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 degrees 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 degrees 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.

The effect of noble metals on the mechanical properties of dispersed phase dental amalgam.

The effects of noble metals added as part of a Ag-Cu dispersant on the compressive strength and creep of dental amalgams was determined. The Ag-Cu eutectic used in high copper dispersant alloy L(0), was altered by adding 15 per cent by weight (wt%) of noble metal in place of Ag. In L(1) the noble metal was Pd. In L(2), Au and Pd were combined in equal proportions. In L(3), the noble metal content was Pd and Pt in equal proportions. A low copper lathe-cut amalgam, Aristalloy was used as the matrix. Amalgams S(0) and S(1) had the same composition as L(0) and L(1) except that the the low copper alloy matrix was Spheralloy, a low copper spherical amalgam. The compressive strength and creep were measured according to American Dental Association specification No. 1 and the results analysed by ANOVA. The addition of noble metals to the dispersant significantly lowered the 1-h compressive strength of amalgams. Compared to the control amalgam L(0), the 24-h compressive strength was increased for L(1) and L(2) but lowered for L(3). The ADA creep values were significantly lowered by addition of all combinations of noble metals. Reported microstructural changes such as an increase in unreacted particles, and a slowed setting reaction may account for the findings.

Marginal leakage of combinations of glass-ionomer and composite resin restorations.

This study compared the microleakage of four different combinations of glass-ionomer and composite resin restorations. Forty class V cavities were prepared in permanent posterior teeth. The gingival margin of the cavities were placed in cementum and the occlusal wall in enamel. The cavities were restored as either 1) light-cured glass-ionomer cement (LC-GIC); 2) chemically cured glass-ionomer cement (CC-GIC); 3) composite resin (with dentin bonding agent); or 4) light-cured glass-ionomer and composite resin (sandwich). Marginal microleakage was assessed by methylene blue dye penetration after thermocycling between 5 degrees C and 60 degrees C for 300 cycles. Microleakage of LC-GIC restorations and the dentin-bonded composite resin restorations were significantly lower than the CC-GIC and the LC-GIC sandwich technique restorations. There was no significant difference in the microleakage between the LC-GIC and the dentin-bonded composite resin restorations. The degree of microleakage of the sandwich restorations was significantly lower than the CC-GIC restorations. Light-cured glass-ionomer and dentin bonded composite resin restorations exhibited a lower degree of leakage than the glass-ionomer/composite sandwich and chemically cured glass-ionomer restorations at the gingival margins of class V restorations.