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Operative Dentistry > Cavity Lining Materials > Flashcards

Cavity Lining Materials Flashcards

1
Q

what are some common materials that are placed in tooth cavities

A

composite resin
glass ionomer
amalgam
precious metal
non precious metal
ceramic

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2
Q

what are disadvantages of restorative materials

A
  • may not make intimate contact with the tooth surface, especially with dentine, which can create gaps that allow for micro leakage of oral fluids, developing caries
  • heat is released during setting and curing which can fry the pulp
  • release of chemicals due to any reactions, which can irritate and lead to pain or pulpal damage
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3
Q

how can microleakage occur with dental materials

A

when the material sets and does not sit tightly to the edge of the tooth, this creates a gap developing at the side

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4
Q

what is the solution to the issues with restorative materials and microleakage

A

using an intermediate restorative material called a lining material, which prevents gaps and acts as a protective barrier

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5
Q

what are cavity base materials and are they the same as the cavity lining materials

A

they are a form of intermediate restoration to put into the tooth cavity in bulk to replace as much of the dentine as possible as well as blocking undercuts for inlays and inlays. they are not the same as lining materials; those are thin coatings with exposed dentine

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6
Q

what is the cavity base

A

a thick mix placed in bulk, dentine replacement is used to minimise the bulk of the material or block out undercuts
most commonly used in metal restorations

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7
Q

what is cavity lining

A

this is a thin coating over exposed dentine, usually no more than 0.5mm

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8
Q

what are the purposes of liners

A
  • pulpal protection
  • therapeutic
  • palliative
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9
Q

what does liner protect the pulp from

A

chemical stimuli
thermal stimuli
bacteria and endotoxins

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10
Q

why does liner need to protect the pulp from chemical stimuli

A

there can be some chemical stimuli from unreacted chemicals in the filling material or the initial pH of the filling which can irritate the pulp

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11
Q

what is the thermal stimuli that the liner protects the pulp from caused by

A

exothermic setting reaction of composite or heat conducted through metal fillings

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12
Q

why is there bacteria and endotoxins present that the pulp are protected from via the liners

A

due to microleakage, oral fluids and bacteria and toxins can enter in the gap between the restorative and cavity walls

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13
Q

describe the therapeutic purpose of liners

A

calms down inflammation within the pulp and promotes pulpal healing prior to or at the time of a permanent restoration being placed

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14
Q

describe the palliative function of liner

A

reduce patient symptoms prior to definitive treatment being carried out, which is most commonly used in patients with reversible pulpits

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15
Q

what are the main properties of lining materials

A

ease of use
thermal properties
mechanical properties
radiopaque
marginal seal
solubility
cariostatic
biocompatible
compatible with restorative materials

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16
Q

describe the ideal ease of use of lining materials

A

they are easy to mix, and the working time is usually long enough to allow easy placement, and the setting time is short due to curing lights

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17
Q

what does command set mean

A

using a curing light to set the material

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18
Q

describe the ideal thermal properties of lining materials

A
  • should be low conductivity so heat is not transferred to the pulp
  • thermal expansion coefficient should be similar to dentine
  • thermal diffusivity should be similar to dentine or lower
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19
Q

what is thermal conductivity

A

how well heat energy is transferred through a material

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20
Q

how is thermal conductivity of a material determinde

A

heat flows through a cylinder of unit cross sectional area and unit length, with a temperature difference of 1 degree celsius between the ends

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21
Q

what are the units of thermal conductivity

A

W/m-1/degree celcius-1

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22
Q

ideal thermal conductivity for denture base

A

high

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23
Q

ideal thermal conductivity for restorative material

A

low

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24
Q

ideal thermal conductivity of lining base

A

as low as possible

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25
Q

why is it important that denture bases have high thermal conductivity

A

so that the people wearing the denture can still feel the heat of what they are consuming, therefore preventing the consumption of anything that is too hot and would burn them

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26
Q

what is the thermal expansion coefficient

A

this is the change in length per unit length for a temperature rise of 1 degree celcius
basically, apply heat to something and see how much it expands

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27
Q

what are the units for the thermal expansion coefficient

A
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28
Q

how should the thermal coefficient of the liner compare to the tooth and why

A

should match the properties to the tooth tissue as much as possible

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29
Q

what is the thermal coefficient value for enamel

A

8.3

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30
Q

what is the thermal coefficient value for dentine

A

11.4

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31
Q

what is the thermal coefficient value for GIC

A

11

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32
Q

what is the thermal coefficient value for RMGIC

A

20

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33
Q

what is the thermal coefficient value for composite

A

25

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34
Q

what is the thermal coefficient value for amalgam

A

25

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35
Q

what is thermal diffusivity

A

this is similar to conductivity, looking at the dissipation of heat through different areas

