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Operative 2 final > Week 6- biomaterials > Flashcards

Week 6- biomaterials Flashcards

1
Q

silicate glass particles

A

provide mechanical reinforcement of the mixture (reinforces fillers)
produce light transmission and scattering

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2
Q

how does composite get its enamel like translucency?

A

silicate glass particles

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3
Q

composite is a mixture of:

A

silicate glass particles and acrylic monomer that is polymerized during application

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4
Q

how are composite parts chosen?

A

with purpose of averaging properties of the different parts

results in intermediate properties

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5
Q

composites are typically a dispersed phase of ______ distributed within _________

A

filler particles distributed within continuous matrix phase

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6
Q

matrix phase of composite

A

(acrylic monomer?)
least desirable
transiently fluid during application/manipulation
minimizing matrix = more desirable composite

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7
Q

categories of material properties

A

physical
mechanical
chemical
biologic

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8
Q

examples of physical properties

A 
mass
thermal
electrical
optical
surface
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9
Q

examples of mechanical properties

A

stress/strain relationship

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10
Q

examples of chemical properties

A

chemical and electrochemical interactions

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11
Q

4 categories of materials

A

metals
ceramics
polymers
composites

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12
Q

why do we need bonding agent?

A

flow of uncured composite is limited

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13
Q

bonding systems are made up of:

A

unfilled acrylic monomer mixture (similar to composite) placed on etch surface of tooth to make thin film

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14
Q

purpose of bonding system

A

micromechanical interlocking with etched surface
seals prep walls
co-polymerizes with composite

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15
Q

true/false? many dental tissues are composites

A

true

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16
Q

Methyl methacrylate monomer problems

A

contracts excessively

marginal leakage

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17
Q

PMMA problems

A

not strong enough for occlusal loads

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18
Q

difunctional monomers:

A

BIS-GMA and UDMA

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19
Q

BIS-GMA and UDMA

A

extremely viscous
difunctional monomers
need to be diluted

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20
Q

dilution of difunctional monomers BIS-GMA and UDMA

A

TEGDMA, low viscosity

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21
Q

modification of filler components

A

ions to make glass easier to crush = small particles

ions to produce filler radiopacity

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22
Q

Pure silica can be ______ or ______. _______ is stronger but harder to finish and polish

A

crystalline or noncrystalline

crystalline is stronger but harder to finish

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23
Q

what controls fluidity?

A

friction between filler particle surfaces and monomer

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24
Q

as filler surface area increases, fluidity:

A

decreases

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25
Q

larger filler = ______ surface area = _____ fluidity

A

less surface area

= increased fluidity

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26
Q

filler particles with 1/10th diameter (smaller) ______ surface area by

A

increase factor of 10

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27
Q

microfiller particles with silicon dioxide (SiO2)

A

tend to agglomerate into chains

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28
Q

a given material that is used must allow for what steps

A 
gross cutting (grinding)
fine cutting (finishing)
smoothing (polishing)

cannot be too hard (crystalline)

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29
Q

filler particle size has a direct effect on:

A

surface roughness of ground, finished, or polished composite

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30
Q

effectiveness of restoration finishing and polishing depends on:

A

use of successively finer abrasive materials

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31
Q

composite classification

A
  1. filler content, particle size, method of filler addition**
  2. matrix composition
  3. polymerization method
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32
Q

important qualities of composites are improved by:

A

using higher filler levels

disadvantage - decreased fluidity

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33
Q

composite filler particles

A 
macrofillers
midifillers
minifillers
microfillers
nanofillers
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34
Q

drawback of using small filler particles

A

compromises amount of filler you can use due to increased SA

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35
Q

flowable composites (first generation)

A

low-viscosity
reduced filler content
allows increased resin to DECREASE viscosity of mixture

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36
Q

second generation flowable composite

A

properties resemble traditional composite

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37
Q

lower filler content (first generation) flowable used for

A

pit and fissure sealants

small anterior restorations

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38
Q

higher filler content (second generation) flowable used for

A

class I-V restorations
first increment during composite restoration
repair resin for margins and non-occluding surfaces
best suited for conservative restorations

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39
Q

true/false? packable composite is comparable to amalgam in that it undergoes condensation

A

false; does not undergo condensation

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40
Q

packable composite

A 
"condensable composites"
handling characteristics similar to amalgam
intended for class I and II restorations
less sticky, high viscosity
do not undergo condensation
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41
Q

microfill and hybrid composites usually use _______ as microfillers

A

Silicon Dioxide (SiO2)

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42
Q

Colloidal silica

A

chemically precipitated from liquid soln as amorphous silica

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43
Q

Pyrogenic silica

A

precipitated from gaseous phase as amorphous silica

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44
Q

matrix monomers in USA usually based on _______ as primary monomer

A

BIS-GMA

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45
Q

light intensity can be inadequate if composite exceeds

A

1.5-2mm

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46
Q

light curing methods

A

Quartz Tungsten Halogen (QTH) curing units
Plasma arc curing (PAC) lights
Lasers
LED curing units

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47
Q

photoinitiator of composites

A

camphoroquinone

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48
Q

camphoroquinone MOA

A

absorbs photons of light energy at ~470nm

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49
Q

light curing variables

A

curing equipment
clinical manipulation of light
restoration effects on light absorption

50
Q

fiberoptic light tip should be placed where?

