DMS- cavity lining materials

Question 1

What is microleakage?

Answer 1

When a gap in the restoration allows the ingress of fluids and bacteria.

Question 2

Compare a cavity lining to a cavity base.

Answer 2

A cavity base is a thicker material placed in bulk. e.g. zinc oxide

Cavity lining is a thin coating put over exposed dentine. e.g. Calcium hydroxide.

RMGI can be used for both.

Question 3

What is the purpose of a liner?

Answer 3

• To provide pulpal protection from:
• Unreacted chemicals in the filling
• pH of the filling
• Thermal stimuli from the fillings
• Bacteria and endotoxins
• Therapeutic function to calm down inflamation
• To reduce patient symptoms prior to definitive treatment.

Question 4

Give examples of some of the ideal properties of a lining material

Answer 4

• Ease of use (long working time and short setting time)
• Thermal characteristics-

does not transfer heat well and has a simular thermal expansion to the tooth.

• Mechancial- has a high compressive strength.
• Radiopaque- allowing us to see the difference between the lining and the tooth (makes it easier to see leakage or secondary caries)
• marginal seal is a chemical bond to dentine
• Low solubility.
• Cariostatic e.g. fluoride releasing or antibacterial to prevent caries.
• Biocompatable (not damage the pulp)

Question 5

What is the setting calcium hydroxide liner?

Answer 5

This is a mixture of calcium hydroxide and a couple of fillers.

Question 6

Discuss the setting reaction of setting calcium hydroxide

Answer 6

It is a reaction between the base (ZnO) and the acid butylene glycol disalicylate

This reaction results in an alkaline environment (pH of 12) which:

• kills carious bacteira
• irritates the tooth causing the production of tertiary dentine. (increasing the rdt)

Question 7

What are the negatives of setting calcium hydroxide as a liner.

Answer 7

It has low compressive strength, is unstable and is soluble.

This means that the lining with disapear if the cavity leaks OR if it comes in contact with moist dentine.

Question 8

Compare powder and liquid zinc oxide

Answer 8

The powder contains mainly zinc oxide whereas the liquid mainly contains phosphoric acid.

Question 9

Describe the setting reactions of zinc oxide?

Answer 9

There are 2 reactions:

• acid based reaction
• Hydration reaction

Which produce a crystalised phosphate matrix.

Question 10

What are the negatives of using zinc oxide as a lining?

Answer 10

• the low pH of 2 causes pulpal irritation
• Setting reaction is exothermic
• Does not stick to the tooth or restoration
• Takes 24 hours to fully set.

Question 11

What is Zinc polycarboxylate?

Answer 11

This is a zinc oxide based cement that replaces the phosphoric acid with polyacrylic acid.

This improves the cement making it bond to the tooth surface. But it is more difficult to use.

Question 12

What would we use Zinc Oxide Eugenol for?

Answer 12

• Linings/ base in deep cavities under almalgam
• Temporary restorations
• Root canal sealer
• Periodontal dressings.

Question 13

What is the reaction of ZOE?

Answer 13

Zinc Oxide Euogenol works by an acid (euogenol) base (ZnO) reaction.

Question 14

How is the solubility of ZOE a benefit?

Answer 14

It can reduce pain in the pulp when eugenol is released.

Question 15

When would be inappropriate for using ZOE and why?

Answer 15

Under composite resin as the resin material won’t set

As a base under amalgam as the packing pressure will damage it

Question 16

Why is glass ionomer cement the ideal lining material?

Answer 16

• It bonds to the dentine & the composite resin.
• It releases fluoride over time.
• It has a simular thermal expansion to dentine
• It has a greater compressive strength than ZnO
• It seals the dentinal tubules (preventing microleakage & post treatment sensitivity)

Question 17

What other benefit does using Resin modified glass ionomer have rather than glass ionomer cement?

Answer 17

It also releases benzoyl iodides and benzoyl bromides which are cytotoxic so will destroy some cavity bacteria.

Question 18

If the cavity is deep and you need to place a direct or indirect pulp cap.

What lining material(s) do you use?

Answer 18

Place calcium hydroxide

Cover it with RMGI.

Question 19

If it is a normal cavity under amalgam

What lining material(s) do you use?

Answer 19

We use RMGI

Question 20

If it is a small cavity

What lining material(s) do you use?

Answer 20

We use RMGI

Question 21

If the cavity exposes deep dentine

What lining material(s) do you use?

Answer 21

The deep dentine would not be good for bonding.

We would use RMGI.