Short Clinical Crown on a Bruxed Maxillary Molar Opposing an Implant
A 48-year-old man is referred for restoration of the maxillary left first molar (FDI 26). The tooth has a large MOD amalgam and a fractured distobuccal cusp; it is asymptomatic, vital, and has no periapical radiolucency. Probing depths are 2–3 mm and mobility is grade I. The clinical crown is short: 3.5 mm buccal and 4 mm palatal from the gingival margin to the occlusal plane. Radiographs show approximately 2 mm of coronal dentin above the cementoenamel junction on the distal aspect and a calcified pulp chamber. The opposing mandibular first molar (36) is an implant-supported monolithic zirconia crown. The patient bruxes at night, has a history of repeated composite fractures, and requests “the strongest crown available.” He declines implant treatment. The gingival biotype is thin, and the distal furcation is 4 mm below the gingival margin.
1. Formulate a restoration plan that provides a predictable ferrule for 26. Compare crown lengthening, orthodontic extrusion, and post-and-core retention using the case numbers, and state your preferred sequence.
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The key problem is not just retention; it is obtaining a 1.5–2 mm circumferential ferrule on a tooth with only about 2 mm of distal coronal dentin and a furcation 4 mm below the gingival margin.
- Crown lengthening would require removing roughly 2–3 mm of bone to move the margin apically and create ferrule. Because the distal furcation is only 4 mm below the gingival margin, this would bring the furcation close to or into the restoration margin, worsening periodontal prognosis and creating a hygiene problem.
- Orthodontic extrusion of 2–3 mm with circumferential fiberotomy can move the fracture line coronally while keeping the furcation at a safer distance. It is my preferred option if the tooth can be extruded without excessive occlusal interference; the extruded tooth will require occlusal adjustment and possibly endodontic treatment if the pulp becomes compromised.
- Post-and-core does not create ferrule and should not be used as a substitute. If a post is ultimately needed, it should have at least 5 mm of apical seal, roughly 1.5 mm diameter, and follow the canal; the calcified chamber makes this less predictable.
Sequence: periodontal assessment and consent, orthodontic extrusion with fiberotomy, stabilization, core build-up, then crown preparation with a 1.5–2 mm ferrule. If extrusion is refused, crown lengthening with furcation risk or extraction should be discussed rather than a heroic post-core.
2. Select the crown material and occlusal scheme for 26, considering the opposing implant crown and bruxism. Justify why not lithium disilicate.
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A monolithic zirconia crown is the most defensible choice. The tooth is a short-crowned molar in a bruxer, and the opposing tooth is an implant-supported zirconia crown. Monolithic zirconia offers high flexural strength and can be made with a minimum thickness of about 1 mm, avoiding a weak veneering ceramic. Lithium disilicate is esthetic but more brittle and less forgiving under heavy parafunction, especially with limited reduction and a short clinical crown; a fracture would likely mean extraction or a less conservative retreatment.
The occlusal scheme should protect the implant. The implant lacks a periodontal ligament, so heavy contacts and off-axis loads are poorly dissipated. I would:
- keep the occlusal table no wider than the implant crown and avoid a broad, flat table;
- establish light, even centric contacts with the implant crown, not heavy shim stock contacts;
- minimize excursive contacts on the implant side and avoid a steep, nonworking interference;
- verify with articulating paper and, if needed, a night guard.
The patient should be warned that the implant crown is the more vulnerable unit and that bruxism control is part of the prosthetic plan.
3. If the patient refuses both orthodontic extrusion and crown lengthening, what is the next best option, and what risks must be explained?
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If the patient refuses both procedures, I would not promise a routine crown. The next best option is either:
- Extraction and replacement with an implant-supported crown or a conventional fixed partial denture, though he has declined implants; or
- A guarded-prognosis core and crown, accepting a short or absent ferrule, with or without a post if retention truly requires it.
The risks of option 2 are substantial and must be documented: crown decementation, root fracture, recurrent caries, periodontal invasion, and possible furcation involvement. A post does not solve the ferrule problem and adds perforation and root fracture risk. I would explain that the long-term prognosis is materially worse than with extrusion, and that if the tooth fails, the site may then require extraction and grafting. The patient should understand that “strongest crown” cannot compensate for inadequate tooth structure.