Proportional Limit — MFDS Part 1 MCQ

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ModerateDental MaterialsProportional LimitMFDS Part 1

On a stress–strain curve for a dental material, which statement defines the proportional limit?

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Correct answer: E — The highest stress for which stress remains directly proportional to strain

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

A is correct. The proportional limit is the greatest stress up to which stress and strain maintain a linear, directly proportional relationship in accordance with Hooke's law. Option C defines the elastic limit: the greatest stress from which the material can recover without residual deformation. The elastic and proportional limits may be close but are not strictly synonymous because some materials show non-linear elastic behaviour between them. Option B describes fracture strength, while D describes ultimate tensile strength. Option E defines Young's modulus, represented by the slope of the linear stress–strain region rather than a limiting stress.

Reference: Friedman CM, Sandrik JL, Heuer MA, Rapp GW. Composition and mechanical properties of gutta-percha endodontic points. Journal of Dental Research. 1975;54(5):921-925. https://pubmed.ncbi.nlm.nih.gov/1058875/