GLASS-IONOMER CEMENTS

  • provide direct chemical adhesion

  • mixture of silicate glass and poly acrylic (acid)

CLASSIFICATION-

  • type 1= luting cement (eg space between crown and tooth)

  • type 2= restorative cements (particles are larger here to give more strength.)

  • type 3= chemically set liners/bases or pit and fissure forms.

  • type4= visible light-activated liners/bases

CLINICAL APPLICATIONS-

  • Restorative materials (type II)

    -non-carious lesions

    -class III - involving exposed root dentine

    -class II- deciduous dentition = easy to use no curing. BUT DONT LAST LONG. HALL TECHNIQUE BETTER.

  • cannot be used in a class II adult because

    -temporary restorations

    -crown margin repair

  • cavity bases and liners (type III/IV)

-base under resin composites aka sandwich restoration

-blocking undercuts

  • luting agents (type I)

    -cementation of crowns and bridges

COMPOSITION-

  • powder

    • fluoro-alumino-silicate glass (contains fluoride and alumino to create as much strength as possible)

    • pigments (match tooth)

  • liquid

    • mainly poly acrylic acid

    • ± tartaric acid (controls working time and setting time)

    • distilled water

      *acidic component decreases shelf life

OR

  • powder

    • fluoro-alumino-silicate glass

    • vacuum dried poly acrylic acid

    • pigments

  • liquid

    • distilled water

SETTING REACTION-

  • acid-base reaction

  • glass+acid= salt + silica gel

  • 3 overlapping stages;

    1. dissolution= powder + acid

    2. gelation = cross linking of molecules of acid trapped in mixture and maturing (ca2+)

    3. hardening = maturing

  • stages occur different times because of differential ion release eg calcium releases faster than aluminium. fluoride has a therapeutic effect doesn’t play a role.

  • GIC structure = cross linked poly acid, glass, silica gel

PROPERTIES-

  • ADHESION= relating to Ca2+ ions, tooth structure. link to poly acid chains easily when in contact with them thats why good adhesion to tooth. H-bonding to collagen. bonds don’t degrade easily strength increased by acids. Some acids on dentine have a negative effect because too strong.

  • SETTING CHARACTERISTICS= viscosity changes time. as chains cross becomes more viscous. Tartaric acid= reacts with the released Ca2+ ions and extends working time. Increases rate of formation of Al ions, poly acid crosslinks and shortens setting time. P/L ratio- increasing powder will increase strength and decrease setting time because more surface of silica glass giving higher rate of ion dissolution.

  • SOLUBILITY= decreased solubility. materials are hydraulic. Appreciate setting mechanism not too much or not too little water. adopt appropriate technique eg vaseline {dissolution-protective layer} . avoid in pt with high acidic diet and bulimic {erosions aka chemical attack} and high abrasion (no adult) {low wear resistance} .

    FLUORIDE RELEASE- helps replace hydroxyl groups in appetite creating fluroapatite in inorganic components. mobile diffuse to surface not involved in salt formation. Increased resistance to erosion and reduce likelihood of caries formation. can absorb F- from surroundings eg topical

  • AESTHETICS= only Âľ shades. particles tend to scatter light more so lack translucency. hard to mimic tooth colour.

ENCAPSULATION

  • powder and liquid have a barrier, break seal and mechanically mix

  • ADVANTAGES;

    • Bulk placement

    • sustained release of fluoride

    • biocompatible

    • direct adhesion to enamel and dentine

  • DISADVANTAGES;

    • Short working time

    • long setting time

    • susceptible to early moisture contamination

    • susceptible to desiccation

    • technique sensitive (p/L ratio)

    • prone to desiccation

    • low strength

    • poor wear resistance

    • poor aesthetics