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AU13 - Operative Biomaterials > au13_-_operative_biomaterials_20141210194830 > Flashcards

au13_-_operative_biomaterials_20141210194830 Flashcards

1
Q

What are the three main classes of materials?

A

metals, ceramics, and polymers

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2
Q

Give the characteristics of metals (hard/soft, ductile/brittle, strong/weak).

A

hard, ductile (tough), strong

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3
Q

Give the characteristics of ceramics (hard/soft, ductile/brittle, strong/weak).

A

hard, brittle, strong

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4
Q

Give the characteristics of polymers (hard/soft, ductile/brittle, strong/weak).

A

soft, ductile (tough), weak

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5
Q

Do metals have high or low processing temperatures?

A

high

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6
Q

Do ceramics have high or low processing temperatures?

A

high

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7
Q

Do polymers have high or low processing temperatures?

A

low

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8
Q

True or false: Polymers tend to be used as direct processing materials.

A

true

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9
Q

What factors contribute to each materials mechanical properties?

A

-Atomic arrangement (crystalline vs. non-crystalline)-Bonding -primary (metallic, ionic, covalent) -secondary (hydrogen, van der Waals)-Composition (elements and phases)-Defects -macroscopic (pores) -atomic scale (microflaws)*Remember: ABCD!

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10
Q

What is key to metallic bonds?

A

Electrons!-metallic elements have 1, 2, or 3 electrons in their outer shell and electrons are loosely bound to nucleus

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11
Q

What two characteristics do metallic bonds possess due to the mobility of electrons?

A

-thermal and electrical conductivity-ductility (can bend without breaking)

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12
Q

When a metal alloy is created (mixture of 2 or more metals), how does the characteristics of the material change?

A

A pure metal is ductile since the atoms are all the same size and are able to slide.An alloy is stronger, but less ductile since there are different sized atoms.

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13
Q

What types of bonds are associated with ceramic bonds? Are they stronger or weaker than metallic bonds?

A

-ionic and covalent bonds (covalent > ionic)-both are stronger than metallic bonds

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14
Q

What makes up the microstructure of ceramics?

A

mixture of metallic and non-metallic elements

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15
Q

What are the most common compounds in ceramics for dentistry? What is the building block of ceramics?

A

-3 metallic oxides: SiO2, Al2O3, and K2O are most common-SiO4 tetrahedron is the building block

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16
Q

What makes up the microstructure of dental porcelain?

A

-SiO4 is the building block-primarily a glass with some crystalline residuals (quartz and leucite)

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17
Q

What type of bond is found in polymer bonds?

A

covalent bonds

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18
Q

What elements primarily make-up polymers?

A

nonmetallic elements (C, O, N, and H)

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19
Q

How may polymerization be initiated?

A

by light, heat, and chemical mixing

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20
Q

Name and describe the 4 stages of chain reaction polymerization.

A
  1. Activation - free radical initiation (with light, heat, or chemical mixing)2. Initiation - free radical combination with monomer unit; double-bond opening3. Propagation - chain growth, volume decrease, shrinkage4. Termination
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21
Q

Name the monomer functional group needed to make a linear polymer.

A

monomethacrylates - each only has one polymerizable unit so it makes linear chains

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22
Q

Name the monomer functional group needed to make a branched and cross-linked polymer.

A

dimethacrylates - has two polymerizable units so it may make branched and cross-linked polymers

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23
Q

What is needed in a direct placement material?

A

-flowable material-stable material-trigger for setting-rapid setting-room temperature setting reaction

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24
Q

What are the pros and cons of a direct placement material?

A

Pros: less preparation needed, one visitCons: material often does not last as long

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25
Q

What are the pros and cons of an indirect placement material?

A

Pros: longevity of restorationCons: multiple visits needed, expensive

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26
Q

Metals are typically used for indirect placement with one exception. What is that exception?

A

amalgam

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27
Q

Ceramics are typically used for indirect placement with one exception. What is that exception?

A

cements

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28
Q

Are polymers generally used for direct or indirect placement?

A

direct placement

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29
Q

What is a composite?

A

a physical mixture of metals, ceramics, and/or polymers in order to achieve some intermediate properties between the two material types

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30
Q

What is the rule of mixtures?

A

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

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31
Q

When the volume of filler increases, does the strength of the material increase or decrease?

