Objective: To compare the efficacy of tooth bleaching after using ozone, before and after application of hydrogen peroxide (H2O2). Method and Materials: In total, 120 extracted teeth were assigned to three groups (n = 40 in each group). Teeth were bleached using 38% H2O2 application for 20 minutes followed by use of the ozone (delivered by means of the healOzone X4 device) for 60 seconds in group 1, via ozone for 60 seconds then 38% H2O2 for 20 minutes in group 2, and via 38% H2O2 for 20 minutes (plus normal air, delivered by the healOzone X4 device for 60 seconds) in group 3 (control). Teeth shades were assessed using a colorimeter before and after bleaching in each group. Significant statistical differences were recorded at P .05. Results: Teeth attained lighter shades (higher L* and lower b* values) subsequent to bleaching in all groups (P .001). Groups 1 and 2 revealed similar bleaching results (P > .05), and showed lighter final teeth shades than group 3 (P .05). Conclusions: Bleaching using 38% H2O2 for 20 minutes (combined with ozone for 60 seconds) produced similar results, regardless of applying the ozone before or after H2O2. Also, bleaching by combining ozone and H2O2 produced better tooth shades than bleaching by H2O2 only. Therefore, it might be practical to consider ozone when H2O2 is used for bleaching as this might potentially reduce treatment time and concentrations of H2O2, thus leading to improved bleaching results. Schlagwörter: esthetic dentistry, healOzone machine, hydrogen peroxide, ozone, tooth bleaching