A maxillary second molar is extracted, and a segment of tissue adherent to the roots is found on histological examination to consist of pseudostratified ciliated columnar epithelium. What structure has been removed?

Correct answer: A. A portion of the maxillary sinus lining (Schneiderian membrane)

• A. CORRECT. Pseudostratified ciliated columnar epithelium — respiratory epithelium — lines the maxillary sinus. The Schneiderian membrane is the mucoperiosteum of the sinus, and because the roots of maxillary molars frequently project into or lie immediately beneath the sinus floor, extraction can strip a portion of it and create an oroantral communication. The finding tells you to assess the size of the defect, warn the patient about the nose-blowing and sneezing precautions, and manage accordingly.
• B. A periapical (radicular) cyst is lined by non-keratinised STRATIFIED SQUAMOUS epithelium derived from the rests of Malassez. Ciliated respiratory epithelium can rarely be found in maxillary radicular cysts, but stratified squamous is the defining feature.
• C. Oral mucosa is stratified squamous epithelium — keratinised on the gingiva and hard palate, non-keratinised elsewhere. It is never ciliated columnar.
• D. A dentigerous cyst is lined by a thin layer of non-keratinised stratified squamous epithelium derived from reduced enamel epithelium, and it surrounds the crown of an unerupted tooth.

Note: Oroantral communication management by size: under 2 mm generally closes spontaneously with sinus precautions; 2 to 6 mm needs a figure-of-eight suture and collagen plug with antibiotics and a decongestant; over 6 mm requires a flap closure — buccal advancement or palatal rotation. Sinus precautions matter: no nose-blowing, sneeze with the mouth open, no straws or smoking for two weeks.