Luting agents
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How does size of filler particles affect the viscosity
Bigger - high viscosity Smaller - lower viscosity
What value should viscosity of luting agents be
Low and increases as it sets
Are dental lutings agents cariostatic
Ideally yes -fluoride releasing -antibacterial
What are the mechanical properties of dental luting agents
High compressive strength -dentine around 275 MPa High tensile strength High hardness value (d-70k e-400k) Young’s modulus similar to tooth (d-15GPa)
What are the types of dental cement
Zinc phosphate Zinc polycarboxylate
What are the types of GI cement
Conventional Resin modified
What are the composite resin luting agents
Total etch with DBA Self etch
What are the contraindications of zinc phosphate cement
Low initial pH can cause pulpal irritation Exothermic setting reaction Brottle Not cariostatic Not adhesive to tooth of restoration
What is the difference between zinc phosphate and zinc carboxylate
Zinc carboxylate contains polyacrylic acid as opposed to phosphoric
Advantages of Zinc polycarboxylate
This material had the advantage of bonding to tooth surfaces in a similar way to glass ionomer cements There is less heat of reaction The pH is low to begin with but returns to neutral more quickly and longer chain acids do not penetrate dentine as easily Cheap
How does GI cement differ from GI filling material
Particle size is less than 20um to allow for suitable film thickness
How does GI cement bond to the tooth
Ionic bonds with calcium and dentine Hydrogen bonds with collagen and dentine
Why can eugenol not be used for some temp fillings
Dont use eugonol when planning to use an RMGI cement in final restorationas it collapses the collagen fibres in dentine
What are the disadv of Zinc polycarboxylate cement
Difficult to mix Difficult to manipulate Soluable in oral environment at lower pH Opaque Lower elastic modulus and compressive strength than zinc phosphate
What are the properties of GI cements
Clinically easy to use and durable cement Low shrinkage Long term stability Relatively insoluble once fully set Aesthetically better than Zinc Phosphates Self adhesive to tooth substance Fluoride release Cheap
How does RMGIC differ from GI
Glass particles size smaller Contains a hyrophillic monomer
What allows for dark curing
A secondary cure - redox reaction
How does RMGIC properties differ from GI
Incorporation of Resin -longer working time -shorter setting time -higher compressive and tensile strength -higher bond strength -decreased solubility
What are the problems with RMGIC
HEMA is cytotoxic (monomer) Hema expands in wet environment No bond to indirect restoration
When should RMGIC NOT be used
To cement a porcelain crown Cement posts
Which cure is better for comp luting agents
Light cure - increases properties by 25%
How does indirect composite bond with comp luting agents
Composite bonds to composite Bond strength is lower to inlay/onlay/crown/veneer fitting surface than to new composite Bond is micromechanical to rough internal surface of indirect restoration Bond is also chemical to remaining C=C bonds on the fitting surface of the indirect restoration Use a dual curing cement as light penetration through the inlay will be poor
What is needed to bond to porcelain
Surface wetting agent -can treat with HF (hydrofluoric acid) to etch surface
What is used alongside comp resin luting agents to bond porcelain
Silane coupling agent -Hydroxyl groupdon silane molecule reacts with oxide groups on ceramic surface -Other end of silane molecule has c=c bond which reacts with similary group on comp