surface discoloration of composite resins: effects of staining and bleaching

background: the purpose of this in vitro study was to evaluate surface discoloration of three microhybrid composite resins (esthet•x hd, clearfi l ap-x, gradia direct) and fi ve nanohybrid composite resins (ceram•x, gc kalore, g-aenial, grandio, grandioso), after staining and bleaching procedures. materials and methods: the composite resins were polymerized with a curing light (celalux ii, voco, cuxhaven, germany) into 160 silicon molds (6,4 mm in diameter and 2 mm in thickness) to obtain identical specimens. twenty samples for each composite resin were prepared. the specimens were polished using an automated polishing machine with the sequence of 600-, 800-, 1000-grit abrasive paper under water irrigation. the specimens were immersed in tea and distilled water: the specimens were dipped for 20 min, once a day (every 24 h), for 14 days into the drinks. the specimens were then bleached with carbamide peroxide at 17% (perfect bleach-voco). the color of specimens was measured with a spectrophotometer according to the cie l*a*b* system after light-polymerization of composite resin specimens, after 7 days, after 14 days, and after bleaching. the color difference h index (deab*) between each measurement was calculated. statistical analysis was made using analysis of variance (anova). results: all specimens showed a signifi cant increase in staining with a similar trend and no signifi cant differences between microhybrid and nanohybrid composite resins. after whitening procedures, materials tested showed both signifi cant and unsignifi cant differences of the h index. conclusions: microhybrid and nanohybrid composite resins had similar in vitro surface discoloration in tea. after bleaching, discoloration was removed from some composite resins tested. key words: bleaching, composite resin, surface discoloration