EFFECT OF MOISTURE PROTECTIVE COATINGS ON THE STRENGTH OF A MODERN METAL-REINFORCED GLASS-IONOMER CEMENT

The strength of a modern, low metal : glass ratio, metal-reinforced gl ass-ionomer cement was measured evaluating a number of protective barr iers: one light-cured resin, two solvent-based dental varnishes and pe troleum jelly. The cement was exposed to water at 10 and 60 min from s tart of mix. The results obtained with these protecting agents were co mpared with those obtained where no protection was applied. A comparis on of uniaxial flexural strength and biaxial flexural strength showed the latter to be more discriminating. Proprietary dental varnishes wer e superior to petroleum jelly, producing similar strengths of 50 MPa. Petroleum jelly was, however, preferable to no protection. Moisture pr otection during the first 30min was found to be beneficial, thereafter no further strength increase was found. A second material, a cermet w hich has a high metal:glass ratio, was found to be more moisture resis tant but weaker in strength than the modern material, with a biaxial s trength of 39 MPa.