Which sequence correctly describes the steps leading to the formation of a periapical cyst?

• A. Trauma to the tooth with immediate bone remodeling and scar formation
• B. Persistent infection; induction of growth of epithelial cell rests of Malassez; growth causes necrosis at center of mass of growing epithelial cells resulting in cystic cavity
• C. Acute pulpitis resolving spontaneously without cyst formation
• D. Metabolic bone disease causing expansion

Answer: (B)

Periapical cysts arise from a chronic inflammatory process at the tooth apex. When a tooth is nonvital and infected, persistent inflammation in the periodontal ligament stimulates the rests of Malassez—the epithelial cell remnants there—to proliferate. This growth forms a mass of epithelial cells; as it enlarges, the center becomes necrotic due to limited blood supply in the inflamed area. The result is an epithelial-lined cavity filled with inflammatory fluid, i.e., a cyst. This sequence—persistent infection triggering epithelial rest proliferation, followed by central necrosis and cavity formation—best explains how a periapical cyst develops. The other options describe situations that don’t produce this chronic inflammatory cascade and cyst formation, such as acute trauma with scar remodeling, spontaneous resolution of acute pulpitis, or a metabolic bone disease.