Week 3 Ch 3: Physical and Mechanical Properties of Dental Materials

primary bonds

strong bonds with electronic attractions: ionic, covalent, metallic

secondary bonds

weaker bonds than primary bonds: hydrogen bonds

ductility

the ability of an object to be pulled or stretched under tension without rupture

malleability

the ability to be compressed and formed into a thin sheet without rupture

edge strength

the ability of a material to withstand fracture at a thin edge (margins of a restoration)

thixotropy

some gels and liquids will flow more easily under a mechanical force (mixing, striring or shaking)

solids

considered stable if crystalline structure is arranged in a regularly spaced pattern; if pattern is arranged in random form with no pattern, it is less stable; has shape and volume

density

measure of weight of a dental material as compared with its volume; measure of the compactness of matter

hardness

resistance of a solid to penetration or indentation; used to define a material’s resistance to wear and abrasion

knoop test

widely used and hardness is generally reported using this measure

rockwell test

measures hardness by using a steel ball to indent the material

ultimate strength

maximum amount of stress a material can withstand without breaking

elasticity

deformation is not permanent and the material recovers from the force completely

stiffness

resistance to deformation of a biomaterial and is measured by Young’s Elastic Modulus; stiffer materials have a higher modulus; high value is rigid; low value is flexible

proportional limit

the greatest stress a structure can withstand without permanent deformation; when a material is subjected to a force causing stress, the strain or change in the material that accompanies the stress is reversible up to a certain point

resilience

the resistance of a biomaterial to permanently deform; ig. orthodontic arch wire

toughness

the ability of a biomaterial to resist fracture ig. restorative material

ductility

the amount of dimensional change a material can withstand without breaking (pulled or stretched); classified as brittle if poor

durability

ability of a material to withstand damage due to pressure or wear

manipulation stage

mixing and working time

reaction stage

initial and final set

mixing time

the amount of time the operator has to bring the components together in a homogenous mix

working time

the time permitted to manipulate the material in the mouth; from mixing until it begins to harden

initial set time

the time begins when the dental material no longer can be manipulated in the mouth

final set time

the material has reached its ultimate state

shelf life

the length of time a material can be stored before it becomes unsuitable for use