Persistent apical periodontitis with a separated file and a missed MB2
A 42-year-old woman attends with a 3-month history of discomfort on biting in the upper left first molar. The tooth had root canal treatment 6 years ago and carries a full-coverage zirconia crown with no detectable marginal defect. Probing depths are 3 mm or less on all aspects, with no mobility and no swelling. A periapical radiograph shows a 4 x 5 mm periapical radiolucency on the mesiobuccal root, gutta-percha ending 2 mm short of the radiographic apex, and a separated size 15 K-file lodged in the apical third of the same canal. Cone-beam CT confirms four canals, an untreated MB2 with a 3 mm apical stop, intact buccal and palatal cortical plates, and no root fracture; there is no post and little residual filling material. She is medically well, takes no medication and wants to keep the tooth if it can be done predictably.
1. How do you decide between nonsurgical retreatment and apical microsurgery for this tooth?
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The decision is not about which technique is 'better' in general but about which failure causes can be reached from where.
Arguments for nonsurgical retreatment first: the untreated MB2 alone can explain persistent apical periodontitis, and no surgical approach treats the coronal two-thirds of a missed canal. The obturation is 2 mm short, another intracanal cause. There is no post and no marginal defect, so access through the crown is feasible and the restoration can be replaced.
Arguments for surgery first: the separated file in the apical third limits how far the mesiobuccal canal can be cleaned; if it cannot be bypassed or removed, the apical 3 mm stays untreated. Surgery also suits this case because the cortical plates are intact, the lesion is small, and the tooth has a good coronal seal to preserve.
The practical sequence: attempt retreatment, because the MB2 must be managed regardless, and try to bypass the fragment. If the fragment can be bypassed and the canals cleaned to length, observe healing for 6-12 months before considering surgery. If it cannot be bypassed and symptoms or the lesion persist, proceed to microsurgical endodontics with root-end preparation and a bioceramic fill. A combined single-visit approach is reasonable if the patient prefers one anaesthetic. Choosing surgery alone leaves the MB2 untreated and risks failure of the surgical site.
2. Describe how you would manage the separated fragment and the untreated MB2 in the same visit.
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Planning: use the CBCT to know the fragment's depth, its relationship to the canal wall, and the curvature before touching anything. Blind retrieval attempts in a curved apical third risk perforation and push the fragment deeper.
Access and MB2: remove the crown or core as needed for a straight-line path, then locate MB2 in the groove between MB1 and MB2, usually 1-2 mm palatal to MB1. Negotiate with a precurved size 8-10 file and glide-path irrigation; the canal often joins MB1, so do not force a separate portal of exit. Confirm working length with an electronic apex locator and a radiograph, and prepare conservatively in the danger zone.
The fragment: attempt to bypass with a fine precurved file and copious NaOCl, then either remove it with an ultrasonic tip under magnification or, if it has been bypassed and the canal cleaned to length, incorporate it and try removal at the end. Do not use ultrasonic energy blindly against the fragment.
If bypass fails: clean and shape to the level of the fragment, irrigate with ultrasonic activation, medicate, and plan surgery rather than drilling around it. Assess the tooth afterwards for remaining wall thickness and restorability before committing to a new crown.
3. What findings would make you abandon the tooth for an implant instead?
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Restorability, not the endodontic diagnosis, drives this decision. I would look for:
- A crack or fracture line extending to the canal floor or below the bone crest; a crown that cannot be removed without destroying the tooth also shifts the balance.
- Insufficient ferrule - less than about 1.5 mm of circumferential sound tooth structure after crown removal.
- A non-bypassable fragment in a very narrow, curved MB root combined with a lesion that has already failed one retreatment, where both retreatment and surgery would be needed and the long-term prognosis falls substantially.
- Periodontal compromise - a deep isolated pocket, furcation involvement, or mobility that would persist after endodontics.
- Root resorption, a perforation, or an unfavourable root-to-crown ratio.
Against these I would weigh that a natural tooth with an intact periodontium and a restorable coronal structure generally outperforms an implant in a patient with no risk factors, and that implants carry their own risks (peri-implantitis, nerve proximity in the posterior mandible, sinus proximity here). The honest answer to give the patient: if the tooth can be retained with a predictable ferrule and no crack, retain it; if the crack or the fragment makes the apical third unreachable and unrestorable, extraction with socket preservation and later implant planning is the more predictable path.