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Dental Materials > Material Properties > Flashcards

Material Properties Flashcards

1
Q

What are the 4 categories of Material properties?

A

Physical

Mechanical

Chemical

Biologic

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2
Q

Physical properties refer to 5 areas of interest which are:

1

2

3

4

5

A

1 mass properties

2 thermal properties

3 electrical properties

4 optical properties

5 surface properties

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3
Q

Mechanical properties refer to:

A

a description of the stresses and strains within a material resulting from an external force.

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4
Q

Chemical properties refer to:

A

chemical and electrochemical interactions

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5
Q

Biologic properties refer to:

A

characterization of toxicity or sensitivity reactions.

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6
Q

Materials respond to environment according to their _____________ and _________________

A

Materials respond to the environment according to their structure and bonding

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7
Q

due to the coefficient of Thermal Expansion what happens during temperature increases or decreases.

A

When temperature increases atomic motion increases which stretches bonds and produces expansion. The opposite is true when temperatures are decreased (ie: shrinkage, *think george castanza* “I was in the pool!”)

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8
Q

Which materials have low coefficient of thermal expansion and which materials have high coefficient of thermal expansion?

ceramics

metals

polymers

tooth structure

A

LOW (dont expand much)

• Ceramics: 1-15 ppm/°C

Tooth Structure: 9-11 ppm/°C

Metals: 10-30 ppm/°C

Polymers: 30-600 ppm/°C

HIGH (expand quite a bit)

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9
Q

What is Percolation?

A

Percolation is where the margins of a restoration become weaker and “leaky” because the restoration undergoes cyclical expansion and contraction at a different rate than the tooth structure around it.

Major cause of loosening restorations and secondary caries

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10
Q
A

This is an example of PERCOLATION! note the expansion and contraction as temperature changes. This weakens the margins and can result in secondary caries.

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11
Q

What is thermal conductivity?

A

thermal conductivity is the ability of a material to conduct heat.

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12
Q

Low conductors are also good insulators

What are some examples of materials that are good insulators/poor conductors?

A

Dentin, Cements, composite resins, cavity liners

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13
Q

High conductivity means the material is a poor insulator and will conduct heat readily. What are some examples of materials that are good conductors/poor insulators?

A

amalgam and gold

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14
Q

What is HEAT DIFFUSIVITY?

A

Heat diffusivity is a measurement of heat conductivity per unit time, it takes the density of the material into account.

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15
Q

Dental pulp can withstand __________ temperature changes for __________amounts of time with ___________ damage

A

dental pulp can withstand small temperature changes (37-42 °C) for short periods of time (30-60 seconds) with no permanent damage.

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16
Q

What is Electrical Conductivity

A

rate of electron transport through a material

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17
Q

What types of materials are best at conducting electricity?

A

Metallic restorations may conduct flow through the pulp.

Amalgam + gold = shock

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18
Q

What does specific gravity refer to?

A

specific gravity refers to the density of a material in reference to water

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19
Q

What are the 4 main categories or Optical Properties

A

Reflection- light bounces off surface

Refraction- light is bent as it passes through (changes directions at surface)

Absorption (and Fluorescence)- light loses energy as it goes through

Transmission- linked to opacity/translucency

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20
Q

What are the 3 categories in the MUNSELL COLOR SYSTEM

A

HUE (wavelength)

VALUE (intensity)

CHROMA (purity)

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21
Q

In dentistry we use a __________ to help us match restorative dental materials to tooth structure.

A

A SHADE GUIDE

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22
Q

What 3 substances are added to composite materials to make them radiopaque on radiographs?

A

Lithium

Barium

Strontium

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23
Q

What does Contact Angle refer to?

A

The angle a drop of liquid makes with the surface it is resting upon.

24
Q

What determines if a material is “Poor/Non Wetting”?

A

Contact Angle greater than 90 degrees and or/ approaching 180 degrees

25
Q

What determines if a material is “Good wetting”

A

contact angle less than 90 degrees

26
Q

What is the relationship between wetting ability and surface dension?

A

the greater the surface tension difference between the liquid and solid the greater the contact angle will be and the lesser the wetting ability.

27
Q

what types of materials have intentionally good wetting properties?

