Prosthodontics & Occlusion · patient case question
What is the most likely cause of the repeated debonding of the crown on #8?
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: A. Excessive occlusal loading from the deep overbite and parafunction
- A. Correct. A deep overbite with minimal overjet places heavy, obliquely directed loading on the maxillary anterior teeth during excursive movements. Combined with nocturnal parafunction, the shear stresses at the cement interface exceed its bond strength, and the crown repeatedly debonds. The examination points to this directly: wear facets, masseter hypertrophy, and morning soreness.
- B. Incorrect. Cement allergy is exceedingly rare and would present as a mucosal inflammatory reaction adjacent to the margin, not as loss of retention.
- C. Incorrect. The stem specifies an adequate 2 mm ferrule, which is the accepted minimum for resisting functional and parafunctional load.
- D. Incorrect. She has 4 mm of attached gingiva with no recession. Attached gingiva relates to periodontal health and soft tissue response, not to retention of a crown.
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