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JK BDS2 CDS DMS > Cavity Linings > Flashcards

Cavity Linings Flashcards

1
Q

What are examples of materials that are places into tooth cavities? (5)

A
  • composite resin
  • glass ionomer
  • amalgam
  • precious metal
    -ceramic
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2
Q

One disadvantage of restorations is that they may not make intimate contact with the tooth surface (especially dentine0 What can this lead to?

A

Any gaps may allow ingress of fluids and bacteria

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3
Q

a disadvantage of restorations is that heat may be released during setting/curing. What can this have an effect on?

A

Potentially detrimental effect on the pulp

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4
Q

A disadvantage of restorations is that there may be a release of chemical. What may this lead to?

A
  • they may be pulpal irritants and lead to pain or pulpal damage
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5
Q

What are the functions of a lining material? (2)

A
  • Prevents gaps
  • Acts as a protective barrier
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6
Q

What is a cavity base?

A

A thick mix placed in bulk

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7
Q

What is a cavity base used for?

A

Dentine replacement used to minimise the bulk of material or block out undercuts

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8
Q

Where are cavity bases more common?

A

In metal restorations (direct or indirect)

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9
Q

What is a cavity lining?

A
  • A thin coating (<0.5mm) over EXPOSED dentine
    -“A dentine sealer able to promote the health of the pulp by adhering to the tooth structure of by an anti-bacterial action” - RMGI does this to a certain extent
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10
Q

One purpose of a liner is for pulpal protection. What is the protection from? (3)

A
  • Chemical stimuli from unreacted chemicals in the filling material or the initial pH of the filling
  • Thermal stimuli e.g. exothermic setting reaction of composite or heat conducted through mental fillings
    -bacteria and exotoxins. Microleakage ( the penetration of oral fluids and bacteria and their toxins between the restorative material and the cavity walls)
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11
Q

What is microleakage?

A

The penetration of oral fluids and bacteria and their toxins between the restorative material and the cavity walls

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12
Q

One purpose of a liner is to have a therapeutic effect. What does this mean?

A
  • to calm down inflammation within the pulp and promote pulpal healing
  • prior to or at the time of a permanent restoration being placed
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13
Q

One purpose of a liner is to have a palliative effect. What does this mean?

A
  • to reduce patient symptoms prior to definitive treatment being carried out. Most commonly in patients with reversible pulpitis
  • More insulation before placing a final restoration
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14
Q

What are the properties of lining materials? ( 9)

A
  • ease of use
  • thermal properties
  • mechanical properties
  • radiopaque
  • marginal seal
  • solubility
  • cariogenic
  • biocompatible
  • compatible with restorative materials
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15
Q

What makes lining materials easy to use?

A
  • easy to mix
  • working time should be long to allow easy placement
  • setting time short- ideally command set
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16
Q

What should the thermal properties of lining materials be? (3)

A
  • thermal conductivity should be low
  • thermal expansion coefficient should be similar to dentine
  • thermal diffusivity should be similar to dentine or lower
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17
Q

What is thermal conductivity?

A

How well heat energy is transferred through a material

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18
Q

What is the thermal expansion coefficient?

A
  • change in length per unit length form a temoerature rise of 1 degree
  • units are ppm/degree celcius^-1
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19
Q

Ideally what should the thermal expansion coefficient of a lining material be?

A

Ideally a liner should match the thermal coefficient of a tooth
- enamel = 8.3
- dentine = 11.4
- GIC = 11
- RMGIC =20
- Composite = 25
- Amalgam = 25

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20
Q

What is thermal diffusivity?

A
  • the thermal conductivity of a substance divided by the produce of its density and its specific heat capacity
    -IT is similar to conductivity
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21
Q

What unit is thermal diffusivity measured in?

A

cm^2/sec

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22
Q

Ideally what should the thermal diffusivity of a lining material be?

A
  • ideally at least as low as the tooth
  • enamel= 0.0042cm^2/sec
  • dentine= 0.0026cm^2/sec
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23
Q

What is the thermal diffusivity of liners like compared to tooth enamel?

A

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

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24
Q

What is the thermal diffusivity of amalgam?

A
  • 1.7cm^2/sec
  • amalgam is 500x more than dentine
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25
Q

What are the mechanical properties of lining materials (2)

A
  • High compressive strength
  • modulus is similar to dentine
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26
Q

What do lining materials need a high compressive strength?

A
  • to allow the placement of a filling on top without it breaking
  • Dentine is about 275MPa
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27
Q

What does the modulus of elasticity of a lining material have to be similar to dentine?

