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BDS2 CDS > Dental materials > Flashcards

Dental materials Flashcards

1
Q

what is a basic requirement of dental materials?

A

CE mark safety

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2
Q

what is an example of hydrocolloid

A

alginate

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3
Q

what is negative and positive replica?

A

negative = impression
positive = gypsum model

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4
Q

3 broad categories of material characteristics

A
  1. mechanical
  2. physical
  3. chemical
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5
Q

mechanical properties

A

hard/soft
strong/weak
flexible/rigid
ductile/brittle
stress
strain
shear
tensile
compressive
elasticity

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6
Q

physical properties

A

thermal conductivity
thermal expansion
viscosity
density
radiodensity

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7
Q

chemical properties

A

setting mechanism
setting time
corrosive potential

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8
Q

what is the formula of stress

A

stress = force/ area

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9
Q

strain formula

A

change in length/ original length

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10
Q

rigidity formula

A

stress/strain

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11
Q

what is young’s modulus

A

young’s elastic modulus = rigidity

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12
Q

hardness

A

Hardness is the ability of surface to withstand indentation

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13
Q

Compressive strength

A

the ability to withstand applied compressive forces without fracturing

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14
Q

compressive vs tensile strength

A

compressive - pushing force that reduces size of material

tensile - pulling force that increases size of material

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15
Q

failure mechanisms

A
  • Fracture
  • Hardness
  • Abrasion
  • Abrasion resistance
  • Fatigue
  • Creep
  • Deformation
  • De bond
  • Impact
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16
Q

elasticity

A
  • Elasticity is the ability to return to its original shape upon removal from mouth using force
  • Elasticity – strain and recovery
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17
Q

abrasion

A

material surface removal due to external factors like toothbrushing

abrasion means erosion is also porbably involved (refer to oral functions)

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18
Q

fatigue vs creep vs deformation

A

fatigue is repetitive small stresses causing material FRACTURE/CRACKS

creep is the gradual dimensional change due to small forces (amalgam)

deformation is permanent change in materials dimensions WITHOUT FRACTURE

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19
Q

when does (permanent) deformation occu?

A

occurs when the stress is beyond the elastic limit

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20
Q

what tells you that enamel is more rigid than dentine

A

enamel has higher fracture stress

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21
Q

on a stress strain curve, what does the peak, the slope, the plateau and the end of the linear gradient tell you?

A

peak - fracture stress

end of the linear gradient = proportional limit

linear slope = stress and strain are directly proportional

slope gradient = rigidit

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22
Q

what is fracture stress

A

the force at which fracture occurs

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23
Q

what is proportional limit?

A
  • The proportional limit in materials denotes the maximum stress they can withstand while still exhibiting a linear correlation between stress and strain. Functionally, it is the stress threshold beyond which plastic deformation takes place. The stress and strain are directly proportional to one another until they reach the proportional limit.
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24
Q

what are properties that dental adhesive must have?

A

high bond strength to tooth
impermeable bond
easy
durable bond
immediate high strength

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25
Q

enamel vs dentine bonding

A

enamel - mechanical

dentine - mechanical, chemical, van der waals

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26
Q

what does etching enamel with 30-50% phosphoric acid do?

A

roughens surface

removes contaminents

increases surface energy and wettability for the resin to flow into the etched enamel prisms

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27
Q

what is needed for enamel micro mechanical interlocking

A

enamel needs to be dry

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28
Q

amalgam is ana lloy made of?

A

mercury liquid
silver tin copper powder

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29
Q

what percentage of amalgam is silver?

A

70%

25% tin

5% copper zinc and mercury

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30
Q

what does the copper powder do?

A

increase strength and hardness

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31
Q

what is gamma phase?

A

silver and tin powder, gamma phase reacts with mercury liquid to form amalgam

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32
Q

why is Hg triple distilled?

A

to make it very pure

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33
Q

what are the two particle types of amalgam

A

lathe cut and shperical cut

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34
Q

Advantages of amalgam

A

strong
hard
durable
radiopaque
user friendly
Half the failure rate for all types of restoration in posterior teeth

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35
Q

disadvantages of amalgam

A

corrosion
leakage - does not bond to enamel or dentine
poor aesthetics
mercury:
- perceived toxicity
- environmental impact

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36
Q

is spherical cut or lathe cut better?