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36
Q

what is thermal diffusivity measured in

A

cm2 / sec

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37
Q

what should the thermal diffusivity value be

A

as low as the tooth

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38
Q

thermal diffusivity value of enamel

A

0.0042 cm2/sec

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39
Q

thermal diffusivity value of dentine

A

0.0026 cm2/sec

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40
Q

what is the thermal diffusivity value of amalgam

A

1.7cm2/sec

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41
Q

what should the mechanical properties of lining materials be

A

high compressive strength and a modulus similar to dentine

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42
Q

why is it important for lining materials to have high compressive strength

A

to allow placement of filling without it breaking

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43
Q

what is the compressive strength of dentine

A

275 MPa

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44
Q

what is the modulus of dentine

A

around 15 GPa

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45
Q

what is modulus

A

looks at how much a material distorts when you apply a force to it

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46
Q

describe how the radiopacity of lining materials should be

A

should be easy to see the difference between the lining and the tooth. this makes it easier to see if there is any leakage or secondary caries

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47
Q

describe how the marginal seal of lining materials should be

A

ideally the tooth should form a chemical bond to dentine, which should be permanent and impenetrable and strong

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48
Q

why is it important that the solubility of lining materials is low

A

if there is a gap and an ingress of oral fluid that reaches the cavity lining material, it would dissolve away and leave a gap in the lining, creating the opportunity for caries and infection within the pulp. so the lower the solubility the less likely this is to happen

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49
Q

describe how lining materials are cariostatic

A

they stop the development of caries through fluoride release, which is an antibacterial ion. this is an important property to prevent secondary caries around the restoration

50
Q

describe the biocompatibility of lining materials in the ideal world

A

non toxic and non damaging to the pulp
pH neutral
no excessive heat release during setting
low thermal conductivity

51
Q

what kind of material is setting calcium hydroxide

A

liner

52
Q

what kind of material are zinc oxide based elements

A

base

53
Q

what kind of material are glass ionomer and resin modified glass ionomer cements

A

bases or liners

54
Q

what kind of material are palliative cements

A

bases, seldom used nowadays, and are mainly historic

55
Q

what is the chemical composition of calcium hydroxide

A

Ca(OH)2

56
Q

what are the two main calcium hydroxide liners used

A

Life and Dycal

57
Q

describe how setting calcium hydroxide liner comes in clinic

A

one tube is the base and the other is the catalyst.

58
Q

describe the base constituent of setting calcium hydroxide liner

A

50% calcium hydroxide
10% zinc oxide, acting as a filler
less than 1% zinc stearate, acting as a filler
n-ethyl toluene sulphonamide (plasticiser) at 40%

59
Q

describe the constituents of the setting calcium hydroxide liner catalyst element

A

butylene glycol dvisalicylate is the reactive element at 40%
titanium dioxide at 13-14% to act as a filler
calcium sulphate at 30% to act as a filler
15% calcium tungstate to act as a filler and to be radiopaque

60
Q

what is the reason for adding a radio pacifier to the setting calcium hydroxide liner

A

so it can be detected on a radiograph as a lining material and not part of the tooth or the restorative material

61
Q

what is the function of the plasticiser in the base constituent of setting calcium hydroxide liner

A

to allow the liner to be manipulated and moved during placement

62
Q

what is the setting reaction for the calcium hydroxide liner

A

a chelation reaction between zinc oxide and the butylene glycol dvisalicylate, which results in a cement with an initial pH of around 12

63
Q

what is a chelation reaction

A

one in which the metal ions reacts with organic agent and this removes the metal ion from the vicinity.

64
Q

what are the two modes of action for the calcium hydroxide liner

A

it is bactericidal to cariogenic bacteria, and it causes irritation which leads to the formation of reparative dentine

65
Q

why is calcium hydroxide liner bactericidal to cariogenic bacteria

A

the cariogenic bacteria need to be in an acidic environment, so the highly alkaline nature of the liner kills them by creating unfavourable conditions.

66
Q

how does the calcium hydroxide liner irritate and form tertiary dentine

A

the cement causes irritation to the odontoblast layer, and necrosis follows which in turn results in a layer of tertiary dentine being produced. this eventually forms a calcified bridge walling the base of the cavity off from the pulp. the calcium comes from the pulp, not the cement.
the tertiary dentine makes the pulp shrink away to protect it.

