Luting Agents
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what are the properties of a luting agent
viscosity and film thickness easy of use radiopaque marginal seal aesthetics solubility cariostatic biocompatible mechanical properties
what is viscosity and film thickness dependent on
size of powder or filler particles in material
what does the viscosity need to be to allow seating of restoration
low
what should the film thickness be
25um or less
ideally, what should the marginal seal be
the luting agent should bond chemically to the tooth and indirect restoration with a permanent and impenetrable bond
why is it important for a luting agent to be cariostatic
prevent secondary caries around crown margins
what are the mechanical properties of a luting agent
high compressive strength high tensile strength high hardness youngs modulus similar to tooth
what are the main types of material used as luting agents
dental cement glass ionomer cement composite resin luting agents
what is the main type of dental cement
zinc phosphate
what is zinc phosphate made of
powder and liquid
what is the reaction of zinc phosphate
acid base then hydration reaction producing crystalised phosphate matrix
what does aluminium oxide in zinc phosphate do
prevent crystallisation leading to an amorphous glassy matrix
what are the problems with zinc phosphate
low pH exothermic setting reaction not adhesive to tooth or restoration not cariostatic brittle opaque
what is the difference between zinc phosphate and zinc polycarboxylate cement
phosphoric acid is replaced by polyacrylic acid can bond to tooth less heat reaction pH returns to normal quicker
what are the problems with zinc polycarboxylate cement
difficult to mix and manipulate soluble in oral environment at lower pH opaque lower compressive strength
what is the difference between glass ionomer and glass ionomer cement
cement particle size is smaller allowing for suitable film thickness
what is the setting reaction of glass ionomer cement
acid base dissolution gelation hardening
how does glass ionomer cement bond to the tooth
ion exchange with calcium in enamel and dentine hydrogen bonding with collagen in dentine
what are the advantages of glass ionomer cements
low shrinkage long term stability insoluble once fully set aesthetically better than zinc phosphate self adhesive to tooth substance fluoride release cheap
what is the difference between RMGIC and RMGI
smaller particle size for film thickness
what is the difference between RMGIC and GIC
addition of hydrophilic monomer HEMA
what is the setting reaction of RMGIC
acid base light activation for polymerisation of HEMA REDOX reaction allowing dark curing
what does the incorporation of resin allow for in RMGIC
shorter setting time longer working time higher compressive and tensile strengths higher bond strength to tooth decreased solubility
what are the potential problems with RMGI
HEMA is cytotoxic HEMA swells - cant be used with conventional porcelain crowns no bond to indirect restoration