Study intervention
gingiva
Two weeks before bleaching, participants underwent prophylaxis to remove extrinsic stains. The ArcFlex retractor (FGM, Joinville, SC, Brazil) was placed. The gingiva was protected by applying the Top Dam light-curing resin (FGM, Joinville, SC, Brazil). The operator then opened the envelope defining the hemiarch and started bleaching, using a tip with or without brush (Sulzer Mixpac™, Sulzer Ltd., Winterthur, Switzerland). The bleaching gel Whiteness HP Automixx 6% (FGM, Joinville, SC, Brazil) was applied ( 
