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

Abstract

The conventional orthopedic Milwaukee brace exerts a large and continuous force that induces malocclusion and a significant deformation of the mandible. Our previous chincup study examined its use in moderately severe mandibular 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° and –1.3° of ANB angle in the prepubertal and pubertal subjects), the resultant changes were maintained after retention. However, research reported that the changes obtained during chincup treatment (average, 4½ years’ use) were often not maintained in severe skeletal Class III malocclusion. The aim of this clinical study was to investigate the immediate and long-term effects of prolonged use (mean, 7 years 2 months) of chincup appliances in subjects with dolichofacial Class III mandibles. Thirty-six female subjects with severe skeletal Class III malocclusions, associated with large gonial angles, were selected from the dental records of a private clinic. At posttreatment (T1, 65 months’ duration) and postretention (T2, 56 months after T1), Ar-Me and Wits appraisal cephalometric parameters were significantly different ( P < .01) between patients and control subjects (n = 230). Furthermore, the Go-Me parameter in treated subjects was longer than that of the controls at T0 but became significantly shorter at T2 ( P < .01). Treatment was associated with a finding that the Ar-Go parameter increased less than the controls at T2. Our results indicate that long-term use of the chincup appliance (>5 years) is effective in subjects with severe skeletal Class III abnormality. (Am J Orthod Dentofacial Orthop 1999;116:610-5)