Softening patterns of light cured glass ionomer cements

Effect of different tetra pack juices on microhardness of direct tooth colored-restorative materials

PURPOSE

To examine the effect of apple and orange juices on the surface hardness of direct tooth-colored restorative materials.

MATERIALS AND METHODS

The materials included resin-modified glass ionomer cement (Vitremer 3M™ ESPE™ Core buildup restorative) and composite resin (Filtek™ 3M™ ESPE™ Z350). A total of 45 disks of each restorative material were prepared. The disks were divided into groups of 15, which were immersed for 7 days in deionized water (G1/G4, control group), apple juice (G2/G5), or orange juice (G3/G6). The pH of the apple juice was approximately 4.8 and the pH of the orange juice was approximately 4.9. Surface hardness tests were performed before immersion and at various times following immersion. Statistical analysis included two-way ANOVA with repeated measurement and Tukey's test.

RESULTS

Exposure to juices significantly reduced the hardness of both materials (p < 0.05), while deionized water did not affect the surface hardness of either material. The ionomer cement experienced a greater reduction than the composite resin (p = 0.000). There was no significant difference in the effect of apple and orange juices.

CONCLUSION

Juice box-type fruit juices reduced the hardness of direct tooth-colored restorative materials. Material selection should be considered when planning restorations in patients who have experienced tooth surface loss. In terms of the materials evaluated in this study, the composite material provides greater durability under acidic conditions.

Effect of liquid rubber additions on physical properties of Bis-GMA based dental resins

OBJECTIVE

The aim of this investigation was to determine the effect of an experimental liquid rubber (LR) toughening agent on fracture toughness, crosslink density and Barcol hardness of polymerized mixtures of 50/50 wt% Bis-GMA and TEGDMA.

METHODS

An experimental LR, was added to a solution of Bis-GMA and TEGDMA containing 1wt% dimethylamino ethyl methacrylate and 0.5 wt% camphoroquinone at concentrations 0-10%. The composites were polymerized by exposure to a visible light curing unit for 60s. Fracture toughness was determined according to ASTM. 399. Crosslink density was evaluated using a swell test in ethanol.

RESULTS

Mean fracture toughness values ranged from 0.39 MPa m(1/2) for samples containing 6% to 1.24 MPa m(1/2) for samples containing 8% LR. Fracture toughness of samples containing 2%, 4%, and 8% LR were significantly higher than controls. The highest degree of cross-linkage was obtained in controls and lowest for samples containing 2% LR. Barcol Hardness values ranged from 36.7 for the control and 4% LR composition to 31.2 for samples containing 10% LR.

SIGNIFICANCE

Addition of 2, 4 and 8% LR increases the fracture toughness of Bis-GMA/TEGDMA composites. Addition of LR shows promise as a method of improving the fracture toughness of Bis-GMA based dental composites.

Influence of 0.05% sodium fluoride solutions on microhardness of resin-modified glass ionomer cements

This study aimed to evaluate the influence of fluoride-containing mouthrinse solutions (Fluorgard and Oral B) on the superficial microhardness of two resin-modified glass ionomer cements (Vitremer and Fuji II LC). Fifteen discs-shaped specimens of each glass ionomer cement (Ø10 mm; 2 mm thick) were prepared, thereby forming two groups. After 24-hour storage in artificial saliva, the microhardness was measure and the data were recorded. Next, each group was divided into three subgroups (n = 5), according to the solution to be immersed in. Control specimens were kept in artificial saliva along the whole experiment. The test specimens were kept in mouthrinse solution for 30 days. Vickers surface microhardness was analyzed at predetermined evaluation periods: 24 h, 48 h, 7, 14, 21 and 30 days after specimens' preparation. Data were subjected to three-way ANOVA and to Tukey test (p<0.05). A better behavior of Fuji II LC was observed and Fluorgard affected most the characteristics of the tested materials. It may be concluded that fluoride-containing solutions influenced the tested characteristics of materials, mainly of Vitremer.

Polymerization of orthodontic adhesives using modern high-intensity visible curing lights

This study was undertaken to assess the efficacy of 3 visible curing lights: a conventional halogen light and 2 high-intensity halogen lights in the polymerization of a polymer-based and resin-modified glass ionomer orthodontic cement. Degree of polymerization was measured by Fourier transform infrared spectroscopy and the development of mechanical properties by Barcol hardness. The results were analyzed with either 2- or 3-way analysis of variance. It was shown that, for the polymer-based material, there was a significant increase in degree of cure and hardness with time of application of the light for each light source. For chemical conversion, there was no significant difference between the lights. However, there was a difference in hardness: the higher intensity lights produced greater hardness in shorter time. Thus, there was poor correlation between degree of polymerization and hardness. For the resin-modified glass ionomer, similar trends were found, but there was a difference in hardness between the top and the bottom of the specimens. It was concluded that the higher intensity lights could aid in the more rapid development of mechanical properties of the tested adhesives.

The glass-ionomer phase in resin-based restorative materials

Glass-ionomer (GI) fillers are added to restorative materials, but it is unclear if they truly react with these materials. This TEM study evaluated the existence of the GI phase in a conventional GIC (ChemFlex), a resin-modified GIC (Fuji II LC), a giomer (Reactmer Paste), a compomer (Dyract AP), and a composite (SpectrumTPH), before and after water uptake. Wafers were stored at 100% RH for 24 hrs, or in water for 7 or 84 days. ChemFlex glass particles were surrounded by 300-nm-thick silica gel layers. In Fuji II LC, we found thinner hydrogel layers (100 nm) that became thicker upon water storage. No appreciable change occurred in Reactmer Paste. Only a very thin hydrogel layer occurred in Dyract AP, and none was seen in SpectrumTPH after water storage for 84 days. We conclude that the variable extent of the GI phase is determined by differences in the resin composition of the restoratives.