Skeletal changes of herbst appliance therapy investigated with more conventional cephalometrics and European norms

We measured the skeletal effects of Herbst appliance treatment in a retrosp ective sample of 25 boys (aged 10.7-14.5 years) and 25 girls (aged 10.7-14. 3 years). Selection criteria were (1) a pretreat ment full Class IT molar r elationship (ANB angle: average, 6.7 degrees; range, 2.5-10.5 degrees) and (2) a posttreatment full Class I or overcorrected sass 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 appr opriate age- and sex-matched European norm, every pre- and posttreatment va lue was transformed into a z-score on the distribution of the norm value an d 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 o f natural growth. Posttreatment, the mandible showed a remarkable forward r epositioning without opening of the genial angle, particularly in males. On ly ANB and Xi-CF-PTV angles were significantly different when the effect of normal growth was excluded. In males, ramus height and mandibular basal le ngth 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 H erbst therapy can be efficacious, with the most frequent effect being mandi bular forward repositioning followed by mandibular ramus elongation. The st atistical procedure used counteracts the effect of growth and sex on the re sults. 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.