Relative inability of a material to deform plastically before it fractures is known as:

  # Relative inability of a material to deform plastically before it fractures is known as:

A. Brittleness

B. Malleability

C. Ductility

D. Pseudoplasticity

The correct answer is A. Brittleness.

Explanation

Brittleness is the property of a material that fractures with little to no preceding plastic deformation.

In terms of a stress-strain curve, a brittle material behaves elastically up to a certain point (the proportional limit) and then fractures almost immediately, without undergoing the "yielding" phase associated with permanent deformation. This means the material absorbs relatively little energy before breaking.

Common examples of brittle dental materials include ceramics, dental stone, and enamel.

Why the other options are incorrect:

• Ductility: This is the opposite of brittleness in tension. It describes a material's ability to withstand significant plastic deformation (permanent stretching) under tensile stress before rupturing. It is often measured by percent elongation.

• Malleability: This describes a material's ability to withstand significant plastic deformation under compressive stress (e.g., being hammered or rolled into a thin sheet) without rupturing. Gold is a classic example of a malleable material.

• Pseudoplasticity: This is a rheological property (flow characteristic) of fluids, not solids. It refers to "shear-thinning" behavior, where a fluid becomes less viscous as the shear rate increases (e.g., silicone impression materials that flow better under the pressure of a syringe).