Objective: To evaluate the effect of temperature on external tooth bleaching. Method and Materials: Human molars and premolars were internally stained and assessed using a standardized tea solution. The mesial aspects of the teeth were assigned to the treatment group (bleaching at 45°C), and the distal aspects of the teeth were assigned to the control group (bleaching at 37°C). An electronic chromometer with a tristimulus color analyzer was used to measure color change. The mean changes in the values of L*, a*, and b* from baseline to posttreatment were recorded, as were the overall color differences of the specimens in each group (ΔE*). Results: Increasing the temperature to 45°C significantly (P .05) increased the bleaching efficacy and reduced the time needed to gain a lighter tooth shade. Conclusion: A controlled increase in the temperature of the bleaching agent might be useful in achieving better tooth bleaching in a shorter period of time. Keywords: at-home tray vital bleaching, bleaching, carbamide peroxide, chromometer, hydrogen peroxide, power bleach, thermocatalytic bleach, tooth whitening, vital bleach