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Module 3 Revision > Dental Materials > Flashcards

Dental Materials Flashcards

1
Q

Define an alloy

A

A mixture of two or more metals

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2
Q

The process that occurs in the formation of a crystal from a solution, liquid or vapour

A

Nucleation

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3
Q

What two types of nucleation are there?

A

Heterogenous & Homogeneous

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4
Q

Describe heterogenous nucleation

A

Many sites of nucleation

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5
Q

Describe homogeneous nucleation

A

Single site and requires specialised equipment

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6
Q

What type of nucleation is more common in dental applications

A

Heterogenous nucleation

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7
Q

What does grain size refer to?

A

Crystal size

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8
Q

What promotes a small grain size?

A

-rapid solidification
-provision of ‘extra’ nucleation sites

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9
Q

What ways can metals and alloys be shaped?

A

-hammering
-rolling
-pressing
-drawing into a wire

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10
Q

What happens to grains when a metal/alloy is drawn into a wire?

A

They are elongated

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11
Q

The maximum degree of extension in response to an applied tensile force

A

Ductility

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12
Q

The maximum degree of compression in response to an applied compressive force

A

Malleability

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13
Q

What is a solid solution? Give an example.

A

Where two metals dissolve in each other and then harden to give a solid solution.

E.g. copper and zinc dissolve in each other and harden to give a solid solution called brass.

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14
Q

Ordered, random and interstitial are three types of what?

A

Solid solution

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15
Q

What are solid solutions in comparison to metals?

A

-harder
-stronger
-higher elastic limits
-hardening effect

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16
Q

What does Tm indicate on a phase diagram?

A

Melting point

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17
Q

What does the plateau on a phase diagram indicate?

A

Temperature constant during crystallisation

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18
Q

Why are phase diagrams useful?

A

Can construct series of cooling curves for alloys of different composition

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19
Q

When one component in an alloy solidifies before the other, this has less than optimal properties. What is this process called?

A

Coring

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20
Q

Which line on a binary alloy graph represents the liquidus

A

The top line

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21
Q

Which line on a binary alloy graph represents the solidus?

A

Bottom line

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22
Q

What would a large separation between liquidus and solidus lines on a binary alloy graph indicate?

A

That the alloy is more susceptible to corrosion and there is greater coring

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23
Q

What application do eutectic alloys have?

A

Solders

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24
Q

Where alloy components are insoluble in each other, there is a specific point where crystallisation occurs at specific temperature. What is this point called?

A

Eutectic point

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25
Q

In dentistry, what are solders used for?

A

-attach a metal component to an appliance
-fit golden laced teeth to restore them

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26
Q

When an alloy reacts with mercury what does this form?

A

Amalgam

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27
Q

What are the two compositions of amalgam?

A

Conventional and high copper

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28
Q

What effect does copper have on amalgam?

A

It strengthens it

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29
Q

What is the role of zinc in alloy production?

A

It acts as a scavenger

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30
Q

How does zinc act as a scavenger?

A

It oxidises in preference to the other metals, attracts oxygen so that the other metal won’t.

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31
Q

What is another word for mixing?

A

Trituration

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32
Q

When mercury diffuses into alloy during setting reaction what occurs?

A

Small shrinkage

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33
Q

What is there risk of if we have a material that expands or contracts too much?

A

-a gap around the restoration
-forces that could shred off cusps of teeth filled with an alloy

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34
Q

What do the international standards organisation (ISO) limit expansion/contraction to?

A

+/- 0.1%

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35
Q

What happens to zinc containing alloys if placed in a moist or contaminated environment?

A

They expand, this is because the zinc ion reacts with water, liberating hydrogen.

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36
Q

How long does it take for final strength of amalgam to be reached?

A

24 hours

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37
Q

What is the minimum depth of amalgam required to counteract weakness in thin sections?

A

2mm

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38
Q

What is strength of amalgam dependant upon?

A

The mercury content

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39
Q

What is the optimum Hg concentration?

A

44-48%

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40
Q

What does packing of amalgam into a cavity do to the mercury?

