الفهرس 
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Abstract
The aim of this study was to evaluate the clinical behavior and surface properties of human enamel bleached with five different bleaching systems.
Methods: The effects of 15, 20 , 38% H2O2 and 15,35% CP on color change of the human teeth ,microhardness and wear resistance of enamel specimens were tested. As regard to color change, Sixty participants with complaint of discolored teeth were entrolled in this study. The color change was recorded at base line, 2 weeks, 3 month,6 month and 1 year after bleaching treatments. For microhardness and wear resistance tests, sound premolar teeth were selected . These premolars were sectioned in a mesio - distal direction in equal halves and embedded in chemically activated acrylic resin. Specimens were divided into six groups according to bleaching systems used. Specimens were pre-measured and post-meaured for surface microhardness and wear resistance by using Vicker’smicrohardness tester and profilometerrespectively .
Results: there was significant differences between bleaching group (Ti-ON 20% H2O2) (Δ=8.97) and other bleaching groups : control group, 15% H2O2, 38% H2O2, 15%CP and 35%CP where P < 0.05 . With respect to microhardness and wear resistance ,there were no significant differences between different bleaching groups(before and after bleaching) where P >0.05.
Significance: Office administered and home bleaching systems were demonstrated as similarly safe to enamel surfaces including maintenance of both hardness and wear resistance. Ti-ON 20% H2O2 had better bleaching effect rather than conventional high concentration hydrogen peroxide.