Pain on chewing in a previously root-treated mandibular first molar with an untreated canal and a separated file
Ms K, 38, attends with a 3-week history of pain on chewing in the lower right quadrant. Tooth 46 was root-canal treated 8 years ago and carries a metal-ceramic crown whose margins are clinically intact. Her medical history is unremarkable; she takes no medication and reports no allergies. There is no swelling, no sinus tract and no mobility. Probing depths are 2-3 mm all round and the tooth is tender to percussion. A periapical radiograph and a small-volume CBCT show a 6 x 5 mm periapical radiolucency on the mesial root, a mesial canal that has never been instrumented, a 4 mm apical plug of gutta-percha in the distal canal, and a separated size 15 stainless-steel file in the apical third of the distal canal. There is no sign of perforation and no crack line. The patient wants to keep the tooth and asks directly what her chances are and how long the treatment will take.
1. Weigh the prognostic factors that determine whether tooth 46 should be retreated or extracted and replaced, and state the recommendation you would give Ms K, with your reasoning.
Read the worked answer
Judge the tooth, not just the radiograph. Work through the four axes that drive prognosis:
- Restorability and structural integrity. Margins are intact, there is no fracture line and no post. The tooth is restorable and can be accessed through the crown, so the biological and financial cost of retreatment is contained.
- Periodontal support. Pockets of 2-3 mm, no mobility, no furcation involvement - the attachment apparatus is not the problem and does not limit prognosis.
- Endodontic status. The most likely cause of the apical lesion is the mesial canal that was never instrumented: an untreated infected canal is a strongly favourable target because removing the cause is straightforward. The separated file is a technical obstacle, not by itself a reason for extraction - fragments in a cleaned canal that is not blocked are usually well tolerated.
- Strategic value and alternatives. A first molar is strategically valuable. Single-molar implants have high survival but carry their own risks (peri-implantitis, biologic width problems, cost) and require adequate bone, which has not been assessed.
Recommendation. Offer orthograde retreatment, with an honest hedge: retreatment of a tooth with apical periodontitis has a good but not guaranteed success rate - typically in the region of 80-85% healing with modern technique - and the separated file may prevent negotiation of the distal canal. Explain that the alternative (extraction plus implant) is a reasonable fallback if retreatment fails, and that referral to an endodontist is appropriate because of the fragment. Do not quote a single figure as a promise; give a range and state what would change the plan (inability to bypass the file, a crack found during access, or a perforation).
2. Describe your access and shaping strategy, explaining how you would manage the existing crown and the separated file.
Read the worked answer
Access. Do not remove the crown if the margins are sound and the access can be made through it: removing it destroys ferrule, risks the remaining tooth structure and adds cost. Access through the occlusal ceramic/metal into the chamber, remove the coronal obturation material and any core, and check the chamber outline with magnification and the CBCT.
Locate everything. Mandibular first molars have a mesial and a distal canal predictably, but the CBCT already tells you the mesial canal has never been treated. Use the operating microscope, look for two mesial orifices, and confirm every canal with an electronic apex locator plus a working-length radiograph.
Handling the file.
- Establish patency coronal to the fragment and create a glide path with a precurved size 08/10 hand file and lubricant (EDTA gel).
- Attempt to bypass the fragment so that the canal can be cleaned to the working length alongside it. If bypassed, instrument and irrigate; the fragment can be left in place at the end.
- Ultrasonic retrieval only where the fragment is visible, the canal is straight and the tip can be positioned under direct vision. Excessive apical dentine removal risks perforation and converts a manageable case into a compromised one.
- If the canal cannot be bypassed but can be irrigated to a reasonable length, treat and monitor; if the canal is completely blocked and infected, refer.
Distal canal. Confirm the position of the existing apical plug before aggressive removal. If it is at working length and well adapted, negotiate gently rather than drilling it out; if the coronal canal is contaminated, the most important step is disinfection of the space you control, not removal of sound apical filling.
3. Set out your irrigation, medication and review plan, and state the criteria you will use at review to call the retreatment a success.
Read the worked answer
Irrigation. Sodium hypochlorite, ideally 3% (5.25% is acceptable with careful confinement), delivered with a side-vented needle kept 1-2 mm short of the working length, aspirating frequently and never wedging. Aim for generous volume per canal rather than a nominal rinse, recapitulating to keep the pulp space clear. Finish with 17% EDTA for about a minute to remove the smear layer, with ultrasonic activation if available. Never mix hypochlorite and chlorhexidine - a precipitate forms.
Medication. If the canals can be cleaned, dried and filled in one visit and there is no exudate, complete it. If time, bleeding or the blocked canal prevent this, place calcium hydroxide for 1-4 weeks. Do not prescribe systemic antibiotics for an asymptomatic apical periodontitis with no swelling; they add nothing and create resistance.
Restoration. Arrange the definitive coronal seal promptly - a cuspal-coverage restoration or an onlay rather than a simple intracoronal filling in a heavily treated molar - because coronal leakage is a common cause of failure.
Review criteria.
- No spontaneous or percussion pain, no sinus tract, normal function and no swelling.
- Radiographic evidence of healing: reduction in lesion size with reforming lamina dura, recognising that complete healing can take 1-4 years and that an unchanged lesion at 6 months in an asymptomatic tooth is not automatically a failure.
- If equivocal at 12 months, CBCT rather than repeated periapicals.
Tell the patient the timeline and the triggers for returning: pain, swelling, or a fracture of the tooth.