Which type of traumatic dental injury to a permanent tooth carries the worst prognosis?

Intrusion — the apical displacement of a tooth into the alveolar bone — carries the worst prognosis among traumatic dental injuries. During intrusion, the periodontal ligament fibers are crushed and torn, the blood supply to the pulp is severed, and the alveolar bone may be fractured or compacted. These combined injuries result in very high rates of pulpal necrosis, inflammatory root resorption, and ankylosis. The prognosis is worst for teeth with closed apices (mature roots), where the neurovascular supply cannot regenerate. Treatment options include spontaneous re-eruption monitoring (for immature teeth), orthodontic repositioning, or surgical repositioning. Extrusion and luxation injuries have better prognoses with prompt repositioning.