A

spherical

o Less mercury required

o Amalgam stronger under tension or compression

o Less sensitive to condensation (not compromised by poor application technique)

o Easier to carve

o Requires less force to pack compared to lathe cut

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37
Q

what is the setting reaction to make amalgam?

A

gamma phase power and liquid mercury =

gamma + gamma 1+ gamma 2

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38
Q

whats gamma , 1,2

A

gamma = silver tin
gamma 1= silver mercury
gamma 2 = tin mercury

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39
Q

out of gamma , 1, 2, which has poor corrosion resistance?

A

gamma2- poor corrosion resistance and weakest tensile strength

gamma - strongest tensile and good corrosion resistance

gamma1 - mid tensile and good corrosion resistance

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40
Q

setting dimensional changes between traditional and modern amalgam

A

traditional contract then expand alot (relative)

modern contract only but very small negligible amount

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41
Q

why are some amalgam zinc free? what is the disadvantages of zinc

A

zinc can react with water in saliva or blood to produced hydrogen gas

this gas causes pressure that can cause expansion or pulpal pain

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42
Q

what does corrosion do to amalgam?

A

can cause weakened marginal integrity, might lead to fracturing or leakage

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43
Q

what decreases the strength of amalgam?

A

undermixing
slow rate of packing
corrosion

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44
Q

why does creep occur?

A

amalgam is viscoelastic

low level stress constantly can cause amalgam to FLOW and result in permanent deformation

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45
Q

what affects marginal intergrity (3 pts)

A

creep
corrosion
cavity design

o Marginal integrity is in relation to the structure of the outline of the cavity, eg. Ditched margins from fracture or high margins from creep

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46
Q

whydo we need to use liner when using amalgam

A

it has poor thermal properties , can damage pulp

thermal expansion is 3 times

thermal conductivity is high

thermal diffusivity is high

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47
Q

ideal thermal properties of amalgam

A

same expansion as dentine and enamel

low conductivity and diffusivity (ie poor conductor)

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48
Q

does amalgam bond to tooth

A

o Does not bond
o Purely mechanical
o Requires undercuts so more tooth tissue removal than desired

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49
Q

is amalgam anticariogenic

A

no

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50
Q

what determines the force needed to pack amalgam?

A

shape of particles, with spherical particles requiring less force

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51
Q

2 other names of copper enriched amalgam

A
  • Aka Non gamma 2
  • Aka high copper
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52
Q

what is the criteria to be classified as copper enriched amalgam

A

more than 6% copper

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53
Q

adv of copper enriched

A
  • Higher early strength and longer term
  • Less creep
  • Less corrosion cause no gamma 2 *****
  • Increased durability at margins , less likely to fracture at margins
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54
Q

which type of amalgam has the fastest early strength?

A

copper enriched single compostion

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55
Q

which type of amalgam has the least creep

A

copper enriched single composition

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56
Q

what is in copper enriched dispersion amalgam

A

conventional lathe cut alloy

extra silver-copper spherical cut
added

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57
Q

what creates the protective halo around spheres in copper enriched amalgam?

A

copper tin

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58
Q

whats the copper % in single comp copper enriched amalgam?

A

12-30%

therefore least creep and highest compressive strength

59
Q

3 components of bonding system

A

etch
prime
adhesive

60
Q

what does etch do

A

o remove contaminants and increases surface energy of enamel

o Opens dentinal tubules

o Removes smear plugs

o Decalcifies uppermost layer of dentine

o Exposes up to 10 microns of collagen network

61
Q

do we want high or low surface energy/ wettability for dentine and enamel

A

want enamel and dentine to have higher surface energy and wettability so that the adhesive can flow over easily.

62
Q

purpose of high wettability

A

adhesive can flow over easily.

63
Q

what increases surface energy of dentine.

A

DBA increases surface energy of dentine.

64
Q

enamel adhesion is through micromechanical interlocking while dentine is ______?

A

molecular entanglement

65
Q

why do we need to prime the surface of dentine?

