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Dental material science > Cavity lining materials > Flashcards

Cavity lining materials Flashcards

(50 cards)

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1
Q

What are disadvantages of restoratives

A

May not make intimate contact with the tooth surface (especially dentine)​
-Any gap may allow ingress of fluids and bacteria​

Heat released during setting/curing​

Release of chemicals​
-These may be pulpal irritants and lead to pain or pulpal damage

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2
Q

What can be used to prevent micro-leakage

A

Intermediate Restorative Material

A lining material​

- Prevents gaps​

- Acts as a protective barrier
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3
Q

What is a cavity base

A

Thick mix placed in bulk​

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

More common in metal restorations (direct or indirect)

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4
Q

What is cavity lining

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 or by an anti-bacterial action’

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5
Q

What is the purpose of a liner

A

Pulpal protection

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6
Q

What is the pulp needing protection from

A

Chemical Stimuli from unreacted chemicals in the filling material or the initial pH of the filling​

Thermal Stimuli. eg. exothermic setting reaction of composite or heat conducted through metal fillings​

Bacteria and Endotoxins. Microleakage – the penetration of oral fluids and bacteria and their toxins between the restorative and the cavity walls.

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7
Q

Why is a liner placed

A

Therapeutic. To calm down inflammation within the pulp and promote pulpal healing. Prior to or at the time of a permanent restoration being placed.​

Palliative. To reduce patient symptoms prior to definitive treatment being carried out. Most commonly in patients with reversible pulpitis.

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8
Q

What is the thermal expansion coefficient

A

Change in length per unit length for a temprise of 1 degree

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9
Q

What is the thermal coefficient of enamel

A

8.3ppmdegrees

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10
Q

What is the thermal coefficient of dentine

A

11.4ppmdegrees-1

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11
Q

What is the thermal coefficient of amalgam and composite

A

25ppmdegrees-1

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12
Q

What is the thermal coefficient of GIC and RMGIC

A

GIC- 11
RMGIC - 20

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13
Q

How is thermal diffusivity measured

A

cm2/sec

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14
Q

What is the thermal diffusivity of enamel and dentine

A

E- 0.0042cm2/sec
D- 0.0026cm2/sec

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15
Q

What is a marginal seal

A

The chemical bond of the lining to the dentine.
Should be permanent and impenetrable

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16
Q

What are some properties of lining materials

A

Easy to mix
Short setting time
Low thermal conductivity
Similar thermal expansion to dentine
Lower or similar thermal diffusivity to dentine
High compressive strength
Radioplaque
Low solubility

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17
Q

How do lining materials prevent secondary caries around the restoration

A

Cariostatic
-fluoride releasing
-antibacterial

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18
Q

What does biocompatible mean

A

Non-toxic​

Not damaging to the pulp​
-pH neutral​
-No excessive heat during setting​

Low thermal conductivity

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19
Q

Are lining materials biocompatible

A

yes

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20
Q

What materials are used as bases

A

Zinc Oxide based cements

Glass Ionomer and Resin Modified Glass Ionomer cements

Palliative cements

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21
Q

What materials are used for liners

Study These Flashcards
A

Setting calcium hydroxide

Glass Ionomer and Resin Modified Glass Ionomer cements

22
Q

Who invented vitrebond

23
Q

When should calcium hydroxide be used

Study These Flashcards
A

Only when the cavity approaches the pulp (as a direct or indirect pulp cap)

