Effects of Mandibular Positional Changes on Airway Dimensions

Objective: The aim of this retrospective study was to investigate the effects of mandibular positional changes on the airway dimensions in a group of orthodontic patients. 

Methods: Following reliability studies, lateral cephalometric radiographs of 118 Caucasian subjects, aged 8-15 years, were selected from the postgraduate orthodontic clinic archives and traced manually for different airway parameters. Each subject had two cephalograms taken on the same day. The cephalograms were classified into 2 groups according to the position of the mandible.  Group 1 consisted of cephalograms taken with the mouth closed (teeth in centric occlusion) and group 2 consisted of cephalograms taken with the mouth open (maximum opening position). Intraclass correlations (ICC) were performed on duplicate measures of 10 cephalograms. Airway parameters were compared between the two groups using nonparametric Wilcoxon signed rank test. Statistical significance was set at P < 0.05.

Results: ICC values were >0.90 for all measures. Significant differences between the mandibular positions were found in most of the airway dimensions. The sagittal depth of the airway at the nasopharynx and oropharynx levels (PNS-ad1, PNS-ad2, PNS-ppw1, PNS-ppw2) and the vertical length of the airway (PNS-E) were significantly increased in group 2. The sagittal depth of the pharyngeal lumen at the level of the hypopharynx (apw4-ppw4) and the soft tissue thickness behind the posterior pharyngeal wall (Ba-ad1) decreased significantly when patients widely opened their mouth.

Conclusion: Increasing the vertical dimension by opening the lower jaw increases the upper airway dimensions in width and length and conversely decreases the lower airway width and the soft tissue thickness of the airway.