Subgingival fracture on a root-filled premolar
48-year-old woman presents with tooth 14 (maxillary first premolar). It had root canal treatment 6 years ago and now has a 2 mm buccal cusp fracture that extends 1 mm subgingivally. The remaining buccal wall is 3 mm above the fracture line; the lingual wall is 1.5 mm above the gingival margin; the palatal cusp is intact. Radiograph: 7 mm of dense gutta-percha, no periapical radiolucency, bone level at the CEJ, crown-to-root ratio 1:1. She grinds at night. The opposing tooth 44 has a large amalgam and a 2 mm cusp. She wants "the least invasive option that lasts".
1. Does this tooth need a post? Justify your answer.
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Probably not.
- A post does not strengthen a root; it retains a core when insufficient coronal tooth remains. Here there is 3 mm of buccal wall and 1.5 mm of lingual wall above the margin, which is enough to retain a core and, critically, enough to develop a ferrule.
- Ferrule of roughly 1.5–2 mm of circumferential dentine, 360°, is the strongest predictor of success for a restored root-filled tooth. A post adds root perforation risk, removal difficulty and root fracture risk without improving ferrule.
- Lingually, 1.5 mm is at the lower limit; the buccal wall after margin exposure (see next task) should provide the rest.
Decision rule: if a 1.5–2 mm ferrule can be created after the margin is brought supragingivally, place a bonded core and no post. If, after exposure, only a thin shell remains, reconsider the tooth's restorability rather than reflexively placing a post.
2. The buccal margin is 1 mm subgingival. How do you manage it - crown lengthening or orthodontic extrusion - and what are the trade-offs?
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The problem: a margin 1 mm subgingival with a 1:1 crown-to-root ratio leaves little room for a biological width and a ferrule.
Crown lengthening
- Requires removing bone to re-establish biologic width plus ferrule - roughly 3 mm of bone in this situation. On a 1:1 crown-to-root ratio, that worsens the ratio further and compromises the tooth's prognosis.
- Also changes gingival architecture on a premolar in the aesthetic zone.
Orthodontic extrusion (forced eruption)
- Extrudes the tooth 2–3 mm so the fracture margin becomes supragingival, carrying the bone and gingiva with it and preserving root length and crown-to-root ratio.
- Requires 4–8 weeks of stabilisation after extrusion (longer if circumferential fibres are not sectioned) before crown preparation, and co-operation with an appliance.
Recommended: orthodontic extrusion, given the 1:1 ratio. Reserve crown lengthening for the case where extrusion is refused or the tooth is not restorable otherwise - and warn that the ratio then becomes unfavourable.
3. What material and occlusal design do you choose, and why?
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- Material: she bruxes and the opposing tooth has a large amalgam. Choose a material with high fracture resistance - monolithic zirconia, or a metal-ceramic crown with a functional palatal/occlusal metal surface. Lithium disilicate is acceptable if thickness and bonding can be guaranteed, but the parafunction makes it the second choice for a posterior unit.
- Occlusal design: keep contacts centred, avoid heavy excursive contacts on the buccal cusp, and confirm the opposing amalgam cusp is not creating a premature contact - recontour or restore 44 if it is.
- Protect the result: prescribe a night guard. She grinds; without one, the material choice only postpones failure.
- Honesty about prognosis: a root-filled premolar with a 1:1 ratio and a subgingival fracture has a guarded long-term outlook. State this and document the alternatives, including extraction and a fixed or removable replacement.