Purpose: In this study we investigated 3D changes in craniofacial architecture, to test the hypothesis that the upper airway can be non-surgically improved in adults using biomimetic oral appliance therapy (BOAT). Methods:After obtaining informed consent, we undertook 3D cone-beam computerized tomographic (CBCT) scans of 17 consecutive Korean adults who had been diagnosed with midfacial hypoplasia prior to BOAT. Post-treatment: follow-up 3D CBCT scans were undertaken with no device in the patient's mouth; 3D craniofacial reconstruction was undertaken, including the upper airway (nasal cavity to retroglossal region), and pre-and post-treatment parameters were calculated; and the findings were subjected to bivariate and multivariate tests. Results:The mean treatment time with BOAT was 16.6 months. Comparing mean pre-and post-treatment parameters: transpalatal bone width increased (p < 0.001); nasal airway volume increased (p < 0.01); inferior nasal concha distance from nasal septum remained relatively unchanged; area of posterior nasal apertures and soft palate length remained unchanged; antero-posterior retropalatal airway distance increased (p < 0.01); medio-lateral retropalatal distance remained unchanged (p > 0.05); retropalatal area increased (p < 0.01); sagittal retroglossal airway distance increased (p < 0.01); medio-lateral retroglossal width remained unchanged, while the retroglossal area increased (p < 0.05) with no device in the patient's mouth. For the upper airway, the multivariate tests also showed a significant treatment effect (p < 0.05). Conclusion:These findings corroborate the notion that craniofacial architecture and upper airway morphology can be non-surgically enhanced in non-growing adults.