Separated rotary instrument in a previously started molar root canal
A 44-year-old woman is referred for completion of root canal treatment in the maxillary right first molar (16). Treatment was started three weeks ago elsewhere and left with a leaking temporary filling. She has no spontaneous pain, no swelling and no sinus tract; the tooth is mildly tender to percussion and probes at 4 mm buccally. The referring dentist's radiograph shows a 4 mm separated rotary instrument in the apical third of the mesiobuccal root, 2 mm beyond the canal curvature, with a 4 × 5 mm periapical radiolucency; the distobuccal and palatal canals are visible but unfilled. The tooth has a large MOD composite, a 2 mm buccal wall of remaining dentine, and visible wear facets on the premolars. She grinds at night and has lost 26 and 46, with opposing teeth drifting. She wants to keep the tooth and is prepared to pay for specialist care, but asks directly: "Is it worth it, or should I just have it out and get an implant?"
1. What factors determine whether this tooth can be managed orthogradely, and what is your recommendation?
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The separated fragment is rarely the reason a tooth fails. The determinants are whether the canal system can be cleaned and sealed to the apex and whether a durable coronal seal can be re-established.
Favourable factors here: the tooth is restorable with a 2 mm buccal wall; the patient is motivated and financially able; two of the three canals are untouched and can be instrumented conventionally; and the fragment is a known, visible object rather than an unknown perforation.
Unfavourable factors: the fragment sits in the apical third beyond a curve, where dentine is thin, so troughing to retrieve it risks a strip perforation or a root fracture; the root is curved; there is already a 4 × 5 mm periapical lesion; and the temporary seal has leaked, so the canal is contaminated regardless of the fragment.
Plan: obtain a small-field CBCT to see whether the fragment lies against a wall or blocks the lumen, and whether the canal can be bypassed. Under the microscope, attempt to bypass with a precurved size 08 or 10 stainless steel file with copious sodium hypochlorite. If the file passes, instrument, disinfect and shape the canal, treating the fragment as an inert obstruction embedded in the filling mass. If it cannot be bypassed, the realistic options are referral for ultrasonic retrieval, apical surgery with a retrograde filling, or extraction.
Recommendation: attempt orthograde management; do not attempt retrieval through the curve yourself, and do not try to push the fragment through the apex. Give a guarded prognosis and explain that success depends on infection control and the final seal, not on the fragment alone.
2. If you decide to bypass and complete the case orthogradely, describe your technique and the specific risks you would discuss with her.
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Technique. Reassess under rubber dam isolation with the operating microscope. Establish a glide path coronal to the fragment with lubricant and copious irrigation. Precurve a fine stainless steel file to the canal's curvature and negotiate gently past the fragment with a watch-winding motion, confirming patency and position with a radiograph. Once bypassed, create a reproducible space with successively larger hand files, then shape conservatively with a controlled-tip rotary system, keeping the coronal third wider than the apical portion so the fragment is not driven apically. Irrigate with sodium hypochlorite, activate the irrigant ultrasonically, use EDTA and a final chlorhexidine or alcohol rinse as per protocol, then obtund with a warm vertical or carrier-based technique so the fragment is incorporated into the mass. Place a well-sealed temporary or an immediate coronal seal.
Risks to discuss. Bypassing may fail, or the fragment may be pushed apically, blocking the canal and requiring referral or apical surgery. Manipulation in the apical third may cause a strip perforation, a ledge or a vertical root fracture, which would make the tooth unrestorable. The tooth may remain symptomatic and the periapical lesion may not heal despite technically adequate treatment, and a previously treated tooth always carries a lower success rate than a first treatment. There is also the cost of a specialist referral if the attempt fails. Document a clear stopping point in advance so that the attempt does not become open-ended.
3. Assuming the endodontic phase succeeds, how will you restore the tooth and what determines its long-term survival?
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Because the tooth has lost both proximal marginal ridges, a large MOD composite and a heavy wear pattern, a direct filling will not protect the remaining cusps. The restoration should provide cuspal coverage: an indirect onlay or a full-coverage crown in a bonded material, such as lithium disilicate where there is adequate enamel and space, or monolithic zirconia where wear resistance is the priority. Preserve as much sound tissue as possible and ensure a 2 mm ferrule of sound axial dentine, because ferrule is one of the strongest predictors of survival in a heavily restored, endodontically treated tooth. Avoid a post unless the tooth cannot be retained otherwise; posts do not strengthen roots and add a fracture risk.
Sequence: finish endodontics, place a sealed interim restoration immediately, then plan the definitive restoration with a diagnostic wax-up and, given the wear and drifting, an assessment of the occlusion. Timing of the final restoration depends on the coronal tissue and the gingival margin, but a well-sealed provisional can serve for several months.
Long-term survival depends on the quality of the coronal seal, the absence of symptoms and a healing periapical lesion at six and 12 months, the ferrule and the residual wall thickness, and control of the bruxism. Provide a hard occlusal splint and discuss that occlusal overload, not the file fragment, is the most likely cause of late failure. Review clinically and radiographically at six months and one year, then annually.