A

increase

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32
Q

When the volume of filler increases, does the modulus (stiffness) increase or decrease?

A

increase

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33
Q

When the volume of filler increases, does the viscosity increase or decrease?

A

increase

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34
Q

When the volume of filler increases, does the shrinkage increase or decrease?

A

decreases

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35
Q

When the filler size increases, does the surface roughness increase or decrease?

A

increase

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36
Q

Rank the thermal expansion coefficient from smallest to largest for polymers, ceramics, and metals.

A

smallest: ceramics (1-15 ppm/*C)metals (10-30)largest: polymers (30-600)

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37
Q

Rank the thermal expansion coefficient from smallest to largest for amalgam, tooth, and composite.

A

smallest: tooth (9-11)amalgam (25)largest: composite (28-35)

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38
Q

When a material is heated, does it expand or contract?

A

expand

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39
Q

Explain heat flow in a tooth. What are the clinical consequences of heat flow in dentistry?

A

-teeth are insulators due to high mineral content-pulp can only withstand small temperature changes for a short time due to the restricted circulation of pulp which cannot dissipate heat and carry it away

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40
Q

Do metals have a high or low thermal conductivity?

A

high thermal conductivity so they need a thermal insulator-like base

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41
Q

Do composites have a high or low thermal conductivity?

A

low thermal conductivity so they do not need a thermal insulator-like base

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42
Q

How many dimensions define color? What are those dimensions?

A

3 dimensions (3D); hue, value, and chroma

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43
Q

What is hue?

A

wavelength and color (ROYGBIV)

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44
Q

What is value?

A

intensity and brightness

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45
Q

What is chroma?

A

purity and density/concentration

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46
Q

What is metamerism?

A

two objects that appear the same color under one light source and different under another light source; they have different spectral characteristics

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47
Q

What are the 3 routes of mercury exposure?

A

-skin contact-inhalation of vapor-airborne droplets

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48
Q

At how many nanograms of mercury per mL blood are symptoms of mercury poisoning observed?

A

100 ng/mL blood

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49
Q

How should mercury be disposed of in a dental practice?

A

-use single-use capsules-use a no-touch technique and clean up any spilled mercury-store/discard dental amalgam scrap in cool space in capped, unbreakable jar holding water with finely divided sulfur

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50
Q

What does the ADA recommend for operators using mercury in their practices?

A

-single-use capsules-no-touch technique to clean any spills-discard old or damaged mixing capsules-store any scraps in a cool space in a capped, unbreakable jar holding water with finely divided sulfur-avoid baseboard heating in operatories where dental amalgam is used-use face mask and water spray with high vacuum evacuation when finishing new dental amalgam restorations or removing old restorations-do not use ultrasonic condensers-check mercury vapor levels frequently-office personal should have mercury levels monitored periodically through urinalysis

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51
Q

What type of reaction may some patients experience with exposure to dental amalgams?

A

allergic skin reaction; other options other than amalgam are available for restorations

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52
Q

Is it better to have high-copper or low-copper materials? Why?

A

high-copper-greater clinical longevity of restorations-much lower creep values measured in laboratory

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53
Q

What are the consequences of placing zinc in a material?

A

-facilitates machining lathe-cut particles (makes it more brittle)-improves corrosion resistance-less plastic amalgam mix

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54
Q

What are the consequences of having a zinc-free alloy?

A

no concerns about moisture contamination during trituration or condensation

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55
Q

If there is a higher mercury-alloy ratio, would the setting time increase or decrease?

A

setting time would increase (slower setting time)

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56
Q

What is the composition of gamma 1?

A

Ag2Hg3

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57
Q

What is the composition of gamma 2?

A

Sn8Hg

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58
Q

In low-copper dental amalgams, what is the setting reaction equation?

A

alloy (gamma) + Hg –> (gamma)1 + (gamma)2 + unreacted alloy particles

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59
Q

In high-copper dental amalgams, what is the setting reaction equation?

A

alloy (gamma) + Hg –> (gamma)1 + n’ + unreacted alloy particles*NOTE: (gamma)2 does not form

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60
Q

What are the three metal elements that are reacted with mercury in high- and low-copper amalgams?

A

silver (Ag), tin (Sn), and copper (Cu)

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61
Q

What is the composition of n’ that is produced in the high-copper amalgam setting reaction?

