Inclusion Criteria:  CBCT scans for patients aged from 20 to 70 years. CBCT scans for patients with at least first and second maxillary premolars and first and secon maxillary molars present on one side (fully erupted teeth and fully formed apices). CBCT scans taken for pre-evaluation of endodontic treatment, implant placement, impacted teeth removal, obstructive sleep apnea treatment, pre-orthodontic or pre-prosthetic evaluation. Good quality CBCT scans.  Exclusion Criteria:  CBCT scans for patients with no maxillary posterior teeth. CBCT scans for patients with history of maxillary sinus operation (including sinus floor elevation). CBCT scans for patients with sign or history of non-odontogenic sinusitis, including air-fluid level, thickening of all the sinus walls and maxillary sinus polyps. CBCT scans for patients with syndromes, congenital or developmental anomalies. CBCT scans for patients with bone disease. CBCT scans for patients with traumatic injuries to the maxillofacial region. Low quality CBCT scans (any artifact).