Prosthodontics & Occlusion · patient case question
All of the following contribute to failure of a fixed partial denture EXCEPT:
Patient case: Three-unit fixed partial denture that has become loose
Patient: Female, 61 years old
Chief Complaint: “My bridge feels loose when I bite.”
Background: Three-unit porcelain-fused-to-metal bridge from #3 to #5 placed eight years ago, replacing #4. Reports night-time clenching. No pain.
Vital Signs: BP 128/80 mmHg · HR 72 bpm
Findings: The prosthesis moves as a unit under digital pressure. Radiographs show short, markedly tapered abutment preparations with minimal occlusogingival height, and a flattened occlusal surface on the #3 retainer. No periapical radiolucency; both abutments respond within normal limits to percussion.
Show answer and explanation
Correct answer: D. A span replacing a single missing tooth between two sound abutments
- A. Inadequate occlusogingival reduction leaves insufficient material thickness and a short preparation, compromising both strength and resistance form — also a genuine contributor.
- B. Parafunctional loading is a well-recognised contributor to both cement failure and porcelain fracture.
- C. Excessive convergence directly reduces retention — this is a genuine contributor.
- D. CORRECT as the exception. A SHORT SPAN replacing ONE tooth between two sound abutments is the most favourable configuration there is. Ante's law holds comfortably, and deflection under load is minimal. Deflection rises with the CUBE of span length — a two-pontic span deflects roughly eight times as much as a single-pontic span, which is why long spans fail. Three units is not a long span.
Note: Ante's law: the combined root surface area of the abutments should equal or exceed that of the teeth being replaced. Useful as a screening principle, though modern evidence treats it as a guide rather than an absolute rule.
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