A

Cu6Sn5

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62
Q

For dispersalloy-type dental amalgams (low-Cu lathe-cut and spherical Ag-Cu particles of eutectic composition), what is the setting reaction equation?

A

Two steps:1. (gamma)1 + (gamma)2 form2. (gamma)2 disappears; n’ phase appears

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63
Q

Which sets faster: high-copper spherical particles of single composition (HCSS) or dispersalloy-type dental amalgams?

A

HCSS is faster because it is only 1 step as opposed to 2

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64
Q

When amalgams set, do they expand or contract?

A

slightly contract; clinical problems would occur with excessive setting expansion (loss of anatomy and postoperative pain) or excessive setting contraction (microleakage)

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65
Q

Describe the steps of the setting process of amalgams.

A

Setting process is combination of solution and crystallization (precipitation).1. initial contraction from absorption of mercury (diffusion) by amalgam alloy particles.2. can be subsequent expansion from formation and growth of (gamma)1 and (gamma)2 or Cu-Sn (n’) phases (matrix)3. final absorption of mercury by remaining amalgam alloy particles causes contractionno free mercury in final set dental amalgam!

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66
Q

What is the strongest phase of dental amalgams?

A

gamma phase (incompletely consumed starting alloy particles)

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67
Q

What is the weakest phase of dental amalgams?

A

(gamma)2 phase (in low-copper amalgams

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68
Q

What are the 6 types of corrosion in dental amalgams?

A
  • galvanic corrosion - at interproximal contacts with gold alloys- electrochemical corrosion - because multiple phases- crevice corrosion - at margins- corrosion 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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69
Q

Limited corrosion is beneficial. Why?

A

because it reduces microleakage ((gamma)2 in low-copper amalgams and n’ in high-copper amalgams)

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70
Q

How can corrosion be minimized?

A

by polishing amalgam restorations (scratches and pits trap debris, enhancing corrosion because lower oxygen concentration under deposit)

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71
Q

What metal may reduce corrosion in amalgam?

A

zinc

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72
Q

Does amalgam have low or high tensile strength?

A

low tensile strength; allows fracture of edges easily

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73
Q

Does amalgam have low or high compressive strength?

A

high compressive strength; strength increases as the amalgam sets until it reaches maximum strength at approximately 1 week

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74
Q

What is creep? How does it occur?

A
  • metals may become elongated or deformed as a result of a load being applied for a long period of time- grain boundary sliding of (gamma)1 phase
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75
Q

Do high-copper amalgams have high or low creep?

A

low creep; the n’ phase blocks sliding of the (gamma)1 phase in high-copper amalgams

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76
Q

Do low-copper amalgams have a high or low creep?

A

high creep; creep is the only mechanical property correlated with clinical marginal fracture of low-copper amalgam restorations

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77
Q

Why is it important to have adequate trituration time?

A

so that all alloy particles are coated with mercury and optimum mechanical properties are obtained

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78
Q

With what type of amalgam is moisture contamination a problem? What will moisture contamination cause?

A
  • zinc-containing dental amalgam- causes delayed setting, excessive increase in setting expansion and decreased strength (H2 is released from Zn reduction of water)
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79
Q

What will happen if amalgam is overtriturated?

A

makes the material hot, reduces working time, and increases creep

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80
Q

What 3 things were considered historically when placing amalgam?

A
  • adapt amalgam to cavity walls- minimize porosity in restoration- control final mercury content of resotration
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81
Q

What elements make up the alloy in amalgam?

A

silver, tin, copper, zinc, indium, mercury, and/or noble metals, gold, platinum, and palladium

82
Q

What are the two methods of making amalgam particles?

A
  • filing or lathe-cut (machined from cast ingot)- spherical (molten alloy blown through nozzle)
83
Q

Which type of amalgam particles (lathe-cut or spherical) are wetted with a lower mercury:alloy ratio?

A

spherical particles

84
Q

Which type of amalgam particles (lathe-cut or spherical) are able to resist forces of condensation more?

A

lathe-cut particles

85
Q

What does a contact angle measure?

A

how a liquid interacts with a solid

86
Q

Explain what a low contact angle (approaching 0) would mean.

A

good wetting because the liquid would rather interact with the surface than itself

87
Q

Explain what a high contact angle (approaching 180) would mean.

