Softening patterns of light cured glass ionomer cements

Objective: The aim of this study was to determine the effects of commonly used food simulating solutions and sodium hydroxide on the softening of light cured glass ionomer cements. Methods: Four types of light cured glass ionomers (classified on the basis of the liquid component) as follows: (1) materials that combine a polymerizable monomer and polyalkenoic acid (PMPA); (2) use of a polymerizable polyalkenoic acid (PPA); (3) acid monomer (AM) in place of the polyalkenoic acid; and (4) replacement of polyalkenoic acid with polymerizable monomer (PMPR). A traditional glass ionomer and a microfil composite were used as controls. Disc-shaped specimens aged for a week at 37°C and 100% relative humidity were stored in water, ethanol, heptane and 0.1 M sodium hydroxide for a period of 28 days. Barcol hardness measurements were made before immersion as well as at intervals of 24 h, 3 days, 7 days and 28 days after immersion. Results: In general the softening effect was lowest on the resin composite control. Hardness could not be measured for the traditional glass ionomer after 24 h due to breakage and dissolution of samples. The different solutions had varying effects on the different classes of light cured glass ionomers. The change in hardness after 28 days ranged from an increase of +6.7% for PMPA material in heptane to a complete disintegration of PPA amd PMPR in NaOH at 60°C. Significance: The softening effect of food simulating solutions is dependent on the formulation of light cured glass ionomers. In clinical use, the role of softening in wear will consequently vary.Objective: The aim of this study was to determine the effects of commonly used food simulating solutions and sodium hydroxide on the softening of light cured glass ionomer cements. Methods: Four types of light cured glass ionomers (classified on the basis of the liquid component) as follows: (1) materials that combine a polymerizable monomer and polyalkenoic acid (PMPA); (2) use of a polymerizable polyalkenoic acid (PPA); (3) acid monomer (AM) in place of the polyalkenoic acid; and (4) replacement of polyalkenoic acid with polymerizable monomer (PMPR). A traditional glass ionomer and a microfil composite were used as controls. Disc-shaped specimens aged for a week at 37°C and 100% relative humidity were stored in water, ethanol, heptane and 0.1 M sodium hydroxide for a period of 28 days. Barcol hardness measurements were made before immersion as well as at intervals of 24 h, 3 days, 7 days and 28 days after immersion. Results: In general the softening effect was lowest on the resin composite control. Hardness could not be measured for the traditional glass ionomer after 24 h due to breakage and dissolution of samples. The different solutions had varying effects on the different classes of light cured glass ionomers. The change in hardness after 28 days ranged from an increase of +6.7% for PMPA material in heptane to a complete disintegration of PPA amd PMPR in NaOH at 60°C. Significance: The softening effect of food simulating solutions is dependent on the formulation of light cured glass ionomers. In clinical use, the role of softening in wear will consequently vary.