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Op Dent 1 > Materials Exam > Flashcards

Materials Exam Flashcards

1
Q

What are the three main classes of materials?

A

Metals
Polymers
Ceramics

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2
Q

Mechanical Properties - Metals

A

— Hard
— Ductile – Tough
— Strong

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3
Q

Mech Properties- Polymers

A

— Soft
— Ductile - Tough
— Weak

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4
Q

Mech Properties - Ceramics

A

— Hard
— Brittle
— Strong

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5
Q

Bonding - Metals

A 
¢ metallic elements have 1,2,3
electrons in their outer shell
¢ electrons are key to metallic bonds
¢ electrons are loosely bound to nucleus
¢ electrons have free mobility
—  thermal and electrical conductivity —  ductility-bend without breaking
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6
Q

Bonding - Ceramics

A

¢ ionic and covalent bonds associated with ceramics ¢ both are stronger than metallic bonds
¢ covalent >ionic
¢ ionic bonds - electron donor and electron acceptor ¢ covalent bonds-equally shared electrons
¢ non mobile ions

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7
Q

Bonding - Polymers

A

Covalent bonds
¢ High molecular weight
¢ Long molecules composed principally of nonmetallic elements (organic chemistry C,O,N,H)
Polymers are Entangled Long Chains “Cooked Spaghetti”
Derive Strength and Properties From the Entanglement

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8
Q

POLYMERIZATION PROCESS

A

¢ Light Activation of Initiator ¢ Initiation of Monomer

¢ Propagation of Free-Radical ¢ Termination of Free-Radical

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9
Q

Thermal Properties

A

(1-15 ppm/°C)

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10
Q

Ceramic processing

A

Processed by Sintering or Melting at High Temperatures (porcelein)

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11
Q
  1. What factors contribute to each materials mechanical properties?
A

Metals - electrons and microstructure
Polymers - Monomethacrylates vs dimethacrylates (
Ceramics - Crystalline vs noncrystalline - Most dental ceramics are semicrystalline or polycrystalline

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12
Q

polymerization can be initiated by

A

light, heat and chemical mixing

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13
Q

RULE OF MIXTURES

A

By knowing the phases present in the structure of any material and interfacial interactions, it is possible to predict the overall properties fairly well

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14
Q

Fillers Affects Properties

A

Increase filler vol: increase strength, modulus, viscosity, decrease shrinkage.

Increase filler size: increase surface roughness

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15
Q

Understand thermal expansion coefficient

A

most things expand when heated and contract when cooled

— Measure:LCTE-linear coefficient of thermal expansion- cm/cm/°C (ppm/°C)

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16
Q

Understand the chemical implication of heat flow

A

Pulps can can withstand small temperature changes for short times (42°C for 60 sec) restricted circulation of pulp cannot dissipate heat and carry it away.
— Metals have high thermal conductivity so they need thermal insulator like base
— Composites have low thermal conductivity so they do not need base

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17
Q

Color

A

Know that color is defined in a 3D coordinate system

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18
Q

Hue

A

Wavelength

— Color (Roy G Biv)

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19
Q

Value

A

intensity

— brightness

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20
Q

Chroma

A

Purity

— Density or concentration

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21
Q

Mercury issues with Amalgams

A

(a) Disposal
(b) Patient issues

Some patients may exhibit an allergic skin reaction to dental amalgams

(c) Operator issues

Because of mercury toxicity, US government has set threshold limit value (TLV) for sustained (40 hr/wk) exposure at 0.05 mg Hg/m3

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22
Q

Creep

A

Creep is only mechanical property correlated with clinical marginal fracture of low-copper amalgam restorations (no correlation for high-copper products – all have low creep)
Creep mechanism is grain boundary sliding of 1 phase (blocked by η in high-copper amalgams)

