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Dental Materials Mrs. Walker > Materials Chapter 3 > Flashcards

Materials Chapter 3 Flashcards

1
Q

Define Mechanical Properties

A

mechanical properties describe a material’s ability to resist forces.

They are dependent on the amount of material and on the size and shape of the object

Ex. strength and stiffness

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2
Q

Define Chemical Properties

A

chemical properties describe the setting reactions as well as the decay of degradation of materials.

Ex. gypsum products set by a precipitation process, whereas dental composite polymerize

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3
Q

Biologic properties

A

the effects that the materials have on living tissue

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4
Q

What is density as it relates to dental materials?

A

the amount or mass of a material in a given volume

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5
Q

What does density depend on?

A

the amount of atoms that are present;

the higher the atomic number and more closely the atoms are packed together, the heavier an object will feel

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6
Q

Boiling and melting points are _______ properties of materials

A

physical

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7
Q

What is vapor pressure

A

a measure of a liquid’s tendency to evaporate and become a gas

as the temperature of a liquid increases, the vapor pressure also increases

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8
Q

Define thermal conductivity

A

the rate of heat flowing through a material

the measurement of thermal conductivity depends on the distance the heat travels

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9
Q

Define specific heat capacity

A

the amount of energy needed to raise the temperature of one unit of mass of that material by 1 degree celsius

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10
Q

What is heat of fusion

A

amount of energy required to melt a material

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11
Q

What is heat of vaporization

A

amount of energy required to boil a material

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12
Q

Define coefficient of thermal expansion

A

a measure of the change in volume in relation to the change in temperature

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13
Q

Define percolation

A

process of heating/cooling, and accompanying opening and closing of the gap

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14
Q

What does percolation result in?

A

micro-leakage, tooth sensitivity, and recurrent decay

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15
Q

What is galvanic shock?

A

it is why a new amalgam filling will hurt when its is touched with a metal fork

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16
Q

Define Viscosity

A

materials ability to flow;

it is temperature dependent

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17
Q

Define wetting

A

doing this to a surface with an adhesive material, such as a sealant, brings the material into intimate association with the surface so that chemical and micro-mechanical bonding can occur

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18
Q

How is hardness measured?

A

Hardness is measured based on the size of the indentation measured

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19
Q

What are Durometer measurements?

A

measures how deep a steel ball will sink into a soft material; used to measure the hardness of impression material

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20
Q

What is abrasion resistance?

A

the wear resistance of dental restorations to food, opposing teeth, and other dental materials

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21
Q

Goldilocks Principle

A

material that is not too hard, not too soft, but just right

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22
Q

Define solubility

A

the amount of a material that dissolves in a liquid, such as water

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23
Q

Define water sorption

A

materials that absorb water; many polymers absorb water over time and slightly swell as a result

24
Q

Define force

A

the weight or load applied to an object

25
Q

Define the color response.

A

a complex phenomenon that is a psychological response (brain processing stimulus) to a physical stimulus (light reaching rods and cones of eye)

26
Q

Define elasticity

A

a measure of push or pull that changes the shape of an object

27
Q

What is stress?

A

force divided by the area on which the force has been applied

28
Q

Define strain

A

the change in length divided by the original length

(the longer an object is, the more it must be stretched)

stress= load/area

29
Q

Modules of elasticity

A

characteristic of a material and its atomic bonds. The higher the modules of elasticity, the stiffer the material

the load (stress) and the length (strain) are proportional and always occur together

Example: Enamel’s modulus of elasticity is high, and a rubber band is low

30
Q

What is elastic deformation

A

When a stress is removed and the object returns to its original length, the initial change in length is called elastic deformation

31
Q

What is plastic deformation or permanent deformation

A

this occurs when an ortho wire bent to fit a patients mouth, force is placed on the wire beyond the point where it can return to its original shape

32
Q

Define elastic limit, proportional limit, yield point

A

the point on the stress-strain plot at which the line starts to curve and plastic deformation begins

33
Q

Define ultimate strength

A

the point at which the strength of the spring has been exceeded

34
Q

What are the types of stress?

A

Compression- pushing or crushing

Tension- pulling

Shear- slip stress occurs when parts of an object slide past each other

Torsion- twisting force

Bending- combination of different types of stress

35
Q

To function properly, a restoration must be hard, strong, and stiff enough to _______

A

withstand the forces of mastication

36
Q

What is Poisson’s ratio?

A

the mechanical property that is the ratio of the strain in the direction of stress to the strain in a direction perpendicular to the stress

37
Q

Define resilience

A

the ability to absorb energy and not become absorbed

38
Q

Define toughness of materials

A

the energy absorbed up to the failure point on the stress-strain diagram

39
Q

Define fracture toughness

A

the measure of the energy required to fracture a material when a crack is present

glass and porcelain have a low fracture toughness value whereas metals have a high fracture toughness value

40
Q

Define fatigue

A

the failure of an item after repeated use

41
Q

Define creep

A

it is the small change in shape that results when an object is under continuous compression

a very slow flow; amalgam or composite

42
Q

Define stress relaxation

A

slow decrease in force over time

43
Q

A drop of water on a popsicle is an example of

a. poor wetting (low contact angle)
b. Good wetting (high contact angle)
c. Good wetting (low contact angle)
d. Poor wetting (high contact angle)

A

c. Good wetting (low contact angle)

Good wetting indicates that the adhesive is in very close contact with the adhered, forming a low contact angle.

