Remaining root of tooth #12 is biopsied. Histopathology shows pseudostratified epithelium with inflammatory cells. From which structure is this epithelium derived?

Correct answer: D. Epithelial rests of Malassez (Hertwig's epithelial root sheath) — Apical (radicular) cyst

• A. Incorrect. Oral epithelium is stratified squamous and not the source of periapical cyst lining.
• B. Incorrect. Junctional epithelium forms the epithelial attachment at the base of the sulcus — not involved in periapical cyst formation.
• C. Incorrect. Reduced enamel epithelium lines dentigerous cysts, not apical/radicular cysts.
• D. Correct. A radicular (apical) cyst is lined by non-keratinized stratified squamous epithelium derived from the epithelial rests of Malassez (remnants of Hertwig's epithelial root sheath). Inflammatory cells in the wall reflect chronic periapical inflammation.