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Glass Ionomers

Glass Ionomers. Biomaterials Course. Aims of lecture:. To demonstrate how the early silicate materials led to the evolution of glass ionomer cements and to introduce the basic chemistry of the setting reactions of glass ionomer cements. Role of Glass Ionomers. Objective:

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Glass Ionomers

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  1. Glass Ionomers Biomaterials Course

  2. Aims of lecture: • To demonstrate how the early silicate materials led to the evolution of glass ionomer cements and to introduce the basic chemistry of the setting reactions of glass ionomer cements

  3. Role of Glass Ionomers • Objective: • a tooth coloured alternative to amalgam • Applications of Glass Ionomer Cements • Tooth coloured filling materials • Luting cement

  4. Evolution of Glass Ionomers Cements Zinc Polycarboxylate cement Zinc Phosphate Cement Zinc oxide Time Phosphoric acid Polyacrylic acid Alumino silicate glass Glass - Ionomer Cement Silicate cement

  5. History • Glass ionomers have evolved from silicates which were the first tooth coloured restorative material introduced over 80 years ago • However, silicates degrade losing colour and properties • Over time the combination of phosphoric and polyacrylic acids with zinc oxide and alumino - silicate glasses has led to the evolution of a range of dental cements

  6. Composition Glass Poly acid A range of compositions A range of acid combinations

  7. The glass

  8. The acid • a wide range of polyacrylic acid analogues • vary in molecular weight and configuration • Formulations: combinations of acrylic, itaconic & maleic acids

  9. Setting reaction • An acid base reaction • MO.SiO2 + H2A MA + SiO2 + H2O • Three overlapping stages • Dissolution - Gelation - Hardening Glass acid salt silica gel

  10. Ion release from glass F Na Release Al Ca Time

  11. Reaction • Calcium and aluminium combine to form salt matrix • Sodium and fluorine combine to form sodium fluoride

  12. Initial stages Poly acid Hydrogen ions Polyions Glass core Silica gel Ca, Al, F, Na ions Polysalts

  13. Gellation Phase • Crosslinking by calcium COO COO Ca2+ Ca2+ COO COO

  14. Ca Al Ca Al Ca Ca Al Ca Hardening Phase

  15. Final Microstructure Glass Silica gel Cross Linked Acid

  16. Handling with tartaric acid Viscosity without tartaric acid Time

  17. COO- COO- COO- Adhesion to dentine and enamel H Ca2+

  18. Bond Strength

  19. Bond Strength

  20. Conclusions • A versatile dental restorative material • A range of properties can be produced via changes to glass • Bonds to dentine and enamel and other things! • reasonable working characteristics

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