Dental Materials (Exam 1)

Front 1

Stress

Back 1

-F/A
-internal force within a material which resists an externally applied force or load
-measured in lb/inch^2 or N/m^2

Front 2

3 basic types of stresses

Back 2

Tensile (bending)
Compressive
Shear
-If value of these stresses exceeds strength of material, the structure fails

Front 3

Strain

Back 3

Change in dimension of a material which results from externally applied force
-becomes "longer"
-INDEPENDENT OF LENGTH OF SPECIMEN
-e (L1-L0)/L0
-directly proportional to load applied when cross sectional area is same

Front 4

Elasticity

Back 4

constant stress and strain = MODULUS OF ELASTICITY

Front 5

Modulus of Elasticity

Back 5

-varies depending on object
-correlates to slope of the initial linear portion of stress/strain
-rigidity of material
-stress/strain (MPa) for linear portion of SS curve
CANNOT BE ALTERED BY HEAT, WORK HARDENING - structurally insensitive

Front 6

proportional limit/elastic limit

Back 6

highest stretch at which stress is proportional to strain (first measurable permanent deformation)
-value at which S/S diagram deviates from initial linear reaction
-useful strength of dental material

Front 7

yield strength

Back 7

-stress related to permanent strain
-always slightly higher than elastic limit
Psi, MPa
SENSITIVE TO WORK HARDENING (can become stronger and harder)

Front 8

ultimate strength

Back 8

stress corresponding to max value of applied load or stress material can withstand without rupturing

Front 9

ultimate tensile strength (UTS)

Back 9

stress at breakage (when material is stretched)

Front 10

fracture strength

Back 10

-value of stress at which material ruptures into 2 or more portions
-permanent deformation of dental appliance under occlusal loading

Front 11

plastic behavior

Back 11

when elastic or proportional limit is exceeded in a material = region of permanent deformation = stress and strain no longer proportional

Front 12

ductility

Back 12

ability of material to undergo permanent TENSILE deformation without fracturing (plastic behavior)
ex. clasp adjustment, burnishing of inlays and crowns, prep of ortho appliances

Front 13

malleability

Back 13

ability of material to undergo permanent compressive deformation without fracturing

Front 14

brittleness

Back 14

material fractures with little or no prior permanent deformation (s/s not proportional)
-materials that undergo little or no plastic behavior are BRITTLE

Front 15

elongation

Back 15

total strain at fracture point/ultimate tensile strength
-when burnishing inlay of crown - gold alloys lower yield strength - more easily stretchable/ductile vs. nickel-chromium and cobalt-chromium which have yield strengths that are too high to burnish

Front 16

elastic strain

Back 16

strain which disappears completely when the applied force is removed

Front 17

permanent/plastic strain

Back 17

strain which remains permanently after applied force is removed

Front 18

resilience

Back 18

amount of recoverable energy stored in material during elastic deformation
-indicates the springiness of material