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Dental material science > Cavity lining materials > Flashcards

Cavity lining materials Flashcards

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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

A

Setting calcium hydroxide

Glass Ionomer and Resin Modified Glass Ionomer cements

22
Q

Who invented vitrebond

A

Sumita mitra

23
Q

When should calcium hydroxide be used

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

A

a chelation reaction between the ZnO and the butylene glycol disalicylate

25
Q

What is the initial ph of the cement formed by calcium hydroxide liner

A

around 12

26
Q

What forms the base of CaOH liner

A

Calcium hydroxide 50%​

Zinc Oxide (filler) 10%​

Zinc Stearate (filler) <1%​

N-ethyl toluene sulphonamide (plasticiser) 40%​

27
Q

What forms the catalyst within CaOH

A

Butylene glycol disalicylate (reactive element) 40%​

Titanium Dioxide (filler) 13-14% ​

Calcium Sulphate (filler) 30%​

Calcium Tungstate (filler and radiopaquer) 15%​

28
Q

What is the benefit to the alkaline cement formed in the setting reaction of CaOH

A

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

29
Q

Why is reparative dentine formed with CaOH

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 of the cavity off from the pulp. (The calcium comes from the pulp not the cement).

30
Q

What are the properties of CaOH liner

A

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
Q

What are the Zinc Oxide based cements

A

Zinc Phosphate​

Zinc Polycarboxylate​

Zinc Oxide Eugenol (ZOE)​

Resin Modified ZOE​

Ethoxybenzoic acid (EBA) ZOE​

32
Q

What are the benefits of zinc phosphate cement

A

In use for 100+ years​

Acid base reaction​

Powder and liquid​

Excellent clinical service​

Easy to use​

Cheap

33
Q

What gives zinc phosphate powder its white colour

A

Magnesium Dioxide

34
Q

What is the main reactive ingredient in the powder of zinc phosphate

A

Zinc Oxide >90%

35
Q

What are the two reactions of zinc phosphate cement

A

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
Q

What prevents crystalisation of zinc phosphate cement

A

Aluminium oxide

37
Q

How is the matrix described

A

Amorphous glassy matrix (almost insoluble)

38
Q

What are the problems with zinc phosphate cement

A

-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
Q

What are the properties of zinc polycarboxylate cement

A

Difficult to mix​

Difficult to manipulate​

Soluable in oral environment at lower pH​

Opaque​

Lower modulus and compressive strength than Zinc Phosphate

40
Q

What is the base and acid in s ZOE reaction

A

The base is ZnO​

The acid is Eugenol

41
Q

How does ZOE set

A

Chelation reaction of zinc oxide with the eugenol to form zinc eugenolate matrix.​

This matrix bonds the unreacted ZnO particles​

42
Q

What are the properties of ZOE

A

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
Q

Why is ZOE’s high solubility good AND bad

A

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
Q

In what cases should ZOE NOT be used

A

Under composite resin materials as it inhibits the set of resin based filling materials softening then and causing discolouration

45
Q

What are the most widely used lining materials

A

Glass ionomer lining materials

46
Q

What are the only lining able to bond to restorative materials

A

Glass ionomer lining materials

47
Q

Why is complete cure of RMGICs needed

A

Any unreacted HEMA may damage the pulp

48
Q

What is the least soluble cement

A

RMGICs

49
Q

What are 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 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
Q

Why is the opacity of zinc phosphate cement bad

A

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 (5 decks)

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