Cavity lining materials Flashcards
What are disadvantages of restoratives
May not make intimate contact with the tooth surface (especially dentine)
-Any gap may allow ingress of fluids and bacteria
Heat released during setting/curing
Release of chemicals
-These may be pulpal irritants and lead to pain or pulpal damage
What can be used to prevent micro-leakage
Intermediate Restorative Material
A lining material
- Prevents gaps - Acts as a protective barrier
What is a cavity base
Thick mix placed in bulk
Dentine replacement used to minimise the bulk of the material or block out undercuts
More common in metal restorations (direct or indirect)
What is cavity lining
Thin coating (<0.5mm) over EXPOSED Dentine
Van Noort ‘a dentine sealer able to promote the health of the pulp by adhering to the tooth structure or by an anti-bacterial action’
What is the purpose of a liner
Pulpal protection
What is the pulp needing protection from
Chemical Stimuli from unreacted chemicals in the filling material or the initial pH of the filling
Thermal Stimuli. eg. exothermic setting reaction of composite or heat conducted through metal fillings
Bacteria and Endotoxins. Microleakage – the penetration of oral fluids and bacteria and their toxins between the restorative and the cavity walls.
Why is a liner placed
Therapeutic. To calm down inflammation within the pulp and promote pulpal healing. Prior to or at the time of a permanent restoration being placed.
Palliative. To reduce patient symptoms prior to definitive treatment being carried out. Most commonly in patients with reversible pulpitis.
What is the thermal expansion coefficient
Change in length per unit length for a temprise of 1 degree
What is the thermal coefficient of enamel
8.3ppmdegrees
What is the thermal coefficient of dentine
11.4ppmdegrees-1
What is the thermal coefficient of amalgam and composite
25ppmdegrees-1
What is the thermal coefficient of GIC and RMGIC
GIC- 11
RMGIC - 20
How is thermal diffusivity measured
cm2/sec
What is the thermal diffusivity of enamel and dentine
E- 0.0042cm2/sec
D- 0.0026cm2/sec
What is a marginal seal
The chemical bond of the lining to the dentine.
Should be permanent and impenetrable
What are some properties of lining materials
Easy to mix
Short setting time
Low thermal conductivity
Similar thermal expansion to dentine
Lower or similar thermal diffusivity to dentine
High compressive strength
Radioplaque
Low solubility
How do lining materials prevent secondary caries around the restoration
Cariostatic
-fluoride releasing
-antibacterial
What does biocompatible mean
Non-toxic
Not damaging to the pulp
-pH neutral
-No excessive heat during setting
Low thermal conductivity
Are lining materials biocompatible
yes
What materials are used as bases
Zinc Oxide based cements
Glass Ionomer and Resin Modified Glass Ionomer cements
Palliative cements
What materials are used for liners
Setting calcium hydroxide
Glass Ionomer and Resin Modified Glass Ionomer cements
Who invented vitrebond
Sumita mitra
When should calcium hydroxide be used
Only when the cavity approaches the pulp (as a direct or indirect pulp cap)
What is the setting reaction for calcium hydrocide liner
a chelation reaction between the ZnO and the butylene glycol disalicylate
What is the initial ph of the cement formed by calcium hydroxide liner
around 12
What forms the base of CaOH liner
Calcium hydroxide 50%
Zinc Oxide (filler) 10%
Zinc Stearate (filler) <1%
N-ethyl toluene sulphonamide (plasticiser) 40%
What forms the catalyst within CaOH
Butylene glycol disalicylate (reactive element) 40%
Titanium Dioxide (filler) 13-14%
Calcium Sulphate (filler) 30%
Calcium Tungstate (filler and radiopaquer) 15%
What is the benefit to the alkaline cement formed in the setting reaction of CaOH
Cariogenic bacterial survive in an acidic environment. The highly alkaline liner kills the bugs
Why is reparative dentine formed with CaOH
The cement causes irritation to 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).
What are the properties of CaOH liner
Quick setting time
Radiopaque
Easy to use
BUT
Low compressive strength
Unstable and soluble
-If the cavity leaks then the lining will disappear
-It may even disappear just because it is in contact with moist dentine
What are the Zinc Oxide based cements
Zinc Phosphate
Zinc Polycarboxylate
Zinc Oxide Eugenol (ZOE)
Resin Modified ZOE
Ethoxybenzoic acid (EBA) ZOE
What are the benefits of zinc phosphate cement
In use for 100+ years
Acid base reaction
Powder and liquid
Excellent clinical service
Easy to use
Cheap
What gives zinc phosphate powder its white colour
Magnesium Dioxide
What is the main reactive ingredient in the powder of zinc phosphate
Zinc Oxide >90%
What are the two reactions of zinc phosphate cement
The initial reaction is acid base
ZnO + 2 H3PO4 Zn(H2PO4)2 + H2O
This is followed by a hydration reaction resulting in the formation of a crystalised phosphate matrix
ZnO + Zn(H2PO4)2 + 2H2O –> Zn3(H2PO4)2.4H2O(Hopiete)
What prevents crystalisation of zinc phosphate cement
Aluminium oxide
How is the matrix described
Amorphous glassy matrix (almost insoluble)
What are the problems with zinc phosphate cement
-Low initial pH approx. 2
Can cause pulpal irritation as pH can take 24hrs to return to neutral
-Exothermic setting reaction
-Not adhesive to tooth or restoration
Retention may be slightly micromechanical due to surface irregularities of cavity
-Not cariostatic
-Final set takes 24hrs
-Brittle
-Opaque
What are the properties of zinc polycarboxylate cement
Difficult to mix
Difficult to manipulate
Soluable in oral environment at lower pH
Opaque
Lower modulus and compressive strength than Zinc Phosphate
What is the base and acid in s ZOE reaction
The base is ZnO
The acid is Eugenol
How does ZOE set
Chelation reaction of zinc oxide with the eugenol to form zinc eugenolate matrix.
This matrix bonds the unreacted ZnO particles
What are the properties of ZOE
Adequate working time
Relatively rapid setting time
-Sets quicker in the mouth due to moisture and heat
-Can be modified by addition of accelerators
Low thermal conductivity
Low strength around 20MPa
-Weak hydrogen bonds between the eugenolate molecules
-Not strong enough to use as a base beneath an amalgam filling. The packing pressure would damage it.
Radiopaque
Why is ZOE’s high solubility good AND bad
Eugenol is replaced by water which disintegration of the material BUT
Eugenol when liberated has an obtundant effect on the pulp and can reduce pain
In what cases should ZOE NOT be used
Under composite resin materials as it inhibits the set of resin based filling materials softening then and causing discolouration
What are the most widely used lining materials
Glass ionomer lining materials
What are the only lining able to bond to restorative materials
Glass ionomer lining materials
Why is complete cure of RMGICs needed
Any unreacted HEMA may damage the pulp
What is the least soluble cement
RMGICs
What are the properties of Glass ionomer lining materials
Thermal conductivity and diffusivity are lower than dentine for both GIC and RMGIC
Thermal expansion is similar to dentine for GIC
Compressive strength is > 170MPa, higher than any of the ZnO based materials
Most materials are radiopaque, the radiopacity varies between materials.
Marginal seal is better than any of the other materials as there is a chemical bond to enamel and dentine.
They are the only material to predictably seal dentinal tubules. This decreases microleakage and helps prevent post treatment sensitivity
Why is the opacity of zinc phosphate cement bad
If it is placed under thin enamel the grey tint from the alumina and silica might shine through giving a grey appearance of the tooth