A

poor wetting because the liquid would rather associate with itself than the surface

88
Q

What is the difference between hydrophobic and hydrophilic?

A
  • hydrophobic is “water-fearing” which means that the surface will not interact well with water- hydrophilic is “water-loving” which means that the surface will interact readily with water
89
Q

True or false: Molecules can have both hydrophilic and hydrophobic components.

A

true

90
Q

What is a hydrophilic primer/adhesive used for?

A

Tooth structure is hydrophilic, but composite is hydrophobic so they wouldn’t be able to attach to one another. A hydrophilic primer/adhesive is used which has a hydrophilic portion that adheres to the tooth structure and a hydrophobic portion that adheres to the composite.This is called surface wetting.

91
Q

When is surface wetting important?

A
  • anytime two different materials come into contact- impression materials- adhesives- bacterial adhesion
92
Q

What affects primary bonding?

A

chemical and electro-chemical reactions

93
Q

What affects secondary bonding?

A

processes such as adsorption (onto) and absorption (into)

94
Q

Define corrosion.

A

the spontaneous destructive oxidation of metals

95
Q

Which are the only metals not to corrode spontaneously in Earth’s normal atmosphere?

A

gold, platinum, and palladium (noble metals)

96
Q

Differentiate between active and passive corrosion.

A
  • active corrosion - leads to destruction ((gamma)2)- passive corrosion - produce corrosion film that prevents further corrosion (titanium implants)
97
Q

What are the 4 types of corrosion? Explain each.

A
  • galvanic corrosion - one metal acts as cathode and one metal acts as anode- structure selective corrosion - each phase in a two-phase mix acts as either a cathode or an anode- crevice corrosion - surface of the restoration acts as a cathode and crack tip of prep acts as anode- stress corrosion - stressed restoration acts as anode and unstressed region acts as cathode
98
Q

What does an anode do during corrosion? What does a cathode do during corrosion?

A
  • anode - corroding metal- cathode - different metal (passive-supplied electrons to solution)
99
Q

How are ceramics affected through chemical dissolution? Give examples.

A

normally occurs through dissolution of oxides created by the hydrogen bonding effects of water in local areas of high acidity- examples: - acids dissolve hydroxyapatite (caries, acid etch for enamel bonding) - acidulated fluoride treatments dissolve ceramic crowns and may roughen surface or remove surface stain

100
Q

How are the primary and secondary bonds of polymers affected over time?

A
  • absorption of water into polymers (secondary bonds) causes dimensional changes- hydrolytic degradation and release of components (primary bonds); water, enzymes (esterases), and bacterial byproducts contribute to wear problem with composites
101
Q

What two molecules are of concern due to their toxicity if amalgam or composite restorations should break down?

A
  • mercury- bisphenol A (BPA) - concern of cancer (especially in children)
102
Q

What metal ions and compound are of concern when they interact with amalgams/composites due to sensitivity? What breakdown product is of concern?

A
  • mercury, nickel, and monomers (latex) are of concern when they interact with amalgams/composites- small organic molecules like formaldehyde is a breakdown product of concern
103
Q

On the stress-strain curve, what is represented at the highest point of the linear portion of each curve?

A

proportional limit (elastic limit) - the highest amount of stress/strain in which the material is still able to return to its original form

104
Q

What is represented by the peak of each curve? Where is this located on the curves for metals? For ceramics? For polymers?

A

ultimate strength - the largest amount of stress that can be applied before the material fails- for metals and ceramics, this is the last point on the curve- for polymers, the curve continues downward from this point

105
Q

Rank the materials (metal, ceramic, and polymer) in order of steepest slope to flattest slope on the stress-strain curve.

A

steepest: ceramicmetalflattest: polymer

106
Q

What is represented by the slope of the linear portion of each curve in the stress-strain graph?

A

elastic modulus - measurement of stiffness of material (higher modulus = more stiff = steeper slope)

107
Q

How is the plastic deformation for a material found on a stress-strain graph?

A

draw a line from the point of ultimate strength (endpoint for ceramic and metal curves) to the x-axis with the same slope as the slope of the curve; the length of the x-axis between the intersection of the curve and the new line is plastic deformation (which is irreversible)

108
Q

A curve with a very steep linear slope and a short rounded curve represents a material that is: stiff/ductile, stiff/brittle, or flexible/ductile?

