and treatment samples were obtained from Japanese Universities where the longitudinal data were gathered. Lateral cephalometric radiographs were taken on the average of every 6 months for the treatment group and every year for the control group. Ten treated patients and seven control patients were studied. The duration of chin cup therapy was variable but averaged 3 years 1 month. The cephalograms were digitized on an electronic screen, and a cephalometric analysis was recorded from a computer program. The rate change values were then compared with those of the control group to yield a comparison of changes in mandibular growth rate, direction, and pattern in the treatment group. Active and posttreatment effects were evaluated. All measurements for the rate of change of absolute mandibular length were reduced by 60% to 68% from the control rate of growth during therapy. The mandible exhibited less downward displacement relative to cranial base during treatment. The mandibular plane angle and the gonial angle closed with growth in the Class III control sample but were variable in the treatment group. The skeletal profile was improved with treatment. This study indicates that the chin cup may be a viable mode of treatment for the preadolescent and adolescent mandibular prognathism patients.