What should the viscosity and film thickness of a luting agent be?
LOW to allow seating of the restoration without interference
- ideally 25um or less
Why is it important that luting agents are radiopaque?
Makes it easier to see marginal breakdown
Why is it ideal if a luting agent is tooth coloured?
Don’t want to be able to see it through a veneer
What should the solubility of a luting agent be?
LOW to avoid marginal breakdown
What are the different types of luting agents?
- dental cement
- glass ionomer cement
- composite resin luting agent
What are examples of dental cements that are used as luting agents?
- zinc phosphate
- zinc polycarboxylate
What type of reaction does zinc phosphate undergo?
Acid base reaction (powder & liquid)
What are the constituents of the powder in a zinc phosphate cement?
- zinc oxide
- magnesium dioxide
- alumina & silica oxides
What are the constituents of the liquid in a zinc phosphate cement?
- phosphoric acid
- aluminium oxide
- zinc oxide
What is the function of magnesium dioxide in a zinc phosphate cement powder?
gives white colour and increases compressive strength
What is the function of alumina oxide and silica oxide in a zinc phosphate cement powder?
- improve physical properties
- alter shade of set material
What is the initial acid base reaction of zinc oxide cement?
ZnO + 2H(3)PO(4) —> Zn(H2PO4) + H2O
What is the secondary hydration reaction of a zinc oxide cement?
ZnO + Zn(H2PO4)2 + 2H2O —> Zn3(H2PO4)2.4H2O
what are the problems associated with zinc phosphate cements?
- low initial pH approx 2
- exothermic setting reaction
- not adhesive to tooth or restoration (actually works like grout and just fills space)
- not cariostatic
- final set takes 24hrs
- brittle
- opaque
How is zinc polycarboxylate different from zinc phosphate as a luting agent?
Zinc polycarboxylate
- bonds to tooth surfaces
- less heat during reaction
- pH low to begin with but returns to neutral quicker
- cheap
What are the problems associated with zinc polycarboxylate as a luting agent?
- difficult to mix
- difficult to manipulate
- soluble in oral environment at lower pH
- opaque
- lower modulus & compressive strength than zinc phosphate
How does glass ionomer luting cement differ from glass ionomer filling material?
particle size of glass in luting cement version is less than 20um to allow for suitable film thickness
Why are glass ionomer cements a good luting agent option?
- no shrinkage
- long term stability
- relatively insoluble once fully set
- aesthetically better than ZnPhos
- self adhesive to tooth substance
- fluoride release
- cheap
How do resin-modified glass ionomer cements differ from conventional GIC?
- the liquid of RMGIC contains HEMA (hydrophilic monomer)
- REDOX reaction occurs
how do RMGIC properties positively differ from conventional GIC?
- shorter setting time
- longer working time
- higher compressive & tensile strength
- higher bond strength to tooth
- decreased solubility
how do RMGIC properties negatively differ from conventional GIC?
- HEMA is cytotoxic (super important that no monomer remains as it can damage pulp)
- HEMA swells in a wet environment
what is porcelain treated with before bonding it to a tooth?
hydrofluoric acid
What is used as a surface wetting agent between porcelain and tooth?
silane coupling agent
How is porcelain cemented to a tooth?
tooth —> dentine bonding agent —> composite luting resin —> silane coupling agent —> porcelain (treated with HF acid)
