Effect of different bleaching systems on enamel surface

Objectives: To evaluate the effects of tooth bleaching on enamel microhardness and surface roughness upon application of hydrogen peroxide activated by light (Beyond™) and laser (LaserSmile™) at day 2, day 7 and day 28. Methods: 25 enamel slabs embedded in epoxy resin was prepared. The enamel surface was polished using 1200-grit silicon carbide paper. The specimens were then divided into three treatment groups; control, light-activated and laser-activated. Baseline data was collected for microhardness and surface roughness. For light-activated bleaching, after application of 35% hydrogen peroxide gel, the specimen surface was activated with light (Beyond™) for 10 minutes. Reapplication of gel is repeated for another cycle. For laser-activated (LaserSmile™) bleaching, 37% hydrogen peroxide was activated with laser; 8 cycles for 10 seconds each cycle. Vickers microhardness testing machine was used to determine changes in enamel microhardness. Surface roughness was evaluated using surface texture analyzer. Changes in enamel microhardness and surface roughness were evalutated on day 7 and 28 after the bleaching treatment for both intervals. Results: The effects of hydrogen peroxide bleaching on enamel surface microhardness were not statistically significant between the specimens groups of different time intervals except for light. Light- activated bleaching caused microhardness reduction. There were statistically significant differences in surface roughness in laser and light groups. Conclusion: Light-activated and laser-activated bleaching caused alterations in the enamel microhardness and surface roughness. Laser-activated bleaching is safe since it does not cause any statistically significant changes in enamel properties.