A

varnishes

liners

cements

bonding agents

All have good wetting properties so that they adapt to microscoptic interstices of the surface.

28
Q

Good wetting=

Poor wetting=

A

Good wetting = hydrophilicity

Poor wetting = hydrophobicity

29
Q

Mechanical properties refer to the materials response to __________

A

LOADING

30
Q

What are some types of loading that can by placed on a material?

A
  • compression
  • tension
  • shear
  • torsion (twisting)
  • flexion (bending)
31
Q

Understand the following graph and know the differences between

Plastic deformation

elastic deformation

A
32
Q

Define:

Elastic Strain/Deformation:

Plastic Strain/Deformation:

Elastic limit:

A

Elastic Strain/Deformation- Reversible strain/deformation

  • *Plastic Strain/Deformation-** irreversible strain/deformation
  • *Elastic limit:** The point after which plastic strain occurs
33
Q

Continuous plastic strain eventually leads to _______________

A

Failure by fracture

34
Q

Ultimate strength refers to

A

highest amount of stress tolerable before the material fractures

35
Q

Materials that are resistant to plastic deformation are called:

A

DUCTILE

36
Q

Materials that cannot tolerate very much plastic deformation are called:

A

BRITTLE

37
Q

In general we want restorative materials that are _____ _____ so that under load elastic deformation will be _____.

A

In general,we want a restorative material that is very stiff so that under load its’ elastic deformation will be very small

38
Q

What are the names of the two common hardness tests:

A

MOHS test: scratch resistance comparison

Rockwell, Brinell, Knoop tests: indentation resistance comparison

39
Q

What is Resilience?

A

Resilience is the amount of energy a material can absorb before it starts to undergo PLASTIC DEFORMATION

40
Q

What is Toughness in regards to materials

A

Toughness refers to the total energy that can be absorbed before a material fractures

41
Q

KNOW THIS CHART AND WHAT IT MEANS

A
42
Q

What is “CREEP”

A

deformation over time in response to a constant stress

Weak materials and materials close to their melting point are more prone to “CREEP”

43
Q

What 2 commonly used dental materials are known to exhibit creep??

A

Dental waxes- will creep under their own weight over time

Amalgam restorations- especially low copper amalgams in proximal boxes

44
Q

What is Fatigue

A

strain that occurs over time through multiple cycling of low stresses.

Over time these cycles cause infinitesimal strain, which can eventually lead to failure after millions of cycles.

45
Q

What is the standard design limit for failure due to fatigue?

(how many cycles are materials made to last for)

A

approximately 10 million cycles

46
Q

What is the difference between primary and secondary bonding?

A

Primary Bonding- occurs during chemical reactions

Secondary bonding- occurs during adsorption or absorption

47
Q

for metals in the mouth, primary bonding results from:

1

2

A

Chemical corrosion (tarnishing)

Electrochemical corrosion

48
Q

Electrochemical corrosion occurs when these 4 elements are present

1

2

3

4

A

1 anode (+ charge, site of corrosion)

2 cathode (-charge)

3 circuit

4 electrolyte (saliva)

49
Q

When amalgam and gold restorations these 4 types of corrosion are possible:

1

2

3

4

A

1 Galvanic corrosion- macroscopically different electrode sites

2 local Galvanic corrosion- electrochemical differences in single material (alamgam covered in plaque)

3 crevice corrosion- provide environment for concentration cell corrosion

4 stress corrosion- distribution of mechanical energy is not uniform

50
Q

What 2 materials DO NOT corrode?

A

Ceramics and Polymers

51
Q

Ceramics may not corrode but they can be effected by ____________

A

SOLUBLE DISSOLUTION usually caused by high local acidity

52
Q

What is the difference between adsorption and absorption?

A

Adsorption • adding molecules to a surface by secondary bonding

Absorption • penetration of moleclues into a solid by diffusion

53
Q

The two main issues with BIOLOGICAL PROPERTIES are:

1

2

A

1 Toxicity

2 Sensitivity

Dental materials interact with a variety of tissues and local reactions to various materials may differ.

54
Q

these 2 factors determine a materials toxicity:

1

2

A

1 Exposure time

2 Concentration

55
Q
A

Dental Materials (15 decks)

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