Dental luting agents
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What is luting agent another word for?
• Dental cement
What is the ideal film thickness of luting agent?
• 25um or less
What is the ideal viscosity for luting agent?
• Must be low to allow seating of restoration without interference • Viscosity increases as material sets therefore must seat restoration quickly and maintain pressure
What ease of use properties should luting agents have?
• Easy to mix i.e via clicker system in encapsulated ones • Working time long to allow for seating of restoration • Setting time short
Why must luting agents be radiopaque?
• Some ceramic crowns are radiolucent • Makes it easier to see marginal breakdown
Ideally how should a luting agent bond to tooth and indirect restoration?
• Bond chemically to tooth and indirect rest with a permanent and impenetrable bond
What is the ideal aesthetics of luting agents?
• Tooth coloured with variation in shades and translucency • Non staining
What is the ideal solubility of luting agent?
• Low
What is the ideal cariostatic properties of luting agents?
• Fluoride releasing • Antibacterial • Important in preventing secondary caries around crown margins
What is the ideal biocompatibility of luting agents?
• Non toxic • Not damaging to the pulp (inappropriate pH and heat on setting) • Low thermal conductivity
What are the ideal mechanical properties of luting agents?
• High compressive strength (dentine 275MPa) • High tensile strength (dentine 50MPa) • High hardness value (dentine 70K and enamel 400k) • Young modulus similar to tooth (dentine 15GPa) • No luting agent gets close to tooth values for more than one or two physical properties*
What are the types of dental cement?
• Zinc phosphate • Zinc polycarboxylate
What are the types of glass ionomer cement?
• Conventional • 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 incorporated
What is zinc phosphate?
• In use for 100+years • Acid base reaction • Powder and liquid • Excellent clinical service • Easy to use • Cheap
What is the constituents of zinc phosphate powder?
• Zinc oxide >90% (main reactive ingredient) • Magnesium dioxide <10% • Other oxides (alumina and silica)
What is magnesium dioxide used for in zinc phosphate powder?
• Gives white colour • Increases compressive strength
What are alumina and silica used for in the powder of zinc phosphate cement?
• Improves physical properties • Alter shade of set material
What are the constituents of zinc phosphate liquid?
• Aqueous sol of phosphoric acid (approx 50%) • Aluminium oxide that ensures even consistency of set material • Zinc oxide slows the reaction giving better working time
What are the reactions of the zinc phosphate cement?
• Initial acid base reaction • Followed by hydration reaction • Results in formation of crystallised phosphate matrix
What does the aluminium oxide prevent in Zinc phosphate?
• Prevent crystallisation leading to amorphous glassy matrix of acid salt surrounding unreacted ZnO powder
What happens when zinc phosphate cement matures?
• Matrix originally insoluble but it is porous and contains free water from setting reaction • When it matures it binds the water • Leads to stronger, less porous material
What are the disadvantages of zinc phosphate cement?
• Low initial pH approx 2 • Exothermic setting reaction (release heat) • Not adhesive to tooth or restoration • Not cariostatic • Final set takes 24hrs • Brittle • Opaque
What can a low pH lead to?
• Pulpal irritation