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Glass Ionomer Cements (Clinical Applications (Restoration of permanent…

- - - - GIC < silicate < zinc phosphate < zinc polycarboxylate
  - - - Recall that phosphoric acid is used to remove HAP and expose collagen fibres
      - GIC bonds to both HAP and collagen fibres
      - As such, phosphoric acid cannot be used bc HAP is removed and GIC cannot bond to it
        
        Must use tissue conditioner to prevent complete removal of HAP
        
        Conditioners clean tooth surface and increase surface energy _ allows cement to come into intimate contact with tooth surface
        
        10-25% aqueous solution of polyacrylic acid is generally accepted (10-20s)
    - - Always better due to the absence of collagen network and the presence of highly organised HAP crystals
    - - Pumice and water
      - Surface conditioners
- - - - Elements are interchangeable due to polarity and atomic size
      - Imparts radioopacity
      - Anticariogenic properties
- - - - Dentine replacement material allow less bulk of restorative materials
      - Can provide thermal insulation under metallic restorations
- - - - Fluoride is in the powder
    - - Itaconic acd: reduces viscocity
      - Tartaric acid: improves handling characteristics
  - - - Polysalt + water
      - Phases: dissolution + gelation
        
        Dissolution
        
        Surface of glass is attacked by polyacid
        
        Limited dissolution of glass
        
        Release of calcium, aluminium and fluoride ions
        
        Aluminium diffuses the slowest
        
        Calcium diffuses the fastest
        
        Both Ca and Al form complexes with fluoride but Al more stable
        
        Outer later is reactive but inner layer remains ntact
        
        Gelation
        
        Initial set brought about by cross-linking of COO- to form calcium polysalt
        
        pH increases
    - - Set cement is a composite of original glass particles sheathed by siliceous hydrogel and bonded by a matrix phase consisting of hydrated fluoridated calcium and aluminium polysalt
    - - Glass composition (higher aluminia: silica ratio, faster set)
      - Lower particle size, faster setting
      - Higher powder: liquid ration, faster set
      - Higher mixing temp, faster set
      - Tartaric acid --> increases rate of setting
    - - Increased pH --> pulp irrittaion
      - Longer working time
      - Longer setting time and lower fracture resistance
      - Brittle material and higher wear resistance