Prosthodontics & Occlusion · patient case question
The crown for #30 will not seat completely and shows an open margin on the distal. What is the most likely cause?
Patient case: The Crown That Keeps Falling Off
Patient: 32-year-old female
Chief Complaint: “The crown on my front tooth has fallen off three times this year.”
Background: Healthy, no medications. Reports jaw soreness on waking and has been told she grinds her teeth. Non-smoker.
Medications: None
Vital Signs: BP 112/70 mmHg · HR 68 bpm · RR 14 · T 98.4°F
Findings: Deep overbite of approximately 80% with minimal overjet. Wear facets on the incisal edges of the mandibular anteriors. Bilateral masseter hypertrophy. Tooth #8 carries a ceramic crown with an adequate 2 mm ferrule and a healthy periodontium: 2–3 mm probing depths, 4 mm of attached gingiva, no recession. A separate new crown for #30 is being tried in at this appointment.
Show answer and explanation
Correct answer: C. An excessively tight proximal contact on the distal
- A. Incorrect. Excessive taper reduces retention and resistance form but makes seating easier rather than harder. It does not create an open margin at try-in.
- B. Incorrect. An undercut prevents the crown from seating at all, or the crown would not have been fabricated, since the die would have been blocked out in the laboratory.
- C. Correct. A proximal contact that is too tight prevents the crown from seating fully on that side. The restoration tips away from the tight contact, lifting the margin on that surface. Marking the contact with articulating paper and adjusting until the crown seats confirms the diagnosis.
- D. Incorrect. Insufficient occlusal reduction produces a high restoration in occlusion or an overcontoured crown, not an open margin on a proximal surface.
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