67
Q

what are the properties of calcium hydroxide liner

A

quick setting time
radiopaque
easy to use
low compressive strength (brittle)
unstable
soluble

68
Q

why is it not good that calcium hydroxide liner is soluble

A

if the cavity leaks then the lining will disappear, and may even disappear just because it is in contact with moist dentine

69
Q

what are the zinc oxide based cements

A
  • zinc phosphate
  • zinc polycarboxylate
  • zinc oxide eugenol
  • resin modified zinc oxide eugenol
  • ethoxybenzoic acid zinc oxide eugenol
70
Q

what is ZOE

A

zinc oxide eugenol

71
Q

what is resin modified ZOE

A

resin modified zinc oxide eugenol

72
Q

what is EBA ZOE

A

ethyoxybenzoic acid zinc oxide eugenol

73
Q

what kind of reaction occurs with zinc phosphate cements

A

acid base reaction

74
Q

what are the two components of zinc phosphate cement

A

powder and liquid

75
Q

describe the powder component of zinc oxide cement

A

this is the main component.
over 90% zinc oxide, which is the main reactive ingredient
less than 10% magnesium dioxide, which gives the white colour and increases the compressive strength
other oxide like alumina and silica improve the physical properties and alter the shade of the set material

76
Q

describe the liquid component of zinc phosphate cement

A

an aqueous solution of phosphoric acid, around 50%.
also contains oxides which buffer the solution to keep it as neutral as possible and to ensure it is consistent when set

77
Q

what are the oxides in the liquid component of zinc phosphate cement and what are their functions

A

aluminium oxide, which ensures an even consistency of the set material

zinc oxide which slows the reaction giving better working time

78
Q

what is the initial reaction for zinc phosphate cement

A

an acid base reaction

79
Q

what is the second reaction for zinc phosphate cement

A

a hydration reaction resulting in the formation of a crystallised phosphate matrix

80
Q

what is the function of aluminium oxide in zinc phosphate cement

A

prevents crystallisation leading to an amorphous glassy matrix of the acid salt surrounding the zinc oxide powder

81
Q

describe the glassy matrix of the acid salt surrounded unreacted zinc oxide powder in the zinc phosphate cement

A

insoluble, porous and containing free water form the setting reaction
the cement binds to the water to create a stronger, less porous material

82
Q

what are the problems with zinc phosphate cement

A
  • low initial pH around 2
  • exothermic setting reaction
  • not adhesive to the tooth or to the restoration
  • not cariostatic
  • final set takes 24 hours
  • brittle
  • opaque
83
Q

describe why a low initial pH for zinc phosphate cement is not a good thing

A

it can cause pulpal irritation as pH can take 24 hours to return to neutral

84
Q

how is the zinc phosphate cement retention increased

A

could be micro mechanical due to surface irregularities in the cavity but it does not adhere to the tooth or to the restoration

85
Q

why is the opacity of zinc phosphate cement not ideal

A

if there are thin areas of enamel with the material underneath, it can shine through and compromise the aesthetic of the tooth

86
Q

describe zinc polycarboxylate cement

A

this is a similar material to the zinc phosphate cement, but the phosphoric acid is reacted by polyacrylic acid

87
Q

why is zinc polycarboxylate cement better than the zinc phosphate

A

it bonds to tooth surfaces in a similar way to glass ionomer cements
less heat of reaction
pH is low to begin with but returns to neutral more quickly and there are longer chain acids which do not penetrate dentine as easily
cheap

88
Q

what are the disadvantages of zinc polycarboxylate cements

A

difficult to mix and manipulate
soluble in an oral environment at low pH
opaque
lower modulus and compressive strength than zinc phosphate

89
Q

what are ZOE cements used for

A

linings and base material in deep cavities, under amalgam restorations
temporary restorations (RMZOE or EBAZOE)
root canal sealer (slow setting though, 24hrs)
periodontal dressings (fast setting, 5 minutes)

90
Q

describe the use of ZOE in periodontal dressings

A

coe pak - eugenol free zinc oxide, protects wounds from being contaminated with saliva as much as possible. kept there for a week

91
Q

describe ZOE

A

base acid reaction
base is zinc oxide
acid is eugenol

92
Q

draw out the chelating reaction of zinc oxide with eugenol

A
93
Q

describe the setting reaction of ZOE

A

chelation reaction of zinc oxide with eugenol to form zinc eugenolate matrix which bonds the unreacted zinc oxide particles

