Luting Agents

Question 1

What are the properties of luting agents?

Answer 1

Viscosity and film thickness
Ease of use
Radiopaque
Marginal seal
Aesthetics
Solubility
Cariostatic
Biocompatible
Mechanical properties

Question 2

Describe the viscosity of luting agents?

Answer 2

Viscosity increases as material sets - must seat restoration quickly and maintain pressure

Question 3

Describe the film thickness of luting agents?

Answer 3

As thin as possible - ideally 25um or less

Question 4

Why are luting agents radiopaque?

Answer 4

Some ceramic crowns are radiolucency so makes it easier to see marginal breakdown

Question 5

Describe the solubility of luting agents?

Answer 5

Low

Question 6

Describe the thermal conductivity of luting agents?

Answer 6

Low - a barrier to heat transfer

Question 7

Describe the mechanical properties of luting agents

Answer 7

High compressive strength
High tensile strength
High hardness
Young’s Modulus similar to tooth

Question 8

What are the types of dental cement?

Answer 8

Zinc phosphate
Zinc polycarboxylate

Question 9

What are the types of glass ionomer cement?

Answer 9

Conventional and resin modified

Question 10

What are the types of composite resin luting agents?

Answer 10

Total etch for use with DBA
Self etch - requires etch but has own bonding agent ioncorporated

Question 11

Describe zinc phosphates reactions

Answer 11

Powder and liquid, acid base reaction
Followed by a hydration reaction resulting in the formation of a crystallised phosphate matrix

Question 12

What makes up the powder in zinc phosphate?

Answer 12

Zinc oxide >90% - main reactive ingredient
Magnesium dioxide <10% - gives white colour and increases compressive strength
Other oxides

Question 13

What makes up the liquid in zinc phosphate?

Answer 13

Aqueous solution of phosphoric acid (50%)
Oxides which buffer the solution - aluminium oxide and zinc oxide

Question 14

What are the problems with zinc phosphate?

Answer 14

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

Question 15

Describe zinc polycarboxylate

Answer 15

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

Question 16

What are the disadvantages of zinc polycarboxylate?

Answer 16

Difficult to mix and manipulate
Soluble in oral environment at lower pH
Opaque
Lower modulus and compressive strength than zinc phosphate

Question 17

When can zinc phosphate be used and why?

Answer 17

When onlay with not much retentive surfaces - for a temporary restoration
When removing temp can remove all zinc phosphate with scaler

Question 18

Describe the glass ionomer setting reaction

Answer 18

Acid base reaction between glass and acid
Reaction stages are dissolution, gelation and hardening stages

Question 19

What are the properties of glass ionomer?

Answer 19

No shrinkage
Long term stability
Relatively insoluble once fully set
Aesthetically better than zinc phosphate
Self adhesive to tooth substance
Flouride release
Cheap

Question 20

How does RMGIC differ from GIC?

Answer 20

Glass particle size is smaller to allow acceptable film thickness
The liquid contains a hydrophilic monomer

Question 21

Describe the RMGIC setting reaction

Answer 21

Initial acid base reaction occurs
Light activation causes polymerisation of the HEMA leading to a rapid initial set
Followed by a short redox reaction

Question 22

What are the problems with RMGIC?

Answer 22

HEMA is cytotoxic - can damage the pulp
HEMA swells - it expands in a wet environment
No bond to indirect restoration

Question 23

Describe composite luting agents

Answer 23

Must be used with a suitable DBA
Can be light cured or dual cured
Need dry tissue - difficult with subgingival crown margins

Question 24

Describe composite luting agents bond to indirect composite

Answer 24

Composite bonds to composite
Use a dual curing cement as light penetration through the inlay will be poor

Question 25

Describe composite luting cements bonding to porcelain

Answer 25

Requires a silane coupling agent to make the porcelain surface hydrophobic
Porcelain must be treated with HF acid to etch the surface

Question 26

Describe metal bonding to composite luting agents

Answer 26

Doesn’t bond directly
Must etch metal by sandblasting
Chemical bonding is required to strengthen the bond using a metal bond agent

Question 27

How should composite luting agents be cured when bonding to metal?

Answer 27

Must use a dual curing material as light will not penetrate metal

Question 28

Describe bonding to precious metal

Answer 28

Difficult
Change precious alloy composition to allow oxide formation
All complicated and technique sensitive

Question 29

What is self adhesive composite resin?

Answer 29

Metal coupling agent is incorporated into the composite resin, simplifying the bonding process
Called Panavia
Mainly for RR bridges

Question 30

What are self etching composite resin cements?

Answer 30

Eg - RelyX, Unicem
Combination of a composite resin cement and a self etching DBA
Tries to do everything, can’t do anything

Question 31

Describe the mechanical properties of luting agents

Answer 31

Better than cement but not as good as composite luting agents

Question 32

What are temporary cements?

Answer 32

Made to cement temporary restorations in place while permanent restoration is fabricated
Soft for easy removal - some don’t set at all

Question 33

Describe the composition of temporary cements

Answer 33

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

Question 34

What are the different types of temporary cements

Answer 34

Two main types, those with and without eugenol