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BDS2 - DMS > Cavity Linings > Flashcards

Cavity Linings Flashcards

1
Q

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

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 dentine). What can this lead to?

A
  • Any gap may allow ingress of fluids and bacteria
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3
Q

A disadvantage of restorations is that heat may be release 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 my 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 points)

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 of indirect)
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9
Q

What is a cavity lining?

A
  • A thin coating (<0.5mm) over EXPOSED dentine
  • Van Noort ‘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 points)

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 metal fillings
  • Bacteria and exotoxins. Microleakage - the penetration of oral fluids and bacteria and their toxins between the restorative 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 points)

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 points)

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 for a temperature 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 product 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 toot h 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 points)

A
  • High compressive strength

- Modulus is similar to dentine

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26
Q

Why 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

Why 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

Why do lining materials need to be radiopaque? (2 points)

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 points)

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 points)

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
  • They have a neutral pH
  • There is 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
  • A liner
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37
Q

Are zinc oxide based cements a base or a liner?

A
  • A base
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38
Q

Are GI and RMGIC’s bases or liners?

A
  • Can be a base or a liner
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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 many pastes are setting calcium hydroxide liners composed of?

A
  • 2 pastes
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41
Q

What are 2 examples of setting calcium hydroxide liners?

A
  • Life

- Dycal (used most of the time in the dental hospital)

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42
Q

What are the 2 constituents of a setting calcium hydroxide liner?

A
  • A base

- A 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? (2 points)

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 where the pulp starts
47
Q

Why is a CaOH liner bactericidal to cariogenic bacteria?

A
  • Cariogenic bacterial suirvive in an acidic environment. The highly alkaline liner kills the bugs
48
Q

Why does irritation of the pulp by CaOH liners result 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 bri dge 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 top of it, it will probably break)
  • It may even disappear just because it if 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 powder 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 powder in Zinc Phosphate cement composed of? (3 points)

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 powder in Zinc Phosphate cements do?

A
  • Improves physical properties

- Alters the shade of the set material

58
Q

What is the liquid component of Zinc Phosphate cements composed of? (2 points)

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

What 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 component 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 points)

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 reasonably hard within 5 minutes

67
Q

Is Zinc phosphate 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 replaced by polyacrylic acid
70
Q

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

A
  • Bonds to tooth surfaces in similar way to GIC’s
  • Less heat of reaction
  • pH is low to begin 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 points)

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 (ZOE) cements used for? (4 points)

A

Linings/base in deep cavities

  • Under amalgam restorations

Temporary restorations

  • Resin modified or EBA ZOE

Root canal sealer

  • Slow setting 24hrs

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 bonds 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 replaced 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 stronger backbone 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 points)

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

Ethoxybenzoic acid (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 encourages 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 60MPa 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 ionomer 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 ling 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 feature of GIC’s decreases microleakage 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 points)

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

Why is complete cure of RMGIC’s required?

A
  • As any unreacted HEMA may damage the pulp
107
Q

Which lining material id 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 points)

A
  • It should only be used when the cavity approaches the pulp
  • Either as a direct or indirect pulp cap over the deepest part of the cavity
  • Calcium hydroxide should be covered with RMGIC prior to the final restoration being placed

BDS2 - DMS (14 decks)

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