ZINC OXIDE EUGENOL CEMENTZinc oxide eugenol (ZOE) cement have been usedextensively in dentistry since 1890s.They are cements of low strength. Also they are theleast irritating of all dental cements and are known tohave an obtundant effect on exposed dentin.
CLASSIFICATIONType I ZOE: For temporary cementationType II ZOE: Permanent CementationType III ZOE: Temporary filling and thermal baseType IV ZOE: Cavity Liners ZOE cement is available asPowder and liquid orTwo – paste system
SETTING REACTION In the First Step Hydrolysis of Zinc Oxide to its hydroxide takes place . Water is essential for the reaction(dehydrated zinc oxide will not react with dehydratedeugenol ) ZnO + H2O →Zn (OH)2 The reaction proceeds as a typical acid – base reaction Zn (OH)2 + 2HE → ZnE2 +2H2O (Zinc hydroxide)( Eugenol)- (Zinc eugenolate ) The Chelate formed is an amorphous gel that tends tocrystallize imparting strength to the set mass. Structure of set cement: The set cement consists ofparticles of zinc oxide embedded in a matrix of zinceugenolate. Setting time is around 4-10min.
FACTORS AFFECTING SETTING TIME Particle size: Smaller zinc oxide particles set faster Powder to liquid ratio: Higher the ratio, faster the set Addition of accelerators, e.g. alcohol, glacial acetic acid and water makes the cement set faster. Cooling the glass slab: Slows the reaction The set can be retarded by addition of glycol and glycerine which act as retarders.
MANIPULATION Power – Liquid System Powder/liquid ratio: 4:1-6:1 wt% After shaking the bottles gently, measured quantity of powder and liquid are dispensed onto a cool glass slab. The bulk of the powder is incorporated into the liquid and saturated thoroughly in acircular motion with a stiff bladed stainless steelspatula. Smaller increments are then added untilthe mix is complete.
TWO PASTE SYSTEMEqual lengths of each paste are dispersed and mixed untila uniform colour is observed.MODIFIED ZINC OXIDE EUGENOL CEMENTSThe modified ZOE cements are as follows: EBA- alumina modified cements Polymer reinforce ZOE cementThese were introduce to improve the mechanicalproperties of zinc oxide eugenol cement.
PROPERTIESCompressive strength – relatively weak cements ranges from a low of 3 to 4 MPa up to 50-55 MPa.Tensile strength – ranges from 0.32 to 5.3MPaModules of elasticity – 0.22 to 5.4GPaThermal properties – their thermal insulating properties are excellentSolubility and disintegration – The solubility of the set cement is highest among the cements (0.4% - wt) they disintegrate inoral fluidsAdhesion – they do not adhere well to the enamel and dentin.This is one reason why they are not often used for finalcementation of crowns and bridges.Biological properties.PH and effect on pulp (pH is 6.6 to 8) they are the least irritating ofall cements. Pulpal responses are mild.They have soothing effect on the pulp.
USESFor temporary and permanent cementationFor temporary fillings.Cavity lines and basePulp capping agentSecondary use – root canal restorations.