Effect of water storage on flexural strength of silorane and methacrylate-based composite resins

OBJECTIVES: This study assessed the effect of water storage on the flexural strength (FS) of low shrinkage composites. MATERIALS AND METHODS: A total of 165 bar-shaped specimens (2 × 2 × 25 mm) were fabricated of 2 low shrinkage composites (Filtek P90 [3M ESPE], GC Kalore [GC International]) and a conventional methacrylate-based composite (Filtek Z250 [3M ESPE]). The specimens were subjected to 3-point bending test at 6 time intervals, namely: immediately after curing, at 24 hours, 1 week, 1 month, 6 months, and 1 year following storage in wet and dry conditions. The FS of the specimens were measured by applying compressive load at a crosshead speed of 1.0 mm/min. Data was analyzed using 3-way analysis of variance (ANOVA) and Tukey's test. RESULTS: Three-way ANOVA revealed significant interactions between time, type of composite, and storage condition (p = 0.001). Tukey's multiple comparison test revealed significant reductions in FS of all composites after 6 months and 1 year of storage in distilled water compared to dry condition. CONCLUSIONS: Filtek P90 showed the highest and GC Kalore showed the lowest FS after 1 year storage in distilled water. The immediate high strength of Filtek Z250 significantly decreased at 1 year and its final value was lower than that of Filtek P90.

Effect of powder/liquid ratio on fluoride release of glass ionomers

Objective: Evidence shows that the powder/liquid mixing ratio recommended by the manufacturers is often not respected when mixing the glass ionomer [GI] powder and liquid, yielding a GI cement with disproportionate powder/liquid ratio. Considering the confirmed effect of powder/liquid ratio on the GI properties, and more importantly, its fluoride release potential, this study aimed to assess the effect of powder/liquid ratio on fluoride release of GI cements

Methods: Fuji II, Fuji II LC Improved and Fuji IX GI cements were used in this experimental study. Of each material, three groups with powder 20% less than recommended, the exact recommended ratio and powder 20% more than recommended, were prepared. To assess the fluoride release potential, 45 disc-shaped specimens measuring 2×4mm were prepared [5 per each group]. After fabrication, the specimens were immersed in 5 mL of distilled water. The amount of fluoride released into distilled water was measured at days 1 to 7, and also at 13, 14, 15, 28, 29, 30, 58, 59, 60, 88, 89, and 90 days, using Ion Selective Electrode [ISE]. After each time of measurement, distilled water was replaced. Data were analyzed using repeated measures ANOVA. Tukey's post hoc test was used for pairwise comparison of groups and powder/liquid mixing ratio. For pairwise comparison of time points, the Bonferroni adjustment was applied [p<0.05]

Results: Based on the results, although the amount of fluoride released from Fuji IX was higher than Fuji II, this difference was not statistically significant [p=0.589]. The lowest fluoride release was seen in Fuji II LC and this difference was statistically significant [p<0.05]. Change by 20% in the powder/liquid mixing ratio in the three GI cements had no significant effect on fluoride release [p=0.650, p=0.103, p=0.082]

Conclusion: Fluoride release from GI was time-dependent and the amount of released fluoride decreased over time. Fuji II LC resin-modified GI [RMGI] released less fluoride than Fuji II and Fuji IX. Also, 20% change in powder/liquid mixing ratio had no significant effect on fluoride release in different groups