In vitro abrasion of resin-coated highly viscous glass ionomer cements: a confocal laser scanning microscopy study.

Abstract

The aim of this study was to evaluate the effect of resin coating on the wear depth of highly viscous glass ionomer cements (HVGICs) after 40,000 cycles, corresponding to over 8years of tooth brushing. A resin composite (Gradia Direct Posterior), two HVGICs (EQUIA Fil and Riva Self Cure), a resin coating (EQUIA Coat) and a conventional varnish (Fuji Varnish) were used in the study. The control groups were the resin composite group and the non-coated HVGICs groups. Samples (n=8) were produced in flat plastic moulds at 23±1°C and stored in artificial saliva sodium acetate-acetic acid-glycerine formalin (SAGF medium) for 7days at 37±1°C. The abrasion test was carried out in a toothbrush simulator (Willytec) with a load of 1N using abrasive toothpaste slurry. Vertical loss was measured at different cycles under confocal laser scanning microscopy (CLSM). Data were analysed using one-way ANOVA, Tukey's HSD test, repeated measures ANOVA and Bonferroni tests (p<0.05). The resin composite group showed significantly lower vertical wear loss than the non-coated groups and the varnished groups of HVGICs (p<0.05). HVGICs with resin coating had better wear resistance than the varnished and non-coated groups (p<0.05). Furthermore, regarding the material-based wear, HVGICs with resin coatings abraded less than the resin composite group tested (Gradia Direct Posterior 5.06±0.54μm, EQUIA Fil 4.06±1.68μm, Riva Self Cure 4.73±2.44μm), but statistically, there were no significant differences between them after 40,000 cycles (p>0.05). After 40,000 cycles, when the total wear loss of the materials including both coatings wear was compared, there were no differences between the non-coated and the resin-coated groups. The results of this study indicate that the resin coating protects the glass ionomer materials from excessive wear until 20,000 cycles making both HVGICs to abrade in a similar manner as the resin composite. If we include the wear of the coating to the general material wear loss at 40,000 cycles, the total wear loss is quite similar for all HVGICs, regardless of the protection with varnish or resin coating. Within the limitation of this study, we have foreseen that resin coating will protect and make the HVGIC materials as wear resistant as resin composites in clinical situations for a long time.