Comparison of the effects of monoblock and twin-block appliances on the skeletal and dentoalveolar structures.

Functional appliances, which are used in the early treatment period of skeletal Class II malocclusions, induce the forward displacement of the mandible by altering the postural activity of the muscles and causing some changes in both skeletal and dentoalveolar structures. The purpose of this investigation was to evaluate the differences between monoblock and twin-block appliances. Two treatment groups composed of 26 growing patients with skeletal and dental Class II, Division 1, malocclusions, were compared to an untreated control group of 13 patients with the same morphologic characteristics and growth rate. These groups were matched according to their age, sex, and vertical and sagittal skeletal cephalometric and dental characteristics. Monoblock was worn by the subjects for 16 hours/day, whereas twin-block was worn 24 hours/day, even while eating. Patients of the control group were followed without any intervention. Treatment effects were identified with a conventional cephalometric analysis. The findings of this study revealed that by using these different functional appliances, the stimulation of the growth of the lower jaw and the correction of Angle Class II relationship were achieved. In the twin-block group, the mandibular plane angle and gonial angle increased, although a decrease in the degree of overbite occurred. In the monoblock group, upper incisors demonstrated a greater degree of retrusion. However, within the twin-block group, the lower incisors showed a greater degree of proclination.