GLASS-IONOMER CEMENTS

  • contain fluoride so help remineralisation of teeth

  • chair side restorative material

  • versatile although some limitations

  • not very tooth coloured restorative

  • can combine resin composites and glass ionomer cements but different chemistries

  • may use for very large cavities as lining material underneath resin composites but use them by themselves more often

Historical perspective

  • come about from intro of silicate cements - no longer use, don’t work well, soluble (don’t last long)

  • based on MTA or root end filling materials - bioactive materials, calcium silicates, help to regenerate tissue

Evolution of glass-ionomer cements

  • silicate cement —> zinc phosphate cement —> zinc polycarboxylate cement —> glass ionomer cement

  • glass ionomer cements provide direct chemical adhesion

  • mixture of fluoroaluminosilicate glass and poly acrylic acid

  • polymer based acid component


CLASSIFICATION (by use)-

reasonably versatile - not as versatile as resin composites

only going to use as type 2

  • type 1= luting cement (used as space between crown and tooth preparation)

  • glass particles diameter - 13 to 19 micrometers diameter

    • cement needs to be thin layer so particles have to be quite small

  • type 2= restorative cements

  • glass particles 50 micrometers diameter

    • (particles are larger here to give more strength as used as a replacement)

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

    • line a deep cavity with adhesive material which potentially releases fluoride for therapeutic purposes

  • type4= visible light-activated liners/bases

    • hybrid types

    • resin modified glass ionomer cements


CLINICAL APPLICATIONS OF GICs-

various clinical applications but also various contraindications due to disadvantages of material

  • Restorative materials (type II)

    • for Class V non-carious lesions - abfraction

    • class III - involving exposed root dentine

    • class II- for deciduous dentition = easy to use, no curing/adhesive. - BUT DON’T LAST LONG. HALL TECHNIQUE BETTER.

    for reference - (The Hall Technique involves no preparation of the tooth or removal of decay. The crown is placed directly over the decayed tooth to seal the tooth and stop the decay. A local anaesthetic to numb the tooth might be used)

    • cannot be used in a class II adult tooth because lacks mechanical and physical properties that amalgam or resin composite would do - not for stress bearing situations

    • temporary restorations

    • crown margin repair


  • cavity bases and liners (type III/IV)

    • base under resin composites aka sandwich restoration

    • blocking undercuts

    • can be used as bases under resin composites - sandwich restorations - chemical bonding properties of glass ionomer and strength, wear and aesthetic properties of resin composite on top

  • luting agents (type I)

    • cementation of crowns and bridges


COMPOSITION-

  • powder

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

    • pigments (to match tooth)

  • liquid

    • mainly poly acrylic acid

      • may be other types that adjust setting speed of material

    • ± tartaric acid (3rd component)

      • essential to controls working time and setting time (handling))

    • distilled water

due to acidic component, shelf life is reduced, acids aren’t that stable so don’t last very long

OR

  • powder

    • fluoro-alumino-silicate glass

    • vacuum dried poly acrylic acid

    • pigments

  • liquid

    • distilled water

vacuum dry or freeze dry acid so turn to solid and unreactive - incorporate it into glass powder - active mix with water, dissolves acidic powder and creates reaction to solidify material


SETTING REACTION-

  • acid-base reaction - acid + base = salt + water

  • glass+acid = salt + silica gel

    • using acidic component to attack glass

    • acid covering all glass particles and dissolving outer layer = ions from glass to leech out into surrounding mixture - causes solidification (dissolution)

    • happens in 3 overlapping stages - not distinct, happen at different rates


  • 3 overlapping stages;

    1. dissolution= powder + acid

    2. gelation

      cross linking of molecules of acid trapped in setting mixture and maturing (ca2+)

    3. hardening = maturation

      slower process of cross linking material together


    different ion release

    reason for overlapping stages that occur at different rates because of the ions release

    • calcium and aluminium are important elements that will cross link and set material hard

    • calcium is slightly smaller than aluminium, moves around faster and released more quickly - involved with initial increase in thickness of material

    • aluminium contributes to long term setting over time

    • sodium and fluoride play no part in setting reaction

    • fluoride released to provide potentially therapeutic effect

    • differential ion release as ions released at diff speeds and affecting setting reaction

