The color of the teeth is an important topic for many people and can be influenced by intrinsic and extrinsic stains. There is an increasing demand for whitening of the teeth year by year. The most popular way of whitening is "bleaching," which is the result of the breakdown of pigments located in the enamel and/or the dentin, caused by reactive oxygen species (ROS) released from bleaching agents. These bleaching agents could increase matrix metalloproteinase (MMP)-mediated collagen degradation in dentin. The aim of this study was to compare biochemical changes and oxidative stress levels of the human premolar dentin-pulp complex after three different bleaching methods containing hydrogen peroxide (H2O2) bleaching agents. Individuals, whose first four premolars were extracted for orthodontic purposes, included into the study. Group 1-Laser: bleaching gel containing 46% H2O2 (LaserWhite20 whitening gel, Biolase Technology Inc., San Clemente, CA, USA) and a diode laser activation (Ezlase 940 nm system). Group 2: 35% H2O2 containing whitening gel (Whiteness HP Maxx, FGM) and halogen light source activation (Optilux 501, Kerr, Orange, CA, USA). Group 3: 35% H2O2 containing whitening gel (Whiteness HP Maxx, FGM). Group 4-Control: No whitening treatment. According to the test results, there were no significant differences among groups in the values of cathepsin B and MMP proteolytic activities (p > 0.05). The total ROS values released from the dentin tissue were higher than those obtained from the pulp tissue (p < 0.05). There were significant differences among the bleaching groups in the ROS values released from the dentin tissue.