Effect of resin coating on highly viscous glass ionomer cements: A dynamic analysis

Objectives: This study determined the effects of self-adhesive resin coatings on viscoelastic properties of highly viscous glass ionomer cements (HVGICs) using dynamic mechanical analysis.Materials and Methods: The HVGICs evaluated were Zirconomer [ZR] (Shofu), Equia Forte [EQ] (GC) and Riva [RV] (SDI). Sixty specimens (12mm x 2mm x 2mm) of each material were fabricated using customized Teflon molds. After initial set, the specimens were removed from their molds, finished, measured and randomly divided into 3 groups of 20. Half the specimens in each group were left uncoated while the remaining half was covered with the respective manufacturers' resin coating. The specimens were subsequently conditioned in distilled water, artificial saliva or citric acid at 37 degrees C for 7 days. The uncoated and coated specimens (n=10) were then subjected to dynamic mechanical testing in flexure mode at 37 degrees C with a frequency of 0.1 to 10Hz. Storage modulus, loss modulus and loss tangent data were subjected to normality testing and statistical analysis using one-way ANOVA/Scheffe's post-hoc test and Ttest at significance level p<0.05.Results: Mean storage modulus ranged from 1.39 +/- 0.36 to 10.80 +/- 0.86 GPa while mean loss modulus varied from 0.13 +/- 0.03 to 0.70 +/- 0.14 GPa after conditioning in the different mediums. Values for loss tangent ranged from 39.4 +/- 7.75 to 213.2 +/- 20.11 (x10(-3) ). Significant differences in visco-elastic properties were observed between mediums and materials. When conditioned in distilled water and artificial saliva,storage modulus was significantly improved when ZR, EQ and RV were uncoated. Significantly higher values were, however, observed with resin coating when the materials were exposed to citric acid.Conclusion: The visco-elastic properties of HVGICs were influenced by both resin coating and chemical environment