Determinants of successful chincup therapy in skeletal class III malocclusion

The purpose of this study was to investigate skeletal characteristics that determine successful chincup therapy in patients with skeletal Class III malocclusions by using longitudinal follow-up data of 40 patients (18 male, 22 female). Lateral cephalometric radiographs were taken before chincup therapy (T0), after chincup therapy (T1), and after fixed orthodontic treatment and retention (T2). From the measurements at T2, the patients were classified into group 1, showing good retention results (n = 21; 9 male, 12 female), or group 2, showing poor results (n = 19; 9 male, 10 female). The differences at each stage and during T0 to T1 and T1 to T2 between the 2 groups were compared by t tests. The major effect of chincup therapy was backward rotation of the mandible in both groups; however, the amount of rotation was greater in group 2. After retention, group 2 showed more forward rotation and forward growth of the mandible than group 1. Cephalometric measurements that showed significant differences in skeletal and dental morphology between the 2 groups at T0 were L1 to occlusal plane (P <.001), upper gonial angle, AB to occlusal plane angle, AB to mandibular plane angle, ANB, anteroposterior dysplasia indicator, Wits appraisal (P <.01), articular angle, gonial angle, facial convexity angle, AB to facial plane angle, and L1 to A-Pog (P <.05). These factors apparently contributed to the difference of long-term results in the 2 groups. It is necessary to evaluate these items in the diagnosis and treatment planning of skeletal Class III malocclusion in growing patients when chincup therapy is being considered.