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Dental Materials I > Properties of Materials > Flashcards

Properties of Materials Flashcards

1
Q

When we talk about dental materials, do we talk about stress or force more?

A

Stress

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2
Q

What is stress?

A

When you put a force on a body there will be a reaction back?

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3
Q

How is stress measured?

A

The force and area to which it is applied are measured and stress is calculated from the ratio of force per area

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4
Q

What is the ratio of force per area measured in?

A

Pascals = 1N/m2

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5
Q

What are the types of stress?

A

Tension, Compression, Shear, Torsion, Bending

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6
Q

What is tension?

A

Elongation forces are directed away from each other in the same straight line. Molecules resist being pulled apart = resistance

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7
Q

What is compression?

A

Elongation forces are directed toward each other in the same straight line. Molecules resist being forced more closely together = resistance

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8
Q

What is a shear stress?

A

Forces directed parallel to each other but NOT along the same straight line. One portion sliding past the other = resistance

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9
Q

What is torsion?

A

Twistin forces = resistance

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10
Q

What is bending?

A

Results from a bending moment = resistance

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11
Q

What is strain?

A

Deformation of a material caused by stress

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12
Q

How is deformation measured?

A

As a unitless value or as percentage. Deformation = deformation/original length

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13
Q

What is the proportional limit?

A

The greatest stress sustained w/o deviation from the linear proportionality of the stress and strain curve

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14
Q

What is the elastic region Vs plastic region?

A

Elastic is reversible strain. Plastic is irreversible or permanent strain (stress past a point where the material will not rebound to its original shape)

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15
Q

What is elastic limit?

A

The greatest stress sustained w/o permanent deformation. Exceptions are super-elastic materials

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16
Q

How does proportional limit and elastic limit compare in linearly elastic material?

A

They can stand the same stress

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17
Q

What is yield strength?

A

The stress at which the material begins to function in a plastic manner. Limited strain has already occured

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18
Q

Which stress is higher, yield strength or proportional limit?

A

Yield strength

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19
Q

Is permanent deformation a bad thing in the oral cavity?

A

No not always

20
Q

What is constructive permanent deformation? Destructive?

A

Ortho wires, partial clasps. Destructive is fillings, crowns, bridges

21
Q

What is ultimate strength?

A

The highest point on the stress/strain curve. Point of greatest strength

22
Q

What is fracture strength?

A

Stress at which material fractures

23
Q

Does a material always fracture at the point of greatest stress?

A

No, may elongate excessively reducing the cross-sectional area causing a reduction in stress

24
Q

For most dental alloys and ceramics subject to tension, how does Ultimate Strength vs Fracture Strength compare?

A

They are very similar

25
Q

What is elongation?

A

Deformation that results from the application of tensile stress. Indicates the workability of alloy. Expressed as a %

26
Q

What is elastic modulus?

A

The measure of elasticity. Stress/strain = elastic modulus. Measure of how rigid or how flexible a material is

27
Q

How does the percentage of elongation affect ductility?

A

Higher elongation means a more ductile material, as in gold margins can be burnished

28
Q

What forces are responsible for the property of elasticity?

A

Interatomic/intermolecular forces

29
Q

What does a higher value of elastic modulus (E) mean?

A

The higher the value of E, the more stiff or rigid the material

30
Q

What is resilience?

A

Resistance of a material to permanent deformation

31
Q

What toughness?

A

Resistance of a material to fracture. Amount of energy needed to cause fracture

32
Q

What is toughness a combination of?

A

Combination of yield strength, ultimate strength, and strain. Increasing any of these, increases toughness

33
Q

What is fracture toughness?

A

Characterizes the behavior of materials with cracks or flaws

34
Q

How do defects affect fracture toughness?

A

Generally weaken a material and may result in fractures at stresses well below the yield stress.

35
Q

Where do fractures occur more?

A

With brittle materials that have no ability to deform and redistribute stresses

36
Q

What is a diametral compression test?

A

A test of tensile properties of brittle materials

37
Q

What is a diametral test good for?

A

For brittle material such as amalgam, cements, ceramics, plaster, and stone

38
Q

Do brittle materials have both elastic and plastic properties?

A

Yes, but the plastic properties will be small

39
Q

What is fatigue strength?

A

The stress at which a material fails under repeated loading. Depends on Magnitude of the load and the Number of loadings

40
Q

What is Endurance Limit?

A

Stress at which the material can be loaded an infinite number of times w/o failing

41
Q

What is rate of loading?

A

How fast a material is deformed or how fast the stress is applied. Viscoelasticity - is important for many materials (alginate elastomeric impression materials, waxes, amalgam, polymers)

42
Q

What is viscoelastic?

A

Materials w/ mechanical properties DEPENDENT on loading rate

43
Q

What is viscosity?

A

The resistance of a fluid to flow.

44
Q

What is the unit of viscosity?

A

Poise

45
Q

What is creep?

A

Increase in strain (deformation) in material under constant stress (amalgam)

46
Q

What is tear strength?

A

Resistance to tearing forces. Important for polymers in thin sections (like when impression material gets into a sulcus). Depends on rate of loading. Rapid loading = higher values

Dental Materials I (9 decks)

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