A
  • If the tooth bends and flexes, want the lining material to do the same
  • want it to be around 15MPa
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28
Q

What do lining materials need to be radiopaque?

A
  • as it should be easy to see the difference between the lining and the tooth
  • makes it easier to see if there is any leakage or secondary caries
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29
Q

Ideally a lining material should form a chemical bond to dentine. What properties do you want from the bond? (2)

A

The bond should be permanent and impermeable

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30
Q

What should the solubility of a lining material be like?

A

solubility should be low

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31
Q

What does cariostatic mean?

A

Tending to inhibit the formation of dental caries

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32
Q

What are the cariostatic properties of lining materials and why are they important? (3)

A
  • fluoride releasing
    -antibacterial
  • important in preventing secondary caries around the restoration
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33
Q

Why are cariostatic features of lining materials important?

A

They are important in preventing secondary caries around the restoration

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34
Q

Are lining materials toxic to the pulp?

A

NO

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35
Q

Lining materials are not damaging to the pulp. What 3 factors ensure this?

A
  • neutral pH
  • no excessive heat during setting
  • they have a low thermal conductivity
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36
Q

Is setting calcium hydroxide a base or a liner?

A

Liner

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37
Q

Are zinc oxide bases cements a base or a liner?

A

base

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38
Q

Are Gi and RMGIC’s bases or liners?

A

can be either

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39
Q

Are palliative cements bases or liners?

A

A base - seldom used nowadays, mainly historic.

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40
Q

How man pastes are setting calcium hydroxide liners composed of?

A

2 pastes

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41
Q

What are 2 examples of setting CaOH liners?

A
  • Life
  • Dycal (used most of time in dental hospital)
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42
Q

What are the 2 constituents of a setting CaOH liner?

A

Base
catalyst

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43
Q

What are the 4 components of the base in a setting Calcium Hydroxide liner?

A
  • Calcium hydroxide 50%
  • zinc oxide (filler) 10%
  • zinc stearate (filler) <1%
  • N-ethyl toluene sulphonamide (plasticiser) 40%
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44
Q

What are the 4 components of the catalyst in a setting calcium hydroxide liner?

A

-Butylene glycol disalicylate (reactive element) 40%
-Titanium Dioxide (filler) 13-14%
-Calcium sulphate (filler) 30%
-Calcium Tungstate (filler and radiopaquer) 15%

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45
Q

What is the setting reaction of setting calcium hydroxide liner?

A

A chelation reaction between the ZnO and the butylene glycol disalicylate

46
Q

The setting reaction of setting calcium hydroxide liners results in a cement with an initial pH of around 12. Why is this good?

A
  • as all of the microbes that cause caries like to live in acidic conditions
  • it also causes a degree of irritation in the pulp which causes the lay down of tertiary dentine so increases the distance between where the cavity was and the where the pulp starts
47
Q

Why is a CaOH liner bactericidal to cariogenic bacteria?

A

Cariogenic bacterial survive in an acidic environment. The highly alkaline liner kills the bugs

48
Q

Why does the irritation of the pulp by CaOH liners results in reparative dentine formation?

A
  • The cement causes irritation to the odontoblast layer
  • necrosis follows which in turn results in a layer of tertiary dentine being produced
  • this eventually forms a calcified bridge walling the base from the pulp ( the calcium comes from the pulp not the cement)
49
Q

What are 3 advantageous properties of CaOH?

A
  • quick setting time
  • radiopaque
  • easy to use
50
Q

What are 2 disadvantageous properties of CaOH?

A
  • low compressive strength ( if try to pack amalgam filling in on top of it, it will probably break)
  • it may even disappear just because it is in contact with moist dentine
51
Q

What are 5 examples of zinc oxide based cements?

A
  • zinc phosphate
  • zinc polycarboxylate
  • zinc oxide eugenol (ZOE)
  • resin modified ZOE
  • ethoxybenzoic acid (EBA) (ZOE)
52
Q

How long has zinc phosphate cement been used for?

A

in use for 100+ years

53
Q

Zinc phosphate cement is produced by an acid base reaction with a powder and a liquid. What is the power and liquid components?

A

powder= zinc oxide
liquid= phosphoric acid

54
Q

What are 3 advantages of using zinc phosphate cement as a lining material?

A
  • excellent clinical service
  • easy to use
  • cheap
55
Q

What is the power in zinc phosphate cement composed of? (3)

A
  • zinc oxide >90% (main reactive ingredient)
  • Magnesium dioxide <10%
  • other oxides (alumina and silica)
56
Q

What 2 things does the magnesium dioxide component of the powder in zinc phosphate cements do?

