The correct answer is c. Decomposition, migration, gelation, post set hardening, maturation
Glass Ionomers are supplied as powders of various shades and a liquid component. The powder is an ion-leachable calcium fluoro-alumino-silicate glass, and the liquid is a water solution of polymers and co-polymers of acrylic acid.
(Although polyacrylic acid is the original, Currently the acid is in the form of a copolymer with Itaconic, Maleic, or Tri-Carboxylic acid. Tartaric acid is also present as it improves the handling characteristics and increases the working time)
The material sets through an acid-base reaction in the presence of water. As a result, metallic salt bridges form between the Al++ and Ca++ ions leached from the glass and the acid groups on the polymers. The resulting glass ionomer matrix will bind both the glass particles and water into a cement structure that will contain up to 24% water. Water in a glass ionomer ensures effective 'wetting' of moist tooth surfaces for strong adhesion. Water bound in a mature glass ionomer facilitates continuous fluoride release and uptake, benefiting adjacent tooth surfaces. The reaction goes to completion slowly, with the formation of a cross-linked gel matrix in the initial set and an aluminum ion exchange strengthening the cross-linking in the final set.
A chelation effect takes place with the calcium in the apatite on the exposed tooth surface, creating an ionic adhesive bond. The surface on the new restoration should be protected from saliva during initial set with a varnish or light cured bonding agent.
Types based on their formulation and potential uses:
Type I: Luting agents
Type II: Restorative material
Type III: Liner and bases
Decomposition - acid reacts with glass, release of metal ions
Migration – ions migrate into aqueous solution
Gelation – metal ions gel and initiate cross-links,
Created 1st are Calcium polysalts, 2nd are Aluminum polysalts
Post-Set Hardening – ions become bound, cross-links continue
Maturation – increased cross-linking, decreased free water, improved physical properties.
This phase can comtinue for several months.
Craig, R.G and Powers, J.M., Restorative Dental Materials 11th Edition, Mosby 2002, page 211-213
Cook, N.B., CAPT, DC, USN, Chair Operative Dentistry, National Naval Dental Center,
NPDS Course 225 Operative Dentistry, Lecture #12, 21 Aug 02, page
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