A

Forces it to the surface

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41
Q

Define creep

A

Plastic deformation under load

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42
Q

How does creep clinically manifest?

A

As protrusions at restoration margins.

(This can fracture off producing a ditch and predisposing area to caries.)

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43
Q

What is the gamma 2 phase largely responsible for?

A

Creep

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44
Q

What is the theory of mercuroscopic expansion?

A

Localised expansion of amalgam due to release of Hg into marginal crevice

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45
Q

What can corrosion products provide?

A

Marginal seal

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46
Q

What is the most accurate way to dispense mercury?

A

Capsules containing mercury and alloy

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47
Q

What particle size of an alloy achieves higher strength?

A

Smaller particle size

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48
Q

What happens if particle size is too small?

A

It will be too rapid a set and cannot remove Hg by manipulation

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49
Q

What material was used as a restorative material in 1950’s-60’s?

A

Silicates

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50
Q

What material was used as a restorative material in 1960’s-80’s?

A

Acrylics

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51
Q

What form could acrylic take?

A

Powder or liquid

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52
Q

What is the type of reaction in the setting reaction for both powder and liquid acrylics?

A

Free radical addition polymerisation

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53
Q

What is a consequence of fast setting of acrylics?

A

Limited working time

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54
Q

What is the bond that splits in a free radical addition polymerisation reaction?

A

C=C

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55
Q

What is a key organic compound used to demonstrate a free radical addition polymerisation reaction?

A

Methyl methacrylate (MMA)

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56
Q

What are the four stages of free radical addition polymerisation reaction?

A

1.activation
2.initiation
3.propagation
4.termination

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57
Q

What happens in the initiation stage?

A

C=C cleaved

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58
Q

What happens in the propagation stage?

A

Multiple units join

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59
Q

What happens in the termination stage?

A

Two free radicals merge/meet which terminates the joining of units

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60
Q

What happens to materials when they undergo polymerisation?

A

They contract

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61
Q

What type of reaction is the contraction of materials upon polymerisation?

A

Exothermic

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62
Q

What is very key, important feature of acrylics?

A

They exhibit low thermal diffusivity (heat transfers slower)

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63
Q

What are some disadvantageous qualities of acrylics?

A

-can be irritant to pulp
-May interact with Eugenol
-poor abrasion resistance

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64
Q

What is a eutectic alloy?

A

An alloy that has a very defined, very narrow ranged melting point and properties

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65
Q

What has been used in acrylic to try and reduce shrinkage, however may also weaken the material?

A

Inert filler

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66
Q

What is the setting reaction for resin composites?

A

Free radical addition polymerisation

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67
Q

What are the two main components of resin composite?

A

-resin matrix
-inhibitors

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68
Q

What does the comonomer,TEGMA, control?

A

Viscosity

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69
Q

What is the role of inhibitors in resin composite?

A

They prevent polymerisation kicking off too readily

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70
Q

What benefit does the use of siloranes have?

A

May minimise polymerisation shrinkage

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71
Q

What is the setting reaction for siloranes?

A

Cationic ring-opening polymerisation

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72
Q

What two important substances do resin composites contain?

A

Fillers and coupling agents

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73
Q

What are the three types of fillers?

A
  1. Quartz
  2. Silica
  3. Glasses
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74
Q

Which type of filler contains a heavy metal within them that allows for opaque radiopacity?

75
Q

What is an example of an excellent coupling agent?

A

Vinyl silane

76
Q

What must fillers be coupled with?

A

Coupling agent

77
Q

As % volume of filler content increases, what happens to the surface hardness?

A

It increases

78
Q

The addition of filler will have what effect on the % volume of setting contraction?

A

Will decrease it

79
Q

What effect does the addition of filler have on the coefficient of thermal expansion?

A

It decreases it

80
Q

How can resin composite set?

A
  1. Chemical
  2. Light
81
Q

In a light set, what photosensitiser is often used?

A

Camphorquionone

82
Q

What does camphorquinone do?

A

Yields necessary free radicals to start polymerisation when it becomes excused by blue light

83
Q

What material is a shock absorber?

84
Q

What is resin susceptible to upon polymerisation?

