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Dental Materials > Fundamentals 2 > Flashcards

Fundamentals 2 Flashcards

1
Q

What are mechanical properties?

A

Change of material dimensions due to external forces, such as mastication

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2
Q

What is viscosity?

A

Resistance of a fluid to flow.

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3
Q

Viscosity measures __________. The higher the viscosity, the ___________ and _______ resistance to flow

A

internal friction

internal friction, greater

Thiccer materials are most viscous

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4
Q

Higher viscosity materials behave like ______ while lower viscosity materials behave like ______

A

solid

liquid

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5
Q

What is the shear thinning phenomena?

A

It describes the affect on viscosity of a material if subjecting to stress.

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6
Q

Shear Thinning describes a ______ in viscosity as stress is ______.

Is this Newtionian?

A

Decrease

Added

no

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7
Q

What word is used to describe materials whose viscosity is unaffected by external stress?

A

Newtionian

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8
Q

Shear Thickening describes a ______ in viscosity as stress is ______.

Is this Newtonian?

A

increase, stress

NO

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9
Q

Shear Thinning examples

A
  1. Squeezing ketchup out of a bottle
  2. Squeezing toothpaste out
  3. Blood in our body as it flows
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10
Q

High to low viscosity describes ______.

The vice versa describes what?

A

Shear thinning

Shear thickning

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11
Q

Examples of Shear Thickening

A

Cornstarch

Moonsand

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12
Q

Why is viscosity important?

A
  1. Viscosity can change during preparation of materials
  2. Dispensing of dental material into tissue so it reaches pits and fissures
  3. Consistency and Manipulation ability of material
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13
Q

What is the ideal viscosity of impression materials?

A

Low viscosity outside the mouth so it captures all anatomy but increasing viscosity in the mouth so it sets!

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14
Q

What is viscoelasticity?

A

Elastic + Viscous Behavior

Springy + Dampening behavior where materials behaves like solid and fluid

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15
Q

What is the difference of the Stress/Strain curve between fully elastic materials and viscoelastic ones?

A

Fully Elastic Materials will have the same linear path for load and unload.

Viscoelastic Materials will have a slight convexity for the load and a slight concavity for the unload.

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16
Q

Viscoelastic materials ______ energy when stress is________ . As a result the Stress Strain curve is ________.

What shape does it form?

A

lose , loaded-unloaded.

NOT proportional

A Hysteresis

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17
Q

Describe the strain vs time graphs for materials with the following properties.

Elastic

Viscoelastic

Viscous

A

Elastic- It will look like a rectangle. Increase in strain on y-axis, strain will be consistent with constant stress. When stress is removed strain will drop right back to zero.

Viscous- Strain will gradually increase linearly (sloped) as stress is applied. Strain will be consistent with constant stress. HOWEVER, when stress is removed, strain does not recover. ( Sloped line + 0 slope line

Viscoelastic - Stress will cause a convexed increase in strain. The elastic property will attempt to recover the material when stress is reduced caused a vertical decrease in strain. However, the viscous property will prevent full elastic behavior and cause a concave decrease. Looks like Shark fin

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18
Q

The more viscoelastic, the more ______ behavior.

A

Viscous

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19
Q

Purely elastic materials dissipate energy when load is applied then removed.

True or False

A

FALSE

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20
Q

Plastic deformation results in a _________ of energy which is uncharacteristic of _____ materials.

A

Loss

Elastic

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21
Q

Viscous materials loose energy through the ______ cycle because the ______________.

How can we quantify this energy?

A

loading/unloading

energy lost during loading is never fully recovered

Area in between hysteresis!

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22
Q

What is creep?

A

Effect of constant stress over TIME on strain

Think coat hanger.

Strain will increase in a convex curve
Stress will remain constant (Slope 0 horizontal)

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23
Q

What is stress relaxation?

A

Effect of constant strain over time on stress.

