Comparison of the effects of Hanks Herbst vs twin block following the removal of fixed appliances in Class II correction: a randomized controlled trial

Objectives: To evaluate and compare the efficiency of Hanks Herbst (HH) and twin block (TB) functional appliances in the treatment of adolescents with Class II malocclusion. Methods: A two-arm parallel randomized controlled trial, stratified by sex, was conducted in a single United Kingdom hospital. Eighty adolescents (10-14 years) with overjet ≥ 7 mm were randomized 1:1 to HH or TB. Participants received either a fixed HH or removable TB appliance, followed by comprehensive fixed appliance therapy. Skeletal and dental outcomes were assessed as well as patient-reported outcomes. The primary outcome was time to reduce overjet to < 4 mm; secondary outcomes included skeletal or dental changes, peer assessment rating scores, treatment duration and failure, and oral health-related quality of life. Results: At the completion of the functional phase (T1), HH demonstrated significantly greater overjet reduction (1.3 mm; P < .001), improved molar relationships, and increased mandibular length (2 mm; P = .03). By the completion of full treatment (T2), most skeletal and dental differences were no longer significant, except for a small residual overjet favoring TB (0.6 mm). Peer assessment rating scores improved substantially in both groups, with no significant differences at T2 (HH = 4.6 ± 4.2; TB = 4.1 ± 3.4; P = .60). Patient-reported outcomes at T2 were largely similar, although TB participants reported higher embarrassment at T1 (46% vs 18%). Treatment failures were higher in the TB group (37.5% vs 17.5%). Conclusions: The HH appliance provides efficient short-term overjet correction. However, following comprehensive fixed appliance therapy, skeletal, occlusal, and patient-reported outcomes are comparable between HH and TB. Both clinical effectiveness and patient experience should guide functional appliance selection.