DML2: Cavity lining materials Flashcards Preview

BDS2; Dental materials > DML2: Cavity lining materials > Flashcards

Flashcards in DML2: Cavity lining materials Deck (43)
Loading flashcards...

What are cavity lining materials

- Intermediate restorative materials lining the cavity
- Applied before the placement of the restorative
- They can remain permanently within deep cavities

They are protective, palliative and therapeutic barriers for penetration through the dentinal tubules for pulp protection


What factors should be taken into account for cavity linings

- cavity position
- tissue conduction
- cavity size and depth
- oral health
- restorative to use


What are the different options for cavity lining materials (7)

1. Varnishes
2. Calcium hydroxide cements
3. Zinc oxide based cements
4. GICs
5. Resin modified GICs
6. Visible light cured resins
7. Calcium silicate based cements


How do cavity liners protect the pulp

Because they can protect the pulp from the leakage of unpolymerised resin at the margin


What can provide the pulp with chemical protection

Cavity varnish


What provides the pulp medication

Cavity liners


What provides the pulp with thermal and electrical protection

Cavity liners or base


What provides the pulp with mechanical protection

Cavity base


What is cavity varnish

This is the thinnest cavity liner which is painted onto the cut surface and is designed to act as a barrier to penetration of chemicals by doing the following
- seal dentinal tubules
- reduce diffusion through dentine
- reduce microleakage

It doesnt provide added strength because it isnt chemically boned to dentine


What are cavity varnishes composed of

1. Natural resins e.g. copal
2. Synthetic resins e.g. polystyrene
3. Solvent e.g. alcohol, acetone, ether
4. Some contain calcium/zinc hydroxide


Why do cavity varnishes contain solvents

Because this allows the varnish to be painted on with a brush onto cut surfaces and the solvent will then evaporate


What is a cavity liner

This is thicker than cavity varnish and will seal the exposed dentine = 0.5mm

It promotes health of pulp as it adheres to the tooth structure and has antibacterial action


Give examples of cavity lining materials

1. Calcium hydroxide (for pup capping)
2. ZOE
3. Zinc oxide non-eugenol


Why is calcium hydroxide cavity lining used for pulp capping

Because it doesn't contain eugenol which cannot be placed directly onto the pulp


What is a cavity base

A thick mix which is placed in bulk and can act as a dentine replacement = >0.75mm

This is used in deep caries as it reduces the bulk of the restorative

It is insulating and of higher strength and blocks out undercuts


Give examples of cavity base materials

1. Reinforced ZOE
2. Visible light cured resins
3. Zinc phosphate
4. Zinc polycarboxylate
5. Glass ionomer
6. Resin modified glass ionomer


What is in the powder component of ZOE cements

- ZnO (MgO)
- SiO2, Al2O3 fillers
- Dicalcium phosphate, mica or rosin (to improve mixing)
- Zinc salts (accelerates set)


What is in the liquid component of ZOE cements (4)

- eugenol
-olive oil (modifying viscosity)
- acetic acid 1% (accelerates set)
- water (small amount is essential to setting)


What is the ZOE cement setting reaction

An acid-base reaction to form zinc eugenolate = chelate complex; this is initiated by water which is also a byproduct of this reaction


What is the issue with the zinc eugenolate complex not being stable

The setting reaction will reverse in the presence of excess water


How is ZOE mixed

- on a glass slab / oil resistant paper
- incremental powder addition (2)
- mixing time of 60-90 seconds
- 2-3 mins working time
- sets in less than 5 mins


What produces a faster and stronger set in ZOE cements

A higher powder to liquid ratio and smaller particle size


What are the advantages of ZOE cements

- easy to mix an handle
- fast set in mouth due to temp and moisture which both accelerate set
- non-irritant pH (close to neutral)
- obtundant (calming effect on pulp due to eugenol when placed on dentine)
- good sealing characteristics
- protects pulp from chemical irritation
- good thermal insulator


What are the disadvantages of ZOE cements

1. Low compressive + tensile strengths 15-25MPa
2. High water solubility
3. Eugenol is a potential allergen and mild irritant
4. Eugenol inhibits vinyl polymerisation (-C=C-) so cannot be used under composites and compomers


What is reinforced ZOE

e.g. IRM

10-40% of a synthetic resin is
- added to the powder
- coated round the powder particles
- styrene or MMA is added to the liquid


What does the addition of powder, coated particles and styrene or MMA result in in reinforced ZOE composites

1. Increased compressive strength 40MPa
2. Increased tensile strength
3. Reduced water solubility


What are the uses of ZOE cements

- Used where strength isnt important but low irritancy is
- Not in direct pulpal contact
- Thermal insulating base = cavity lining
- Temporary restorations
- Intermediate restorations
- Long-term cementation
- Endodontic useage


What is a ZOE cement alternative

Ethoxybenzoic acid cement = EBA


What is in the powder part of EBA cements

1. ZnO = 60-75%
2. Filler SiO2, Al2O3 = 20-35%
3. Hydrogenated rosin = 6% (helps add viscosity)


What is in the liquid part of EBA cements

1. 50-60% of the eugenol in ZOE is replaced by ethoxybenzoic acid
2. 35-50% eugenol