Stress will decrease in a convex fashion
Strain will remain constant (Slope 0)

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24
Q

What are the 5 viscoelastic dental materials?

A
  1. Dentin
  2. Enamel
  3. Cells
  4. Impression Material
  5. SOME acrylic dentures
25
Q

How do we calculate dimensional change?

A

((New-Initial)/ Initial ) / 100

26
Q

What can cause contraction and expansion?

A

Temperature
Water Intake
Mechanical (Stress)
Polymerization

27
Q

We want the material with the ____ dimensional changes.

A

Least

28
Q

What are bulk properties?

A

Mechanical, electrical or thermodynamical properties

Effect on organism, taste, nutritional value

Material density

Size and distribution

29
Q

What are surface properties?

A

Wettability

Flowability

Reactivity

30
Q

Why are surface properties important?

A

This is what interacts with environment.

31
Q

Why are bulk properties important ?

A

The add functionality to the material

32
Q

What is hardness?

A

The measure of the resistance to localized plastic deformation induced by either mechanical indent or abrasion.

33
Q

What is the hardness test?

A

Describes how much a material indents due to the load of a material.

TIP of load insertion in indentation of material is measured

34
Q

What is the difference between the hardness tests?

A

The shape of the tip

35
Q

The ______ properties of the tip material must be similar to the ______ of the material being measured in a hardness test.

A

Surface

Bulk

36
Q

Brinell Hardness Test

Tip Shape
What materials are tested with this?

A

Ball

Metals

37
Q

Rockwell Hardness Test

Tip Shape

A

Cylinder with 120 degree cone shaped indenter

Widely used

38
Q

Vickers Hardness Test

Tip Shape
What materials are tested with this?

A

Square-based pyramid shape tip

VERY SMALL material

39
Q

Why is the Vickers Hardness test important?

A

It has a very high resolution so it can be used for materials that change at the MICRON level

100 micron view

40
Q

Nano-indentation

Tip Shape
What materials are tested with this?

A

BERKOVICH TIP- 3-side Pyramidal

Diamond tip

very very small shape

4 micron view

41
Q

Which hardness test has the SMALLEST spatial resolution?

A

Nano-indentation w/ berkovich tip

42
Q

High hardness correlates with high ___________.

A

Wear resistance

43
Q

What is wettability?

A

How well does a liquid spread over a surface?

44
Q

How is wettability measured?

A

Contact angle between surface and tangent of water

45
Q

Non-wetting surface

A

180 degree contact angle

Water is a perfect ball

46
Q

Perfectly wetting surface

A

0 degree contact angle

Water is spread and coating surface

47
Q

Wetting

A

90 degree contact angle

Water is a flatter hemisphere

48
Q

Hydrophilic surfaces will produce contact angles _____________.

A

Less than 90 degrees

High surface detal

49
Q

Hydrophobic surfaces will produce contact angles at __________.

A

More than 90 degrees

Low surface detail

50
Q

What is surface detail?

Which material have highest surface detail?

A

How much can the material pick up of a surface?

Hydrophilic because hydrophobic materials will not coat the surface

51
Q

High surface energy describes the property of just one material.

True or False?

A

FALSE

TWO Material interaction

52
Q

High surface energy indicates _________ interaction.

These tend to be hydro______.

A

High

Hydrophilic

53
Q

What materials have high surface energy?

A

Metal, Kapton, Polyester, ABS, Acrylic

54
Q

What materials have low surface energy?

A

Polyestyrene

Acetal

EVA

Teflon

55
Q

Pan material is made of _____. This is why things don’t stick!

A

TEFLON

56
Q

What can affect the wettability/surface energy of a material?

A

Cleanliness of substrate (dust,saliva, particles)

Roughness

57
Q

What word can be interchanged with surface energy?

A

Adhesion

58
Q

The less wettable a substance is, the _________ contact angle.

A

Higher

Dental Materials (6 decks)

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