85
Q

What controls properties of resin composite?

A

The type, concentration and particle size distribution of fillers

86
Q

What are the four classification of resin composites?

A
  1. Conventional
  2. Microfilled
  3. Hybrid
  4. Nano-composite
87
Q

What classification of composite has large size of filler particles which in turn can result in poor aesthetics

A

Conventional resin composite

88
Q

What classification of resin composite has smaller filler particles, therefore a larger surface area and difficulty gaining high filler loading?

A

Microfilled resin composite

89
Q

What classification of resin composite is a blend of conventional and Microfilled composite?

A

Hybrid resin composite

90
Q

What classification of resin composite is most commonly used today and could be described as a variation of microfilled composite?

A

Nano-composite

91
Q

What standard must resin composites conform with to be on the market?

92
Q

Composite sets toward light source. True or false?

A

False.

This is a common misconception that composite sets towards light source

93
Q

What is the effect on the working time of resin composite if it is chemically activated?

A

Limited working time

94
Q

What is the effect on working time if resin composite is light activated?

A

Extended working time

95
Q

What is required for good light curing?

A

Light must be in very close proximity to composite restoration

96
Q

What do thermal (mechanical) properties depends upon?

A
  • filler content type
  • efficiency of coupling
  • degree of porosity
97
Q

What influences overall success of restoration?

A

Cavity shape

98
Q

What is the equation for C-factor?

A

C-factor = number of bonded surfaces/number of un-bonded surfaces

99
Q

Why does C-factor matter?

A

The higher the c-factor, the greater the stress from polymerisation shrinkage. Risks of debonding and micro leakage of restorations.

100
Q

What photosensitiser do modern resin composites contain that means they can be light activated?

A

Camphorquinone

101
Q

Camphorquinone becomes excited on exposure to what type of light and at how many nanometres?

A

Blue light ( 460-480nm)

102
Q

What is good practice in order to maximise curing of resin composite?

A

To have the light as close to the composite as possible

103
Q

What are the two different types of light sources for curing units?

A

Quarts Tungesten Halogen
LED’s

104
Q

What is a downside to quartz tungsten halogen curing units and why?

A

They generate a fair amount of heat which may distress and cause damage to the pulp

105
Q

What light source is known for having a narrow spectrum?

106
Q

What should be avoided when using LED light curing units?

A

Sequential activation as this may damage the pulp. Wait at least 30n seconds between activations.

107
Q

Due to the narrow spectrum of LED’s, what are the risks?

A

That the light unit may nit coincide with the photosensitiser in some resin composites. If this is the case, another light unit must be used.

108
Q

What happens to a resin composite material when it cures?

A

It contracts

109
Q

When should you change your light curing unit?

A

Once it reads a measurement that is 25% lower than it’s original maximum radiation measurement.

110
Q

What are the three main wear mechanisms of resin composites?

A
  • abrasive
  • erosive
  • fatigue
111
Q

How does abrasion effect a resin composite restoration?

A

Hard angular particles (asperities) penetrate polymer matrix removing material by sheering and cutting

112
Q

How does erosion effect a resin composite restoration?

A

Hard angular particles (asperities) damage polymer matrix

113
Q

How does fatigue effect resin composite restorations?

A

Localised deformations of the polymer are subject to repeated stresses and this can result in failure.

114
Q

How can various stages of resin composite wear be visualised?

A

By staining with silver (Ag)

115
Q

What are the two main factors that cause softening of the resin matrix?

A
  • inhibition of polymerisation due to entrapped air pockets
  • chemical softening ( foods and plaque acids)
116
Q

What coupling agent unites resin and filler?

A

Vinyl silane

117
Q

Why might the resin/filler interface become stressed?

A
  • thermomechanical fatigue
  • water sorption
  • polymerisation shrinkage
  • mechanical stresses upon restoration
118
Q

How do cracks propagate at the resin/filler interface?

A

Leakage of filler constituents

119
Q

What is hydrologic filler degradation a result of?

A

Stress corrosion

120
Q

What are the tow main consequences of polymerisation shrinkage of resin composite?

