Luting Agents Flashcards
What are some typical properties desirable of a luting agent?
Low viscosity to allow seating of restoration
Easy to mix, long working time, short setting time
Marginal seal with ideally chemical bond to tooth
Good aesthetics - tooth coloured, and no staining
Low solubility
Cariostatic and fluoride releasing to prevent secondary caries at crown margins
Biocompatible so it is non toxic and wont damage the pulp
Low thermal conductivity
High mechanical properties e.g. CS, TS, Hardness
What are some examples of luting agents?
Dental cement - zinc phosphate
GIC - conventional or RMGI
Composite resin luting agents - etch and DBA
How do zinc phosphate cements work?
Acid base reaction of powder + liquid
Powder
- zinc oxide
- magnesium dioxide - to give white colour
- alumina and silica - mechanical properties
Liquid
- aqueous phosphoric acid
- aluminium and zinc oxides - even setting and slows setting
Good things about zinc phosphate cements?
Cheap
Easy to mix and use
Strong
Low porosity and solubility
Problems with zinc phosphate?
Low initial pH of 2 - pulpal irritation
Exothermic setting
Not adhesive to tooth or restoration, works like tile grout
Not cariostatic
Opaque and brittle
What is and Pros of zinc polycarboxylate cement?
Similar to zinc phosphate except polyacrylic acid instead of phosphoric
Bonds to tooth similar to gic
Less exothermic
Returns to neutral pH faster
Cheap
How does GIC bond to the tooth surface? What about restoration?
Ion exchange with calcium in enamel and dentine
Hydrogen bonding with the collagen in dentine
Surface of restoration should be sandblasted to allow mechanical adhesion
Pros of GIC’s?
Low shrinkage
Long term stability
Relatively insoluble once set
Better aesthetics than ZnPhos
Adhesive to tooth surface And metal
Fluoride release
Cheap
Cons of zinc polycarboxylate cement
Hard to mix
Hard to manipulate
Soluble at lower pH
Low compressive strength and modulus
How does incorporating resin into GIC improve material properties?
It decreases setting time
Longer working time
Higher compressive and tensile strengths due to filler
Higher bond strength to tooth
Decreased solubility
Issues with RMGI for luting?
HEMA hydrophilic molecule is cytotoxic
HEMA swells in a wet environ meant
No bond to direct restoration
- basically good moisture control is needed, and all monomer needs to be set
What is a typical composite luting agent? Any pros??
Variant of composite filling material with smaller filler particles and lower viscosity
Light or dual cure
Better physical properties, lower solubility and better aesthetics
How do resin luting agents bond?
Composite bonds to composite
Bond is micro mechanical to rough internal surface of inlay
Also bond is chemical to remaining C=C bonds on the fitting surface of inlay
Use a dual cure for inlay as light penetration will be poor
How does one bond to porcelain?
Through a wetting agent as the surface is not compatible with resin luting agents
It needs to chemically bond as porcelain is brittle and will fracture if not
What is a silane coupling agent? How used? When?
Used when bonding to porcelain
Applied to etched porcelain surface
Forms strong bond between oxide groups on the porcelain and the silane
Other end has C=C bond which reacts with composite resin
What material use for MCC?
GIC or RMGIC
What to use for metal post?
GIC
