Functional appliance therapy and upper airway dimensions

Abstract

The aim of this study was to investigate the effects of functional appliance therapy on the upper airway dimensions of Chinese children.

Firstly, associations between craniofacial characteristics and daytime sleepiness (a symptom of sleep disordered breathing [SDB]) were identified in an orthodontic clinic. The extra- and intra-oral craniofacial characteristics, and a self-completed Paediatric Daytime Sleepiness Scale were recorded in a group of 265 Chinese adolescents aged 11-17 years. The data demonstrated that a bilateral Class II molar relationship, increased overjet, hypertrophic tonsils and a relatively large tongue were positively associated with daytime sleepiness. The results implied that Class II malocclusion was a risk factor of SDB.

Secondly, to derive upper airway cephalometric norms for Chinese children, lateral cephalograms of 425 randomly selected 12-year-old Chinese children from 10 schools in Hong Kong were used to establish sex-specific cephalometric norms for the upper airway. Ethnic and age differences were determined by comparing the norms with the results of 108 12-year-old Caucasian children and 74 Chinese adults, respectively.

Thirdly, a retrospective study was conducted to investigate the effects of Herbst appliance therapy on the upper airway of different sexes. Pre- and post-treatment lateral cephalograms from 44 Herbst-treated adolescents were analysed. Longitudinal cephalometric data of 34 untreated adolescents were used as growth data for comparison. The results indicated that Herbst appliance therapy enlarged the upper airway dimensions at two different levels for girls and boys with Class II malocclusion. For girls, it was the retroglossal oropharynx, and for boys, it was the hypopharynx. The boys displayed a significantly greater increase in the anterior and posterior facial heights than the girls, potentially accounting for the level dissimilarities. Furthermore, the Herbst appliance improved the inclination of the soft palate and restricted growth of the nasopharynx in both the boys and girls.

Finally, a randomised controlled trial was carried out to investigate changes in the upper airway dimensions and the sleep-related breathing disordered (SRBD) scale following functional appliance therapy. Twenty-six adolescents with Class II malocclusion were randomised to receive either Herbst or Twin Block appliance therapy. Lateral cephalograms, magnetic resonance imaging, and parents-completed 22-item SRBD scale were obtained at baseline and after functional appliance treatment. The results indicated that increases in upper airway dimensions - width, depth and area - were observed for most parameters and several reached statistical significance by one year of combined growth and functional appliance therapy. In addition, improvements in sleep-related behaviour were evident and significantly correlated with airway dimension changes. The significant difference between the effects of the Herbst and Twin Block appliances was only significant in lower anterior facial height, but not in upper airway structures.

In conclusion, the results demonstrated that Class II malocclusion is associated with the paediatric SDB; and that both Herbst and Twin Block appliance therapies can increase the upper airway dimensions and improve the sleep-related breathing.