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In order to evaluate the initiation of treatment of Angle class II malocclusion at an early age, seventy-six patients, 34 girls aged on average 10.1 years and 42 boys, average age 11.3 years, were selected for the study. For the treatment we used the Klammt open activator. For evaluation purposes we used casts and cephalograms taken before and after treatment. The results showed distinctive differences between Angle class II/1 and II/2. The sagittal correction in class II/1 was a result of the reduction of the SNA angle, the mandibular protrusion, and the retrusion of the upper incisors. The face high index was normalized. No labial inclination of the lower incisors was registered. In the Angle class II/2 cases the SNA angle was unchanged. The sagittal correction was brought about exclusively through mandibular translation. The deep bite and the retrusion of the upper incisors weren't markedly improved. The lower incisors showed a labial tip. The incisor angle was unchanged. Our study showed that the ANB reduction on an annual basis is highest, when treatment is initiated at an age of 10 to 11 years for girls and 12 years for boys. On the growth curve this is a point in time below the accelerated growth phase of puberty.

Prior to treatment the participants suffering from Class II, Division 1 malocclusion exhibited distinct growth deficits in vertical direction. In the control group, the principal direction of mean growth was found to be anterior-inferior. Under the influence of the activator, growth was found to develop in the same direction as in the controls, so that anterior positioning of the lower jaw and an increase in lower facial height were attained.