title: The role of aluminium and silicon in the setting chemistry of glass ionomer cements.
abstract: A model of the setting chemistry of glass-ionomer cements (GICs) is proposed based on 27Al and 29Si solid state nuclear magnetic resonance spectroscopy data on three GICs. All the precursor glasses are found to contain three aluminium species viz.: four, five and six-coordinate aluminium environments as well as four-bridging silicate tetrahedra. Upon cement formation, Al3+ ions in the glass are leached out from the surface layer of the glass. On entering the cement matrix, these ions adopt six-coordination and crosslink the polymer chains as part of the setting reaction. The remaining four-coordinate aluminium is distributed between two species: one in the inert core of the glass particles; and a second, less concentrated, in the surface layer of the glass particles, modified by the curing reactions. There is some evidence for residual five and six coordinate aluminium species in the final cement in some of the systems. In the case of the silicate tetrahedra, the curing reactions result in a decrease in the number of aluminium atoms in the second coordination sphere, with a subsequent recondensation of silicate network of the glass.
authors.affiliation: Departamento de Engenharia de Materiais, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1, Lisboa 1049-001, Portugal. rpires@dep.uminho.pt
authors.forename: Ricardo A
authors.initials: RA
authors.lastname: Pires
authors.forename: Teresa G
authors.initials: TG
authors.lastname: Nunes
authors.forename: Isaac
authors.initials: I
authors.lastname: Abrahams
authors.forename: Geoffrey E
authors.initials: GE
authors.lastname: Hawkes
mesh_terms: D000535:Aluminum / Q000737:chemistry*; D001672:Biocompatible Materials / Q000737:chemistry; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D005898:Glass; D005899:Glass Ionomer Cements / Q000737:chemistry*; D007477:Ions; D009682:Magnetic Resonance Spectroscopy; D008422:Materials Testing; D015394:Molecular Structure; D011108:Polymers / Q000737:chemistry; D012823:Silicate Cement / Q000737:chemistry*; D017640:Silicates; D012825:Silicon / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D001672:Biocompatible Materials; D005899:Glass Ionomer Cements; D007477:Ions; D011108:Polymers; D017640:Silicates; D012823:Silicate Cement; D000535:Aluminum; D012825:Silicon