94
Q

what are the properties of ZOE

A

adequate working time
rapid setting time, sets quicker in the mouth due to moisture and heat
modified by additional of accelerators
low thermal conductivity
low strength around 20 MPs
weak hydrogen bonds between eugenolate molecules
not strong enough to use as a base beneath an amalgam filling, packing pressure damages it
radiopaque

95
Q

describe the solubility of ZOE

A

high solubility and prone to disintegration eugenol is constantly released, which is replaced by water which leads to disintegration of the material but when eugenol is liberated, there is an obtundant effect on the pulp which can reduce pain

96
Q

why should ZOE materials not be used under composite resin materials

A

the released eugenol inhibits the set of resin based filling materials, and softens them to cause discolouration

97
Q

describe RMZOE

A

resin modified zinc oxide eugenol
resins are added to the powder and the liquid, they do not take part in the reaction by give a stronger backbone to the set material which increases the compressive strength to over 40MPa to make it a suitable cavity liner.
the resin reduces the solubility as well

98
Q

what is the resin in IRM

A

polymethylmethacrylate

99
Q

what is the resin in kalzinol

A

polystyrene

100
Q

describe EBA ZOE

A

ethoxybenzoic acid cement, is another modification for ZOE
EBA is the reactive agent, and there are different filler particles to toughen the material up

101
Q

what are the components of the powder part of EBA ZOE

A

65% zinc oxide
35% quartz or alumina (fillers)
hydrogenated rosin 6%

102
Q

what are the components of the liquid part of the EBA ZOE

A

37% eugenol
63% EBA

103
Q

describe the setting of EBA ZOE

A

same as with ZOE, but with EBA to encourage a crystalline structure which imparts greater strength to the set material

104
Q

what are the properties of EBA ZOE

A

stronger than ZOE or resin modified ZOE, around 60MPa, and less soluble

105
Q

describe glass ionomer lining materials

A

these are the most widely used lining materials, and they can bond and seal to the dentine
can also bond to composite resin filling placed over it, and can release fluoride over time to be cariostatic

106
Q

describe the use of glass ionomer lining material

A

easy, mixing is simple and many materials will come as two paste clicker system
light cured and command set. gives a long working time and a conveniently short setting time of around 30 seconds

107
Q

describe the properties of glass ionomer lining materials

A

thermal conductivity and diffusivity are lower than dentine for both GIC and RMGIC
thermal expansion is similar to dentine
compressive strength is over 170MPa, higher than any zinc oxide based materials
most materials are radiopaque, with radiopacity varying between each
marginal seal is better than any other materials as there is a chemical bond to the enamel and the dentine

108
Q

describe the interaction of glass ionomer cements with dentinal tubules

A

they predictably seal the tubules, decreasing microleakage and helping prevent post treatment sensitivity

109
Q

which lining cement is the least soluble

A

resin modified glass ionomer

110
Q

what is released from GIC materials

A
  • fluoride (cariostatic)
  • benzoyl iodides and benzoyl bromides
  • unreacted HEMA
111
Q

describe the release of benzoyl iodides and bromides from glass ionomer lining materials

A

they are released during the polymerisation reaction of resin modified glass ionomer cements, and are cytotoxic which is effective against residual cavity bacteria

112
Q

why is complete cure of RMGIC required

A

unreacted HEMA can damage the pulp

113
Q

why should RMGIC never be placed over direct pulp exposure

A

materials released can be cytotoxic which can also kill the pulpal cells alongside bacteria.

114
Q

which lining material can bond to restorative materials

A

glass ionomer cements

115
Q

do RMGIC require surface treatment

A

no

116
Q

what are the dental hospital lining guidelines for cavities in dentine

A

consider using a lining of RMGIC such as vitrebond for amalgam and for larger cavities to be filled with composite

117
Q

when should calciumhydroxide be used as a lining material in the dental hospital

A

only when the cavity approaches the pulp, either as direct or indirect pulp cap over the deepest part of the cavity

118
Q

what should calcium hydroxide be covered with prior to the final restoration being placed

A

RMGIC

119
Q

what is an indirect pulp cap

A

when the cavity is close to the pulp but there is still dentine covering it

120
Q

what is a direct pulp cap

A

when the pulp is exposed

121
Q

why should calcium hydroxide be covered with RMGIC before placing the restorative material

A

shields the layer from any liquids that could dissolve it away

Operative Dentistry (22 decks)

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