Resin modified glass-ionomers: Strength, cure depth and translucency

Background: According to the classification suggested by McLean, Wilson and Nicholson only three materials, currently marketed, fit the designation of resin modified glass-ionomers. These materials will undergo an acid/base setting reaction but also contain a limited quantity of a monomer that will polymerize as a result of irradiation. The quantity of polymer is limited to the extent that it will not interfere with the normal acid/base setting reaction and will therefore allow for the ion exchange adhesion with tooth structure that is typical of glass-ionomer. There is a third setting reaction incorporated to ensure remaining monomer, that is not affected by irradiation, will still polymerize. A series of experiments were carried out to determine the effect of the three types of setting reaction on the strength, depth of cure and translucency of these three materials. Methods: Specimens, both with and without irradiation, were subjected to a shear punch strength test. To determine the depth of cure brought about through irradiation, specimens were tested immediately after construction according to the test in ISO - 4049 2000 (E). Translucency is clinically significant and will vary according to whether the material has been subjected to irradiation or cured through the acid/base reaction alone. Results: The strength of all materials tested was higher in specimens subject to irradiation. The depth of cure was found to be both shade and irradiation time dependent. Irradiated specimens were found to be only marginally more translucent than those allowed to set without irradiation. Conclusions: It was concluded that, for cavities more than 3mm deep, these materials should be placed incrementally to allow for a full irradiation initiated cure.