Prosthodontics & Occlusion · patient case with 2 questions
Crown that repeatedly debonds, and a new crown that will not seat
Patient: Female, 32 years old
Chief Complaint: “The crown on my front tooth keeps coming off, and it does not look right.”
Background: Crown on tooth #8 recemented three times in two years. No systemic disease. No reported grinding.
Vital Signs: BP 116/72 mmHg · HR 70 bpm
Findings: DEEP anterior overbite with heavy contact on the lingual surface of #8 in centric and on protrusive excursion. The abutment preparation is adequate in height and taper. Periodontium healthy: 2 mm probing depths, 4 mm of attached gingiva, no recession. At try-in of a replacement crown for #9, the restoration will not seat fully and a visible open margin remains, though the internal surface shows no interference on inspection.
Question 1
For the repeatedly debonding crown on #8, which intervention is NOT required?
Show answer and explanation
Correct answer: B. A free gingival graft
- A. Reviewing the preparation for resistance form is always part of investigating a debonding restoration, even when it looks adequate — short or over-tapered preparations are the other common cause.
- B. CORRECT as the answer — a FREE GINGIVAL GRAFT is not needed. It is indicated where attached gingiva is INADEQUATE or recession is progressing. This patient has 2 mm probing depths, 4 mm of attached gingiva and no recession. The periodontium is healthy and is not the problem.
- C. Occlusal analysis is exactly what IS needed. A deep overbite loading the lingual surface of a maxillary central in centric and protrusion applies a repeated horizontal dislodging force to the crown — the cement fatigues under shear and the restoration debonds. Adjusting or redistributing that guidance is the definitive fix.
- D. Mounted diagnostic casts let the anterior guidance be evaluated and modified on the articulator before anything irreversible is done in the mouth. In a repeatedly failing anterior restoration this is standard.
Note: When a restoration fails repeatedly, the question is never 'which cement next'. It is WHY. The three causes in order of frequency: inadequate retention and resistance form, occlusal overload or an unfavourable guidance, and a compromised margin or contaminated cementation field.
Question 2
The replacement crown for #9 will not seat fully despite an apparently clean internal surface. What is the most likely cause?
Show answer and explanation
Correct answer: A. Excessively tight proximal contacts
- A. CORRECT. An over-tight PROXIMAL CONTACT is the commonest reason a casting will not seat, and it is the one most easily missed because the internal surface looks perfect. The crown binds against the adjacent tooth before it reaches the finish line, holding it high and leaving an open margin. The test is direct: check the contacts with unwaxed floss and shimstock, and adjust them until the crown drops fully before ever assessing the margin or the occlusion.
- B. Excess cement causes incomplete seating at CEMENTATION, but this is a dry try-in — no cement has been used.
- C. Insufficient occlusal reduction produces a HIGH restoration in occlusion but does not prevent it from seating on the preparation.
- D. An over-tapered preparation reduces RETENTION. It makes a crown come off, not fail to go on — the opposite problem.
Note: The seating checklist in order: proximal contacts first, then internal interferences using a disclosing medium such as fit-checker or an aerosol indicator spray, then any residue or blebs from the casting, then the margin, and only then the occlusion. Verify seating with a RADIOGRAPH before cementation on posterior teeth — an open margin discovered after cementation costs the restoration.
Practice patient cases Prosthodontics & Occlusion study notes