Explains how a stress-strain curve is built and what its four key points mean: proportional limit, elastic limit, yield strength and maximum strength. Shows how the modulus of elasticity is calculated from the straight part, with a worked example and a table of values for dental materials. Also covers how stiffness guides material choice, and brittleness, toughness, ductility, flexibility and fracture toughness read from the curve, with a comparison table.
Topic 15 of 52 in the MU Sofia syllabus for Dental Materials (Dental Medicine, Year 1). The free AceMed note covers it in 7 sections, about 564 words (5 min of reading), with 14 flashcards.
In this note
Introduction
Why deformation matters
How the diagram is built
The four points to know
Modulus of elasticity
Why E guides the choice of material
Other properties read from the curve
Introduction
A crown or bridge can look perfect in the mouth while it bends a little with every bite. The stress-strain diagram records how a material behaves as the load on it rises, from the first small change in shape until it breaks. Most of the mechanical properties in this subject can be read straight from this one curve.
Why deformation matters
Damage often starts long before anything visibly breaks, so the way a material deforms under load can matter more in practice than the load that finally fractures it.
A bridge pontic that flexes during chewing overloads the periodontium of its abutment teeth.
A crown or filling that deforms can break its adhesive bond to the tooth and lose its correct contact with the opposing teeth.
How the diagram is built
A test body is loaded steadily, in tension or in compression, and the result is plotted on two axes:
Vertical axis: stress, in MPa.
Horizontal axis: strain, as a percentage change in length. This is lengthening in a tensile test and shortening in a compressive test.
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