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1
Q

What are the three main classes of materials?

A

metals, ceramics, polymers

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2
Q

What are the mechanical properties of metals?

A

Hard, ductile, strong

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3
Q

What type of structure do metals have?

A

crystalline, forms grains

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4
Q

What is an alloy?

A

mix of 2 or more metallic elements, can be homogenous or multi-phase, stronger but less ductile

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5
Q

What type of bonds do metals form?

A

Metallic bonds

1-3 electrons in outer shell held loosely to nucleus

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6
Q

What results from metal electrons being able to move freely?

A

thermal/electrical conductivity and ductility

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7
Q

T or F: metals act as thermal conductors

A

true

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8
Q

What are the mechanical properties of ceramics?

A

hard, brittle, strong

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9
Q

What is the composition of ceramics?

A

a mixture of metal and non metal elements

metal oxides are most common in dentistry

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10
Q

What type of bonds do ceramics form?

A

ionic or covalent

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11
Q

Relative bond strengths

A

Covalent > ionic > metallic

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12
Q

What are the mechanical properties of polymers?

A

soft, ductile, weak

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13
Q

What type of bonds do polymers form?

A

covalent bonds

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14
Q

What is the composition of polymers?

A

long molecules of non metallic elements, “cooked spaghetti”

entanglement gives strength and properties

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15
Q

What temperatures are required for processing of metals, ceramics, and polymers?

A

high, high, low

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16
Q

Steps of polymerization

A

activation, initiation, propagation, and termination

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17
Q

Activation

A

step 1: initiator molecule is activated by light, heat, or mixing to form free radicals

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18
Q

Initiation

A

step 2: free radicals combine with monomer units in polymer mixture, attachment of free radical opens up double bond on monomer, creating new free radical

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19
Q

Propagation

A

step 3: constantly forming monomer free radicals continue to bind with other monomers, polymer chain grows

volume of polymer mix decreases and shrinks as chain grows

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20
Q

Termination

A

step 4: floating free radical bonds to free radical end of the polymer chain creating double bond and capping off chain

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21
Q

Linear polymers

A

form from monomethacrylates, only one free radical end, “tangled spaghetti”

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22
Q

Crosslinked polymers

A

form from dimethacrylates, short chain with two free radical ends, “fishing net”, network is formed

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23
Q

What is composite?

A

a physical mixture of metals, ceramics, and polymers

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24
Q

What is the rule of mixing for composites?

