The mechanism of Class II correction in Herbst appliance treatment. A cephalometric investigation.

Sagittal skeletal and dental changes contributing to Class II correction in Herbst appliance treatment were evaluated quantitatively on lateral roentgenograms. The material consisted of forty-two Class II. Division 1 malocclusion cases. Twenty-two of these were treated with the Herbst appliance for 6 months. The other twenty cases served as a control group. The results of the investigation revealed the following: (1) Bite jumping with the Herbst appliance resulted in Class 1 occlusal relationships in all treated cases. (2) The improvement in occlusal relationships was about equally a result of skeletal and dental changes. (3) Class II molar correction averaging 6.7 mm. was mainly a result of a 2.2 mm. increase in mandibular length, a 2.8 mm. distal movement of the maxillary molars, and a 1.0 mm. mesial movement of the mandibular molars. (4) Overjet correction averaging 5.2 mm. was mainly a result of a 2.2 mm. increase in mandibular length and a 1.8 mm. mesial movement of the mandibular incisors. (5) Anterior condylar displacement (0.3 mm.), redirection of maxillary growth (0.4 mm.), and distal movement of the maxillary incisors (0.5 mm.) were of minor importance in the improvement in molar and incisor relationships seen. (6) A direct relationship existed between the amount of bite jumping at the start of treatment and the treatment effects on the occlusion and on mandibular growth. For a maximal treatment response, it is suggested that the Herbst appliance be constructed with the mandible jumped anteriorly as much as possible, namely, to an incisal edge-to-edge position. The clinician should be aware of the dental changes occurring during Herbst appliance treatment and make sure that these changes are not incongruous with his over-all treatment goal.