THE MECHANISM OF CLASS-II CORRECTION IN LATE HERBST TREATMENT

The aim of this study was to analyze quantitatively the sagittal skele tal and dental changes contributing to Class II correction in patients treated with the Herbst appliance after the pubertal growth peak. The sample consisted of 21 subjects with a Class II, Division 1 malocclus ion treated during the skeletal maturity stages MP3-H and -I, correspo nding to a period after the maximum of pubertal growth (late treatment ). Acomparison was made with 22 Herbst subjects treated during the ske letal maturity stages MP3-E and -F, corresponding to a period before t he maximum of pubertal growth (early treatment). Lateral head films fr om before and after Herbst therapy were analyzed, according to the met hod of Pancherz. As a result of the Herbst therapy, all patients attai ned a Class I or overcorrected Class I occlusal relationship. Class Ii molar correction averaging 6.1 mm was due to 37% skeletal and 63% den tal changes, Overjet correction averaging 8.4 mm was due to 27% skelet al and 73% dental changes. Differences between the late and the early treated patients were only found for the dental changes. The upper ant erior teeth were retroclined and the lower anterior teeth were proclin ed more in the late cases. The conclusion of the study was that the He rbst appliance is equally efficient in patients treated before and aft er the pubertal peak of growth. However, proclination of the lower inc isors (anchorage loss) in late treated subjects is larger than in earl y treated subjects. This should be considered in treatment planning.