Treatment and posttreatment effects of acrylic splint Herbst appliance therapy

This study evaluated the skeletal and dentoalveolar changes induced by acrylic splint Herbst therapy of Class II malocclusion. The treated group comprised 55 subjects with Class II malocclusion treated with the acrylic splint Herbst appliance followed by comprehensive edgewise therapy. The mean age at Time 1 (immediately before treatment) was 12 years and 10 months +/- 1 year and 2 months. The mean age at Time 2 (immediately after debonding of the Herbst appliance) and Time 3 (posttreatment) was 13 years and 10 months +/- 1 year and 2 months and 15 years and 2 months +/- 1 year and 4 months, respectively. The two control groups were one group of 30 subjects with untreated Class II malocclusion and another group of 33 subjects with Class I occlusion. The three groups were homogeneous as to the stage of maturation of cervical vertebrae at all observation times. A modification of Pancherz's cephalometric analysis was applied to the lateral cephalograms of the three groups at Time 1, Time 2, and Time 3. Linear and angular measurements for mandibular dimensions, cranial base angulation, and vertical relationships were added to the original analysis. Differences for all the variables from Time 1 to Time 2 (active treatment effects), from Time 2 to Time 3 (posttreatment effects), and from Time 1 to Time 3 (overall treatment effects) were calculated for the treated group and contrasted to corresponding differences of both untreated groups by means of ANOVA (P <.05). The study showed that two thirds of the achieved occlusal correction was due to skeletal effects and only one third to dentoalveolar adaptations. Both skeletal and dentoalveolar effects were due mainly to changes in mandibular structures. A significant amount of relapse in molar relationship occurred during the posttreatment period, and this change could be ascribed to the mesial movement of the upper molars.