glass ionomer cements

> conventional GI > resin modified GI

> restorative - filling material eg riva, vitremer > core build up - prior to restoration with crown eg vitremer, crown core > lining - underneath permanent fillings eg vitrebond, ionoseal > luting - cementing indirect restorations eg fuji luting, vitremer luting cement, aquachem

• zinc polycarboxylate cement - silicate cement

ability to stick to teeth

fluoride release it is an anterior filling material based on fluoro-alumino-silicate glass combined with phosphoric acid

2 components > acid = liquid > base = glass powder

> polyacrylic acid (ionic monomers) - usually copolymers of acrylic and itaconic acid or acrylic and maleic acid > tartaric acid - added to control the setting characteristics of the material (shorter setting time, same working time)

○ Silica, SiO2 (silicone dioxide) 30-40% ○ Alumina, Al2O3 (aluminium dioxide) 15-30% ○ Calcium fluoride, CaF2 15-35% ○ Aluminium fluoride 2-10% ○ Aluminium phosphate 4-20% ○ Sodium fluoride 4-10%

strontium and lithium salts (heavy metals) these play no part in the reaction chemistry (setting reaction)

the ratio of alumina / silica more silica = more translucent

the acid is freeze dried and added to the powder the liquid is distilled water this makes for easier handling of the material, particularly mixing

• consistent powder / liquid ratio • easier to use • should be consistent properties for the mixed material

advantage > no variation > consistent result disadvantage > cannot change consistency of material - sometimes want it to be thicker the make the procedure easier

• need <20 micrometres for luting cement to give a low film thickness (needs small size so it wont interfere) • the smaller the particle size the quicker the setting reaction and the more opaque the set cement • bigger particles = better aesthetics

• generally the higher the weight the better the mechanical properties of the set material • longer chain acid = better properties but the liquid is less liquid so it is more difficult to mix • however the higher molecular weight acids are viscous and difficult to mix • need a happy medium between the mechanical properties and the mixing of the material

MO.SoO2 + H2A -> MA + SiO2 + H2O Glass + acid -> salt + silica gel M = metal A = polyacid water absorbed into surface of silicone

• dissolution • gelation • hardening

acid into solution H+ ions attack the glass surface (acid dissolves the surface of the glass particles) Ca, Al, Na and F ions are released (go into solution) leaves silica gel around unreacted glass

• initial set is due to calcium ion crosslinking with the polyacid by chelation with carboxyl groups • calcium ions are bivalent so they can react with 2 molecules joining them • crosslinking is not ideal as the calcium can chelate with 2 carboxyl groups on the same molecule • this gelation equate to the initial set of the material and takes several minutes depending on the particular mateial • this initial set is caused by formation of calcium polyacrylate (calcium bonding happens quickly) • following this reaction the material will appear hard in the mouth (although it is not properly hard at this point)

• trivalent aluminium ions ensure good crosslinking with an increase in strength (sticks to 3 molecules at the same time, greater degree of crosslinking, makes for a stronger material) • aluminium polyacrylate formulation takes a long time • this process does not start for at least 30 minutes and can take a week or longer to complete • the aluminium reaction ensures a much higher degree of cross linking • this process greatly improves the mechanical properties of the material

> aluminium ions diffuse out of the material excessive drying means water will be lost saliva contamination causes absorption of water so extra ions will be flushed out all of these lead to a weak material which will be rough, break up / be weaker and have poorer aesthetics

• varnishes > copal ether > acetate • resins > dentine / enamel bonding agents (layer of resin then light cured - will last a little longer than other methods but still not last a week - remember aluminium takes this long) > unfilled Bis-GMA resins • greases or gels > vaseline

varnishes and resins provide the best vaseline is quickly removed by the action of the lips and tongue and offers little protection

if desiccation of the restoration is possible during work on other areas in the mouth - a thin layer of varnish or resin should be applied at this time to prevent surface damage due to excessive drying (vaseline does work in this scenario)