Effectiveness of incremental vs maximum bite advancement during Herbst appliance therapy in late adolescent and young adult patients]

Introduction: The purpose of this research was to compare the effects of Herbst appliance therapy using incremental vs maximum advancement in late adolescent and young adult patients with Class II skeletal malocclusion. Methods: Forty-two patients with skeletal Class II malocclusion were treated with cast-splint Herbst appliances. The subjects were randomly allocated into 2 groups according to activation type: incremental advancement (IA) and maximum advancement (MA). Initial forward movement in the IA group was 4 to 5 mm and was followed by subsequent bimonthly advancements of 2 mm. Single-step advancement was achieved in the MA group until an edge-to-edge incisor relationship or an overcorrected Class I molar relationship was obtained. Total treatment times were 9.7 +/- 1.1 months for the IA group and 9.5 +/- 1.1 months for the MA group. Dental, skeletal, and soft tissue measurements were performed on lateral cephalograms taken just before and at the end of the Herbst appliance therapy. Statistical significance was set at P <= 0.05. Results: All mandibular skeletal dimensions increased, and improvements of the sagittal maxillomandibular parameters were found in both groups. Protrusion and proclination of the mandibular incisors were greater in the IA group (95.90 degrees +/- 5.34 degrees) compared with the MA group (92.04 degrees +/- 7.92 degrees). Other dentoalveolar changes in both groups were intrusion of the maxillary first molars, and extrusion of the mandibular first molars and maxillary incisors. The mentolabial sulcus was flattened, soft tissue convexity was reduced, and forward movement of mandibular soft tissues was seen after Herbst therapy. Conclusions: Similar skeletal, dental, and soft tissue changes were obtained in both groups after Herbst therapy. Greater proclination and more protrusion of the mandibular incisors were found in the IA group.