Maryam Karimi - Department of Polymer Engineering, Science and Research branch, Islamic Azad University,Tehran,Iran
Naghmeh Fazeli - Department of Polymer Engineering, Science and Research branch, Islamic Azad University,Tehran,Iran
Mohammad Atai - Iran Polymer and Petrochemical Institute, P.O.Box 14965/115,Tehran ,Iran

Resin modified glass-ionomer cements (RMGI), as good dental restorative materials, are hybrid of conventional glassionomers and composite resins. The formulation of thesematerials are usually consist of calcium fluoro-alumino silicate (CaFAlSi) glass powder, water, poly acids and watersoluble methacrylate monomers such as 2-hydroxyethyl methacrylate (HEMA). These materials harden by two different mechanisms simultaneously; partly via an acid-basereaction and partly via a photochemical (visible light) freeradical polymerization process. Despite the unique propertiesof these hybrid materials such as good hardness, high dimensional stability, good adhesion to the tooth structure, no shrinkage, no exothermic reaction and no free monomer in theset matrix, they still suffer from some low mechanical or physical properties including moisture sensitivity, lowresistance to wear and pressure, low tensile and flexural strengths and higher tendency to fracture as compared to amalgam. In this study, in order to improve the mechanicalproperties of resin modified glass-ionomer cements, different amounts of polyethylene glycol dimethacrylate (PEGDMA)were added to the formulation of the cement and fracture toughness samples were investigated. According to theobtained data, the fracture toughness was significantly improved.