Compressive strength, fluoride release and recharge of fluoride-releasing materials.

Aim To compare the weight loss of eight different root-canal sealers in water and in artificial saliva with different pH values.

Methodology  For standardized samples (n = 12 per group), ring moulds were filled with epoxy resin (AH 26, AH Plus)-, silicone (RSA RoekoSeal)-, calcium hydroxide (Apexit, Sealapex)-, zinc oxide–eugenol (Aptal-Harz)-, glass-ionomer (Ketac Endo)- and polyketone (Diaket)-based sealers. These samples were immersed in double-distilled water or artificial saliva with different pH values (7.0, 5.7 and 4.5) for 30 s, 1 min, 2 min, 5 min, 10 min, 20 min, 1 h, 2 h, 10 h, 24 h, 48 h, 72 h, 14 days and 28 days. Mean loss of weight was determined and analysed statistically using a one-way anova and Student–Newman–Keuls test for all pairwise comparisons.

Results  Most sealers were of low solubility, although Sealapex, Aptal-Harz and Ketac Endo showed a marked weight loss in all liquids. Even after 28 days of storage in water, AH 26, AH Plus, RSA RoekoSeal, and Diaket showed less than 3% weight loss. At exposure times greater than 14 days, Sealapex showed the significantly greatest weight loss of all sealers tested (P < 0.05). Aptal-Harz and Ketac Endo were significantly more soluble in saliva (pH 4.5) than in water (P < 0.05).

Conclusions  Under the conditions of the present study, AH Plus showed the least weight loss of all sealers tested, independent of the solubility medium used. Sealapex, Aptal-Harz and Ketac Endo had a marked weight loss in all liquids.

Solubility of root-canal sealers in water and artificial saliva.

Statement of problem Information related to the effect of night-guard vital bleaching procedure on the surface properties of esthetic dental restorative materials is incomplete. Purpose The aim of this study was to examine the effects of 3 proprietary carbamide peroxide bleaching agents on the surface properties of 3 dental esthetic restorative materials. Material and methods Three bleaching products (Nite White, Opalescence, and Rembrandt Lighten Gel) and 3 restorative materials (Duceram, Fuji II LC, and Silux Plus) were studied. A stainless steel mold and a 6-mm–thick polytetrafluoroethylene plate with a 1-cm–diameter hole were used to prepare 30 standardized specimens for each of the 3 restorative materials tested. Each group was divided into 3 subgroups (n=10). Two specimens from each subgroup were selected to form a control group. Three different carbamide peroxide bleaching agents were applied to each restorative material group for 8 hours per day for 30 days, respectively. Initial roughness measurements (Ra measured in μm) were made by use of a profilometer, at repeated intervals of 24 hours, 48 hours, 1, 2, 3, and 4 weeks (30 days). Surface topography of the specimens was assessed by scanning electron microscopy, and results were compared with the control group graphically. Surface structure and alterations of atomic weight percentages of element were made by use of energy-dispersive x-ray microanalysis. One-way analysis of variance was used to evaluate the surface roughness measurements. Significant results were evaluated with Fisher and Duncan's multiple range test ( P Result Surface roughness values for all restorative materials increased during the bleaching procedure. The only significant increase was found with the effect of Rembrandt bleaching gel on modified glass ionomer cement (mean Ra was 0.48 μm initially, 0.5 μm at 24 hours, 0.75 μm at 2 weeks, and 0.83 μm at 30 days). Surface roughness values increased significantly during the first 2 weeks ( P 2 content in the feldspathic porcelain and the microfilled composite groups for all bleaching agents. Modified glass ionomer specimens bleached with Nite White and Rembrandt showed an increase in mass percentage of SiO 2 , whereas Opalescence specimens showed a decrease. However, there were no significant differences between the groups. Conclusion Within the limitations of this study, no significant difference was found between bleaching agents. Most changes occurred in the first 2 weeks; the products tested were relatively stable in the following test periods. No significant change in the surface roughness of feldspathic porcelain was observed. On the other hand, the microfilled composite tested showed slight changes in the surface roughness. Significant changes were found for the modified glass ionomer cement ( P >.005).

Effect of three bleaching agents on the surface properties of three different esthetic restorative materials

The purpose of this study was to measure the release of fluoride, sodium, silicon, calcium, strontium, and aluminum from light-cured glass ionomers. The materials tested were: (1) Baseline VLC thick mix; (2) Baseline VLC thin mix; (3) Fuji Lining LC; (4) Vitrebond; and (5) XR-Ionomer. A conventional glass ionomer, Ketac-FilAplicap, and a silver-reinforced glass ionomer, Ketac-Silver, were used as controls. Each test specimen was first stored for 16 days in de-ionized water, followed by a further 16 days in 0.01 mol/L lactic acid (pH 4.0); both solutions were replaced at predetermined intervals. After that, the specimens were immersed for up to 122 days in de-ionized water. During the immersion, light-cured glass ionomers showed considerable variation in the release of fluoride and other elements. In lactic acid, all cements eluted the matrix-forming cations, aluminum and calcium or strontium. This suggests that light-cured materials are as equally susceptible to erosion as are chemically cured glass ionomers. During the immersion, some of the light-cured materials showed a considerable weight gain.

Release of fluoride and other elements from light-cured glass ionomers in neutral and acidic conditions

Mechanical behavior of glass ionomer cements affected by long-term storage in water

The behavior and mechanism for erosion of glass-ionomer cements in organic-acid buffer solutions were studied as a function of time, pH, and citric-acid concentration. In acidic solutions, the dissolution of the cement was controlled by the diffusion of the eluted species in the cement matrix, which depended on H+ ion concentration. In citric-acid solutions, the dissolution of the cement was controlled by both the diffusion and the surface reaction between the acid anion and the eluted species. Contribution of the latter reaction was larger with the increase in the acid concentration.

The Mechanism for Erosion of Glass-ionomer Cements in Organic-Acid Buffer Solutions:

In order to clarify the mechanism for erosion of glass-ionomer cements, we immersed two commercial luting cements in an acidic buffer solution under various conditions. The amounts of F, Al, Si, and Ca eluted from the cement were (1) in proportion to the square root of immersion time, (2) unrelated to shape or volume of the sample, (3) dependent on its surface area, and (4) not affected by shaking of the solution. It was concluded that the dissolution was controlled by the diffusion of those species in the cement matrix, which was influenced by the structure of the matrix and the concentration of H+ ion at the cement surface. The unreacted glass particles near the cement surface were dissolved by the long immersion, and many pores were left in the surface region.

M. Fukazawa

Papers

The Mechanism for Erosion of Glass-ionomer Cements in Organic-Acid Buffer Solutions:

Mechanism for Erosion of Glass-ionomer Cements in an Acidic Buffer Solution