A

stiff/brittle

109
Q

A curve with a very flat slope and a very long curved portion represents a material that is: stiff/ductile, stiff/brittle, or flexible/ductile?

A

flexible/ductile

110
Q

A curve that has a slightly steep slope and a longer curve represents a material that is: stiff/ductile, stiff/brittle, or flexible/ductile?

A

stiff/ductile

111
Q

What does modulus measure?

A

stiffness

112
Q

What is the difference between resilience and toughness?

A
  • resilience - the amount of absorbed energy before deformation occurs- toughness - the amount of absorbed energy before failure or fracture occurs
113
Q

If a metal is heated, how does its stress-strain curve change?

A

becomes more similar to the stress-strain curve of a polymer with a flatter slope and longer curve

114
Q

What is the definition of creep?

A

the deformation over time in response to low constant stress

115
Q

What is the definition of fatigue?

A

under many cycles, small amounts of deformation accumulate until failure occurs at low stresses

116
Q

What does fracture toughness measure?

A

measures a material’s resistance to crack propagation; deliberately put a crack in a sample and pull it apart to measure how much stress is needed to propagate crack

117
Q

True or false: Teeth are completely rigid.

A

FALSE. Teeth are not completely rigid. When teeth are subject to chewing forces (stresses), they undergo subclinical movements (strains).

118
Q

What can the lack of rigidity in teeth lead to?

A

abfraction

119
Q

What does an abfraction look like clinically?

A

heavy wear facets near the CEJ

120
Q

What is buccal-lingual stability?

A

the stability that is created when the buccal and lingual cusps meet each other in the central groove; they stabilize each other

121
Q

What may happen to the buccal-lingual stability during a cavity prep? What could this result in?

A
  • buccal-lingual stability will be weakened if the prep removes the central groove and part of the buccal and lingual cusps because the cusps would no longer be able to support each other- this could result in cusp fracture
122
Q

What makes up a composite?

A

hybrid material of an organic phase (resin) and an inorganic (filler) phase

123
Q

What is the role of resin in a composite?

A

helps processing and handling

124
Q

What is the role of filler in a composite?

A

helps modulus and wear resistance

125
Q

What are the characteristics of organic polymers?

A

tougher, but not as strong or wear resistant

126
Q

What are the characteristics of inorganic materials?

A

strong and wear resistant, but brittle

127
Q

What type of reaction occurs in order to cure composite?

A

cross-linking reaction

128
Q

What triggers the cross-linking of polymers when composite is cured?

A

visible light

129
Q

What are 2 ways to change the density of cross-linking?

A
  • number of cross-linking groups- degree of cross-linking or degree of curing
130
Q

What are the 4 components of composite resin?

A
  • resin system- filler- bonding agent- visible light initiator
131
Q

What are the 3 types of fillers?

A
  • micron (fine)- nano (microfine)- nano (microfine) in polymer matrix
132
Q

What are the benefits of having a smaller filler size?

A
  • teeth are nanocomposites- smaller fillers should have better wear properties- allows for better polishing and finish- expectation of better mechanical properties
133
Q

What is the difference between a nano (microfine) filler and a nano (microfine) filler in a polymer matrix? In other words, which has a tendency to aggregate? Which has poorer filler to matrix bonding?

A
  • nano (microfine) filler has a tendency to aggregate- nano (microfine) filler in a polymer matrix has poorer filler to matrix bonding because there is no coupling agent
134
Q

What is a coupling agent?

A

a chemical substance that can react with the resin and the filler and enhance filler-to-matrix bonding

135
Q

When a composite polymerizes, does it swell or shrink? Why?

A

shrink because there is a density change when it goes from monomer to polymer

136
Q

What are the clinical consequences of polymerization shrinkage?

A
  • causes stress on the tooth structure- can cause microleaks and lead to secondary caries
137
Q

What are the components of glass-ionomer cement?

A
  • acidic polymer in aqueous solution- basic glass- water- modifiers (+) tartaric acid (*don’t need to know?)
138
Q

What type of reaction cures glass-ionomer cement?

A

acid/base reaction

139
Q

What type of bond is formed between polyacids and basic glass in the setting of glass-ionomer cement?

A

salt bridges

140
Q

Explain the steps of the setting process of glass-ionomer cement.

