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Knoop Indenter Shape — MFDS Part 1 MCQ

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HardDental MaterialsKnoop Indenter ShapeMFDS Part 1

A polished enamel section is being evaluated for directional microhardness. The investigator intends to align the long axis of each indentation with the enamel-prism orientation and calculate hardness from the major diagonal. Which indenter geometry should be fitted to perform the Knoop hardness test?

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Correct answer: B — Four-sided diamond pyramid with an elongated rhombic base

The Knoop test uses an elongated four-sided diamond pyramid with a rhombic base, producing an asymmetric indentation with distinct major and minor diagonals. Its elongated geometry permits orientation of the major axis when investigating hardness anisotropy, as in enamel. ([pubmed.ncbi.nlm.nih.gov](https://pubmed.ncbi.nlm.nih.gov/9391873/?utm_source=openai)) A square-based diamond pyramid is the Vickers indenter. A hardened-steel or tungsten-carbide ball is used in Brinell-type testing, while a rounded diamond cone is associated with Rockwell testing. A flat-ended cylindrical punch is not the standard indenter for Knoop microhardness measurement.

Reference: Riches PE, Everitt NM, Heggie AR, McNally DS. Microhardness anisotropy of lamellar bone. Journal of Biomechanics. 1997;30(10):1059–1061. https://pubmed.ncbi.nlm.nih.gov/8937644/