Background: Odontogenic infections, particularly periapical lesions and periodontal bone loss, are known to influence the maxillary sinus mucosa. This study aimed to evaluate the relationship between odontogenic pathologies and mucosal thickening of the maxillary sinus using cone-beam computed tomography (CBCT). Methods: A retrospective analysis was conducted on CBCT scans of 350 patients (700 sinuses) aged 18–75 years. Patients were divided into two groups: those with odontogenic pathologies (study group) and those without (control group). Mucosal thickening (≥3 mm) was assessed, and associations with periapical lesion size, periodontal bone loss severity, and proximity to the sinus floor were analyzed. Results: Mucosal thickening was observed in 52.3% of sinuses in the study group compared to 28.1% in the control group (*p* < 0.001). Severe periodontal bone loss was significantly associated with mucosal thickening (*p* = 0.005), while periapical lesion size and proximity to the sinus floor did not show a significant correlation (*p* = 0.42 and *p* = 0.38, respectively). Periodontal bone loss was found to increase the likelihood of mucosal thickening by 2.5 times compared to periapical lesions alone. Conclusion: Periodontal bone loss is a significant predictor of maxillary sinus mucosal thickening, whereas periapical lesion characteristics may have a lesser influence. CBCT is an effective imaging modality for evaluating sinus changes related to odontogenic pathologies

Cone-Beam Computed Tomography, Maxillary Sinusitis, Mucosal Thickening, Odontogenic Infection, Periodontal Bone Loss.