Abstract
We measured the skeletal effects of Herbst appliance treatment in a retrospective sample of 25 boys (aged 10.7–14.5 years) and 25 girls (aged 10.7–14.3 years). Selection criteria were (1) a pretreatment full Class II molar relationship (ANB angle: average, 6.7 degrees; range, 2.5–10.5 degrees) and (2) a posttreatment full Class I or overcorrected Class I molar relationship within 6–8 months. A first t-test was used to evaluate variations between pre- and posttreatment cephalometric measures. Then, compared with the appropriate age- and sex-matched European norm, every pre- and posttreatment value was transformed into a z-score on the distribution of the norm value and a second t-test was performed. The second t-test was to study variations between pre- and posttreatment z-scores in order to neutralize the effect of natural growth. Posttreatment, the mandible showed a remarkable forward repositioning without opening of the gonial angle, particularly in males. Only ANB and Xi-CF-PTV angles were significantly different when the effect of normal growth was excluded. In males, ramus height and mandibular basal length were significantly increased when total variation was considered (ie, not excluding the effect of normal growth). In females, only the mandibular ramus height was significantly increased. In conclusion, even short-term Herbst therapy can be efficacious, with the most frequent effect being mandibular forward repositioning followed by mandibular ramus elongation. The statistical procedure used counteracts the effect of growth and sex on the results. Moreover, z-scores are adimensional measures with which any kind of parameter may be compared and scaled to each other in the perspective of a more reliable mutivariated interpretation of cephalometric variables.
