Upper Airway Changes after Orthodontic Extraction Treatment in Adults: A Preliminary Study using Cone Beam Computed Tomography

<div><p>Objective</p><p>Whether the orthodontic treatment with premolar extraction and maximum anchorage in adults will lead to a narrowed upper airway remains under debated. The study aims to investigate the airway changes after orthodontic extraction treatment in adult patients with Class II and hyperdivergent skeletal malocclusion.</p><p>Materials and Methods</p><p>This retrospective study enrolled 18 adults with Class II and hyperdivergent skeletal malocclusion (5 males and 13 females, 24.1 ± 3.8 years of age, BMI 20.33 ± 1.77 kg/m²). And 18 untreated controls were matched 1:1 with the treated patients for age, sex, BMI, and skeletal pattern. CBCT images before and after treatment were obtained. DOLPHIN 11.7 software was used to reconstruct and measure the airway size, hyoid position, and craniofacial structures. Changes in the airway and craniofacial parameters from pre to post treatment were assessed by Wilcoxon signed rank test. Mann-Whitney U test was used in comparisons of the airway parameters between the treated patients and the untreated controls. Significant level was set at 0.05.</p><p>Results</p><p>The upper and lower incisors retracted 7.87 mm and 6.10 mm based on the measurement of U1-VRL and L1-VRL (P < 0.01), while the positions of the upper and lower molars (U6-VRL, and L6-VRL) remained stable. Volume, height, and cross-sectional area of the airway were not significantly changed after treatment, while the sagittal dimensions of SPP-SPPW, U-MPW, PAS, and V-LPW were significantly decreased (P < 0.05), and the morphology of the cross sections passing through SPP-SPPW, U-MPW, PAS, and V-LPW became anteroposteriorly compressed (P <0.001). No significant differences in the airway volume, height, and cross-sectional area were found between the treated patients and untreated controls.</p><p>Conclusions</p><p>The airway changes after orthodontic treatment with premolar extraction and maximum anchorage in adults are mainly morphological changes with anteroposterior dimension compressed in airway cross sections, rather than a decrease in size.</p></div

Measurements of the sagittal airway dimension, craniofacial structures, and hyoid position.

<p>Measurements of the sagittal airway dimension, craniofacial structures, and hyoid position.</p

Measurements of the sagittal airway dimension in the mid-sagittal plane of CBCT.

<p>Measurements of the sagittal airway dimension in the mid-sagittal plane of CBCT.</p

Landmarks and measurements of condylar-fossa relationship on a sagittal slice.

<p>SF, the most superior aspect of the temporomandibular fossa; SC, the most superior aspect of the condyle; PC, the posterior tangent point of the condyle; AC, the anterior tangent point of the condyle; Line 1, tangent to SF and parallel to the FH plane; Line 2, tangent to SC and parallel to line 1; Line 3, starting from SF and tangent to the most anterior aspect of the condyle; Line 4, starting from SF and tangent to the most posterior aspect of the condyle; PS, posterior joint space; SS, superior joint space; AS, anterior joint space.</p

Measurements of the craniofacial structures and hyoid position in the lateral cephalograms generated by CBCT.

<p>(1) A-VRL; (2) B-VRL; (3) U1-VRL; (4) L1-VRL; (5) H-MP; (6) H-C3; (7) H-Rgn; and (8) H-HRL.</p

Changes in the volume, height, and cross sectional area of the upper airway after orthodontic extraction treatment in adults with Class II and hyperdivergent pattern (n = 18).

<p>* P<0.05</p><p>** P<0.01</p><p>^a Wilcoxon signed rank test</p><p>Changes in the volume, height, and cross sectional area of the upper airway after orthodontic extraction treatment in adults with Class II and hyperdivergent pattern (n = 18).</p

Differences in the volume, height, and cross sectional area of the upper airway between the post-treatment adult patients and the matched untreated controls.

<p>^a Mann-Whitney U test</p><p>Differences in the volume, height, and cross sectional area of the upper airway between the post-treatment adult patients and the matched untreated controls.</p

Descriptions of measurements.

<p>P, posterior joint space; A, anterior joint space; AP, anteroposterior; ML, mediolateral.</p><p>Descriptions of measurements.</p

Measurements of the area and morphology of the cross-sectional planes passing the sagittal linear measurements.

<p>(A) Pink area defines the upper airway, and the yellow line indicates the plane passing the sagittal airway parameter of U-MPW. (B) Coronal view of the cross section passing the U-MPW. The A-P dimeter, lateral dimeter, and area are measured. (C) and (D) showed the typical changes of the morphology from pre to post treatment in the same cross section passing U-MPW.</p

Mandibular measurements and chin deviation.

<p>(A) Ramal height; (B) Mandibular body length; (C) Total mandibular length; (D) Gonial angle; (E) Chin deviation.</p