Herbst appliance treatment has been described to result in an increase of the posterior airway space (PAS). However, the literature shows large inter-individual variations and is based on rather small samples. Therefore, the current aim was to investigate the PAS changes during as well as after Herbst and subsequent multibracket appliance (MBA) treatment in a large sample of Class II:1 patients, and to search for possible pre-treatment influencing factors. Therefore, the records of 503 former Class II:1 patients (overjet = 7.8 ± 2.4mm, ANB angle = 5.0 ± 2.1°) who had undergone Herbst-MBA treatment at the age of 13.8 ± 3.4 years (Department for Orthodontics, University of Gießen, Germany) were assessed. Lateral headfilms from before (T0), after 24.9 ± 9.2 months of treatment (T1) and 26.1 ± 8.0 months after treatment (T2) were analysed for the area-size of the PAS and the changes of linear distances (p, t, pC2, pC3, pC4). In addition, possible influencing pre-treatment characteristics were evaluated: overjet, ANB angle, Wits appraisal, ML/NSL angle, ArGoGn angle, age and skeletal maturity. On average, the PAS area increased by 23% during Herbst-MBA treatment (T1-T0) and remained constant (± 0%) thereafter (T2-T1). All linear distances also increased (6-19%) during T1-T0 and showed further increase (1-7%) during T2-T1. For all variables a large inter-individual variation existed. With regard to possible pre-treatment influencing factors, significant associations were observed for pre-treatment age and Wits appraisal of the patients. In younger patients and those with a large Wits appraisal before therapy, more pronounced increases in the PAS area were observed.