A

adjacent to surface being cured

51
Q

filler particles do what to curing light?

A

scatter

smaller filler particles maximize scattering

52
Q

darker colorants do what to curing light?

A

absorb

53
Q

depth of cure

A

boundary between somewhat cured and uncured material

5mm for shades A2 and A3 material

54
Q

what to do in cases of poor access or dark shades

A

place and cure in 1.5-2mm increments

55
Q

true/false? increasing curing time helps with light penetration significantly

A

false

56
Q

curing time

A

at least 20 seconds

57
Q

true/false? You can postcure to ensure adequate curing

A

true; improves surface layer properties such as wear resistance

58
Q

acrylic resin monomer polymerization stages

A
  1. activation
  2. initiation
  3. propagation
  4. termination
59
Q

acrylic resin monomer activation stage

A

production of free radicals

affected by light curing

60
Q

acrylic resin monomer initiation stage

A

free radicals react with monomer to start polymer chain

61
Q

acrylic resin monomer propagation stage

A

addition of monomer to growing chain

62
Q

acrylic resin monomer termination stage

A

end

result of steric hindrance, lack of monomer, etc

63
Q

makes up most of unreacted monomer in system

A

TEGDMA

64
Q

why are BIS-GMA restorative matrices poorly converted ?

A

problems with steric hindrance (leads to termination stage)

65
Q

why does shrinkage occur?

A

during polymerization monomer -> polymer = monomer-monomer bonds lead to shrinkage

66
Q

LCTE for composite

A

28-45ppm/*C
2x amalgam
3-4x tooth structure

67
Q

consequences of interfacial bond failure

A

microleakage - staining
pulpal sensitivity from dentinal fluid flow
pulpal irritation from bacteria
recurrent caries

68
Q

true/false? well cured composites are resistant to chemical change

A

true

69
Q

most composites can be cured to ________ degree of conversion

A

55-65%

70
Q

composite with high elastic modulus

A

cannot accomodate changes in tooth shape associated with flexural forces (esp cervical restorations on facial surfaces)

71
Q

high elastic modulus limitation

A

result in debonding of composite restoration from enamel or dentin

72
Q

composite wear events

A
  1. contract free area (food) (CFA)
  2. occlusal contact area wear
  3. functional contact area wear
  4. proximal contact area wear
  5. toothbrush abrasion
73
Q

CFA wear resistance related to

A 
filler spacing (smaller, better)
filler particles harder than polymer matrix and resist wear
74
Q

microprotection

A

filler particles closely spaced and shelter intervening matrix polymer

75
Q

_______ composite shows exceptionally good CFA wear resistance due to ___________

A

microfill composite

particles are very small with small spacing

76
Q

macroprotection

A

restorations with narrow preps minimize food contact and shelter restoration

77
Q

composite monitoring categories

A 
color matching
interfacial staining
secondary caries 
anatomic form 
marginal integrity
78
Q

true/false? color matching goes beyond initial color matching

A

true; also in relative changes that occur with time

79
Q

when should color matching be done?

A

when tooth is properly hydrated

80
Q

composite type most likely to undergo yellowing

A

anterior restorative materials with high matrix content and self cured

81
Q

composite yellowing

A

matrix polymer chemical changing

accelerated by UV light, oxidation, moisture

82
Q

qualities that resist color change

A

visible light cured
higher filler contents
modified with UV absorbers and antioxidants

83
Q

true/false? it is difficult to avoid a color mismatch after several years

A

true due to color changing of dentin in middle age

84
Q

true/false? bleaching affects when a restoration should be done?

