Previously started root canal treatment with a separated file in a curved mesiobuccal canal
A 42-year-old woman attends for a second opinion on her upper right first molar (16). Another clinician started root canal treatment six weeks ago; the tooth was left with a cotton pellet in the pulp chamber and a temporary filling that has partly washed out. She has no pain now, but three months ago her GP prescribed two courses of amoxicillin for what was called "a gum abscess". Radiographs show a 5 mm periapical radiolucency on the mesial root, a short and thin root filling in the palatal canal, and a separated size 15 K-file in the apical third of the mesiobuccal canal beyond the curvature. The tooth has a large MOD amalgam, and after caries removal the clinician estimates about 3 mm of sound dentine above the alveolar crest on the mesial and distal. She has no relevant medical history, is a regular runner, and says she wants "the tooth sorted out properly" rather than an implant.
1. Formulate the assessment and retreatment plan. What specifically would a small-field CBCT add, and why is her lack of symptoms not reassuring?
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Diagnosis. This is a failed, previously initiated root canal treatment with asymptomatic apical periodontitis. Absence of pain does not mean the infection has resolved: the 5 mm lesion is evidence of persisting intraradicular infection, and the leaking temporary has recontaminated the system.
What CBCT adds
- Whether the mesiobuccal root has one canal or a second (MB2) that has never been treated, which is a common cause of failure.
- The position of the fragment relative to the canal wall and apical foramen: is it within the canal, lying in an isthmus, or perforating the furcation or lateral surface? A perforating fragment changes the plan from orthograde retreatment to surgery or extraction.
- The size and cortical integrity of the periapical lesion, and whether the palatal canal filling is short with untreated apical anatomy.
- Whether there is a vertical root fracture or a strip perforation, either of which would make retreatment futile.
Sequence
- Decide restorability and periodontal status first; retreatment of an unrestorable tooth is wasted effort.
- Informed consent covering file fracture, perforation, loss of the tooth and the alternatives.
- Rubber dam, remove the temporary, cotton pellet and old filling; regain patency with sodium hypochlorite (2.5% to 5.25%) and EDTA, working to a confirmed terminus with an apex locator and a working-length radiograph.
- Treat the palatal canal as untreated apical anatomy and re-prepare it; do not assume the existing filling is acceptable.
- Place a well-sealed provisional restoration at the end of the appointment, whatever else is staged.
2. The separated file cannot be bypassed easily. Discuss the options for managing it and the reasoning that determines which one you choose.
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Options and how to choose between them
- Bypass and clean around the fragment. If any pathway exists beside it, a pre-curved file or a small ultrasonic tip under magnification can create one. If the canal above the fragment can be cleaned, shaped and sealed and the fragment lies in a portion that has been disinfected, this is often acceptable.
- Retrieve it. Ultrasonic or tube-and-glue techniques. The more apical and curved the fragment, the greater the risk of ledging, perforating or pushing it beyond the foramen, which worsens the prognosis rather than improving it.
- Leave it in situ. A fragment confined within the canal, not beyond the apex and not perforating the wall is a risk factor, not automatically a failure. The prognosis depends mainly on whether the canal can be disinfected and sealed; a clean canal and a good coronal seal around an apically confined fragment can still heal, although healing may be slower and should be reviewed radiographically at 1, 2 and 4 years.
- Surgery. Microsurgical apical surgery with root-end resection removes the fragment entirely, so you do not have to win the retrieval attempt orthograde to save the tooth.
- Extraction if the tooth is unrestorable or there is a fracture or an unmanageable perforation.
Decision logic for this tooth. With a 5 mm lesion, a curved apical third and a fragment beyond the curvature, plan a single careful orthograde attempt at bypass and cleaning under magnification with CBCT guidance, with a pre-agreed stopping point. If the attempt fails, the fallback is apical surgery rather than repeated instrumentation. Discuss both stages with her now, including that surgery may be needed and what it costs.
3. Evaluate restorability, including timing of the definitive restoration, and comment on the antibiotic prescribing.
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Restorability. Roughly 3 mm of sound dentine circumferentially above the crest is borderline. The target is a ferrule of 1.5 to 2 mm of circumferential dentine. If the palatal and distal walls are intact, an adhesive core with a full-coverage cusp-protected crown or a bonded onlay can work. If the mesial wall is lost below the crest, the options are:
- surgical crown lengthening, which sacrifices bone on the adjacent teeth and may expose the furcation;
- orthodontic extrusion, which is slow, needs stable anchorage and alters the periodontal relationship of the neighbours;
- extraction and replacement.
Decide this before committing to retreatment; the endodontic result is worthless if the tooth cannot be sealed.
Timing. Never leave a cotton pellet and a leaking temporary. If retreatment is staged, place a properly sealed provisional restoration at the first visit and check it at review. The definitive crown should wait until the tooth is asymptomatic, functionally stable and the endodontic outcome is on track (typically 3 to 6 months), but the coronal seal must be continuous in the interim.
Antibiotics. Two courses of amoxicillin from the GP for a "gum abscess" was inappropriate: the likely problem was a draining sinus or a periodontal abscess needing drainage and debridement, not systemic antibiotics. There is no indication for antibiotics in asymptomatic apical periodontitis or routinely after instrumentation in a healthy patient. Record this, and do not repeat the prescription.