Effects of headgear Herbst and mandibular step-by-step advancement versus conventional Herbst appliance and maximal jumping of the mandible.

The aims of this study were to compare dental and skeletal treatment changes in Class II division 1 malocclusions with two modes of maxillary control and two modes of bite-jumping. The subjects comprised Chinese children with severe Class II division 1 malocclusions, i.e. 21 consecutive subjects (13.4 +/- 1.4 years) treated with a headgear Herbst appliance and step-by-step advancement (HHSSA) of the mandible, and 24 consecutive subjects (13.2 +/- 1.4 years) treated with a 'conventional' Herbst appliance with maximal jumping (HMJ) of the mandible. Lateral cephalograms obtained at the start and end of treatment were analysed. The results showed that the improvement of the sagittal jaw relationship was significantly larger (2.9 mm; P < 0.001) in the HHSSA group than in the HMJ group due to the increased effect on the maxilla (-1.5 mm, P < 0.001) and the mandible (+1.4 mm, NS). There was no significant difference in the change in lower anterior face height, being 2.7 and 3.1 mm, respectively. The mandibular plane angle decreased significantly in the HHSSA group (-0.7 degree; P < 0.05) and increased insignificantly in the HMJ group (0.4 degree, NS), the difference being statistically significant (P < 0.01). The maxillary molars moved significantly more distally (1.1 mm, P < 0.05) and were intruded in the HHSSA group (-1.0 mm, P < 0.001) compared with a small extrusion in the HMJ group (+0.3 mm, NS), the difference being statistically significant (P < 0.001). There was no significant difference in the effect on the mandibular teeth. Treatment with HHSSA seems to result in a greater effect on the sagittal jaw relationship, improved vertical control and more maxillary molar movement. Mandibular anchorage loss was not reduced with step-by-step advancement of the mandible.