Correlation between fluoride release, surface hardness and diametral tensile strength of restorative glass ionomer cements

Abstract

Background The aim of this study was to determine if there is a correlation between fluoride release, surface hardness, and diametral tensile strength of restorative glass ionomer cements (GICs). Material and Methods Conventional (Riva Self Cure) and resin-modified (Riva Light Cure) GICs were used. Thirty-four samples (ø 6 x 3 mm) were prepared for each cement. The kinetics of fluoride release (n=4) was evaluated over 28 days using a fluoride-selective electrode (ISE 4010-C00). The analysis of surface hardness (n=10) was performed using a microhardness tester (Shimadzu HMV-2000, Japan) with a Knoop indenter and a load of 25 gf for 30 seconds. The diametral tensile strength test (n=10) was conducted on a universal testing machine at a speed of 0.75 mm/min. Fluoride release data were analyzed by two-way repeated measures ANOVA and Bonferroni post hoc test, while independent t-test was used for other analyses (α=0.05). Results Overall, the groups showed higher fluoride release until day 7 and a progressive decrease until day 28. On day 1 and day 21, Riva Self Cure showed a higher level of release than Riva Light Cure ( p =0.026). Riva Light Cure showed higher diametral tensile strength ( p <0.0001) and surface hardness ( p =0.034) than Riva Self Cure. A negative correlation was found, indicating that higher fluoride release is associated with lower surface hardness and diametral tensile strength. Conclusion Fluoride release and mechanical performance are related properties of GICs, and these properties exhibit different values depending on the type of material. Resin-modified GIC release less fluoride but exhibit better mechanical performance compared to conventional GIC. Key words: Diametral Tensile Strength, Fluoride, Glass Ionomer Cement, Surface Hardness.