Tooth whitening can occur through stain removal or stain decolorization respectively.  On enamel surfaces – both processes can take place in parallel.  Objective:  This study examined effects of bleaching gel both with and without dentifrice use on the rate of tooth whitening and observed disposition of surface stains in vitro.  Methods:  Human enamel crowns were sectioned and mounted in methacrylate blocks.  Enamel was polished with prophylaxis paste and exposed to PCR standardized staining procedures.  Following staining surface color was determined quantitatively in CIELAB color space L*, a*, b*.     Following staining ½ of each stained surface was cleaned of extrinsic stains using prophylaxis paste and surface color of the still stained and now-prophied sides were re-measured.  Teeth were then cycled where continuous immersions in pooled human saliva at 37°C were interrupted by bleach applications daily. Treatments included Crest Night Effects CNE bleaching gel (8 hour overnight treatment as paint on film) applied with and without Crest Regular dentifrice toothbrushing (bid 40 seconds) and water brushed control.   Color assessments on stained and prophied sample sides were made at all treatment points, and CLSM/SEM were assessed on baseline, day 3, 14. Results:   L* color was improved immediately on CNE treatment with stain portion of specimens showing L* color response of 33.1±3.0; 64.5±3.8; 69.7±2.4; 74.4±1.7 (baseline; day 1; 3; 14).   Despite day 3 readings showing color response comparable to prophy cleaned side, evidence was present in CLSM/SEM for sporadic retention of bleached film.  Clean surfaces were derived for CNE treated through day 14 however.   Conclusions:  These microscopic analyses reveal the dual nature of bleach derived whitening from CNE peroxide bleaches – including both lightening of substrate through oxidative chemistry as well as macroscopic loosening and debridement of stain films.