A
  • glass-ionomer mix is applied- acid matrix dissolves periphery glass- glass releases ions: Ca, Al, and F- divalent Ca ions quickly chelate with acid polymer chains- in the next 24-72 hours, Al replaces Ca which increases the strength and F is released- acid side groups can also chelate with glass and hydroxyapatite
141
Q

Why does the glass-ionomer cement become stronger when Al replaces Ca in the salt bridges?

A

because Ca has a +2 charge so it can bind 2 of the acid or base together, but Al has a charge of +3 so it can bind 3

142
Q

Is a coupling agent required in the setting reaction of glass-ionomer cement?

A

No, but it is required in the composite setting reaction

143
Q

What is released during the setting of glass-ionomer cement?

A

fluoride and sodium which continue to be released over time

144
Q

True or false: Glass-ionomer cement is a water-based restorative material.

A

true

145
Q

What are some similarities or differences between adhesives and composites?

A

Similarities:- light cured- made of dimethacrylates (?)Differences:- composite is hydrophobic while adhesives are hydrophobic and hydrophilic- adhesives may be unfilled (or lightly filled)

146
Q

What is the difference between a macrotag and microtag of an adhesive?

A
  • macrotag - interprism (between prisms) resin penetration- microtag - intraprism (within prism) resin penetration
147
Q

Which side of the adhesive (hydrophilic or hydrophobic) binds to the enamel of the tooth? Which side binds to the composite?

A
  • hydrophilic binds to the tooth- hydrophobic binds to the composite
148
Q

What are some similarities and differences between sealants and composites?

A

Similarities:- has a BisGMA/TEGDMA systemDifferences:- no filler in sealants

149
Q

What is the oxygen inhibition layer? With what type of material is this more of a problem?

A

When a material is being cured with radical polymerization, free radicals are generated in order to form cross-links. But oxygen can terminate the free radicals so the top layer that is exposed to the atmosphere may not be cured. This is a problem with thin layers like sealants.

150
Q

What are the requirements of ideal impression materials?

A
  • low cost- long shelf life- biocompatibility- pleasant to patient- dimensionally stable- good handling properties
151
Q

What are the 3 main classes of impression materials? Name the 2 subtypes of each class.

A
  • rigid: ZOE and plaster- plastic: wax and compound- viscoelastic: hydrocolloid and elastomers
152
Q

True or false: Alginate is an irreversible hydrocolloid impression material that is water-based.

A

true

153
Q

What is formed when alginic acid is soluble in water?

A

sol which resembles a solution, but is made up of colloidal particles dispersed in a liquid

154
Q

What ion cross-links alginate?

A

calcium

155
Q

What two parameters control the setting reaction of alginate?

A
  • temperature controlled (reversible)- chemically controlled (irreversible)
156
Q

What is dimensional stability of alginate? How can you minimize it?

A
  • Because it is a gel, it undergoes shrinkage or expansion upon loss or gain of water.- minimize it by storing it in 100% humidity and by pouring quickly after removal from mouth
157
Q

What is syneresis?

A

loss of water to the surroundings (part of dimensional stability)

158
Q

What is imbibition?

A

pick up of water from the surroundings (part of dimensional stability)

159
Q

What are the advantages of water-based alginate?

A
  • economical- easy to use- quick setting- fair taste- hydrophilic- can displace blood and saliva- stock trays
160
Q

What are the disadvantages of water-based alginate?

A
  • limited detail reproduction- low tear resistance- single pour only- quick pouring required- low dimensional stability
161
Q

Is polysiloxane impression material normally a hydrophilic or hydrophobic material?

A

hydrophobic

162
Q

How can polysiloxane material be made hydrophilic?

A
  • adding a surfactant- chemical incorporation of hydrophilic moieties into the silicone backbone
163
Q

Why is the hydrophobicity of polysiloxane a problem in taking impressions and transferring detail to a model?

A
  • the oral cavity is hydrophilic so it may cause some difficulty in registering oral structure- when pouring the stone slurry into the impression, it may cause voids since the slurry is water-based
164
Q

What reaction forms the cross-links of polysiloxanes?

A

hydrosilation reaction

165
Q

Does polysiloxanes have good or bad dimensional stability?

A

good

166
Q

What is the role of a surfactant in polysiloxanes?