24
Q

What is the setting reaction for calcium hydrocide liner

Study These Flashcards
A

a chelation reaction between the ZnO and the butylene glycol disalicylate

25
What is the initial ph of the cement formed by calcium hydroxide liner
around 12
26
What forms the base of CaOH liner
Calcium hydroxide 50%​ Zinc Oxide (filler) 10%​ Zinc Stearate (filler) <1%​ N-ethyl toluene sulphonamide (plasticiser) 40%​
27
What forms the catalyst within CaOH
Butylene glycol disalicylate (reactive element) 40%​ Titanium Dioxide (filler) 13-14% ​ Calcium Sulphate (filler) 30%​ Calcium Tungstate (filler and radiopaquer) 15%​
28
What is the benefit to the alkaline cement formed in the setting reaction of CaOH
Cariogenic bacterial survive in an acidic environment. The highly alkaline liner kills the bugs
29
Why is reparative dentine formed with CaOH
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 of the cavity off from the pulp. (The calcium comes from the pulp not the cement).
30
What are the properties of CaOH liner
Quick setting time​ Radiopaque​ Easy to use​ BUT Low compressive strength​ Unstable and soluble​ -If the cavity leaks then the lining will disappear​ -It may even disappear just because it is in contact with moist dentine​
31
What are the Zinc Oxide based cements
Zinc Phosphate​ Zinc Polycarboxylate​ Zinc Oxide Eugenol (ZOE)​ Resin Modified ZOE​ Ethoxybenzoic acid (EBA) ZOE​
32
What are the benefits of zinc phosphate cement
In use for 100+ years​ Acid base reaction​ Powder and liquid​ Excellent clinical service​ Easy to use​ Cheap
33
What gives zinc phosphate powder its white colour
Magnesium Dioxide
34
What is the main reactive ingredient in the powder of zinc phosphate
Zinc Oxide >90%
35
What are the two reactions of zinc phosphate cement
The initial reaction is acid base ZnO + 2 H3PO4  Zn(H2PO4)2 + H2O This is followed by a hydration reaction resulting in the formation of a crystalised phosphate matrix ZnO + Zn(H2PO4)2 + 2H2O --> Zn3(H2PO4)2.4H2O(Hopiete)
36
What prevents crystalisation of zinc phosphate cement
Aluminium oxide
37
How is the matrix described
Amorphous glassy matrix (almost insoluble)
38
What are the problems with zinc phosphate cement
-Low initial pH approx. 2​ Can cause pulpal irritation as pH can take 24hrs to return to neutral​ -Exothermic setting reaction -Not adhesive to tooth or restoration​ Retention may be slightly micromechanical due to surface irregularities of cavity​ -Not cariostatic -Final set takes 24hrs -Brittle -Opaque​
39
What are the properties of zinc polycarboxylate cement
Difficult to mix​ Difficult to manipulate​ Soluable in oral environment at lower pH​ Opaque​ Lower modulus and compressive strength than Zinc Phosphate
40
What is the base and acid in s ZOE reaction
The base is ZnO​ The acid is Eugenol
41
How does ZOE set
Chelation reaction of zinc oxide with the eugenol to form zinc eugenolate matrix.​ This matrix bonds the unreacted ZnO particles​
42
What are the properties of ZOE
Adequate working time​ Relatively rapid setting time​ -Sets quicker in the mouth due to moisture and heat​ -Can be modified by addition of accelerators​ Low thermal conductivity​ Low strength around 20MPa​ -Weak hydrogen bonds between the eugenolate molecules​ -Not strong enough to use as a base beneath an amalgam filling. The packing pressure would damage it.​ Radiopaque
43
Why is ZOE's high solubility good AND bad
Eugenol is replaced by water which  disintegration of the material BUT​ Eugenol when liberated has an obtundant effect on the pulp and can reduce pain​
44
In what cases should ZOE NOT be used
Under composite resin materials as it inhibits the set of resin based filling materials softening then and causing discolouration
45
What are the most widely used lining materials
Glass ionomer lining materials
46
What are the only lining able to bond to restorative materials
Glass ionomer lining materials
47
Why is complete cure of RMGICs needed
Any unreacted HEMA may damage the pulp
48
What is the least soluble cement
RMGICs
49
What are the properties of Glass ionomer lining materials
Thermal conductivity and diffusivity are lower than dentine for both GIC and RMGIC​ Thermal expansion is similar to dentine for GIC​ Compressive strength is > 170MPa, higher than any of the ZnO based materials​ Most materials are radiopaque, the radiopacity varies between materials.​ Marginal seal is better than any of the other materials as there is a chemical bond to enamel and dentine.​ They are the only material to predictably seal dentinal tubules. This decreases microleakage and helps prevent post treatment sensitivity​
50
Why is the opacity of zinc phosphate cement bad
If it is placed under thin enamel the grey tint from the alumina and silica might shine through giving a grey appearance of the tooth

Dental material science (13 decks)

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