Covers hardness as resistance to indentation and the two main ways of measuring it: scratch methods, including the Mohs scale with its mineral table, and indentation tests such as Brinell, Vickers, Knoop and Rockwell, with a comparison table. It also explains microhardness, the Shore test for elastic materials, and conversion between Brinell and Vickers values, then compares hardness values of enamel, dentin, porcelain, alloys, composites and acrylic resin.
Inside: 5 sections · 2 labelled pictures · 2 tables · 1 formula · 15 flashcards · 2 min
Topic 16 of 52 in the MU Sofia syllabus for Dental Materials (Dental Medicine, Year 1). The free AceMed note covers it in 5 sections, about 241 words (2 min of reading), with 15 flashcards.
In this note
Introduction
Scratch methods
Indentation methods
Shore hardness
Values
Introduction
Hardness is the resistance of a material to a harder body pressing into it. It gives a rough guide to strength and wear resistance. There are two common ways to measure it: by scratching and by indentation.
Scratch methods
Mohs scale: ten minerals ranked from talc (1) to diamond (10), where each scratches the one before it. It is a rough comparison, used for abrasive dental materials.
Microcharacter and sclerometer: a diamond pyramid scratches the surface. Hardness is read from the depth or width of the groove.
Indentation methods
A body of a set shape is pressed into a polished surface with a set load. It overcomes the elasticity of the material and leaves a permanent dent. Hardness comes from the size of the dent and the load, in kg/mm² or MPa.
Brinell and Vickers values are very close and can be converted:
For very small objects, Vickers testing uses loads under 9.8 N and a microscope. This is called microhardness.
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