A

improves (along with polyethers) detail registration and detail transfer by making the polysiloxane more hydrophilic

167
Q

Of these two hydrophobic compounds (polysiloxanes and polyethers), which is more hydrophilic?

A

polyethers

168
Q

Do polyethers have good or bad dimensional stability?

A

good

169
Q

With what is gypsum cured?

A

water

170
Q

Through what process is gypsum dehydrated?

A

calcination

171
Q

What is the dehydration/rehydration reaction that is responsible for the synthesis of gypsum and the curing of it?

A

(CaSO4/0.5H2O) + 1.5H2O –> (CaSO4/2H2O) + 3900 cal/g*mol)- hemihydrate is converted back into a dihydrate via an exothermic reaction

172
Q

The properties of gypsum are dependent on what 2 characteristics? How does this affect the gypsum?

A
  • density and crystal structure- if the crystals are dense, regularly-shaped, and relatively non porous, the material will not require much water and will be stronger (dental stone - alpha form)- if the crystals are less dense, irregularly-shaped, and porous, it will require more water to mix and the material will be weaker (dental plaster - beta form)
173
Q

Which type of gypsum (dental plaster or dental stone) is used to make dental models?

A

dental stone

174
Q

How is Triad (denture base material) cured?

A

visible light cured (VLC)

175
Q

How are provisionals cured?

A

chemically cured (by mixing)

176
Q

Why is there a difference in composition between denture bases and provisionals?

A
  • denture bases need to last a long time, have fillers, and dimethacrylates that cross-link- provisionals are more temporary and need to be removed, no cross-linking; chemistry is very similar to the “cold cure” Triad (denture base)
177
Q

Are mouth guards made of thermoplastic or thermoset material?

A

thermoplastic(low softening point, thermally processed with hot water, vacuum formed so it required a dye)

178
Q

What controls the properties of the thermoplastic mouth guard material?

A

copolymer of ethylene and acetate

179
Q

What is the function of cements?

A

used to bind restorations or appliances to tooth structure

180
Q

What are the requirements for cements?

A

low viscosity (needs to fill voids) but good mechanical properties

181
Q

If you wanted a cement to become more viscous, how would you modify it?

A

add more filler (powder)

182
Q

If you wanted a cement to become less modulus, how would you modify it?

A

add less filler (powder)

183
Q

Would a low powder:liquid ratio increase or decrease the working and setting time?

A

increase

184
Q

What are resin-based cements generally used for?

A

orthodontics, ceramic crowns and bridges, veneers, inlays/onlays

185
Q

What can be added to promote binding in resin adhesives?

A

4-meta modifier

186
Q

What are liners?

A

a 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

187
Q

Do liners have a low or high viscosity?

A

low

188
Q

When is a calcium hydroxide liner used?

A

when there is exposure or near exposure of the pulp during a caries restoration

189
Q

What is an indirect pulp cap?

A

the decay close to the pulp is left during restoration and secondary dentin is formed and after awhile, decay can be removed without damaging the pulp

190
Q

What is a direct pulp cap?

A

expose the pulp to medicament to stimulate secondary dentin formation

191
Q

How does a calcium hydroxide liner work?

A

liner releases hydroxide ions (pH>11); when ionized in low concentration, it stimulates odontoblast formation

192
Q

What is ZOE (zinc oxide eugenol) used for?

A

pain reduction

193
Q

Why can ZOE not be used with composite restorations?

A

because it inhibits polymerization

194
Q

Does calcium hydroxide lines inhibit polymerization?

A

no

195
Q

Why are liners and bases used?

A

to protect the pulp and minimize post-op sensitivity- acts as a thermal and chemical barrier- controls inflammation of the pulp- controls fluid movement

196
Q

What is the function of bases?

A

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)

197
Q

Do bases or liners require greater mechanical properties?

A

bases because they are providing physical protection

198
Q

What is the most common base?

A

glass-ionomer

199
Q

What do glass-ionomers release?

A

fluoride

200
Q

What are the requirements of waxes?

A
  • temporary materials- should melt at lower temperature- be carveable- burn off- dimensionally stable
201
Q

True or false: higher molecular weight materials are in between polymers and organic liquids

A

FALSE. Lower molecular weight materials (waxes) are in between polymers and organic liquids.

AU13 - Operative Biomaterials (1 decks)

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