The skeletal and dental effects of Hanks Herbst versus twin block appliances for class II correction in growing patients: a randomized clinical trial.

Background: Despite the popularity of the Twin Block (TB) and the Hanks Herbst (HH) functional appliances, there is limited prospective research comparing these removable and fixed designs, respectively.
Objectives: To evaluate and compare the skeletal and dental effects associated with TB and HH functional appliances as well as to detect factors that might influence the success or failure of treatment in adolescents with Class II malocclusion.
Design and Setting: A parallel-group randomized controlled trial was undertaken in a single-centre hospital in the United Kingdom.
Methods: A total of 80 participants (aged 10-14 years) with overjet of 7 mm or more were randomized to receive either the HH or TB appliance. Cephalometric radiographs were collected at the start of the study and immediately after the withdrawal of the functional appliances and measured using Pancherz analysis. Participants were allocated to the TB or HH group, based on an electronic randomization, stratified for gender and allocation concealed. Blinding to the allocated arm was not possible. However, all data were coded and anonymized to ensure that assessors were blinded to the group allocation. The main outcome was the anterior-posterior skeletal and dento-alveolar changes at the end of the functional phase.
Results: Fifteen (37.5%) participants from the TB group and 7 (15.5%) from HH failed to achieve full overjet reduction (<4 mm) after 12 months of treatment. Overjet reduction was 2 mm greater with HH compared to TB (P = .05; 95% CI: 0.2, 3.2). No significant differences regarding skeletal and dental changes were reported, with the exception that participants in HH group experienced greater lower molar protraction (P = .002; 95% CI: -2.8, -0.8) and mandibular incisors advancement (P = .001; 95% CI: -2.9, -1), indicating greater dental than skeletal effects.
Conclusion: The TB appliance was associated with a higher rate of treatment discontinuation. No significant clinical differences were observed in the skeletal and dental effects, although the HH may be associated with more pronounced effects on the mandibular dentition.
Clinical Trial Registration: The protocol was registered online before the start of the trial (ISRCTN11717011).
(© The Author(s) 2023. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: journals.permissions@oup.com.)