Glass-ionomer cements have established an important role in clinical dentistry since their introduction over 20 years ago. More recently, in an attempt to enhance the strength of the material, resin additions have been made to conventional glass-ionomer cements. This study established the long term flexural strength of two hybrid glass-ionomer cements, by use of a bi-axial flexural strength test (Shell test), and compared the values with those obtained for a light curing composite resin and a conventional glass-ionomer cement. The results demonstrated that those materials with a high resin component relying on polymerization as the main method of setting had a greater initial flexural strength than those with little or no resin addition. Those materials where the glass-ionomer acid-base reaction provided a substantial contribution to the setting reaction showed an increase in strength as they matured, whereas a decline in strength with time was observed for those materials where the resin setting reaction predominated.