Cone-beam computed tomography evaluation of short- and long-term airway changes in patients with skeletal Class Ⅲ malocclusion treated by orthodontic therapy and bimaxillary surgery with or without mandibular setback surgery

Objective: To evaluate the short-term and long-term effects of pharyngeal airway in skeletal Class Ⅲ malocclusion patients who underwent bimaxillary surgery or isolated mandibular setback-orthodontic treatment.

Methods: The sample included 54 patients (28 males, 26 females) who were diagnosed with skeletal Class Ⅲ malocclusion. Patents in group A (n=28) underwent mandibular setback surgery and orthodontic treatment. Cone-beam CT (CBCT) was taken at one week before treatment (T0), 6 months (T1) and 3 years after surgery (T2).Patents in group B(n=26) underwent Le Fort I procedures with bilateral split ramus osteotomies-orthodontic treatment; The raw data reconstructed into 3D model. Sagittal and transversal measurements, cross sectional areas, partial and total volumes were evaluated. The data were statistically analyzed using SPSS 17.0 software package to determine the changes in each group.

Results: Six months after surgery, the sagittal diameters and cross sectional areas of each section in group A were significantly decreased (P<0.05). Oropharyngeal volume, hypopharyngeal volume and total volume were significantly narrowed (P<0.01). Three years after surgery, only sagittal and cross sectional areas in the first cervical vertebra plane were returned to the original levels (T2-T0：P>0.05, T2-T1: P<0.05). In group B, the sagittal diameters and cross sectional areas of each section (except CV1 plane) were significantly decreased(P<0.05) 3 years after surgery, but most measurements returned to the original levels.

Conclusions: Pharyngeal airway space decreased after combined therapy in the short term; however, relapse occurred and not to its original position in the long term.