Mechanical Properties of Dental Materials

Comprehensive vocabulary flashcards covering the mechanical properties of dental materials, including various types of stress, strain, strength limits, and material behaviors from the lesson transcript.

Mechanical Properties

Properties defined by the laws of mechanics, which deal with forces acting on bodies and the resultant motion, deformation, or stresses they experience.

Strain ($\epsilon$)

The relative deformation of an object subjected to a stress, calculated as $\frac{\text{Change in Length}}{\text{Original Length}}$.

Elastic strain

Reversible deformation where the object fully recovers its original shape when the force is removed.

Plastic strain

Permanent deformation of a material that does not decrease when the force is removed.

Stress ($\sigma$)

The internal resistance to an external load, calculated as $\frac{\text{Force}}{\text{Area}}$ and measured in Megapascals ($MPa$).

Stress

described by its magnitude and the type of deformation it produces.

tensile, compressive, and shear

Three

types of “simple” stresses can be classified:

Tensile stress

A stress caused by a load that tends to stretch or elongate a body.

Compressive stress

The internal resistance to a load that tends to compress or shorten a body.

Shear stress

A type of stress that resists the sliding or twisting of one portion of a body over another.

Elastic modulus

A property describing the relative stiffness or rigidity of a material, measured by the slope of the elastic region of the stress-strain graph (Young’s modulus)

Flexibility

high value for the elastic limit is a necessary requirement because the structure is expected to return to its original shape after it has been stressed and the force is removed (elastic recovery)

Resilience

The energy absorbed by a material as long as the stress is not greater than the proportional limit.

Toughness

The total amount of elastic and plastic deformation energy required to fracture a material.

Poisson's ratio

The ratio of transverse strain (x direction) to the axial strain (y direction), measuring how a material squishes outward or pinches inward under force.

Proportional limit

The stress above which stress is no longer proportional to strain and the stress-strain graph ceases to be a straight line.

Elastic limit

The greatest stress to which a material can be subjected such that it returns to its original dimensions when the force is released.

Yield strength (Proof stress)

The stress required to produce a specified amount of plastic strain; used when the proportional limit cannot be determined with sufficient accuracy.

Flexural strength

Also called transverse strength or modulus of rupture, it is essentially a strength test of a bar supported at each end or a thin disk under static load.

Cold working

Also known as strain hardening or work hardening; a state where a metal alloy's hardness and strength increase at the area of deformation while its ductility decreases.

Fracture toughness

The mechanical property describing the resistance of brittle materials to the catastrophic propagation of flaws under applied stress.

Brittleness

The relative inability of a material to sustain plastic deformation before fracture occurs.

Ductility

The ability of a material to sustain a large permanent deformation under a tensile load up to the point of fracture.

Malleability

The ability of a material to sustain considerable permanent deformation without rupture under compression, such as hammering or rolling into a sheet.

Hardness

The ability of a material to resist scratching.

Hardness tests

Methods used to determine the hardness of dental materials, including the Barcol, Brinell, Rockwell, Shore, Vickers, and Knoop tests.

Hooke’s law

A principle stating that the elastic stress will be proportional to elastic strain.

Stress concentration causes

Surface defects, interior flaws, sharp corners, mismatched materials, and point contacts.