Abstract: PURPOSE: To observe changes of upper airway in three dimensions and tongue position after correction with Twin-block combined with maxillary expansion appliance in children with mandibular retrusion and history of mouth breathing. METHODS: Twenty children with Class Ⅱ malocclusion and mandibular retrusion were selected and treated with Twin-block combined with maxillary expansion appliance. Cone-beam CT(CBCT) data before and after treatment were imported into Mimics 21.0 software to measure the total volume of the upper airway (nasopharyngeal segment + oropharyngeal segment), as well as segmental airway volume of nasopharyngeal, glossopharynx and oropharyngeal space. The cross-sectional area and maximum sagittal diameter at the tip of uvula in glossopharyngeal airway,and maxillary width were measured, too. Anterior-posterior and height changes of tongue position were observed. SPSS 26.0 software package was used to perform paired sample t test and Wilcoxon signed rank test of the data. RESULTS: The total upper airway volume and the airway volume of the nasopharyngeal, oropharyngeal and glossopharyngeal segments increased significantly after correction. The cross-sectional area and maximum sagittal diameter at the tip of uvula in glossopharyngeal segment, and the maxillary width were increased significantly.Tongue position increased and moved forward. All the above data had significant different(P<0.05). CONCLUSIONS: Twin-block combined with maxillary expansion appliance can increase the total volume of the nasopharyngeal segment, oropharyngeal segment, glossopharyngeal segment and upper airway in children with Class Ⅱ malocclusion and mandibular retrusion and expand the anterior-posterior depth of oropharynx airway.In addition,the treatment can increase maxillary width and normalize the tongue position, and contribute to the improvement of airway patency.

Key words: Mandibular retrusion, Twin-block appliance, Tongue position, Upper airway, Maxillary expansion