A
  • gives white colour
  • increases compressive strength
57
Q

What 2 things does the oxide components (alumina and silica) of the power in zinc phosphate cements do?

A
  • improved physical properties
  • alters the shade of the set material
58
Q

What is the liquid component of zinc phosphate composed of? (2)

A

-Aqueous solution of phosphoric acid (approx. 50%)
-Oxides which buffer the solution:
-aluminium oxide = ensures even consistency of set material
-Zinc oxide = slows the reaction giving better working time

59
Q

why does the aluminium oxide component of the liquid in zinc oxide cements do?

A

ensures even consistency of set material

60
Q

What does the zinc oxide components of the liquid in zinc oxide cements do?

A

slows the reaction giving better working time

61
Q

What reactions are involved in producing zinc phosphate cement? (5)

A
  • the initial reaction is acid base
  • this is followed by a hydration reaction resulting in the formation of a crystallised phosphate matrix
  • the aluminium oxide prevents crystallisation leading to an amorphous glassy matrix of the acid salt surrounding unreacted ZnO powder
    -this matrix is almost insoluble, but it is porous and contains free water from the setting reaction
  • ## the cement subsequently matures binding this water leading to a stronger, less porous material
62
Q

One problem with zinc phosphate cement is that it has a low initial pH of approx 2. Why is this a problem?

A

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

63
Q

Is zinc phosphate cement an endothermic or exothermic reaction?

A

Exothermic

64
Q

One problem with zinc phosphate cement is that it is not adhesive to the tooth or restoration. Why is this a problem?

A

Retention may be slightly micromechanical due to the surface irregularities of the cavity

65
Q

is zinc phosphate cement cariostatic?

A

No

66
Q

How long does it take for zinc phosphate cement to completely set?

A
  • Final set takes 24 hours
  • It is reasonable hard within 5 mins
67
Q

Is zinc oxide cement brittle?

A

Yes

68
Q

is zinc phosphate cement opaque?

A

Yes

69
Q

Zinc polycarboxylate is similar to zinc phosphate. What is the difference?

A

Phosphoric acid is replaces by polyacrylic acid

70
Q

What are the advantages of zinc polycarboxylate cement as a liner? (4)

A
  • Bonds to tooth surfaces in similar way to GIC’s
  • less heat of reaction
  • pH is low to being with but returns to neutral more quickly and longer chain acids do not penetrate dentine as easily
  • cheap
71
Q

What are the disadvantages of zinc polycarboxylate cement as a lining ? (5)

A
  • difficult to mix
  • difficult to manipulate
    -soluble in oral environment at lower pH
  • opaque
  • lower modulus and compressive strength than zinc phosphate
72
Q

What are Zinc Oxide Eugenol cements used for? (4)

A

Linings/base in deep cavities:
- under amalgam restorations
Temporary restorations
- resin modified of EBA ZOE
Root canal sealer
- Slow setting 24 hours
Periodontal dressings
- fast setting- 5 mins

73
Q

zinc oxide eugenol cement is a base acid reaction. What is the base and what is the acid?

A

Base= ZnO
Acid= Eugenol
Base+ Acid -> salt + water

74
Q

What is the setting reaction of zinc oxide eugenol?

A
  • chelation reaction of zinc oxide with the eugenol to form zinc eugenolate matrix
  • this matrix bond the unreacted ZnO particles
75
Q

What is the working time of ZOE like?

A

Adequate working time

76
Q

What is the setting time of ZOE like?

A

Relatively rapid setting time:
- sets quicker in the mouth due to moisture and heat
- can be modified by the addition of accelerators

77
Q

What is the thermal conductivity of ZOE like?

A

Low thermal conductivity

78
Q

What is the strength of ZOE like?

A

low strength, around 20MPa
- weak hydrogen bonds between the eugenolate molecules
- not strong enough to use as a base beneath as amalgam filling. The packing pressure would damage it

79
Q

Is ZOE radiopaque

A

Yes

80
Q

What is the solubility of ZOE like?

A
  • highly soluble
  • eugenol is constantly released:

This is good and bad:

=eugenol is replaces by water which -> disintegration of the material BUT
= eugenol when liberated has an obtundent effect on the pulp and can reduce pain

81
Q

Why should ZOE materials NOT be used under composite resin materials?

