Luting Agents Flashcards
What are the properties of luting agents?
Viscosity and film thickness
Ease of use
Radiopaque
Marginal seal
Aesthetics
Solubility
Cariostatic
Biocompatible
Mechanical properties
Describe the viscosity of luting agents?
Viscosity increases as material sets - must seat restoration quickly and maintain pressure
Describe the film thickness of luting agents?
As thin as possible - ideally 25um or less
Why are luting agents radiopaque?
Some ceramic crowns are radiolucency so makes it easier to see marginal breakdown
Describe the solubility of luting agents?
Low
Describe the thermal conductivity of luting agents?
Low - a barrier to heat transfer
Describe the mechanical properties of luting agents
High compressive strength
High tensile strength
High hardness
Young’s Modulus similar to tooth
What are the types of dental cement?
Zinc phosphate
Zinc polycarboxylate
What are the types of glass ionomer cement?
Conventional and resin modified
What are the types of composite resin luting agents?
Total etch for use with DBA
Self etch - requires etch but has own bonding agent ioncorporated
Describe zinc phosphates reactions
Powder and liquid, acid base reaction
Followed by a hydration reaction resulting in the formation of a crystallised phosphate matrix
What makes up the powder in zinc phosphate?
Zinc oxide >90% - main reactive ingredient
Magnesium dioxide <10% - gives white colour and increases compressive strength
Other oxides
What makes up the liquid in zinc phosphate?
Aqueous solution of phosphoric acid (50%)
Oxides which buffer the solution - aluminium oxide and zinc oxide
What are the problems with zinc phosphate?
Low pH (2) can cause pulpal irritation
Exothermic setting reaction
Not adhesive to tooth or restoration
Not cariostatic
Final set takes 24 hours
Brittle
Opaque
Describe zinc polycarboxylate
Similar to zinc phosphate but phosphoric acid replaced by polyacrylic acid
Bonds to tooth surface
Less heat of reaction
pH is low to begin with, but returns to neutral more quickly
Cheap
What are the disadvantages of zinc polycarboxylate?
Difficult to mix and manipulate
Soluble in oral environment at lower pH
Opaque
Lower modulus and compressive strength than zinc phosphate
When can zinc phosphate be used and why?
When onlay with not much retentive surfaces - for a temporary restoration
When removing temp can remove all zinc phosphate with scaler
Describe the glass ionomer setting reaction
Acid base reaction between glass and acid
Reaction stages are dissolution, gelation and hardening stages
What are the properties of glass ionomer?
No shrinkage
Long term stability
Relatively insoluble once fully set
Aesthetically better than zinc phosphate
Self adhesive to tooth substance
Flouride release
Cheap
How does RMGIC differ from GIC?
Glass particle size is smaller to allow acceptable film thickness
The liquid contains a hydrophilic monomer
Describe the RMGIC setting reaction
Initial acid base reaction occurs
Light activation causes polymerisation of the HEMA leading to a rapid initial set
Followed by a short redox reaction
What are the problems with RMGIC?
HEMA is cytotoxic - can damage the pulp
HEMA swells - it expands in a wet environment
No bond to indirect restoration
Describe composite luting agents
Must be used with a suitable DBA
Can be light cured or dual cured
Need dry tissue - difficult with subgingival crown margins
Describe composite luting agents bond to indirect composite
Composite bonds to composite
Use a dual curing cement as light penetration through the inlay will be poor
Describe composite luting cements bonding to porcelain
Requires a silane coupling agent to make the porcelain surface hydrophobic
Porcelain must be treated with HF acid to etch the surface
Describe metal bonding to composite luting agents
Doesn’t bond directly
Must etch metal by sandblasting
Chemical bonding is required to strengthen the bond using a metal bond agent
How should composite luting agents be cured when bonding to metal?
Must use a dual curing material as light will not penetrate metal
Describe bonding to precious metal
Difficult
Change precious alloy composition to allow oxide formation
All complicated and technique sensitive
What is self adhesive composite resin?
Metal coupling agent is incorporated into the composite resin, simplifying the bonding process
Called Panavia
Mainly for RR bridges
What are self etching composite resin cements?
Eg - RelyX, Unicem
Combination of a composite resin cement and a self etching DBA
Tries to do everything, can’t do anything
Describe the mechanical properties of luting agents
Better than cement but not as good as composite luting agents
What are temporary cements?
Made to cement temporary restorations in place while permanent restoration is fabricated
Soft for easy removal - some don’t set at all
Describe the composition of temporary cements
Two pastes - base and catalyst
Base contains ZnO, Starch and mineral oil
Accelerator contains resins, eugenol and carnauba wax
Material can be modified to make it weaker still by incorporating petroleum jelly
What are the different types of temporary cements
Two main types, those with and without eugenol