A
  • leakage
  • cuspal flexural and post operative sensitivity
121
Q

What restorative material contains nano fillers?

A

Resin composites

122
Q

What are the potential downfalls of nano materials?

A

They are thought to have potential toxilogical and environmental concerns

123
Q

Describe the “ ideal restorative material”

A
  • strong
  • good marginal seal
  • bonds to tooth substance
  • wear resistant
  • cariostatic
  • goof aesthetics
  • easy to manipulate
  • non-toxic
  • non irritant to dental tissues
124
Q

What does cariostatic mean?

A

Inhibits the formation of dental caries

125
Q

What happens to the flexural strength of a tooth the closer you get to the root apex?

A

Flexural strength decreases

126
Q

What is the filler in resin composites made up of?

A

Ground down glass

127
Q

How are resin composite post-op fracture risks counteracted?

A

By placing the resin composite in increments before curing

128
Q

What is the preferred name for glass ionomers?

A

Glass polyalkeonate cements

129
Q

What are the two earlier cements that glass polyalkenoate cements derive from?

A
  • silicate cements
    -polycarboxylate cements
130
Q

What early version of polycarboxylate cement had unfavourable characteristics such as poor appearance and mechanical properties?

A

Zinc containing polycarboxylate cements

131
Q

What material was used to replace zinc in polycarboxylate cements so that appearance, solubility and mechanical properties would improve?

A

Ion leachable glass

132
Q

What are the three presentations of glass polyalkenoate cements?

A
  1. Powder + liquid
  2. Powder mixed with water
  3. Encapsulated form
133
Q

What material is the powder component of glass polyalkenoate cements made up of?

A

Sodium aluminosilicate glass

134
Q

What is the most beneficial quality of sodium aluminosiliacte glass as a restorative material?

A

It has contains high concentration of fluoride

135
Q

What component of the liquid aspect of glass polyalkenoate cements is important in controlling setting characteristics of the material?

A

Tartaric acid

136
Q

What two ways can encapsulated glass polyalkenoate cements be mixed?

A

By hand spatulation
OR
By oscillator

137
Q

Are cements normally viscous or fluid?

138
Q

Will viscous cements have low or high porosity and why?

A

Low porosity as difficult to incorporate air

139
Q

What makes mechanical mixing of fluid cements incorporate more porosity?

A

The frothing of mixed material due to oscillation

140
Q

What group of chains of poly-acid cross link in acid base setting reaction?

141
Q

What two components react together in the setting reaction of glass polyalkenoate cements?

A

Aluminosilicate glass reacts with poly acid

142
Q

What do the side chains present in the setting reaction of glass polyalkenoate cements require in order to improve handling properties of the material?

A

Modifying and cross-linking agents

143
Q

what does an acid base reaction produce?

A

Salt + water

144
Q

What do set glass polyalkenoate cements consist of?

A
  • glass particles
  • silaceous hydrogel
145
Q

What are the two phases of the setting reaction of glass polyalkenoate cements?

A
  • initial set
  • final set
146
Q

When does initial set of glass polyalkenoate cement occur and what ions ( liberated from glass particles) cross-link the poly acid chains?

A

Occurs in the first few minutes of mixing. Ca2+ ions predominate

147
Q

When does final set of glass polyalkenoate cements occur? And what ions ( liberated from glass particles) involve cross linking of poly acid chains?

A

Finals et occurs 24 hours after set. Al3+ ions predominate

148
Q

Why does initial reaction use Ca2+ ions over Al3+ ions?

A
  • Ca2+ ions are:
    More accessible ( on outer surface of glass particle)
    More mobile, due to relative ionic radii ( come along first before Al3+ which are less mobile)
    Ca2+ only has to cross link with two chains whereas Al3+ has to cross link with 3 chains
149
Q

Until final set of glass polyalkeonate cements is complete, what is the material rendered?

A

Moisture sensitive

150
Q

How would you protect glass polyalkeonate cements from moisture?

A

Using a varnish to infilled resin

151
Q

What substance could you use to prevent drying out of glass polyalkenoate cement on polishing?

