External root resorption is caused by what mechanism?

• A. Inflammatory mediators induce osteoclastic transformation of non-differentiated connective tissue cells
• B. Bacterial invasion of dentin
• C. Occlusal overload
• D. Autoimmune processes

Answer: (A)

External root resorption is driven by inflammatory signals that push undifferentiated connective tissue cells in the periodontal ligament to become osteoclast-like cells (odontoclasts). Once these clastic cells form, they attack and resorb the cementum and underlying dentin on the root surface. Inflammatory mediators (and the RANKL/M-CSF pathway) guide this differentiation, so the resorption follows from inflammation-triggered formation of resorbing cells rather than direct bacterial invasion of dentin, simple occlusal overload, or autoimmune processes.