Poor wetting “stays as a drop: and a big contact angle is formed

44
Q

The tightening of a guitar string is an example of which of the following stresses?

a. compression
b. torsion
c. Shear
d. Tension

A

d. Tension

Tension is a pulling or stretching stress, which many times is referred to as tensile stress.

Compression is a crushing or pushing force.

Torsion is a twisting stress

Shear is a sliding stress

45
Q

The modulus of elasticity is an indication of what property of a material?

a. resilience
b. strength
c. stiffness
d. tension

A

c. Stiffness

The higher the modulus of elasticity, the stiffer the material.

The modulus is a measure of flexibility. A rubber band has a low modulus, a mouth mirror has a high modulus

Resilience is the ability of a material to absorb energy without deforming, whereas toughness is the ability of a material to absorb energy up to and include failure or fracture.

46
Q

Cooled Materials will contract and heated materials will expand. A measurement of this change in volume in relation to change in temperature is called the coefficient of thermal expansion.

a. there first statement is true, the second it false
b. the first statement is false, the second statement is true
c. both statements are true
d. both statements are false

A

c. .Both statements are true

Nearly all materials will contract when called and expand when heated. Measuring this change in size in relation to the change in temperature is called the coefficient of thermal expansion. In dentistry, this property holds importance because, ideally, the tooth structure and the restorative material should expand and contract by the same amount

47
Q

When a stress is induced in a material that is greater than the material’s yield strength, the stress is ______________ proportional to the strain, and the material does not return to it’s original shape.

a. always
b. no longer
c. equally
d. None of the above

A

b. no longer

remember that you cannot have stress without strain. They occur together

when they are proportional, as illustrated on a graph, it is a straight line

As we increase the load, eventually, the spring will not go back to the original length. This stress is no longer proportional to the strain

we have reached the yield strength on the graph and the line begins to curve

48
Q

Which formula defines the modulus of elasticity?

a. stress/strain
b. stress 2/strain
c. strain/stress
d. 2 x stress/strain

A

a. stress/strain

the modulus of elasticity is defined as the stress divided by the strain in the linear portion of the stress strain graph

49
Q

An example of a physical property is:

a. density
b. strength
c. stifness
d. setting reaction

A

a. density

other examples of physical properties are color and thermal conductivity

strength and stiffness are mechanical properties, and setting relations are chemical properties

50
Q

A twisting force is termed

a. compression
b. shear
c. tension
d. Torsion
e. Bending

A

d. torsion

torsion is twisting stress, such as turning a door knob

shear stress occurs when parts of an object slide past each other

tension is pulling stress

bending is a combination of compression, tension, and shear stresses

51
Q

The ability of a material to dissolve in liquid is termed:

a. viscosity
b. water sorption
c. solubility
d. wetting

A

c. solubility

solubility is calculated as the amount of material that dissolves in a given time.

viscosity is the ability of a material to flow.

water sorption is the ability of a material to absorb water

wetting is the interaction of a liquid with the surface

52
Q

Elasticity is an example of which of the following properties?

a. physical
b. mechanical
c. chemical
d. biological

A

b. mechanical

Mechanical properites include stress, strain, resilience, toughness, fatigue, and elasticity, to name a few

physical properties include thermal conductivity, heat capacity, vapor pressure, viscosity, hardness, and many more

chemical properties describe setting reactions and decay and degradation.

biologic properties are the effects materials have on living tissue

53
Q

Elasticity is an example of which of the following properties?

a. physical
b. mechanical
c. chemical
d. biological

A

b. mechanical

Mechanical properties include stress, strain, resilience, toughness, fatigue, and elasticity, to name a few

physical properties include thermal conductivity, heat capacity, vapor pressure, viscosity, hardness, and many more

chemical properties describe setting reactions and decay and degradation.

biologic properties are the effects materials have on living tissue

54
Q

Jennifer is a practicing hygienist who goes to a nearby restaurant each day for lunch. She often orders a cola with ice and a bowl of homemade soup. As she eats and drinks her composite restorations (tooth colored) and tooth structure are expanding and contracting at different rates. This change in volume or length of these materials due to the hot food and cold drink is referred to as?

a. heat of fusion
b. coefficient of thermal expansion
c. heat capacity
d. thermal conductivity

A

b. coefficient of thermal expansion

55
Q

Fingernal polish remover has “solvent” properties as it will remove the polish from our fingernails. Another property polish remover has is it’s tendency to evaporate. Fingernail polish remover can be said to have:

a. high vapor pressure
b. a low vapor pressure
c. no vapor pressure
d. an intermitten vapor pressure

A

a. high vapor pressure

56
Q

14-16:
Match the properties listed below with the procedure or situation in question:

a. solubility
b. compression
c. stress concentration
d. viscosity
14. ________________ is the force used to condense an amalgam in a preparation
15. A hardened cement having “low” _________ can firmly hold a patient’s gold crown in place for years in a wet environment
16. _________ is the term given to the incerase of stress around defects within an object

A
  1. b. compression
  2. a. solubility
  3. c Stress concentration

Dental Materials Mrs. Walker (3 decks)

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