[Three-dimensional changes of oropharyngeal airway after orthodontic extraction treatment in skeletal class Ⅰ adolescents]

Objective: To explore the effect of extraction on upper airway in skeletal class Ⅰ adolescents. Methods: According to random number table method, 30 skeletal class Ⅰteenagers who underwent orthodontic straight wire treatment were selected randomly in Department of Orthodontics, School of Stomatology, The Fourth Military Medical University between January 2016 and December 2019. There were 13 males and 17 females, aged (13.7±1.5) years (12.2-15.7 years). In all patients, four first premolars were removed and the upper and lower anterior teeth were retracted under non-maximal anchorage (non-implant anchorage or face bow). The cone-beam CT (CBCT) data before and after orthodontic extraction treatments were studied. The three-dimensional model of the upper airway was reconstructed and segmented, and the relevant indexes of oropharyngeal volume and cross-sectional area were measured. Cephalograms was generated to measure tooth-jaw indexes and hyoid position. The changes of each index before and after orthodontic treatment were compared. The correlation between the changes in the volume or sectional area of the oropharyngeal airway and the changes in the dental and maxillary indexes and the hyoid position was tested. Results: Compared with those before treatment, palatopharyngeal volume, glossopharyngeal volume, oropharyngeal total volume, and minimum transection area increased by 632 (558) mm³, 758 (549) mm³, 1 454 (955) mm³ and 14 (29) mm² respectively, and statistically significant differences were found (P<0.05). The minimum oropharyngeal area was mostly located in the glossopharynx. The cross-sectional area and the maximum anterior-posterior diameter of uvula tip decreased by (4±10) mm² and (0.4±0.8) mm respectively, and the difference was statistically significant (P<0.05). There was no significant difference in the maximum lateral diameter before and after treatment (P>0.05). The ratio of the maximum antero-posterior diameter to the maximum lateral diameter at the uvula tip decreased from 0.589 (0.034) before treatment to 0.535 (0.047) after treatment (P<0.05), indicating that its shape tends to be more elliptic after treatment. In addition, the change of cross-sectional area at the apex of uvula was positively correlated with the changes of mandibular central incisor lip inclination and the distances from the upper and lower central incisor points to the Frankfort plane perpendicular to the sella point (UI-FHp and LI-FHp) (P<0.05). Conclusions: The impact of orthodontic extraction treatment on oropharyngeal airway was generally small in skeletal class Ⅰ adolescents. However, it could change the shape of the airway to some extent. The change of airway cross-sectional area at the uvula tip was positively correlated with the retraction of anterior teeth.