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Fatigue Failure — MFDS Part 1 MCQ

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ModerateDental MaterialsFatigue FailureMFDS Part 1

A ceramic restoration fractures after several years of routine mastication. Individual occlusal loads were below the load required to cause immediate fracture, and fractographic examination shows progressive extension of a surface flaw before catastrophic failure. Which mechanism best explains the failure?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: B — Repeated subcritical occlusal loading causing progressive crack extension until fracture

Explanation lettering: C = shown as A · A = shown as B · E = shown as C · B = shown as E

The correct answer is A. Fatigue failure results from repeated loading that is individually insufficient to cause immediate fracture. Surface flaws act as stress concentrators and extend incrementally during successive masticatory cycles until the remaining material can no longer support the applied load, producing catastrophic fracture. Option B describes acute overload rather than fatigue. Option C describes static fatigue or stress-corrosion crack growth under a sustained load, not specifically failure from repeated loading. Dissolution and water sorption may degrade some dental materials, but options D and E do not describe the progressive mechanically driven crack growth demonstrated in the stem.

Reference: Kelly JR et al. Academy of Dental Materials, “ADM guidance—ceramics: Fatigue principles and testing,” Dental Materials, 2017;33(11):1192–1204. https://pubmed.ncbi.nlm.nih.gov/29017761/