Dental Materials: Glassionomer Cements

Glassionomer Cements and Polymer Materials

• Glassionomer cements are a type of dental restorative material
• They are also used as liners and luting agents
• Different types include:
  • GIC (Glass Ionomer Cements)
  • RMGI (Resin-Modified Glass Ionomers)
  • Alkasite
  • PAMR (Polyacid-Modified Resin, compomer)
  • IMCR (Ionomer-Modified Composite Resins)
  • CR (Composite Resins)

Glassionomer Cement

• ISO terminology: polyalkenoate cement
• Meaning: ionomer = ionic polymer
• Consists of a matrix and filler particles

Matrix of Glass Ionomer Cement

• Matrix (liquid) = polialkenoate

• Contains several acids:

  • poliacrylic acid
  • itaconic acid
  • maleinic acid
  • metacrylic acid

• Filler particles contain different materials:

  • Reactive silicate glass: Ca-Al-F, Sr-Al-F
  • La, Sr, Ba, ZnO - radiopacity
  • Ca2+ - translucency
  • F- caries prevention
  • continuous outflux
  • influx to topical treatment

• Filler particle size:

  • 50µm - compatible

  • <50µm - for liners and cement

Mixing

• Best powder:liquid ratio achieved by machine mixing in capsule
• Mixing by hand on glass slab with metal spatula

Powder:Liquid Ratio

• Powder:liquid
  • Flowable consistency
  • Smaller thickness: luting cement, liner
• Powder:liquid
  • Compatible
  • Greater thickness: base, filling

Setting

• Chains are acidic in water base

• React with ions of particles

• Ionic poliacrylate chains are formed:

  • Al3+ polyacrylate chains
    • Not soluble, does not absorb water
    • Strong
  • Ca2+ polyacrylate chains
    • Absorbs water

• Ratio of polyalkenoate chains determines water balance during setting

• First phase: hardening, not stable and soluble in water

• Second phase: physical properties enhance, further cross-links, not soluble

Setting Times

• Slow set 24 hours:
  • Aesthetic restorative
  • Sensitive to water uptake
  • No finishing and polishing for 24 hours
  • Water resistant coating until setting (24hrs)
  • 2-layer coating
• Fast set ~5 minutes:
  • Reinforced restorative
  • Not sensitive to water uptake
  • Finish and polish after 5 minutes
  • Sensitive to drying
  • Isolation will dry restoration avoid for 2 weeks

Classification of Glassionomer Cements

• Categorised by setting
  • Self-curing
  • Light-curing
  • Tri-curing
• Categorised by use
  • Luting cements
    • Cementation of inlays, onlays, crowns, bridges, posts and cores
    • Filler size of powder - fine, small
    • Powder:liquid 1.5:1
    • Fast setting
    • Snap set
    • Sensitive to drying
    • Less soluble
    • Good physical properties
    • Radiopaque
  • Restorative cements
    • Aesthetic: I, V class fillings, filling after tunnel prep (class II.), fissure sealing (greater filler size 50µm.)
    • Powder/liquid 2.5-3.1 Ratio
    • Compactible
    • Slow setting
    • Sensitive to water uptake - needs protective layer
    • Finishing polishing after 24 hrs
    • Does not withstand loading force
    • Good adhesion to dentin/enamel
    • Shade, translusency acceptable
    • Reduced radiopacity
  • Reinforced restorative cement
    • I class filling, filling after tunnel prep (class II), core-build up.
    • Ultrafine silver particles 40 weight% (silver cermet).
    • Reduced chemical adhesion– mechanical retention needed
    • Radiopaque
    • Powder:liquid 3-4:1
    • Compactible
    • Fast setting
    • Finish/polish after 5 min
    • Sensitive to drying for 2 weeks
    • Good physical properties
  • Liner cements
    • Under gold or amalgam restorations, to cover root canal obturation
    • Powder:liquid 1.5-4:1
    • Semi-solid
    • Fast setting
    • Increase powder amount physical properties enhanced
    • Release F-
    • Radiopaque

Surface Pretreatment

• Removal of smear layer
• Weak organic acids (e.g., poliacrylic acid)
• 10 seconds

Compomers

• Polyacid modified composite+glassionomer-cement
  • Not glassionomer cement
  • Setting: free radical polymerization
  • Binds to tooth but not with ion exchange
  • F- depo can be made
  • Minimal F- release
  • Absorbs water during setting
  • Polimerization shrinkage is compensated by expansion at this stage.
  • Acid-base reactions take place.

Alkasite Composite

• Modified composite
• Two component, capsule
• Matrix = liquid
• Metacrylates forming cross-links (UDMA, TMX-UDMA, DCP)
• Iniciator, photoiniciator, stabilizer
• Filler = powder
• Filler size: 0.1-7µm
• Silicate glass fillers: wear resistance, surface hardness, radopacity
• 58-59 weight% filler concentration
• Bioactive: F-, Ca2+, OH- ions are released
• Self-curing/light curing optional

Ormocer

• Organically modified ceramic
• Silicone dioxide polymer backbone
• Inorganic silanized filler particles
• Methacrylate groups form cross links
• It is a polymer before light-curing
• Polymerization shrinkage around 1-3%
• Filler concentration 77-78 weight%
• Greater biocompatibility
• Compactible restorative material
• Prep similar to composite
• Etch&rinse adhesive technique + own adhesive