Objectives: Although profusion of bleaching systems exists on the market today, there are no objective comparisons of their efficacy. The purpose of this study was to compare the color changes of clinically well-used bleaching systems. Methods: In this study, two different commercial　10% carbamide peroxide bleaching systems were used for 48 patients. Subjects who have natural intact maxillary anterior teeth void of any restorations or decay and have not been subjected to bleaching were recruited at Iwate Medical School of Dentistry in Japan. Bleaching with Opalescence 10% PF^® (Ultradent, USA) was performed for 23 patients and Nite White^® Excel (Discus Dental, USA) for 25 patients for 14 days. Tooth color of upper central incisor and canine for one-third region was measured by a spectrophotometer (MSC-2000, Olympus, Japan) before bleaching and after 14 days bleaching completed. Color difference dE and color coordinates of dL*, da* and db* of CIELAB color system were calculated. Efficacy of two bleaching systems was compared and Student t-test was used for statistical analysis. Results: CIE color coordinates were shown:

	dE	dL*	da*	db*
Opalescence (n=46)	7.1±3.3	4.1±3.4	-1.9±1.3	-4.5±2.3
Night White Excel (n=50)	7.7±4.4	4.6±3.3	-1.8±1.4	-5.4±3.4

Mean dE values for both systems were over 7.0. L* values were increased after bleaching, and values for both of a* and b* were decreased. There were no significant differences for dE, dL*, da* and db* (P<0.05). Conclusions: It was concluded that the two modern bleaching systems tested in this study indicated a significant color difference dE and no statistical differences for their efficacy.