Objectives <p>The presented study aimed to evaluate the effect of mandibular protrusion with a temporarily applied mandibular advancement device (MAD) on the posterior airway space and to determine a reliable metric constant based on a three-dimensional computed tomography (CT) evaluation.</p> Materials and methods <p>The study population consisted of patients with oral squamous cell carcinoma who were treated at least six months prior to the follow-up CT in supine position. Each patient received an individually adjusted MAD that was temporarily applied with three different protrusion distances (P₀ = 0 mm, P₄ = 4 mm, and P₈ = 8 mm) during follow-up CT. The open-source software Slicer was used to calculate three parameters: minimum cross-sectional area (minCSA), mean cross-sectional area (meanCSA), and volume.</p> Results <p>The results showed a significant increase for all three parameters. The minCSA increased as follows: P₀ = 236.4 mm² ± 192.2; P₄ = 309.2 mm² ± 235.4; and P₈ = 430.6 mm² ± 265.3. The meanCSA increased significantly (<i>p</i> &lt; 0.001) in all protrusion steps and all parts of the pharynx. The volume changed as follows: P₀ = 24.0 cm³ ± 5.0; P₄ = 29.6 cm³ ± 18.1; and P₈ = 33.6 cm³ ± 19.0. The minCSA increased by 24.9 mm² ± 13.0 per millimeter mandibular protrusion.</p> Conclusion&#xa0;and clinical relevance <p>The results are interesting for both conservative and surgical therapy and could find future application in dental, orthodontic, and combined oral surgical therapy. With the results of this study, surgeons and dentists may better predict the change of PAS parameter in order to better prepare for orthognathic surgery. They also could ensure the right protrusion distance for mandibular advancement devices in the case of obstructive sleep apnea.</p>