Evaluating the Maxillary Sinus on CBCT: A Clinical Guide

The Maxillary Sinus in Dental CBCT

The maxillary sinus is one of the most important structures to evaluate on dental CBCT scans. It's directly relevant to implant planning in the posterior maxilla, endodontic assessment of upper premolars and molars, and detection of incidental sinus pathology. CBCT sinus evaluation provides information that panoramic radiographs simply cannot deliver.

Normal Sinus Anatomy on CBCT

On CBCT, a healthy maxillary sinus appears as a well-defined, air-filled cavity (dark/black) bordered by cortical bone (white line). Key landmarks to identify:

• Sinus floor: The inferior boundary, which undulates between tooth roots in the posterior maxilla
• Schneiderian membrane: The mucosal lining of the sinus, normally 1-2mm thick (often not visible when healthy)
• Sinus septa: Bony ridges that project from the sinus floor or walls, dividing the sinus into compartments
• Ostium: The drainage opening into the middle meatus, visible on coronal views

Common Sinus Findings on CBCT

Mucosal Thickening

The most frequent finding. A thickened Schneiderian membrane appears as a soft-tissue density (gray) lining the sinus floor or walls. Mild thickening (2-5mm) is common and often incidental. Significant thickening may indicate sinusitis, allergic rhinitis, or odontogenic infection from an adjacent tooth.

Mucous Retention Cyst

Dome-shaped, well-defined, soft-tissue density masses arising from the sinus floor. They're benign and usually asymptomatic, found incidentally in 10-15% of CBCT scans. They rarely require treatment unless they occupy a significant portion of the sinus.

Sinus Septa

Present in approximately 30-50% of patients. Septa are critically important for sinus lift surgery planning — they can complicate membrane elevation and may require modification of the surgical window location. CBCT coronal views show their exact position, height, and orientation.

Odontogenic Sinusitis

Infection from a dental source (periapical pathology, failed root canal, periodontal disease) can spread to the sinus. CBCT shows the communication between the tooth apex and the sinus, along with localized mucosal thickening or opacification directly adjacent to the offending tooth.

Sinus Evaluation for Implant Planning

When planning implants in the posterior maxilla, use CBCT to assess:

• Available bone height: The distance from the alveolar crest to the sinus floor
• Bone quality: Density of available bone (the posterior maxilla often has thin cortical plates and low-density trabecular bone)
• Sinus floor morphology: Flat vs. scalloped floor affects sinus lift approach
• Presence of septa: Plan the lateral window position to avoid septa, or prepare to navigate around them
• Membrane thickness: Very thin membranes have higher perforation risk during sinus augmentation

Documenting Sinus Findings

When you identify sinus pathology on CBCT, document the finding, its location, and your recommendation. Online CBCT viewers with annotation and reporting features allow you to pin comments to specific slices, making it easy to share findings with referring dentists or ENT specialists.