The pro- gressive deformation of a material at constant stress is called creep

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23
Q

Amalgam corrosion

A

Galvanic corrosion at interproximal contacts with gold alloys
Electrochemical corrosion because multiple phases
Crevice corrosion at margins
At unpolished scratches or secondary anatomy — lower pH and oxygen concentration of saliva
Corrosion under retained plaque because of lower oxygen concentration
Chemical corrosion from reaction with sulfide ions at occlusal surface

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24
Q

Gamma 1

A

Strongest phase – incompletely consumed starting alloy particles

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25
Q

Gamma 2

A

Weakest phase – 2 in low-copper amalgams (most corrosion prone)

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26
Q

Effect of Alloying on Amalgam

A

Setting expansion changes, other compositional changes.

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27
Q

Elements that are useful in Alloying

A

Copper- High-copper products should be selected — benefit: greater clinical longevity of restorations — much lower creep values measured in laboratory

Zn: Zinc is considered to facilitate machining lathe-cut particles (makes ingot more brittle) and improves corrosion resistance of amalgam, but results in less plastic amalgam mix

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28
Q

Expansion vs. Contraction amalgam

A

Initial contraction from absorption of Hg (diffusion) by amalgam alloy particles
Can be subsequent expansion from formation and growth of 1 and 2 or Cu-Sn (η) phases (matrix)
Final absorption of mercury by remaining amalgam alloy particles causes contraction
No free mercury in final set dental amalgam

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29
Q

Lathe cut vs. Spherical

A

Lathe: Filing or lathe-cut (machined from cast ingot)
Spherical (molten alloy blown through nozzle)

Spherical: Spherical particles are wetted with a lower mercury:alloy ratio than lathe-cut particles
Spherical particles resist forces of condensation less than lathe-cut particles

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30
Q

Phases formed

A

Strongest phase – incompletely consumed starting alloy particles ()
Weakest phase – 2 in low-copper amalgams (most corrosion prone)
Completely interconnected nature of 2 can result in bulk corrosion of low-copper dental amalgam
High-copper amalgams – Cu6Sn5 (η) is corroding phase that provides margin-sealing – because η is not interconnected, corrosion limited to marginal regions without bulk corrosion
Weaker interface between alloy particles and reaction phases

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31
Q

Heat treatment - amalgam

A

Eliminates compositional nonuniformity that exists in ingot before lathe-cutting (machining) or in spherical alloy particles (from freezing process in both cases)
Relieves stresses in alloy particles (both lathe-cut and spherical)
Provide manufacturer control of setting time ― great clinical importance

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32
Q

Hydrophobic vs. Hydrophilic - surface properties

A

Hydrophilic: ¢ Allow penetration into areas with water
¢ Usually mixed with a solvent (alcohol, acetone)
¢ Very low viscosity
¢ Allows for attachment to composite

Hydrophobic: Wetting can be anticipated on the basis of the Hydrophobicity (water-hating) and hydrophilicity (water loving) of materials

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33
Q

Contact Angle

A

contact angle used to measure how liquid interacts with solid
— Good wetting –low contact angle (approach 0)
— Poor wetting- high contact angle (approach 180)

Clinical consequence:
—  Bonding and adhesives
—  Protein and cell attachment
—  Hyrophilic/phobic
—  Surfacearea/rougness
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34
Q

Molecules can have both

A

Hydrophobic and hydrophilic parts

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35
Q

Types of corrosion

A

Galvanic: Metal 1 beside metal 2.
Structure selective corrosion: Phase 1 and 2 interspersed - difference in solidification patterns.
Crevice Corrosion: Crack tip is anode, surrounding is cathode.
Stress corrosion: stress point is anode, unstressed is cathjode.

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36
Q

METAL CORROSION

A

Active - lead to destruction (Gamma 2)
¢ Passive - produce corrosion film that prevents further
corrosion (titanium implants) ¢ Immune - noble metals (gold)

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37
Q

Galvanic

A

metal 1 beside metal 2

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38
Q

Structure selective corrosion

A

Phase 1 and 2 interspersed - difference in solidification patterns.