A

true, wait until teeth have assumed a stable lighter shade

85
Q

transition in color between restoration and tooth structure

A

beveling enamel blends color difference associated with margin over 0.5-1mm
instead of abrupt transition

86
Q

incidence of secondary caries after 10 years

A

3%

87
Q

primary reasons for composite failure

A

poor aesthetics

excessive wear

88
Q

causes of postoperative sensitivity

A

marginal diffusion of species that induce fluid flow in dentin
dimension changes of actual restoration

89
Q

composite biocompatibility

A

unpolymerized matrix cytotoxic and carcinogenic

poorly soluble and polymerized into bound state before dissolution/diffusion can occur

90
Q

glass ionomers

A

ion-cross-linked polymer matrices surrounding glass reinforcing filler particles

91
Q

early glass ionomer based on

A

polyacrylic acid liquid + aluminosilicate powder with Ca and Fluoride

92
Q

advantages of glass ionomer

A

chemical adhesion and fluoride release

aqueous systems that wet tooth structure well

93
Q

disadvantages of glass ionomer

A

high viscosity

do not readily adapt to micromechanical spaces

94
Q

glass ionomer adhesion achieved not by acid etch but instead by

A

mechanical retention and partly by chemical chelation

95
Q

silicate cement

A

fluoride containing
no associated secondary caries
significant marginal disintegration and restoration solubility

96
Q

cause of replacing glass ionomer restoration

A

aesthetic problems

97
Q

who are good candidates for glass ionomer restorations?

A

high caries risk
more caries susceptible
reduced or no saliva flow
oral diseases that accelerate pathogenicity

98
Q

method to reduce caries risk during microleakage in gingival areas with little or no enamel

A

glass ionomer liner extended just short of margin

99
Q

when glass ionomers exposed to unusually high levels of external fluoride ions (topical fluoride, rinses, etc)

A

concentration gradient reverses and fluoride diffuses into glass ionomer

100
Q

recharging

A

when glass ionomer exposed to high external fluoride levels and concentration gradient reverses, allowing fluoride to diffuse into GI

discharging occurs just as quickly

doesn’t significantly improve secondary caries prevention

101
Q

true/false? recharging provides a steady, continuous release of fluoride

A

false; discharging occurs as quickly as recharging began

102
Q

biocompatibility issues with glass ionomers

A

sensitivity and pulpal irritation at time of initial mixing

pH starts very low (1)

103
Q

why are GI pulpal effects limited to area immediately adjacent to material?

A

acid groups are attached to polymer molecules that have limited diffusibility

104
Q

when is it necessary to use a liner with glass ionomer?

A

if remaining dentin thickness less than 0.5mm

protect from unset glass ionomer

105
Q

type of liner used for glass ionomer

A

calcium hydroxide

106
Q

fluid filled dentin tubules in direct contact with setting cement what happens?

A
  1. high ion concentrations in unset GI cause dentinal fluid to diffuse out into cement. fluid movement sensed by pressure receptors = pulpal sensitivity
  2. unset components such as hydrogen ions move into tubules and towards pulp. Tubule fluid contents buffer ions when RDT is adequate
107
Q

methods to increase mechanical strength of GI materials used for restorations

A

mix at higher powder:liquid ratio
(higher filler:matrix)
reduced matrix content decreases postop sensitivity or pulpal problems.

Line preps with CaOH to provide barrier from unset GI while material is curing

108
Q

true/false? It is safe to dry demineralized dentin during etch and rinse adhesives

A

no! can result in collagen collapse

109
Q

goal of etch and rinse adhesives

A

find moist bonding techniques by combining hydrophilic and hydrophobic monomers into organic solvent

110
Q

advantage of etch and rinse adhesives

A

can re-wet dentin after drying to raise bonding strengths

demineralized dentin collagen matrix reexpands and recovers original dimensions

111
Q

2 step self etch

A

nonrinsing conditioners of self priming etchants
prime/etch enamel and dentin simultaneously
not as good as phosphoric acid

no deep depth of demineralization or resin infiltration
doesn’t completely remove smear layer = less postop sensitivity

112
Q

1 step self etch

A

etch, prime, bond in one solution
uncured, ionic monomers that contact restorative resin directly
some hydrophilic = water degradation
multiple coats increase bond strength, decrease leakage
hydrophobic bonding layer is helpful
do NOT provide hermetic seal for deep dentin

113
Q

etch and rinse adhesive solvent

A

displaces water from dentin surface and promotes infiltration of resin monomers throughout nanospaces of collagen web

114
Q

if you get too much water onto primer can you continue?

A

no, excess moisture makes it ineffective

115
Q

what should happen BEFORE application of etch and rinse adhesive system?

A

uniform layer of water over dentin

116
Q

role of water in self-etch systems

A

added to ionize acidic methacrylate monomers

solubilize calcium and phosphate ions that form from interactions of monomer with dentin/enamel

117
Q

true/false? water can compromise properties of one step self etch adhesives

A

true (hydrophilic monomers = water degradation)

118
Q

role of protein in dentin bonding

A

partial removal of phosphor-proteins from root lesions enhances remineralization otential

119
Q

demineralized dentin treated with adhesive layer leads to

A

remineralization

120
Q

nanoleakage

A

small porosities in hybrid layer or transition between hybrid and mineralized dentin allow penetration of AgNO3 dye

121
Q

nanoleakage results in

A

reticular pattern on adhesive layer and spotted pattern on hybrid layer

Operative 2 final (8 decks)

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