Failed Root Filling With a Separated File: Retain, Retreat or Replace
A 45-year-old man is referred about his lower left first molar (36). It had root canal treatment nine years ago and now aches on chewing. There is a buccal sinus tract adjacent to the mesial root; the tooth is not tender to percussion, but gutta-percha tracing follows the tract to the mesial root. The crown margin is supragingival and intact, and there is about 4 mm of sound tooth structure above the bone on the mesial and distal. The tooth is not mobile. He is a non-smoker with well-controlled type 2 diabetes (HbA1c 7.2%).
Radiographs and a small-field CBCT show a cast post and core in the distal canal, a 6 × 8 mm periapical radiolucency on the mesial root, a middle mesial canal calcified in its coronal third, and a separated 4 mm rotary file in the apical third of the mesial root beyond the curvature. The distal root filling is 2 mm short and the isthmus is unfilled. Bone height at the site is 13 mm, with the sinus floor 4 mm above the apices.
He asks you to extract the tooth and "put in an implant, because implants always work".
1. Give your diagnosis and assess the prognosis of each option - non-surgical retreatment, apical surgery, and extraction with an implant - for this tooth.
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Diagnosis: post-treatment apical periodontitis on 36 with a draining sinus tract. The cause is a missed middle mesial canal, an unfilled isthmus and a short distal fill - failure of cleaning and of the coronal seal, not a new disease. The cast post is a complicating factor, not the cause.
Non-surgical retreatment. The obstacle is the separated file beyond the curvature and the calcified middle mesial canal. If the file can be bypassed or removed and the mesial system cleaned, healing rates for retreatment of post-treatment disease are in the order of 70–85% over 4–6 years. Removing a cast post carries a risk of root fracture or perforation, and the 4 mm ferrule is favourable but not unlimited. Prognosis fair to good if negotiable, guarded if not.
Apical surgery. Mesial root resection and retrofill; the sinus floor 4 mm above the apex is manageable. Surgery does not clean the coronal space or the isthmus, so it works best when the coronal restoration is sealed - which it is. Prognosis fair to good. Leaving a file in situ is acceptable if the canal has been adequately cleaned around it.
Extraction and implant. Predictable, with roughly 95% ten-year survival for single implants, but survival is not the same as trouble-free: peri-implant mucositis and peri-implantitis are common, and the site is only 4 mm from the sinus. Extraction is irreversible and the tooth is strategically valuable with a sound crown and good ferrule.
Order of preference: retreatment or referral for it first; surgery if retreatment fails or is impossible; extraction and implant last.
2. How would you manage the separated file and the calcified middle mesial canal, and what are your limits?
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Under rubber dam and the microscope, gain straight-line access to the mesial orifices through the crown and core. The distal cast post does not need to come out to access the mesial canals unless it obstructs the access - avoid removing it if you can.
For the file: trough around it with a fine ultrasonic tip under magnification, using EDTA gel, and try to bypass it with a pre-curved 8 or 10 file. If the file can be bypassed, clean and shape alongside it, flood with sodium hypochlorite and activate passively with ultrasound. If it cannot be bypassed, attempt removal with ultrasonics or a file-braiding technique only if you can see the coronal few millimetres of it - blind retrieval in the apical third is how roots get perforated.
For the middle mesial canal: trough along the developmental groove between the mesiobuccal and mesiolingual orifices with ultrasound and EDTA, with the microscope, looking for a catch. Isthmus cleaning matters as much as finding the canal.
Limits: transportation, strip perforation of the danger zone, a shorter file segment left behind, or root fracture are the real risks. If after one genuine attempt I cannot bypass the file or negotiate the middle mesial canal, I stop, temporise, and refer to an endodontist - and I tell the patient now, not after the fact, that apical surgery leaving the file in place is a reasonable alternative if the rest of the system is cleaned.
3. How would you structure the consent conversation with a patient who believes implants always work?
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Start by taking the belief seriously rather than correcting it dismissively. Acknowledge that implants are excellent, then be precise: ten-year survival is around 95%, but success is more than staying in the mouth, and a meaningful proportion of patients develop peri-implant mucositis or peri-implantitis. An implant also will not fix the reason this tooth failed - canal anatomy, bacterial access and coronal leakage - and he needs to know that before deciding.
Then explain what is in his favour: the crown margin is supragingival, there is 4 mm of ferrule, the tooth is not mobile and it is a first molar with two roots. Keeping it preserves bone and costs considerably less than extraction, grafting, implant placement and a crown.
Present all options side by side - retreatment (or referral), apical surgery, extraction with implant, and extraction with no replacement - with realistic timeframes, costs in New Zealand private practice and public hospital waiting times, and the specific risks of each. Explain that extraction is irreversible and that if he chooses it, planning for the site must start straight away because the ridge will change.
Ask what is driving the request: fear of repeated treatment, time off work, cost, or a friend's good experience. Offer a written plan and a second opinion. Document the options discussed and his decision - consent is a process, not a signature on a form.