Dental and orthopedic effects of Bass and Herbst therapy for correction of severe class II division 1 malocclusions

Functional appliance therapy to correct Class II division I malocclusions has been a subject of debate throughout this century. The aims of this thesis, based on six publications, were to evaluate the dental and orthopedic effects of Bass appliance therapy in relation to treatment intensity, age, and somatic maturation, and to compare initial and post-treatment effects of Herbst and Bass therapy. Finally, the increased spacing in the lower jaw during Bass therapy was analysed. Fifty-four boys and 24 girls were treated with Bass appliances and 18 boys with Herbst appliances. The analyses were performed on lateral cephalograms in centric occlusion and on dental casts. Longitudinal records of standing height were used to assess the growth periods.

The jaw base relationship was improved during treatment with the Bass appliance by advancement of the mandible and restraint of the maxilla. A rapid effect on the mandible was found in boys 8 to 10 years old and in boys treated during the pubertal growth spurt. Compliance was better if the patients were instructed to wear the appliance day and night. Initially the Bass appliance gave a larger skeletal treatment effect than the Herbst appliance, but due to dental effects the Herbst therapy resulted in more complete correction of overjet and sagittal molar relationship. At the end of growth, 5 to 10 years after the initial treatment, there were no significant differences in skeletal or dental changes during the total observation period. An increase in mandibular dental arch space was observed during initial treatment with the Bass appliance.