Cavity Lining Materials

Question 1

Purposes of cavity lining materials

Answer 1

• 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

Question 2

Why does RMGI require no surface treatment to bond?

Answer 2

Chemical bonding occurs due to resin

Question 3

What are the components of Glass Ionomer?

Answer 3

Acid - polyacrylic acid & tartaric acid

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

Question 4

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

Answer 4

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

Question 5

Advantages of GI

Answer 5

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

Question 6

Disadvantages of GI

Answer 6

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

Question 7

What effect does adding tartaric acid have on GI?

Answer 7

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

Question 8

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

Answer 8

Without - 5MPa

With - 20MPa

Question 9

Why does RMGI have to be placed in layers?

Answer 9

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

Question 10

Components of RMGI

Answer 10

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

Question 11

Difference between RMGI and GI

Answer 11

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.

Question 12

Is there contraction shrinkage on setting for GI and RMGI?

Answer 12

GI - NO contraction on setting

RMGI - has contraction stress upon setting because it shrinks

Question 13

Properties of RMGIC compared to conventional GIC and composite resin.

Answer 13

Compared with conventional GIC

• Better aesthetics
• Easier to use
• Stronger

Compared with Composite Resin

• Easier to use
• Fluoride release

Question 14

What is calcium hydroxide lining material used for?

Answer 14

Used as a direct pulp-capping material

It is extremely alkali.

Question 15

State some drawbacks of calcium hydroxide liner

Answer 15

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

Question 16

Advantages of calcium hydroxide liner

Answer 16

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

Question 17

What are the properties of Zinc Oxide Eugenol cements?

Answer 17

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

Question 18

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

Answer 18

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

Question 19

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

Answer 19

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

Greatly decreases solubility

Question 20

Benefits of EBA compared with Resin modified ZOE ad ZOE?

Answer 20

Stronger than both - around 60MPa

Less soluble than conventional material

Better crystal structure and sets better

Question 21

What are the components of calcium hydroxide liner?

Answer 21

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)

Question 22

What does CaOH do to the pulp?

Answer 22

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).

Question 23

Why is Zinc phosphate rarely used nowadays? Drawbacks

Answer 23

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

Question 24

What is the 3 phase setting reaction of Glass Ionomer?

Answer 24

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.

Question 25

Why should ZOE not be used under amalgam fillings?

Answer 25

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

Question 26

Compressive strength of ZOE

Answer 26

20MPa