A

PRIMER GIVES THE SURFACE HIGH ENERGY SO THAT THE RESIN CAN FLOW

dentine is wet, it is hydrophilic, but the resin adhesive is hydrophobic

therefore we need primer to help then interact

66
Q

what is smear layer

A

organic debris that remains after the preparation of dentine

about 0.5-5um thick

67
Q

why do we need to removed smear layer?

A
  • weak bond as the smear layer not firmly attached to the underlying dentine
  • Generally contaminated with bacteria
  • Interferes with adhesion
68
Q

what removes the smear layer

A

phosphoric acid

69
Q

why cant dentine be too dry or too wet when putting primer and adhesive

A
  • If too dry, collagen fibres will collapse and the primer cannot infiltrate because of decreased porosity
  • If too wet, primer is diluted and reduced strength
70
Q

what happens when you over etch dentine?

A

collagen fibres collpase

too deep an etch and primer cannot penetrate full length

71
Q

chemical structure of primers

A

Hydrophobic end - bind adhesive, has C=C bonds for polymerisation

Hydrophilic end – bind dentine, binds to the polar groups on HA or amine groups on collagen

72
Q

characteristics of DBA

A
  • SURFACE WETTING AGENTS
  • Ability to flow
  • Low viscosity
  • Adhesion to substrate
    o Mechanical
    o Chemical
    o Van dear waals
73
Q

is it ionic or covalent bond to organic dentine?

A

 Mineralised dentine -> ionic bond
 Organic dentine -> covalent bond

74
Q

2 types of DBA

A

total etch - removes smear layer

self etch - incorporates smear layer

75
Q

what are some common primers

A

Bifunctional molecules eg. HEMA (hydroxy ethyl methacrylate) or NTG-GMA

76
Q

what is the function of the adhesive

A

form hybrid layer of collagen plus resin

77
Q

what is the name of the thing in adhesives that can light cure

A

Camphorquinone

78
Q

benefits of self etch

A
  • Do not need to control how much to dry the dentine
  • Reduced sensitivity since no chance of collapse of collagen architecture
  • HA crystals remain around the collagen , protecting against hydrolytic breakdown
  • remaining calcium ions can allow ionic bonding
79
Q

key component in self etch

A
  • Acidic methacrylate phosphatase

bifunctional monomers ^ with a hydrophilic end to infiltrate dentine and a polymerizing hydrophobic end like a bis GMA

80
Q

Molecular entanglement definition

A

absorbed component of adhesive can form long chain polymers, this polymer meshes with the substrate, leading to high bond strenght

81
Q

Adhesion Decalcification Concept

A

phase 1 all acids strong or weak adhere to the calcium ions in HA

phase 2 option 1
mild self etch will remain bonded and stabilize the HA crystals, protected the vulnerable collagen fibrils

phase 2 option 2
strong acids like phosphoric acid will debond with the loaded calcium ions, resulting in decalcification

82
Q

properties of bonding adhesive

A

high bond strength
immediate bond
durable bond
impermeable bond
easy
safe

83
Q

definition of critical surface energy

A

the surface tension of a liquid that will JUST spread on the surface of a solid

a low surface liquid will spread better on a higher surface energy substrate

84
Q

what material is the adhesives

A

mixture of resins, usually BisGMA and HEMA

filler particles

85
Q

is adhesive hydrophilic or hydrophobic

A

hydrophobic

86
Q

how deep does the self etch incorporate the smear layer into the hybrid layer?

A

2um

87
Q

potential problems with self etch

A

if smear layer is thick, the mild self etch may not be able to penetrate through it

