Exam 1 review

Question 1

stress refers to?

Answer 1

intensity of the internal force acting on a specific plane (area) passing through a point

units usually pascal
1N/m2 = 1 pascal
MPa - mega (1,000,000)
GPa- giga (1,000,000,000)

Question 2

Changes in load-displacement curve to the stress strain curve

Answer 2

units switch to pascal (not newton)

because load is newton

Question 3

ideal poisson ration

Answer 3

0-.5

direction is seen perpendicular to the load

Question 4

Diametral tensile strength?

Answer 4

use compressive force but it is an indirect test of the tensile strength of a material

the break is under tensile force even though compressive

seen through the middle of the object

Question 5

three point bending tests what? aka

why important

Answer 5

FLEXURAL
- biaxial flexural strenght

need to know that the three point bending is testing flexural strength and is is standardized and important test for dental materials

materials must meet a certain flexural strength

Question 6

flexural strnegth is?

Answer 6

(or bend strength) is the stress at fracture

Question 7

fracture usually always starts where?

Answer 7

at the tensile part

Question 8

flexural strength requirements

Answer 8

800 MPa in the posterior over 4 units with monolithic

Question 9

griffith’s theory

Answer 9

with a brittle material *

the ACTUAL tensile strength of materials is less than the theoretical values we see

the catestrophic growht of the crack ca be understood in simple terms – the amount of energy stored elastically - exceeds teg required for creation of new surfaces

the larger the crrack - the smaller amount of energy to break it

larger specimen - more change of a bigger flaw

Question 10

materials appear how much stronger in compression than tension?

Answer 10

8x stronger in compression

Question 11

brittle materials withstand which strnegth better?

Answer 11

compressive strength

Question 12

resiliance vs toughness

Answer 12

resiliance - under elastic zone and looks at ability to absorb energy before deforation
- without any deformation (why it stays in elastic zone)

toughness - area under both elastic and plastic and looks at HOW MUCH energy a material can withstand / absorb before it fails

Question 13

hardness test?

three examples

Answer 13

looks into indentations

• looking at the SIZE OF THE INDENTATIONS
  1. rockwell
  2. vikers
  3. knoop

Question 14

units for fracture toughness?

what does this look like?

Answer 14

MPa x METERS SQUARE ROOT m^(1/2)

also Kc1 – higher of this then better at resisting
critical stress intensity factor

looking at ability to resist crack propagation

Question 15

test used to test crack propagation

Answer 15

SENB

• single edge notch beam
• indentation cracking
• can use notch with 3-pt bending (flexural test)

Question 16

strain energy

Answer 16

energy stored in a material due to its deformation
if mesaured up to the proportional limit –> resiliance
if measured up to the ,point of fracture –> toughness

Question 17

strength is?

Answer 17

the stress at the point of failure / rupture

depending on testing it can be flexural, compressive, shear bond strength, etc

Question 18

main 7 points of information you can get from a stress- strain curve

Answer 18

see notes

Question 19

thermal expansion of enamel and dentin

Answer 19

11. 4

8. 3

Question 20

thermal expansion of wax?

Answer 20

HIGH – 240-400 or higher

Question 21

thermal expansion of zirconia and emax CAD?

Answer 21

10.3 and 10.5

Question 22

thermal expansion of dental cement and composite

Answer 22

cement - 10-12

composite 20-50

Question 23

usually a polymer or wax has what type of thermal expansion?

Answer 23

HIGH

vs enamel and ceramics have lower

Question 24

T/F the viscosity of a fluid is highly temperature dependent

Answer 24

TRUE

Question 25

pseudoplastic aka?

n value?

Answer 25

shear thinning and nis >1

Question 26

newtonian aka?

n value?

Answer 26

ideal liquid

n value = 1

Question 27

dilatant aka?

n value?

Answer 27

shear-thickening

n<1

Question 28

bingham aka?

examples

Answer 28

plastic liquids

- toothepaste, ketchup, mainaise

Question 29

example of material that has a high viscosity?

value?

Answer 29

Bis GMA

515

Question 30

viscosity of saliva

Answer 30

.16

Question 31

viscosity of impregum F (polyether)

Answer 31

89.0

Question 32

which dental materials show pseudoplastic shear thinning characteristics

Answer 32

Polycarboxylate cements

mixed glass ionomer cements

VPS impression paste (vinyl polysiloxane)

flowable composites

pit and fissure filling composites

Question 33

which dental materials show dilatant - shear thickening properties

Answer 33

traditional resin composites

liquid denture base resin

Question 34

which dental materials show thixotropic properties

Answer 34

rophy pastes

some light cured composites

topical fluoride jels

impression material

Question 35

describe thixotropic materials

Answer 35

becomes LESS VISCOUS WHEN SUBKECTED TO REPEATED PRESSURE

STILL SHEAR THINNING

load and unload and more load - more thinning

Question 36

Surface properties related to bulk materials

Answer 36

1. hardness
2. color
3. gloss
4. roughness
5. ware

Question 37

what the implication of having ahigh surface energy

Answer 37

small contact angle and thus increased wetability

Question 38

hydrophilicty has which characteristics?

Answer 38

small contact angle and higher surface energy

Question 39

use of silane?

Answer 39

how you get good wetting when using silicate and metal based bonding

Question 40

use of 10-MDP

Answer 40

how you get good wetting when using alumina or zirconia based bonding

Question 41

high or low surface energy is seen with restorative materials that will be better able to resist plaque formation

Answer 41

if have low surface energy

but adhesive materials need good wwtting / high surface enregy to achieve adhesion

Question 42

hydrophilic or phobic are more color stable?

Answer 42

phobic