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1

Mechanical Properties of Dental Materials

Properties defined by the laws of ____.

The response of a material to an
____ force. A sub-set of ____ properties.

mechanics
applied
physical

2

Forces on Dental Materials

Three types of forces or loads may be applied to a solid material.
____
____
____

tensile
compressive
shear

3

Stress and Strain

We can define force intensity because if
we have the same force on two materials of different sizes, we need to be able to describe the effects of the force on the two different sizes of material. We use what I'm calling a force intensity, which is referred to as ____. Stress is ____ divided by the ____ of the object, so if we are putting a tensile force on this material, we are pulling it apart, there will be an increase in ____. We can describe this increase in ____ divided by the ____, that is the fractional change in length of the material, which is referred to as ____

stress
force
area
length
length
original length
strain

4

Stress

The internal force within a material which ____ an externally applied force or load.

stress = ____ (lb/inch^2), (psi), ____, ____)

Tensile
Compressive
Shear

resists
F/A
N/m^2
Mpa

5

Strain

Change in ____ of a material which results from an externally applied force.

e = ____ (inch/inch, mm/mm)

dimensions
(L1 - L0)/L0

6

Modulus of Elasticity

(1) Two springs, difference in the stiffness (same force applied to both)
Dividing stress by strain > ____ (measure of stiffness of material)

Continue pulling on spring: becomes permanently ____, where you exceed its elastic limit; plot the stress vs strain

young's modulus
elongated

7

S/S curve for stainless steel

(2) Initially, force is ____ to elongation (straight line) up to proportional limit; once you exceed this point it begins to deform ____ > continue elongation until the spring breaks (____)

Use it to describe mechanical properties of materials > the slope of the initial portion: measure of the ____ of the spring; next property of importance is the ____ > want to deform 0.2% of starting length > and can use comparatively between two materials

proportional
permanently
ultimate tensile strength

stiffness/rigidity
yield strength (YS)

8

Stress/Strain Curves

(3) Degree to which a material deforms permanently is a measure of its ____, so when we measure we are looking at the full range of the material

ductility

9

Stress/strain Curves

Elastic Strain
Strain which ____ completely when the applied force is removed

Permanent (Plastic) Strain
Strain which remains ____ after the applied force is removed

disappears
permanently

10

Elastic Limit

Stress corresponding to the first measurable ____.

- Yield Strength
Stress corresponding to a designated amount of permanent strain - ____ - ____
Units: Psi, Mpa

Units for YS are the units for ____

permanent deformation

0.1%
0.2%

stress

11

Proportional Limit (PL)

The value of stress at which the stress/strain diagram deviates from the initial ____ relation

The useful ____ of a dental material

linear
strength

12

Elastic Limit vs. Proportional limit vs. Yield Strength

All of these are essentially ____

equal

13

Modulus of Elasticity

____ of the initial linear portion of the stress/strain diagram

____ of a material

Modulus of elasticity = ____

slope
rigidity
stress (MPa) / Strain

14

Ultimate Strength

The stress corresponding to the ____ value of applied load or stress a material can withstand without rupturing

Units: psi, MPa

Some materials fracture at the maximum stress, so the UTS is the ____; some materials you exceed the UTS, so you will have a ____ fracture strength from the UTS

maximum
fracture strength
different

15

Failure of Dental Restorations

A permanent deformation of a dental appliance under occlusal loading represents a functional failure - by changes in ____ and ____

occlusal relationship
fit

16

Ductility/Elongation

The ability of a material to undergo
permanent ____ deformation without ____.

Clasp adjustment, ____ and crowns, preparation of ____ appliances

The material shown on graph has some ductility to it; a good example of ductility is ____ to improve the marginal fit on the tooth

tensile
fracture
burnishing of inlays
orthodontic
burnishing inlays

17

Malleability

The ability of a material to undergo permanent ____ deformation without fracturing.

Brittleness:
Material behavior characterized by fracture with little or no prior ____

Opposite of the two is brittleness (i.e. ceramic plates, drinking glasses > not able to deform permanently when a stress is placed upon them) (i.e. all dental ____ materials, porcelain)

compressive
permanent deformation
ceramic

18

Modulus of Resilience

Resilience:
Amount of ____ energy stored in a material during ____ deformation

Indicates ____ of material
Area under ____ portion of SS
curve

R=(1/2) P^2/E

recoverable
elastic
springiness
linear

19

Resilience and Toughness

Resilience is the ____ portion of the stress-strain curve; ____ of material is the energy that is stored throughout the curve before it fractures

linear
toughness

20

Toughness

Total energy absorbed
by a unit volume of material prior to ____ of the material specimen.

Tough materials have high ____, ultimate strength and ____ at rupture

Ceramic plate on one hand, and a metallic plate on the other; if you drop both, the ceramic plate will crack and the metal plate will recoil > metallic plate only deformed up to the elastic limit, ceramic plate has little ____ so it cracks

fracture
proportional limit
strain
resilience/toughness

21

S/S Curves for Materials with Different Properties

Materials with high slope of linear portion > ____; the non-linear part, has a significant amount of plastic deformation (top left, ____, the one next is brittle); strong material has a high ____ and high ____; tough because of the ____ located under the curve

stiff
ductile
YS
UTS
large area

22

S/S curve for stainless steel

Curve is different; look at S/S Curves for Enamel/Dentin; enamel has higher ____ and it is stronger because the ____ is higher, however it is not as ____ as dentin (dentin is also more ____)

stiffness
UTS
tough
ductile

23

Other Mechanical Properties

Transverse strength, bend test:
The maximum ____ which a material can support before failure when loaded as a beam supported at ____ ends.

stress
two

24

Three Point Bend Test

Stress at where it breaks is the ____ strength (same as flexural); modulus of rupture: determining the ____ using the bend test

transverse strength
modulus of elasticity

25

Diametral Tensile Strength

Tensile properties of ____ materials are obtained by loading a ____ of the sample:

epsilon = 2P/piDT (psi, MPa)

brittle
disk

26

Diametral Tensile Strength

Stresses are ____ to the force and it breaks right down the ____; calculate tensile strength using this test (used for ____ and ____)

perpendicular
middle
amalgam
composites

27

Hardness

Resistance of a material to ____ or to being ____ by another material

permanent indentation
scratched

28

Hardness Measurements

Brinell
Rockwell
____
____
____

Vickers
Knoop
Barcol

29

Hardness Measurements

Bronell uses a hardened ____ and loaded, and the projected area of indention (load/projected area of indentation); rockwell has a ____, similar principle; vickers, knoop and barcol are more useful for ____ measurements; vickers and knoop are ____ indentations

round-tip
steel-tip
dental
diamond-tipped

30

Cyclic Mechanical Properties (Fatigue)

Failure of materials due to ____ of loading and unloading

Failure occurs at stresses lower than the ____

Growth of small ____ which become larger upon cycling until failure

cycles
UTS
surface cracks