Effect of Different Surface Coatings on Flexure Strength and Surface Roughness of Glass Ionomer Restorations

Abstract

Glass ionomers are highly sensitive to moisture contamination especially in the first 24 hours so their surfaces should be protected in order to avoid any water loss or gain. This investigation was done to study the effect of different coating materials on the flexural strength and the surface roughness of two different types of glass ionomer restorative materials; HVGI and RMGI. For the Flexural strength testing; 80 rectangular samples (12×2×2 mm); 40 HVGI and 40 RMGI were prepared and divided into 4 groups (n=20) according to the applied surface coat; Group 0: no coat, Group 1: nano-filled resin coat, Group 3: total etch adhesive and Group 4: petroleum jelly. For the surface roughness testing; another 80 cylindrical samples (6×2 mm) of the same materials (40 HVGI and 40 RMGI) were prepared and allocated to the same 4 groups as for FS testing (n=20). Samples were subjected to mechanical tooth brushing once per day for 13 sec with a speed of 280 rpm for either 24 hr or 7 days using a custom made tooth brushing simulating device and then stored in distilled water at room temperature for either 24 hr or 7 days. For FS testing; a 3-point loading test was performed using a universal testing machine running at a crosshead speed of 0.5 mm/min up to failure. For SR testing; mechanical profilometer was used with a cut-off value of 0.25mm. Flexural strength and surface roughness data were analyzed using One-Way ANOVA followed by Turkey’s HSD post hoc test. The results of this study showed that the nanofilled resin coat gave the highest flexural strength values for both HVGI and RMGI after 24 hr and 7 days. Nanofilled resin coat also showed the lowest surface roughness values for both materials after 24 hr and 7 days except for RMGI after 7 days where no significant differences between all groups were observed.