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Flashcards in Cavity Lining Materials Deck (26)
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1

Purposes of cavity lining materials

- Protects pulp from chemical stimuli
- Protects pulp from thermal stimuli – EXOTHERMIC setting reaction, heat conducted through metal fillings
- Protects from bacterial invasion if there is microleakage.
- Therapeutic – calms down pulp inflammation and promotes pulpal healing

2

Why does RMGI require no surface treatment to bond?

Chemical bonding occurs due to resin

3

What are the components of Glass Ionomer?

Acid - polyacrylic acid & tartaric acid

Powder - silica, alumina and calcium fluoride (+ others but these are the main)

4

Give reasons why Glass Ionomer is better than its Zinc Oxide predecessors
(drawbacks of zinc oxide)

Zinc phosphate
- Low initial pH
- Not adhesive to tooth or restoration
- Not cariostatic (not fluoride releasing)
- Exothermic setting reaction

Note - zinc polycarboxylate - similar bonding to tooth as GI

GI
- Can bond to enamel and dentine without surface treatment - and STABLE BOND.
- Thermal properties similar to dentine
- No contraction on setting
- Fluoride releasing

5

Advantages of GI

Stable bond to enamel and dentine
Low microleakage
Fluoride releasing
Good thermal properties
No contraction on setting

6

Disadvantages of GI

Brittle
Poor wear resistance
Moisture susceptible when first placed - especially between gelation and hardening setting steps.
Poor aesthetics
Poor handling characteristics
Susceptible to acid attack and drying out over time
Possible problems bonding to composite
Etching damages surface

7

What effect does adding tartaric acid have on GI?

Tartaric acid shortens the setting time (but working time is the same as without)

8

What is the bond strength of GI to enamel with and without acid etch?

Without - 5MPa

With - 20MPa

9

Why does RMGI have to be placed in layers?

It may not set otherwise - the material is quite opaque so light does not penetrate deeply into the material.

10

Components of RMGI

fluoro-aluminosilicate glass
photo-initiators
polyacrylic acid
water
water-soluble methacrylate monomer, such as hydroxyethyl methacrylate (HEMA)

11

Difference between RMGI and GI

RMGI - hybrid material of composite and GI.

Same as GI - bonding to tooth, fluoride release
Added advantages of RMGI - light-curing (command set), improved physical properties, better aesthetics.

12

Is there contraction shrinkage on setting for GI and RMGI?

GI - NO contraction on setting

RMGI - has contraction stress upon setting because it shrinks

13

Properties of RMGIC compared to conventional GIC and composite resin.

Compared with conventional GIC
- Better aesthetics
- Easier to use
- Stronger

Compared with Composite Resin
- Easier to use
- Fluoride release

14

What is calcium hydroxide lining material used for?

Used as a direct pulp-capping material
It is extremely alkali.

15

State some drawbacks of calcium hydroxide liner

Low compressive strength
Unstable and soluble - if cavity leaks then lining will disappear.
May even disappear because of contact with moist dentine.

16

Advantages of calcium hydroxide liner

Quick setting time
Easy to use
Radioopaque
Bactericidal to cariogenic bacteria - extremely alkali - initial pH of 12

17

What are the properties of Zinc Oxide Eugenol cements?

Adequate working time
Low thermal conductivity
Low compressive strength
Radio opaque
Relatively quick setting reaction
Very soluble

18

What lining materials should not be used under composite resin materials?

ZOE (zinc oxide eugenol) - the released eugenol inhibits the set of resin-based filling materials. Softens them and causes dis-colouration.

19

What are some improvements of Resin modified ZOE compared with ZOE?

Increases compressive strength to >40MPa making it suitable as a cavity lining

Greatly decreases solubility

20

Benefits of EBA compared with Resin modified ZOE ad ZOE?

Stronger than both - around 60MPa

Less soluble than conventional material

Better crystal structure and sets better

21

What are the components of calcium hydroxide liner?

Base

CaOH - 50%
Zinc oxide (filler) 10%
Zinc stearate (filler) <1%
N-ethyl toluene sulphonamide (plasticiser) 40%


Catalyst

Butylene glycol disalicylate (reactive element) 40% ACID
Fillers - Titanium dioxide, calcium sulphate, calcium tungstate (and radioopaquer)

22

What does CaOH do to the pulp?

Irritates it - specifically 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).

23

Why is Zinc phosphate rarely used nowadays? Drawbacks

Low compressive strength
Contraction on setting
Low initial pH (bacteria flourishes in acidic conditions)
Not adhesive to tooth or restoration
Final set takes 24 hours
Exothermic setting reaction

24

What is the 3 phase setting reaction of Glass Ionomer?

Dissolution

Gelation - initial setting - what makes material hard = 30 mins. Caused by formation of calcium polyacrylate

Hardening - formation of aluminium polyacrylate.
Takes a long time, can take a week or longer to fully set. But AP increases strength.

Particularly moisture sensitive between gelation and hardening.

25

Why should ZOE not be used under amalgam fillings?

Low compressive strength - not strong enough, the packing pressure would damage it. Tendency to break up.

26

Compressive strength of ZOE

20MPa