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39
Q

Crevice Corrosion

A

Crack tip is anode, surrounding is cathode.

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40
Q

Stress corrosion

A

stress point is anode, unstressed is cathjode.

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41
Q

Ceramics - Hydrolysis

A

¢ Chemical Dissolution –normally occurs through dissolution of oxides created by hydrogen bonding effects of water in local areas of high acidity.
¢ Examples
— Acids dissolve HA (caries, acid etch for enamel bonding)
— Acidulated fluoride treatments dissolve ceramic crowns may roughen surface or remove surface stain

42
Q

Polymers- Hydrolysis

A

Hydrolytic degradation and release of components (primary bonds)
— Water, enzymes (esterases), bacterial byproducts — Contributes to wear problem with composites

43
Q

Degradation products are related to

A

toxicity

44
Q

Stress-Strain Curve

A

Review this

45
Q

Toughness

A

before failure occurs

46
Q

Modulus

A

Stiffness

47
Q

creep

A

(strain relaxation)
— Deformation over time in response to low constant
stress

48
Q

Fracture toughness

A

Measures a Materials Resistance to Crack Propagation

¢ Has High Clinical Correlation to Clinical Wear Data (Composites)

49
Q

Teeth are not completely Rigid can lead to

A

abfrations- cyclic stresses

50
Q

Buccal-Lingual Stability

A

Cusp flexure, stress transfer lessened due to filling rigidity.

51
Q

Know the components of composite resins

A

A composite filling is a tooth-colored plastic and glass mixture used to restore decayed teeth. Composites are also used for cosmetic improvements of the smile by changing the color of the teeth or reshaping disfigured teeth.

52
Q

Resin helps

A

processing and handling

53
Q

Filler helps

A

modulus and wear resistance

54
Q

Know what a coupling agent does

A

as a compound which provides a chemical bond between two dissimilar materials, usually an inorganic and an organic.

55
Q

Filler size

A

Viscosity and Strength Controlled by Filler Loading - Increased Filler Loading = Increased Viscosity
and Modulus

56
Q

Glass ionomer cement components

A

Glass other phase, mixed with liquid.

57
Q

Glass ionomer mech

A

l GICs contain a basic glass and an acidic polymer liquid, which set by an acid-base reaction. The polymer is an ionomer, containing a small proportion - some 5 to 10% - of substituted ionic groups. These allow it to be acid decomposable and clinically set readily.

The glass filler is generally a calcium alumino fluorosilicate powder, which upon reaction with a polyalkenoic acid gives a glass polyalkenoate-glass residue set in an ionised, polycarboxylate matrix.

The acid base setting reaction begins with the mixing of the components. The first phase of the reaction involves dissolution. The acid begins to attach the surface of the glass particles, as well as the adjacent tooth substrate, thus precipitating their outer layers but also neutralising itself. As the pH of the aqueous solution rises, the polyacrylic acid begins to ionise, and becoming negatively charged it sets up a diffusion gradient and helps draw cations out of the glass and dentine. The alkalinity also induces the polymers to dissociate, increasing the viscosity of the aqueous solution.

The second phase is gelation, where as the pH continues to rise and the concentration of the ions in solution to increase, a critical point is reached and insoluble polyacrylates begin to precipitate. These polyanions have carboxylate groups whereby cations bind them, especially Ca2+ in this early phase, as it is the most readily available ion, crosslinking into calcium polyacrylate chains that begin to form a gel matrix, resulting in the initial hard set, within five minutes. Crosslinking, H bonds and physical entanglement of the chains are responsible for gelation. During this phase, the GIC is still vulnerable and must be protected from moisture. If contamination occurs, the chains will degrade and the GIC lose its strength and optical properties. Conversely, dehydration early on will crack the cement and make the surface porous.