88
Q

Function of Cavity lining materials

A
  • Protective barrier from
  • Heat
  • Chemical
  • Bacteria
  • Make intimate contact with tooth surface especially dentine
  • Protect from microleakage
  • Prevents gaps
89
Q

whAt is a pulpal irritant if not cured properly

A

HEMA

90
Q

2 types of cavity lining materials

A

base
liner

91
Q

differences between base and liner

A
  • Base
    o Thicker
    o Placed in bulk
    o Replace dentine
    o Block out undercuts
  • Liner
    o Thin coating over EXPOSED dentine
    o Seals dentine
    o Prevents penetration of bacteria into dentine
    o Thermal insulation
    o Therapeutic – calm inflammation
    o Palliative – reduce symptoms
92
Q

what thermal properties should cavity lining materials have

A

low thermal conductivity - pulp sensitivity

similar thermal expansions - wont stress

  • low thermal diffusitivity
93
Q
  • Compressive strength of cavity lining materials?
A
  • Compressive strength
    o High
    o Around same as dentine is ideal
94
Q
  • Elastic modulus/ rigidity of cavity lining materials?
A

o Ideally same as dentine
o Teeth bend
o When tooth bends, liner should be able to bend with the tooth so that it will not debond

95
Q

Marginal seal of cavity lining materials?

A

o Chemically bond to dentine ideally like GIC
o Impenetrable
o Permanent

96
Q

should solubility be Low or high for cavity lining materials?

A

LOW
o Inside cavity is wet, dentinal fluid
o if Soluble, it will wash away when there is microleakage or dentinal fluid

97
Q

what cavity liner is cariostatic

A

o Fluoride releasing GIC
o Antibacterial
o CaOH also produces alkaline pH which kills bugs

98
Q

what material is most commonly used for pulp caps?

A

CaOH aka dycal

direct or indirect pulp cap

99
Q

what does Setting calcium hydroxide do? (liner)

A

alkaline pH kills cariogenic bacteria

Irritates pulp, tertiary dentine laid down, calcification walls off cavity from pulp

100
Q

does zinc phosphate or Zinc polycarboxylate bond to tooth

A

Polycarboxylate binds to the calcium in the tooth so there is chemical bonding, long chain bonding surface of the tooth to the zinc oxide

101
Q

whats ZOE

A
  • Zinc oxide eugenol
102
Q

what is ZOE used for

A
  • Base in deep cavities
103
Q

acid base rxn formula for ZOE

A

Zinc oxide + eugenol = zinc oxide eugenolate matrix

104
Q

what can ZOE materials not be used with

A
  • ZOE materials cannot be used under composite resin materials, comp doesn’t set above ZOE, eugenol also softens comp and causes discolouration
105
Q

what the advantage and disadvantage of eugenol being highly soluble

A

Eugenol disintegrates in contact with water bad

eugenol released can reduce pulpal pain good

106
Q

what makes RMZOE different from zoe

A

resin gives stronger backbone to the set material

  • Increase in compressive strength allows it to be a liner
  • Low solubility compared to ZOE high solubility
107
Q

what does eba stand for EBA ZOE cement

A
  • Ethoxybenzoic acid
108
Q
  1. EBA ZOE vs ZOE and RMZOE
A
  • Stronger than ZOE and RMZOE
  • Less soluble than ZOE and RMZOE
109
Q

which material is the ONLY MATERIAL to seal dentinal tubules, preventing microleakage and sensitivity

A

GIC AND RMGIC

  • Bond and Seals dentine!
  • Bonds to composite resin over it
110
Q

what should be placed over calcium hydroxide?

A

RMGIC

111
Q

what is the ideal thermal diffusivity of all liners

A

all commercially available liners have similar or lower thermal diffusivity than tooth enamel

112
Q

disadvantages of CaOH

A

low compressive strength
unstable
soluble
lining will disappear when there is microleakage and contact with moist dentine

113
Q

what sort of reaction does zinc phosphate undergo?

A

acid base reaction

zinc oxide powder with phosphoric acid liquid

114
Q

problems with zinc phosphate

A

low initial pH causes pulpal irritation

exothermic reaction

does not bond to tooth

final set takes too long 24 h

brittle

115
Q

what is the solubility of GIC and RMGIC

A
  • Less soluble than any other liners except zinc phosphate
116
Q

is GIC or RMGIC more soluble?

A

GIC More soluble than RMGIC

117
Q

functions of GIC

A
  • Restorative fillings
  • Lining
  • Luting
118
Q

2 types of GIC

A

original glass and polyacrylic acid

anhydrous freeze dried polyacrylic acid added to powder

119
Q

what is added to gIc to speed up setting time without changing the working time?