A

As the release of eugenol inhibits the set of resin based filling materials. It softens them and can cause discolouration

82
Q

Resins can be added to the powder and liquid of ZOE to make resin modified ZOE. What resins are added to IRM and Kalzinol?

A

IRM= Polymethylmethacrylate
- Kalzinol = polystyrene

83
Q

Resins added to ZOE do not take part in the reaction. What do they do?

A

They give a stringer back bone to the set material

84
Q

Adding resins to ZOE increases the compressive strength to >40MPa. What does this make ZOE suitable for?

A

suitable as a cavity lining

85
Q

What does adding resins to ZOE do to the solubility of it?

A

greatly decreases the solubility

86
Q

Ethoxybenzoic acid (EBA) cement is a modified ZOE. What is the composition of the powder component of this ? (3)

A
  • ZnO 65%
  • Quartz or Alumina 35%
  • Hydrogenated rosin (around 6%)
87
Q

EBA cement is a modified ZOE. What is the composition of the liquid component of this ? (2 points)

A
  • Eugenol 37%
  • ethoxybenzoic acid EBA 63%
88
Q

What does the inclusion of quartz and alumina in EBA do?

A
  • makes the cement stronger
  • it is reinforcing
89
Q

The setting reaction of EBA is similar to that of ZOE. What is the difference ?

A

EBA encouraged a crystalline structure which imparts greater strength to the set material

90
Q

EBA is stronger than ZOE or Resin modified ZOE. What is the strength of EBA?

A

around 60 MPa which is more than strong enough to place an amalgam filling onto it

91
Q

is EBA more or less soluble than ZOE?

A

Less soluble

92
Q

What are the most widely used lining materials ?

A

Glass ionomer lining

93
Q

Can glass ionomers bond to dentine ?

A

Yes, can bond to and seal dentine

94
Q

Can glass ionomer bond to composite?

A

Yes

95
Q

Is glass ionomer cariostatic?

A

Yes, as it releases fluoride over time

96
Q

Are glass ionomer lining materials easy to use?

A

yes, mixing is simple and many materials come as a two paste ‘clicker’ system

97
Q

Glass ionomer lining materials are generally light cured and so are command set. What does this allow?

A

Gives a long working time and a conveniently short setting time (30 seconds)

98
Q

What is the thermal conductivity and diffusivity of glass ionomer lining materials like compared to dentine ?

A

Lower than dentine for both GIC and RMGIC

99
Q

What is the thermal expansion of GIC and RMGIC’s like compared to dentine

A

similar to dentine
-RMGIC is a little bit less so

100
Q

What is the compressive strength of GIC’s ?

A

> 170MPa, higher than any of the ZnO based materials
- not quite as high as dentine though

101
Q

Are GIC’s radiopaque?

A

Yes, most of them are, but the radiopacity varies between materials

102
Q

What is the marginal seal of GIC’s to dentine like?

A

Better than any other materials as there is a chemical bond to enamel and dentine

103
Q

What features of GIC’s decreases micro-leakage and helps to prevent post treatment sensitivity?

A

As GIC’s are the only material to predictably seal dentinal tubules

104
Q

What is the solubility of GIC and RMGIC’s like compared to other lining materials? (3)

A
  • Solubility is greater for GIC than RMGIC and is greatest initially
  • However, GIC materials are less soluble than any of the other liners apart from Zinc phosphate cement
  • RMGIC is less soluble than any other cement
105
Q

Benzoyl iodides and benzoyl bromides are released during the polymerisation reaction of RMGIC’s. What does this lead to?

A

These are cytotoxic and can be effective against residual cavity bacteria

106
Q

What is complete cure of RMGIC’s required?

A

As any unreacted HEMA may damage the pulp

107
Q

Which lining material is the only one able to bond to restorative materials?

A

GIC’s

108
Q

What do some conventional glass ionomers require prior to bonding?

A

Some require to be etched

109
Q

Do RMGIC’s require any surface treatment

A

No

110
Q

Is it possible to bond amalgam to a tooth using RMGIC?

A

Yes

111
Q

What are the dental hospital guidelines for cavities in dentine?

A

Consider the use of a lining RMGIC (such as vitrebond) for amalgam and for larger cavities to be filled with composite

112
Q

What are the Dental Hospital lining guidelines for Calcium hydroxide? (2)

A
  • It should only be used when the cavity approaches the pulp
  • either as a direct or indirect pulp cap ober the deepest part of the cavity
  • calcium hydroxide should be covered with RMGIC prior to the final restoration being places

JK BDS2 CDS DMS (4 decks)

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