Tooth #18 has DO decay, vestibular edema, and active purulent drainage. Radiolucency at distal root biopsied as radicular cyst. From what tissue are the cells lining this cyst derived?

Correct answer: D. Epithelial rests of Malassez

• A. Striae of Retzius are incremental growth lines visible in enamel histology.
• B. Tomes processes are ameloblast extensions involved in enamel matrix secretion.
• C. Stratum intermedium is a layer of the enamel organ involved in enamel formation.
• D. Correct. Radicular (periapical) cysts are lined by epithelium derived from the Epithelial Rests of Malassez (ERM) — remnants of Hertwig's Epithelial Root Sheath in the PDL, activated by pulpal infection.

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