A

tartaric acid

120
Q

what makes GIC more radioopqaue

A

Lithium and strontium salt
aluminium

121
Q

what makes gic more radiolucent

A

silica

122
Q

what is the benefits of anhydrous gic compared to traditional gic?

A

anhydrous is easier to mix

123
Q

for gic:

smaller glass particles = faster or slower setting time?

A

smaller = more rxn = faster settig time = more opqaue cement

124
Q

higher molecular weight of acid in gic adv vs disadv

A

adv = better mechanical properties

disadv = harder to miix

125
Q

3 phases of acid base rxn in GIC

A

dissolution
gelation
hardening

126
Q

what happens during the dissolution phase in gics

A

a. Acid added to powder
b. Acid attacks glass surface
c. Calcium aluminium sodium and fluoride released from glass surface
d. Silica gel left around unreacted glass

127
Q

what happens during the gelation phase in gics

A

a. Calcium ion that were liberated from the silicate glass crosslink with the polyacrylic chains
b. Bivalent calcium can link 2 chains
c. Or sometimes it links different sections of the same chain (ie not as much crosslinking as you would like)
d. Hard material but not fully set yet

128
Q

when does gelation start?

A

e. Gelation starts as soon as you start mixing

129
Q

what is the bonding in gelation vs hardening

A

gelation = earlier bonding of bivalent calcium

hardening = later bonding of trivalent aluminium

130
Q

what occurs during hardening that makes gic much stronger?

A

a. Trivalent aluminium ions ensures good crosslinking of polyacrylic chains
b. Increases strength
c. But takes a few days to week
d. Improves mechanical properties of material

131
Q

why do we need to keep GIC dry

A
  • Keep dry
  • Not set yet
  • Aluminium ions could diffuse out
  • Don’t get trivalent loading
  • Saliva might cause absorption of water
  • Weaken the material
132
Q

how do we keep GICs dry?

A

i. Varnish
ii. Resins
iii. Vaseline BAD
iv. Best is using DBA and light cure

133
Q

why should we Never condition surface with phosphoric acid before GICs?

A

Phosphoric acid removes the calcium on tooth surface that is needed for GIC to bond to

134
Q

compare gics to composite

A

GIC have poorer
-tensile strength
-wear resistance
-hardness
-compressive strength
-higher solubility making it more susceptible to erosion by acids

135
Q

how does GICs act as a fluoride reservoir

A

recharge fluoride, fluoride reservoir

Refresh fluoride content with toothpaste and mouthwash

136
Q

what rxn occurs in rmgic

A

dual curing = acid base + polymerisation

tri curing = acid base + polymerisation + redox

137
Q

what is the purpose of redox in tricuring of rmgc

A

light cure cannot penetrate super deeply

in case the light cure doesnt fully polymerize the acids, redox can also produce the free radicals needed for polymerisation to occurs

138
Q

what are the materiasl in rmgic

A

glass similar:glass from silcate cement

acid
- HEMA resin
- polyacrylic acid with pendant methacrylate groups (C=C)

139
Q

how is rmgic better than gic

A
  • Improved physical properties, stronger
  • Better aesthetics
  • Better handling since theres light curing so no need to keep dry for entire duration
  • Lower solubility
140
Q

disadvantages of rmgic

A
  • Polymerisation contraction
  • Exothermic
  • Swelling due to HEMA uptake of water
  • HEMA toxic if not polymerised completely so might consider use of pulp cap
  • Redox catalysts benzoyl iodides and bromides are cytotoxic
141
Q

how long does gic take to fully set

A

about days to a week or longer

142
Q

what happens if GIC is contaminated

A

aluminium ions diffuse out, no trivalent crosslinking

weaker bonding which will break or have poorer aesthetics

prevent contamination after gelation phase, use resin or dba to create a protective layer

143
Q

how does gic and rmgics have a good marginal seal

A

they bond to teeth

the polyacrylic acid binds to the calcium in the tooth structure

144
Q

what do you condition tooth with before gic

A

polyacrylic acid NOT phosphoric acid

BDS2 CDS (15 decks)

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