A patient has a fixed bridge from the upper second premolar to the second molar. The second premolar abutment was previously root canal treated and now has a 9 mm vertical bone defect on the mesial. The root has adequate length remaining. What is the best treatment for this abutment tooth?

A 9 mm vertical (angular) bone defect on the mesial of an endodontically treated bridge abutment carries a poor prognosis. While vertical bone defects can sometimes be treated with regenerative periodontal therapy (GTR, bone grafting), a 9 mm defect with the tooth under occlusal load as a bridge abutment makes: (1) the tooth structure severely compromised; (2) the bone support critically reduced; (3) re-treating the RCT unhelpful as it does not address the bone defect. Extraction of the compromised abutment and replacement with an implant or redesigned bridge is the most definitive treatment. Re-treating the root canal alone would fail to address the primary problem — the 9 mm vertical bone loss that has destroyed the structural foundation of the tooth.