58
Q

Glass ionomer cements release

A

releases fluoride, can be water based

59
Q

Understand similarities and differences between adhesives and composites

A

ADHESIVES
¢ Based on Composite Resin Chemistry
¢ Contains Acidic Groups to Promote Bonding ¢ Dimethacrylates that Are Visibly Light Cured ¢ Unfilled or Lightly Filled

Composites tend to be hydrophobic, so you need to be able to bridge that gap.

60
Q

Hydrophilic modifiers

A

promote bonding to tooth structure.

61
Q

How sealents differ from composities:

A

Also hydrophilic, but made with a BisGMA-TEGDMA system. Polymeric coating for protection.

62
Q

oxygen inhibition layer

A

Oxygen Interferes with Radical Polymerizations
¢ Surface of VLC Materials are often Uncured
¢ For thin Layers such a Sealants more of a Problem

63
Q

hydrocolloid vs. elastomers

A

Hydrocolloid: Also called “alginate impression material” Used to make dental impressions for:

  • removable partial dentures
  • preliminary impressions for complete dentures - orthodontic models and study models

Elastomers: rubber-like polymers that show an elastic behavior at the time of loading.

64
Q

Alginates are

A

Water based, Calcium Crosslinked

65
Q

Alginate problems

A

Dimensional stability:
Because it is a gel, it undergoes shrinkage or expansion upon loss or gain of water.
Syneresis
Loss of water to the surroundings
Imbibition
Pick up of water from the surroundings
For least dimensional change/avoid distortion: Store impressions in 100% relative humidity Pour quickly after removal from mouth

Limited detail reproduction
Low tear resistance L Single pour only
Quick pouring required
Low dimensional

66
Q

Alginate benefits

A

¢ Generally easy to use
¢ Powder (supplied in can) shaken up before
use for aeration
¢ Water to Powder (W/P) ratio to be carefully
followed as specified by the manufacturer ¢ Lower W/P ratio increases strength, tear
resistance, and consistency; decreases
working and setting times and flexibility
¢ Lower water temperature increases working and setting times
¢ Insufficient mixing produces a grainy mixture and poor recording of detail
¢ Adequate spatulation produces smooth, creamy mix with minimum of voids

67
Q

Polysiloxanes

A

Hydrophobic - Consequences for taking impressions: Hydrophobic but Chemically and Dimensionally Stable n Addition type can be made hydrophilic by:
— simple addition of surfactant, or
— chemical incorporation of hydrophilic moieties into the silicone backbone.

Can Cause Voids Upon Addition of Stone Slurry
¢ Slurry in Water Based

Have Good dimensional stability

68
Q

Polysiloxanes Crosslinked by hydrosilation reaction

A

Additiona silicone

Part A: Siloxane with terminal silane groups
¢ Part B: Siloxane with vinyl terminal groups
¢ Many will Contain surfactants to make this material
hydrophilic.
¢ Cross linking Initiated by chloroplatinic acid.
¢ For extensive impressions, working time of addition
silicones may be lengthened by the addition of a retarder without adversely affecting the other properties.

69
Q

Polyethers

A

Hydrophobic - but better surface characteristics

Many of the Same Characteristics of
Polysiloxanes ¢ Differences
— Hydrophillic — Bad Taste

Good Dimensional stability

70
Q

Gypsum

A

Water cured- calcination occurs to be rid of H20. When mixed with water, reverse reaction takes place, forming stone and releasing heat.

(c) Properties dependent on density and crystal structure
(d) Dental stone used for models not plaster

71
Q

Denture Base and Provisionals composition differences

A

Different fillers provide Hardness and Rigidity to the

72
Q

Denture base is normally

A

VLC

73
Q

Provisionals are normally

A

chemically cured

74
Q

Mouthguards

A

Thermoplastic not Thermoset

Has a Low Softening Point
¢ Thermally Processed with Hot Water ¢ Vacuum Formed – Requires a Die

