The mechanism of Class II correction in late Herbst treatment.

The aim of this study was to analyze quantitatively the sagittal skeletal 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 malocclusion treated during the skeletal maturity stages MP3-H and -1, corresponding to a period after the maximum of pubertal growth (late treatment). A comparison was made with 22 Herbst subjects treated during the skeletal maturity stages MP3-E and -F, corresponding to a period before the maximum of pubertal growth (early treatment). Lateral head films from before and after Herbst therapy were analyzed, according to the method of Pancherz. As a result of the Herbst therapy, all patients attained a Class I or overcorrected Class I occlusal relationship. Class II molar correction averaging 6.1 mm was due to 37% skeletal and 63% dental changes. Overjet correction averaging 8.4 mm was due to 27% skeletal and 73% dental changes. Differences between the late and the early treated patients were only found for the dental changes. The upper anterior teeth were retroclined and the lower anterior teeth were proclined more in the late cases. The conclusion of the study was that the Herbst appliance is equally efficient in patients treated before and after the pubertal peak of growth. However, proclination of the lower incisors (anchorage loss) in late treated subjects is larger than in early treated subjects. This should be considered in treatment planning.