Told to extract —
saved with microscope retreatment.

The presentation

The patient arrived with a three-year history of intermittent flare-ups in the same tooth — a lower-left first molar that had undergone root canal treatment elsewhere. Pain episodes would settle with antibiotics, only to return six to eight weeks later. A second clinic had recommended extraction and implant placement.

On examination: tenderness on percussion, a sinus tract tracing to the distal root, and a well-defined periapical radiolucency visible on the pre-existing radiograph. The tooth was restorable — the crown margins were intact, the remaining structure was sound, and the patient had no medical contraindication to retreatment.

The diagnosis

Under the dental operating microscope, review of the previous obturation revealed the most common reason these cases fail: an untreated fourth canal. The mesiobuccal root of a lower first molar reliably contains two canals (MB1 and MB2) in 60–70% of cases. The original treatment had addressed three canals; a fourth was present and had been the source of chronic low-grade infection.

The conversation with the patient was simple. The tooth did not need to be extracted. It needed to be finished.

The treatment

Retreatment was completed across two visits.

Visit one (90 minutes). Rubber dam isolation. Removal of the existing coronal restoration and gutta-percha from the three previously treated canals. Location of the missed MB2 canal under microscope using controlled troughing with ultrasonics. Working length determination with apex locator and confirmatory radiograph. Instrumentation of all four canals with modern rotary files, copious sodium hypochlorite irrigation, and calcium hydroxide interim dressing.

Visit two (75 minutes). Reassessment — the sinus tract had resolved, the tooth was asymptomatic. Canals dried and obturated three-dimensionally using warm vertical compaction. A fibre post was placed in the distal canal for coronal reinforcement. Same-day core buildup, and an impression for a full-ceramic crown to be delivered ten days later.

The outcome

At the six-month review, the radiolucency had reduced significantly. At twelve months, it was no longer detectable. The patient reports zero symptoms since the day of obturation. The tooth is functioning normally, the crown is stable, and what was on an extraction list is now part of the patient's dentition for the foreseeable future.

This is the case the brand was built on: not because it was unusual, but because it wasn't. Failed root canals fail for a reason. Under magnification, that reason is usually findable — and fixable.

Treatment

Endodontic retreatment + fibre post + zirconia crown

Duration

2 visits · 10-day crown lead time

6-month follow-up

Lesion resolved · tooth asymptomatic

12-month review

Radiolucency no longer detectable