A roentgenocephalometric study of skeletal changes during and after chin cup treatment.

Skeletal changes before and during chin cup treatment and the stability of results after treatment were studied. Materials consisted of longitudinal lateral cephalometric roentgenograms of twenty-six Japanese females with skeletal Class III malocclusion treated with the chin cup. Treatment was started when patients were 6 to 9 years of age. Annual changes in linear and angular measurements before, during, and after treatment were analyzed statistically. The results were as follows: (1) There was some reduction in the amount of expected growth increment in the mandible; a change in mandibular form and distal displacement of the mandible took place during treatment. (2) There was no obvious change in the cranium and maxilla during treatment. (3) Neither acceleration nor restraint of expected growth increment was found after treatment. The exception was forward displacement of the mandible during the first year after removal of the chin cup. To illustrate these results, the skeletal changes of one individual Japanese Class III female during and after chin cup treatment were analyzed with the use of fifteen parameters indicating area ratios, linear ratios, and angles. The control sample consisting of 426 nontreated Japanese females with skeletal Class III malocclusion was observed, varying between 3 years and 30 years of age. The growth in this case showed a trend similar to that of the control sample for the observation period, but it was redirected from the expected natural growth for the treatment period.