Background: Obstructive sleep apnea is a sleep-related breathing disorder associated with craniofacial morphology and dental arches. The aim of this study was to evaluate the correlation between obstructive sleep apnea and the morphometry of dental arches and upper airways. Methods: Forty patients were enrolled in the study, and the polysomnographic parameters evaluated were the apnea hypopnea index (AHI) and the oxygen desaturation index (ODI). Dental measurements taken from the 3D models included anterior arch widths, posterior arch widths, maxillary and mandibular arch lengths, and palatal surface area. A cone beam computed tomography (CBCT) evaluation was also performed. Results: In patients with moderate OSA, posterior maxillary width was significantly correlated with both minimal airway area (rho = 0.65, p < 0.01) and its transverse diameter (rho = 0.68, p < 0.01). Similarly, in patients with severe OSA, posterior maxillary width showed a significant correlation with total airway volume (rho = 1, p < 0.01), minimal airway area (rho = 1, p < 0.01), and its transverse diameter (rho = 1, p < 0.01). Conclusions: Craniofacial morphology and malocclusion can contribute to obstructive sleep apnea syndrome.