A

want composite properties to be as similar to tooth structure as possible

can predict properties fairly well by knowing phases present

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25
Dispersed phase
glass filler: low flow, high strength
26
Matrix phase
monomer resin: high flow, low strength
27
What impact does more filler volume have on final properties?
increase strength, modulus, toughness, and viscosity, decrease shrinkage
28
What impact does smaller filler size have on final properties?
smoother surface
29
What is the thermal expansion coefficient?
rate of change of a material's size upon heating/cooling (in ppm/decree C)
30
Chemical implications of heat flow
thermal conductivity and diffusivity
31
Are dentin and enamel thermal insulators or conductors?
insulators, because high mineral content
32
Do lines have to be used with metals? composites?
yes, no
33
How is color defined?
3D coordinate system
34
What are the components of the color system?
hue, value, chroma
35
What is metamerism?
when 2 objects appear the same color under one light, but different under another because of special characteristics
36
What issues does mercury in amalgam cause?
disposal, pt issues, operator issues
37
What is creep?
a solid material deforming permanently over time under low constant stress
38
What metals are immune to corrosion?
noble metals: gold, platinum, palladium, titanium?
39
What are the two types of corrosion?
active: destruction of metal passive: produces film on surface preventing further corrosion
40
What elements are used in alloying of amalgam?
copper and zinc
41
What is the effect of alloying on amalgam?
amalgam becomes stronger, but less ductile (differently sized atoms prevent sliding)
42
What are the phases of amalgam?
gamma 1, gamma 2
43
What is the chemical composition of the gamma phases?
Ag3Sn
44
What type of chemicals wet hydrophilic surfaces?
hydrophilic chemicals
45
What is a contact angle?
angle between tangent to liquid droplet and surface
46
What does a large contact angle indicate?
poor wetting (droplet NOT spread out)
47
What are the types of active corrosion in metals?
galvanic, structure selected, crevice corrosion, stress corrosion
48
What is the degradation process for ceramics?
hydrolysis via chemical dissolution
49
What is the degradation process for polymers?
hydrolysis via 1. absorption of water into polymers 2. hydrolytic degradation and release of polymer components
50
What are some concerns about degradation problems
sensitivity and toxicity
51
What does a steeper modulus on a stress-strain curve indicate?
stiffer material
52
What are the characteristics on a stress strain curve of a stiff and brittle material?
steep modulus, small plastic region
53
What are the characteristics on a stress strain curve of a stiff and ductile material?
steep modulus, large plastic region
54
What are the characteristics on a stress strain curve of a flexible and ductile material?
loe modulus, plastic region continues past ultimate strength *can reach deformation without failing
55
How does heat effect mechanical properties?
materials become more flexible and less tough
56
What is fatigue?
weakening of a material caused by repeatedly applied loads
57
What is fracture toughness?
a measure of a material's resistance to crack propagation (ability of cracked material to resist fracture)
58
T or F: teeth are completely rigid
false, leads to abfractions
59
Why is buccal lingual stability important?
so B and L cusps can all withstand biting chewing forces
60
How do preps lead to B L instability?
an overextended prep, or unequally extended prep can lead to cusp fracture
61
What are the components of composite resin?
1. resin (organic phase) | 2. filler (inorganic phase)
62
What is the role of resin in composite resin?
helps processing and handling
63
What is the role of filler in resin composite?
helps modulus and wear resistance
64
What happens to composite resin when resin amount is increased?
increases toughness, flowability, decreases wear resistance
65
What happens to composite resin when filler volume is increased?
higher modulus (stiffer)
66
What is cross linking?
inducing polymerization of resin, forms bonds between polymer chains and resin
67
What results from smaller filler sizes?
better material, lower modulus but more surface area = better wear resistance
68
What does a coupling agent do?
adds methacrylate groups that can bond with polymer chains to surface of filler, forms very strong bonds between filler and resin
69
What causes polymerization shrinkage?
resin portion shrinks upon polymerization because density change from monomer to polymer
70
What is a result of shrinkage?
stress of tooth, microleaks leading to secondary caries
71
What are the components of glass ionomer cements?
acidic polymer (polycarboxylate cement) in aqueous solution and basic glass
72
How are glass ionomers cured?
acid/base rxn, salt bridges for cross linkages
73
GI is a _____ restorative
water based
74
GI release of fluoride
from toothpaste, releases daily, more so in early life span of GI
75
What type of modifiers promote bonding?
hydrophilic
76
How are adhesives similar to composites?
based on composite resin chemistry, hydrophilic AND hydrophobic
77
How do sealants differ from composites?
only contain 0-10% filler, not intended for longevity, bonding is mostly mechanical
78
What is the oxygen inhibition layer?
the top layer of sealant that doesn't solidify well because of O2 in environment, needs to be wiped off
79
What are the two major classes of impression materials?
hydrocolloid (includes alginate and ager-ager) and elastomers (viscoelastic)
80
What are the ideal properties of impression materials?
low cost, long shelf life, biocompatible, pleasant to pt, dimensionally stable, good handling properties
81
Alginates are _____ based
water
82
What type of crosslinkages occur in alginates?
calcium
83
What are advantages of alginate being water based?
surface energy allows for good wetting of tooth and gypsum
84
What are disadvantages of alginate being water based?
bad dimensional stability (water loss and gain), limitied detail reproduction, low tear resistance
85
Polysiloxanes are hydro____
phobic
86
What are the consequences of taking impressions with polysiloxanes?
because hydrophobic, can repour, excellent accuracy, expensive, difficult to vary setting time, good dimensional stability
87
How are polysiloxanes crosslinked?
via hydrosilation rxn
88
What is the role of surfactants?
can make silicone hydrophilic, improve detail registration and transfer
89
Polyethers are hydro_____
phobic
90
Do polysiloxanes or polyethers have better surface characteristics?
polyethers
91
How is gypsum cured?
water
92
What is the hydration-dehydration sequence?
gypsum is first the dihydrate form of calcium sulfate, then dehydrated to calcium sulfate hemihydrate (calcination)
93
What are the properties of gypsum dependent upon?
density and crystal structure (interlocking contributes to strength)
94
Is dental stone or plaster used for models?
stone plaster is weaker because of irregularly shaped particles
95
What causes the difference in composition between denture bases and provisionals?
filler, leads to differences in mechanical characteristics
96
How is denture base usually cured?
visible light
97
How are provisionals usually cured?
chemically TRIM and JET are more workable than TRIAD
98
Are mouthguards thermoplastic or thermoset?
thermoplastic
99
What controls properties of mouthguards?
copolymer (Poly Vinyl Acetate-co-Ethylene)
100
What is the role and function of cements?
to bind restorations or appliances to tooth structure
101
What are the requirements for cements?
low viscosity (but good mech properties), 25 um thick
102
How is viscosity and handling properties of cements modified?
``` powder to liquid ratio (lower ratio = increased setting and working time) filler loading (more filler = higher viscosity) ```
103
What are the different types of cements?
resin cements, GIs
104
What is the function of bases and liners?
to protect pulp and minimize post op sensitivity (thermal and chem barrier, control inflammation and fluid movement)
105
What does calcium hydroxide do as a base?
cap pulp, acts as insulator, stimulates repairative dentin
106
What does ZOE do?
dulls pulpal pain, expands when set to seal exposure, CANNOT put composite on ZOE because limits polymerization
107
What are the requirements of waxes?
melt at lower materials, carvable, able to be burned off, dimensionally stable
108
What are waxes?
lower molecular weight materials in between polymers and organic liquids

Dental Materials (1 decks)

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