Copolymer controls properties

75
Q

Role and function of cements

A

Used to Bind Restorations of Appliances to Tooth
Structure. Sometimes Light Cure Not Possible ¢ Cold-Cure for Methacrylate
¢ Water Cure for Cements

76
Q

Requirements for cements

A

Low Viscosity but Good Mechanical Properties

¢ 25 μm Thickness

77
Q

How viscosity and handling properties are modified

A

¢ For Glass-Ionomers it is the Powder to Liquid Ratio
¢ Powder = Filler
¢ More Filler = More Viscosity More Filler = More Modulus

78
Q

Resin Cements

A

Typically One Component Systems
¢ Viscosity and Strength Controlled by Filler Loading
¢ Also by Low Molecular Wt. Monomers
¢ Increased Filler Loading = Increased Viscosity
and Modulus
¢ Orthodontic Bonding Needs to be Reversible for Example
¢ Different Balance of Properties

79
Q

Glass-ionomers

A

Just know this can be used as a cement

80
Q

Understand the function of bases and liners

A

Liner: relatively thin layer of material used to protect the dentin from residual reactants that diffuse out of the restoration or oral fluids that may penetrate leaky restoration interface
¢ Thin Layer so Materials are Lower Viscosity

Bases: Are used to provide thermal protection for the pulp and to supplement mechanical support for the restoration by distributing local stresses from the restoration across the underlying dentin surface during amalgam condensation (or cementation of indirect restorations)
¢ Require Greater Mechanical Properties

81
Q

Calcium Hydroxide

A

Pulp capping

82
Q

ZOE

A

ZOE - Pain reduction

83
Q

Requirements of waxes

A

Temporary Materials
¢ Should Melt at Lower Temperatures ¢ Be Carveable
¢ Burn off
¢ Dimensionally stable

Lower molecular weight materials inbetween polymers and organic liquids

84
Q

Polysiloxanes

A

Hydrophobic covering materials. Really good tear resistance, very stable. Won’t have water issues.

85
Q

Polyethers

A

Similar to siloxanes. A little more hydrophilic. Kind of a half way house.

86
Q

Zinc

A

improves corrosion, makes it more brittle.

87
Q

Alloy

A

improve corrosion resistance, mechanical properties.

88
Q

Linear part of stress-strain

A

modulus (stiffness). This is how much stress it takes to start the bend. Deformation in this region is considered to be reversible. Past this is irreversible. Area under curve is amount of energy material can absorb before failure.

89
Q

Fillers are primarily composed of

A

resin. Composites are 70-80% filled, adhesives are around 20%.

90
Q

Mouthguard

A

two monomers, these two work together to control properties.

91
Q

Waxes

A

in between, not low MW, but doesn’t have entanglement issues as much as polymer.

92
Q

Stress

A

(weight) how much it deforms.

93
Q

Strain

A

– a pull – how much the stress relaxes.

94
Q

Glass ionomers

A

Liquid w/acidic polymer (acrylic acid ex) w/basic glass. Mixing forms a salt, with slight exothermic reaction. This forms aqueous cement. Due to acidity, it bonds to tooth structure. Glass has fluoride, slowly releases over time.

95
Q

More crosslinking

A

higher modulus

96
Q

Polymerization

A

oxygen quenches free radicals, hence why there is an exposed top layer.

97
Q

TRIAD

A

Used for custom tray materials. Comes as a sheet composed of polymethyl… uncured methaculoid monomer in there. This allows the sheet to be flexible, and once it goes into curing machine, it solidifies.

98
Q

TRIM/JET

A

Cold cured – provisional materials. In general these do not have dimethacylates as TRIAD. As it polymerizes it does essentially the same thing as TRIAD.

99
Q

Crosslinking

A

higher modulus, also free monomer can leech out in lower crosslinked materials.

100
Q

Bond

A

You need an acidic portion of a molecule to bind to HA. You also need methacylate portion for polymerization (for adhesive), and it needs hydrophobic portion for binding to composite.

Op Dent 1 (17 decks)

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