A

Vaseline ( as a lubricant)

152
Q

What would enhance adhesion of glass polyalkenoate cements to tooth substance?

A

Application of a tooth cleanser

153
Q

What are the two common examples of tooth cleansers?

A
  • critic acid
  • poly acrylic acid ( increases bond strength)
154
Q

How do tooth cleansers enhance adhesion of glass polyalkenoate cement to tooth substance?

A

They remove smear layer

155
Q

What are the beneficial properties of glass polyalkeonate cements?

A
  • tooth coloured and translucent
  • adhesion to tooth substance
  • fluoride release from glass
  • biocompatible
156
Q

What property is the ‘selling point’ of glass polyalkeonate cements?

A

Fluoride release from glass component

157
Q

What is the disadvantages of glass polyalkenoate cements?

A

Brittle and relatively poor abrasion resistance

158
Q

What are the three applications of glass polyalkenoate cements?

A
  • restorative material
  • luting cements
  • lining/base material
159
Q

What is the disadvantages of glass polyalkenoate cements on a radiograph?

A

They lack radiopacity

160
Q

What are the three variants ( related materials) of glass polyalkeonoate cements?

A
  1. Modified composite
  2. Giomers
  3. Resin modifies glass ionomer cements (RMGIC)
161
Q

Why is HEMA an important component of RMGI cements?

A

It allows resin + acid to coexist in aqueous solution

162
Q

What does removal of the smear layer on dentine, through acid etch, achieve?

A

Exposes tubules (collagen networks), resin and solvents able to penetrate tubules, soaking into collagen networks and locking in.

163
Q

What can be a result of over-drying etched dentine?

A

Collapse of the collagen lattice, resulting in reduced bond strength.

164
Q

What does acid etch facilitate?

A

Micro-mechanical retention

165
Q

What is the cause of the smear layer on dentine that includes tubules?

A

Cavity preparation

166
Q

What are the three main components of dentine bonding agents?

A
  • dentine conditioners
  • primers
  • sealers
167
Q

What are dentine conditioners and what do they do?

A

They are acids that alter the surface appearance and characteristics of dentine

168
Q

What are two examples of dentine conditioners?

A
  • phosphoric acid
  • nitric acid
169
Q

What does a primer do in dentine bonding?

A

Acts as the adhesive, bonding hydrophobic composites to hydrophilic dentine

170
Q

What do sealers do in dentine bonding?

A

Flow into dentinal tubules, sealing dentine and ensuring bonding to resin composite

171
Q

What is the most common example of a primer used fro feint bonding?

172
Q

What procedure risks nano-leakage?

173
Q

What are the three presentations of dentine and enamel bonding?

A
  • three stage bonding
  • two stage bonding
  • one stage bonding
174
Q

What are three different types of cements that can be used as lining/base materials?

A
  • phosphoric acid based cements
  • zinc oxide euganol cements
  • calcium hydroxide cements
175
Q

Which cement based lining is the most irritant to the dental pulp and why?

A

Phosphoric acid based cements, because of their low pH and molecular weight of parent acid

176
Q

Which cements lining contains euganol and why is this important to consider if you aim to place a resin composite restoration?

A

Zinc oxide euganol cement
Euganol is not compatible with resin composites as it impairs their polymerisation. Therefore another lining material or restorative material should be used.

177
Q

What effect does euganol have on the pulp?

A

A calming/cooling effect

178
Q

Which lining cement has insufficient strength to withstand amalgam condensation and packing?

A

Calcium hydroxide cement

179
Q

What is a commonly used resin-modified glass ionomer for lining on clinic?

180
Q

What are the advantages of a composite bulk fill?

A

Reduces polymerisation shrinkage and clinical working time

181
Q

What lining technique is claimed to foster formation of reparative dentine and posses excellent adhesive properties prior to placement of restorative material?

A

Bulk dentine replacement

182
Q

What is beneficial irritancy?

A

Stimulation of the pulp by the lining material being slightly acidic or alkali to produce tertiary dentine which protects the pulp

183
Q

what restorative material can you not place in a pregnant or breastfeeding woman?

Module 3 Revision (20 decks)

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