Glass Ionomers

Conventional Resin modified

Restorative Core build up Lining Luting (cementing indirect restorations)

Acid (liquid) Base (powder)

Polyacrylic acid Tartaric acid

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%

The ratio of alumina/silica alters the translucency.​ More silica more translucent.

Anhydrous materials​ -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 Encapsulated materials​ -Consistent powder/liquid ratio​ -Easier to use​ -Should be more consistent properties of the mixed material

For luting cements for a low film thickness and quicker setting reaction

Better mechanical properties however too high can make the material difficult to mix

MO.SiO2 + H2A —> MA + SiO2 + H2O​ glass + acid —> salt + silica gel

Dissolution Gelation Hardening

Acid into solution​ H+ ions attack the glass surface​ Ca, Al, Na & F ions are released​ Leaves silica gel around unreacted glass

Initial set is due to calcium ion crosslinking with the polyacid by chelation with the carboxyl groups.​ Calcium ions are bivalent so they can react with two molecules joining them​ Crosslinking is not ideal as the Ca can chelate with two carboxyl groups on the same molecule This GELATION equates to the initial set of the material and takes several minutes depending on the particular material.​ This initial set is caused by formation of Calcium polyacrylate​ Following this reaction the material will appear hard in the mouth.​

Trivalent Aluminium ions ensure good crosslinking with an increase in strength.​ Aluminium Polyacrylate formation takes a long time​ This process does not start for at least 30 minutes and can take a week or longer to be complete.​ The Aluminium reaction ensures a much higher degree of crosslinking​ This process greatly improves the mechanical properties of the material.​

Up to a week or longer

Not for atleast 30 mins

Aluminium ions diffuse out of the material​ Excessive drying means water will be lost​ Saliva contamination causes absorption of water​ All lead to a weak material which will be rough, break up and have poorer aesthetics​

Varnishes​ -Copal ether​ -Acetate Resins​ -Dentine/Enamel bonding agents​ -Unfilled Bis-GMA resins Greases or gels​ -Vaseline

Increases viscosity

Can bond to enamel and dentine without the need for use of an intermediate material​ Bond strength not high compared with composite to acid etched enamel​ -About 5MPa vs 20MPa​ -Probably not measuring the bond itself as GIC tends to fail cohesively​ Good sealing ability with little leakage around margins

COO- Carboxyl groups

Clean surface​ Conditioned surface​ -Conditioned, not etched.​ -Little or no tissue is removed.​ -Best conditioner appears to be polyacrylic acid​ -Purpose is to produce clean smooth surface

Lack translucency Not suitable where aesthetics are of prime improtance (anterior teeth)

Poor tensile strength​ Lower compressive strength than composite​ -Less than half. 80 – 110MPA vs 300+MPa​ Poorer wear resistance than composite​ -Subject to abrasion​ Lower hardness than composite​ Higher solubility than composite​ -Dissolution of unprotected material during gelation phase​ -Long term erosion by acids