Initial stages : dissolution

  • freeze dried acid + add water - activate acid

  • then attacks silicate glass particles

  • as acid is dissolving into surface of particle - then releases calcium, aluminium, fluoride and sodium ions and will start to cross link remaining polymer molecules to create matrix/set structure

  • end up with aqueous layer around particle itself

Gelation

  • calcium ions are good at bringing molecules together

  • low pH creates ions and then they move around and start linking molecules together by carboxyl groups

  • calcium then produces calcium carboxylate groups

  • molecules can’t move, become cross linked

  • material is more and more viscous till sets hard

Hardening

  • aluminium does same thing but at slower rate/over longer period

  • initial working time - 4/5 mins

  • full setting time - days, even weeks

  • designed to reach most of strength within few hours of placement


GIC structure

  • set glass ionomer - see matrix

  • poly acid chains cross linked together with calcium, fluoride and aluminium ions

  • rigid matrix

  • remaining particle attacked by particle initially????

  • silica gel layer around outside of particle


PROPERTIES-

  • ADHESION=

    • relating to Ca2+ ions

    • inorganic tooth structure - hydroxyapatite contains calcium

    • calcium link to poly acid chains easily when in contact with them thats why good direct adhesion of glass ionomers to tooth tissue

    • H-bonding to organic portion - less inorganic component in dentine so bond strength less in dentine

    • bonds don’t degrade easily - bonds can be continuously broken and reformed

    • bond strength increased by acids - some acids on dentine have a negative effect because too strong


  • SETTING CHARACTERISTICS=

    • viscosity changes over time.

    • as chains cross link together material becomes more viscous.

    • setting time can be adjusted by manufacturers - particle size can alter setting reaction

    • Tartaric acid =

      • modifies setting reaction by extending working time

      • acts as calcium sink, reacts with released Ca2+ ions and stops them linking with polyacid chains - extend working time

      • increases rate of formation of Al ions - poly acid crosslinks and shortens setting time.

      • appropriate handling properties


      • Powder/Liquid ratio can affect property of material

      • increasing powder will increase strength and decrease setting time because more surface of silica glass giving higher rate of ion dissolution.

      • encapsulation - pre determined ratios


  • SOLUBILITY=

    • decreased solubility -

      • materials are hydraulic - require water in order to set - not too much or not too little water - apply small layer of varnish over top of placed material to prevent too much water getting in or out - only temporary

      • acid soluble - avoid putting in patients with highly acidic diet, bulimic patients - susceptible to erosion and abrasion - not on occlusal surface esp adult teeth

      • {dissolution-protective layer required}, {low wear resistance}


  • FLUORIDE RELEASE -

    • helps replace hydroxyl groups in inorganic components of tooth tissue (in apatite to create fluoroapatite)

    • not involved in salt formation - F- ions will diffuse through material towards surface and get released from surface

    • known to reduce incidence of caries

    • increased resistance to erosion

    • can act as a fluoride reservoir - can absorb F- from surroundings eg topical fluoride paste, brushing teeth


  • AESTHETICS=

    • only 3 or 4 shades

    • down to size of glass particles in material

    • particles tend to scatter light more so lack translucency and appear more opaque

    • larger filler particles get in way of light more so more cloudy/opaque and more difficult to mimic natural colour of teeth


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

    • technique sensitive (p/L ratio)

    • prone to desiccation

    • low strength

    • poor wear resistance

    • poor aesthetics

    • acid soluble



active recall questions

describe glass ionomer cements

what material do glass ionomer cements come about from

describe the development of glass ionomer cements

what are the classifications by use of glass ionomer cements

what are the clinical applications of GICs

what are the two different compositions of GICs

what is the setting reaction for GICs

what are the 3 overlapping stages

describe the ion release

describe the initial stage - dissolution

describe gelation

describe hardening

describe the structure of GIC

what are the properties of GIC

describe adhesion

describe setting characteristics and the role of tartaric acid in the setting reaction

describe solubility

describe fluoride release

describe aesthetics

describe encapsulation

what are the advantages of GIC

what are the disadvantages of GIC

what does prone to dessication mean

how is it susceptbile to moisture contamination