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)
- Varnishes
- Calcium hydroxide cements
- Zinc oxide based cements
- GICs
- Resin modified GICs
- Visible light cured resins
- 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
- Natural resins e.g. copal
- Synthetic resins e.g. polystyrene
- Solvent e.g. alcohol, acetone, ether
- 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
- Calcium hydroxide (for pup capping)
- ZOE
- 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
- Reinforced ZOE
- Visible light cured resins
- Zinc phosphate
- Zinc polycarboxylate
- Glass ionomer
- 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
- Low compressive + tensile strengths 15-25MPa
- High water solubility
- Eugenol is a potential allergen and mild irritant
- 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
- Increased compressive strength 40MPa
- Increased tensile strength
- 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
- ZnO = 60-75%
- Filler SiO2, Al2O3 = 20-35%
- Hydrogenated rosin = 6% (helps add viscosity)
What is in the liquid part of EBA cements
- 50-60% of the eugenol in ZOE is replaced by ethoxybenzoic acid
- 35-50% eugenol
Why do EBA cements provide greater strength
because it contains carboxyl groups making it more acidic
What is an issue with EBA cements
Though they are less water soluble than ZOE cements, they are more soluble over time
When are zinc oxide non-eugenol cements used
- used with resin composites and compomers formed by polymerisation
- if patients are allergic to eugenol
What is the composition of calcium hydroxide cement
Paste 1 = base
- salicylate ester = acidic component
- fillers = TiO2, CaSO4, BaSO4 (prove set + radiopacity)
Paste 2 = catalyst
- Ca(OH)2 = 50%
- ZnO = 10%
- Plasticiser = 40% (important for adequate mixing, viscosity and fast setting)
Describe the setting reaction of calcium hydroxide cements
- an acid-base reaction
- disalicylate reacts with Ca(OH)2 and ZnO forming calcium and zinc disalicylates
Describe the mixing of calcium hydroxide cements
Take equal volumes of two pastes on an oil-resistant pad
- mixing time = 5-30 seconds
- working time = +30-60 seconds
- setting time = +1-2 mins
What are the advantages of calcium hydroxide cement (8)
- easy to mix and handle
- rapid hardening in thin layers
- moisture and temperature accelerates set
- good seal to dentine
- alkaline pH 9-12 so can neutralise acidic materials
- alkalinity makes it antibacterial
- stimulates reparative/sclerotic/secondary dentine
- compatible with composites
How does calcium hydroxide cement stimulate secondary dentine production
Contact with pulp causes necrosis layer which will calcify into secondary dentine
What are the disadvantages of calcium hydroxide cements (4)
- low strength
- weakened by moisture exposure
- can dissolve completely in acidic conditions where marginal leakage can occur
- can undergo plastic deformation at mouth temperature (becomes flowable under load)
What are the uses of calcium hydroxide cements
- cavity lining; especially deep cavities and pulp capping
- with composites (as ZOE with inhibit the setting)
- strong enough to withstand amalgam condensation pressure
- thermal insulating agent to the pulp
Care must be taken when acid etching because it can wash away the calcium hydroxide layer so bonding wont occur
What is a suspension liner
Non-setting calcium hydroxide which is 20-25um thick
- it is a thick solution of calcium hydroxide suspended in water
- methyl or ethyl cellulose can be added for strength making it more like a gel
Why are visible light-cure resins used as cavity liners
- Because they are tougher and less soluble
- Give an increased resistance to etchants
- Can have an an alkaline surface pH
What are calcium silicate-based or MTA cements used for
- endodontic applications
- they are high strength alkaline and bioactive so help the pulp repair