Knoop Hardness
Pronunciation: noop HAR-dness
A microindentation hardness value obtained using an elongated pyramidal diamond indenter, used to assess the surface hardness of brittle dental materials.
Full Definition
Knoop hardness (KHN) is determined by pressing a rhombus-shaped (elongated pyramidal) diamond indenter into a material surface under a defined load and measuring the long diagonal of the resulting indentation. Because the indentation is shallower than that produced by the Vickers test, Knoop hardness is particularly suited to thin specimens, enamel, and brittle ceramics where cracking is a concern. In dental materials research, it is used to assess depth-of-cure of resin composites, surface hardness of enamel, and the effect of surface treatments on ceramics. Editors must not conflate KHN with Vickers Hardness Number (VHN), as the two tests produce non-interchangeable values.
Usage
Usage note: Abbreviate as KHN (Knoop Hardness Number) and distinguish clearly from VHN (Vickers Hardness Number). The two are measured differently and values are not directly comparable.
In Context
- "Knoop hardness values were used to assess the depth of cure, as the shallow indentation minimises cracking in the partially cured resin." — Dental materials research article
- "The table incorrectly labelled Knoop hardness values as 'VHN'; the unit should read 'KHN' to reflect the test methodology." — Copyediting correction log