# Glass Ionomer Cement > Glass ionomer cement for BDS Dental Materials — acid-base setting, chemical adhesion, fluoride release, types I-VI, RMGI and clinical handling rules. - Canonical URL: https://prepelephant.com/topics/bds/dental-materials/glass-ionomer-dm - Exam / course: BDS · Subject: Dental Materials - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Glass Ionomer Cement", PrepElephant, https://prepelephant.com/topics/bds/dental-materials/glass-ionomer-dm ## Direct answer Glass ionomer cement, introduced by Wilson and Kent in 1972, sets by an acid-base reaction between a fluoroaluminosilicate glass powder and a polyalkenoic acid liquid, bonding chemically to enamel and dentine while releasing fluoride for the life of the restoration — a combination no other material offers. The set proceeds in two waves, calcium polyacrylate forming first and aluminium cross-links maturing over about a day, which is why the young cement must be shielded from both moisture and desiccation with a varnish. Its honest weaknesses are brittleness, wear and modest aesthetics; its clinical kingdom is the cervical Class V lesion, the luting seat, the paediatric restoration, and Atraumatic Restorative Treatment. ## What you must remember - Setting chemistry: glass particles are attacked by the polyacrylic-itaconic acid copolymer, releasing calcium, aluminium, fluoride and strontium ions; calcium polyacrylate chains cross-link within minutes (initial set), aluminium cross-links mature over about 24 hours; tartaric acid sharpens the set and extends working time. - Adhesion is ionic: carboxylate groups displace phosphate and chelate calcium at the tooth surface — no etch, no bond agent; conditioning with 10% polyacrylic acid for 10–20 seconds cleans the smear layer to prepare the bond. - Fluoride is released continuously and recharged from toothpaste and varnish, suppressing demineralisation and mutans activity around the restoration — the material's signature benefit. - Types (McLean): I luting, II restorative, III liner/base, IV fissure sealant, V orthodontic band cement, VI core build-up; high-viscosity versions (the Fuji IX class) anchor Atraumatic Restorative Treatment. - Resin-modified glass ionomer (RMGI) adds HEMA and a light-cured resin component: command set, better early strength and aesthetics, but the acid-base cure still completes underneath, and unset HEMA carries allergy and cytotoxicity concerns. - The compomer is not a glass ionomer: a polyacid-modified composite with no true acid-base set, weaker adhesion and less fluoride — a distinction exams reward. - Protection protocol: after placement, paint varnish or petroleum jelly — moisture contamination in the first hours causes chalky, crumbling surfaces; desiccation cracks them. - Properties in one line: low tensile strength, brittle, high modulus; coefficient of thermal expansion close to tooth; kind to the pulp; opaque aesthetics inferior to composite; radiopaque modern versions. - The sandwich technique layers glass ionomer at the gingival floor of a Class II (dentine-adhesive, fluoride) under composite (wear, aesthetics) — "open" if the ionomer meets the oral environment, "closed" if fully covered. ## Why GIC wins the cervical Class V A 62-year-old with root-surface caries and gingival recession presents the field where composite struggles and glass ionomer reads like the purpose-built answer. The surface cannot be kept dry: recession, crevicular fluid and proximity to the sulcus defeat rubber dam, while GIC tolerates a gently dried field. Adhesion is chemical to both enamel and cementum — composite bonds poorly to cementum at best, and none of the etching ritual is available here. Fluoride release protects a surface that is a caries magnet. The restoration is placed after 10% polyacrylic conditioning: the mixed material is pressed in, carved to contour before the snap set, then varnished, and the maturing aluminium cross-links finish their work over the next day. Change the site and the calculus changes. A Class IV incisal corner restoration would fail in GIC — no fracture toughness, no enamel-like polish — so composite takes it. A core build-up under a crown in a badly broken tooth takes Type VI or an RMGI where moisture control is doubtful, but a heavy occlusal load on a thin isthmus is amalgam or bonded composite territory. A non-cooperative child's primary molar, or a field clinic without electricity, is high-viscosity ART glass ionomer's home ground. The viva answer is always this matching exercise — material to field, load, aesthetics and caries risk. ## Viva angles on glass ionomer "Is glass ionomer's bond micromechanical or chemical?" — chemical, ionic to tooth calcium, which is why it needs no etch and why it fails cohesively rather than adhesively. "Why 10% polyacrylic acid and not 37% phosphoric?" — phosphoric over-etches and demineralises beyond the cement's ability to bond, while polyacrylic merely cleans and conditions the smear layer. "Why protect the fresh restoration?" — the initial calcium cross-links are water-soluble, vulnerable to both contamination and drying until aluminium maturation completes. Expect also the RMGI-versus-compomer distinction, the ART association, fluoride recharge, and the biocompatibility line that GIC is among the most pulp-friendly of all restorative materials, usable without a liner in moderate-depth cavities. ## Frequently asked questions ### What is the setting reaction of glass ionomer cement? An acid-base reaction: polyalkenoic acid attacks the fluoroaluminosilicate glass, and released calcium then aluminium ions cross-link the polyacrylate chains into a gel matrix embedding glass particles. ### How does glass ionomer adhere to tooth structure? By ionic bonding of carboxylate groups to calcium in enamel and dentine after conditioning with 10% polyacrylic acid — a chemical bond requiring no etching or separate adhesive. ### What distinguishes an RMGI from a compomer? RMGI retains a true acid-base glass ionomer set plus a light-cured resin phase; a compomer is a polyacid-modified composite with no acid-base cure, less fluoride and weaker adhesion. ### What is the sandwich technique? Layering glass ionomer as a dentine-substituting, fluoride-releasing base (especially the Class II gingival floor) under a composite occlusal restoration — open if the ionomer is exposed, closed if fully covered.