Zinc Polycarboxylate Cement Lecture Notes PDF

Zinc Polycarboxylate cement Zinc Polyacrylate cement  Objectives By the end of this lecture you should be able to : ◼ describe the composition, chemistry, manipulation and properties of zinc polycarboxylate cement.  Zinc Polycarboxylate cement Zinc Polyacryl...

Zinc Polycarboxylate cement Zinc Polyacrylate cement  Objectives By the end of this lecture you should be able to : ◼ describe the composition, chemistry, manipulation and properties of zinc polycarboxylate cement.  Zinc Polycarboxylate cement Zinc Polyacrylate cement Applications: ◼ Cementation of - cast restorations - orthodontic brackets  Zinc Polycarboxylate cementApplications (cont’d) ◼ Bases and liners under other restorations. ◼ Temporary restorations.  Zinc Polycarboxylate cement Presentations 1. Powder & Liquid  Presentations 2. Powder & distilled water Anhydrous type (Water settable) Luting cement Zinc Polycarboxylate cement Composition Powder ZnO 90% MgO 8.2% SiO2 1.4% Bi2O3 0.1% Stannous Fluoride 0.1% Strength Modify ST Enhance manipulation  Zinc Polycarboxylate cement Composition (contd) Liquid 32-40% polyacrylic acid COOH COOH Polyacrylic acid COOH COOH Itaconic acid prevents gelation on standing Tartaric acid modify working & time Water  POLYCARBOXYLATE CEMENT Polymer-Based Dental Cement Setting reaction +2 Zn -OOC -- HOOC -- --COO- PAA --COO- in --COOH ZnO H2O ZnO Zn+2 -OOC-- --COO- Zn+2 -- COO- -OOC -- -OOC-- --COOH Residual Glass Particle ZINC POLYACRYLATE GEL ZnO Zinc Oxide + Polacrylic Acid Zinc Polycarboxylate + unreacted ZnO powder  Microstructure of set Poly carboxylate cement Unreacted ZnO powder Amorphous gel matrix Mixing Procedure and Precautions Polycarboxylate Cement A C Dispensing Folding P P and L. into L. D B E Mixing  Polycarboxylate cement ◼ Mixing time 30 sec ◼ Working time 2.5 min ◼ Setting time 6 min Shear stress during mixing.  Viscosity Polycarboxylate cement ◼ High initial viscosity compared to Zn Ph. ◼ Reduced by pressure during mixing and seating. ◼ Low film thickness 25µ Zinc phosphate  Polycarboxylate cement Viscosity ◼ Increased by time  POLYCARBOXYLATE CEMENT ◼ Removal of excess cement before setting just after seating of the restoration After setting with sharp instrument  Clinical considerations Applya shearing stress during spatulation. Apply vibration and pressure during insertion of the restoration.  POLYCARBOXYLATE CEMENT Bonding Bonding to tooth structure: ◼ Chemical bond (adhesion) to calcium of the enamel and dentin. ◼ The adhesion depends on the unreacted carboxyl group. ◼ Apply the cement while shiny i.e. before loss of gloss.  Clean and dry tooth structure. Conditioning of dentin with 10% polyacrylic acid to remove the smear layer  POLYCARBOXYLATE CEMENT Bonding Bonding to restorations ◼ bonds chemically to St.St. and non-precious alloys (active surface chemistry). ◼ bonds mechanically to gold alloy restorations. through surface irregularities. Sandblasting or Electroetching  POLYCARBOXYLATE CEMENT bonding to restoration (cont’d) Chemical bond to gold alloys attained through tin platting  Solubility ◼ Soluble in organic fluid of the oral fluids ◼ Increased solubility with reduction of P/L ratio.  POLYCARBOXYLATE CEMENT Mechanical properties ◼ Compressive strength: lower than ZnPh cement. ◼ Tensile strength: higher than Zn Ph cement. Less brittle. ◼ Modulus of elasticity (Stiffness): less than Zn pH cement.  POLYCARBOXYLATE CEMENT Biological properties ◼ Biologically compatible (Bland effect) on the pulp - Rapid neutralization - Large molecules - Immediate bonding ◼ Deep cavity near the pulp Ca(OH)2 liner Ca(OH)2 Liner in deep cavity before application of zn polycarboxylate cement  Polycarboxylate Cement ◼ Advantages ◼ Disadvantages ◼ low irritancy ◼ accurate ◼ adhesion to tooth proportioning ◼ easy manipulation ◼ Short working time ◼ Higher tensile ◼ lower compressive strength ZnPh strength zn Ph ◼ Low solubility ◼ greater viscosity ◼ Low film thickness zn ph (controled) Study questions ◼ How can you extend the working time of Zinc phosphate cement ? ◼ What is the role of water in water based cements? How it affect the working time? ◼ The best way to control the setting reaction of zinc phosphate cement is done ------------ and the clinically unacceptable method is----  ` ◼ How can you control the viscosity of polycarboxylate cement ? ◼ How can you attain good bonding to tooth structure ? THANK YOU