Long-term application of chincup force alters the morphology of the dolichofacial Class III mandible

The conventional orthopedic Milwaukee brace exerts a large and continuous f orce that induces malocclusion and a significant deformation of the mandibl e. Our previous chincup study examined its use in moderately severe mandibu lar prognathism without retrusion of the maxilla, The orthopedic force was approximately 500 g at the center of chin and was applied during sleep for 6 to 24 months. For mandibular prognathism subjects (means, 1.0 degrees and -1.3 degrees of ANB angle in the prepubertal and pubertal subjects), the r esultant changes were maintained after retention. However, research reporte d that the changes obtained during chincup treatment (average, 4 1/2 years' use) were often not maintained in severe skeletal Class III maloc-clusion. The aim of this clinical study was to investigate the immediate and long-t erm effects of prolonged use (mean, 7 years 2 months) of chincup appliances in subjects with dolichofacial Class III mandibles. Thirty-six female subj ects with severe skeletal Class III malocclusions, associated with large ge nial angles, were selected from the dental records of a private clinic. At posttreatment (T1, 65 months' duration) and postretention (T2, 56 months af ter T1), Ar-Me and Wits appraisal cephalometric parameters were significant ly different (P < .01) between patients and control subjects (n = 230). Fur thermore, the Go-Me parameter in treated subjects was longer than that of t he controls at TO but became significantly shorter at T2 (P < .01). Treatme nt was associated with a finding that the Ar-Go parameter increased less th an the controls at T2, Our results indicate that long-term use of the chinc up appliance (>5 years) is effective in subjects with severe skeletal Class III abnormality.