A radiograph shows a tooth root with excessive, bulbous radiopaque enlargement and a thin radiolucent line (representing the periodontal ligament space) around the enlarged root. What is the most likely diagnosis?

Hypercementosis is excessive deposition of cementum along the tooth root, producing a bulbous, enlarged radiopaque root outline, typically with a normal-appearing, thin radiolucent periodontal ligament space surrounding the enlarged structure — distinguishing it from ankylosis, where the PDL space is lost/obliterated.