Calcium Hydroxide and Zinc Oxide Based Materials for Liners
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what are the main constituents of setting calcium hydroxide liner?
base and catalyst
what types of base are used in settling calcium hydroxide?
calcium hydroxide, zinc oxide, zinc stearate, N-ethyl toluene sulphonamide
what types of catalyst are used in setting calcium hydroxide?
butylene glycol disalicylate, titanium dioxide, calcium sulphate, calcium tungstate
what is the setting reaction for calcium hydroxide liner?
chelation reaction between the ZnO and the butylene glycol disalicylate
what is the mode of action of CaOH liner?
bacteriocidal to cariogenic bacteria, causes irritation to odontoblast layer which drives reparative dentine formation
what are the properties of CaOH?
quick setting time, radiopaque, easy to use BUT low compressive strength, unstable and soluble
what are the zinc oxide based cements?
zinc phosphate, zinc polycarboxylate, zinc oxide eugenol (ZOE), resin modified ZOE, ethyoxybenzoic acid (EBA) ZOE
what are the powder components of zinc phosphate cement?
zinc oxide, magnesium dioxide, other oxides (alumina and silica)
what are the liquid components of zinc phosphate cement?
aqueous solution of phosphoric acid, oxides which buffer the solution
what is the reaction of zinc phosphate cement?
acid base followed by a hydration reaction resulting in the formation of a crystalised phosphate matrix
what are the problems with zinc phosphate cement?
low pH, exothermic setting reaction, not adhesive to tooth or restoration, not cariostatic, final set takes 24hrs, brittle, opaque
what is the difference between zinc phosphate cement and zinc polycarboxylate cement?
the phosphoric acid is replaced by polyacrylic acid
what is the advantage of zinc polycarboxylate cement?
it bonds to tooth surfaces in a similar way to glass ionomer cements, less heat of reaction, pH turns neutral quicker, cheap
what are the problems with zinc polycarboxylate cement?
difficult to mix and manipulate, soluble in oral environment at lower pH, opaque, lower modulus and compressive strength than zinc phosphate
what are zinc oxide eugenol cements (ZOE) used for?
linings/base in deep cavities, temporary restorations, root canal sealer, periodontal dressings
what reaction does ZOE cement have?
acid base
what is the acid and base in ZOE cement?
base = ZnO and acid = eugenol
what is the setting reaction of ZOE?
chelation reaction of zinc oxide with the eugenol to form zinc eugenolate matrix
what are the properties of ZOE?
adequate working time, relatively rapid setting time, low thermal conductivity, low strength around 20MPa, radiopaque, high solubility
when should ZOE materials not be used?
under composite resin materials
what is resin modified ZOE?
resin added to the powder and liquid of ZOE
what is the impact of resin on resin modified ZOE?
give a stronger backbone to the set material, increases the compressive strength to >40MPa, greatly decreases solubility
what is the difference between EBA ZOE and normal ZOE?
ethyoxybenzoic acid is used in the liquid for EBA ZOE
what are the properties of EBA ZOE?
greater strength to set material, stronger than ZOE or resin modified ZOE, less soluble