Prosthodontics & Occlusion · patient case question
Given her parafunctional habit, which material is most appropriate for the definitive crown on #30?
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: B. Monolithic zirconia
- A. Incorrect. Feldspathic porcelain has the lowest strength of these options and is unsuitable for posterior occlusal loading, let alone in a bruxer.
- B. Correct. Monolithic zirconia has the highest flexural strength and fracture toughness of the available ceramic options, and because it has no veneering layer there is no porcelain to chip. That combination makes it the standard choice for a posterior tooth in a bruxing patient.
- C. Incorrect. A porcelain occlusal surface remains vulnerable to chipping and will abrade the opposing dentition. A metal occlusal surface would be far more durable, but the patient’s esthetic concerns and modern zirconia performance make monolithic zirconia the better answer.
- D. Incorrect. Lithium disilicate is strong in monolithic form, but a layered design introduces a veneering porcelain that becomes the weak point under parafunctional load.
Note: Note the trade-off in monolithic zirconia: polish the occlusal surface thoroughly after any adjustment. Unpolished, roughened zirconia is markedly abrasive to opposing enamel; well-polished zirconia is comparatively kind to it.
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