Objectives: To compare two in-office bleaching methods with respect to tooth color change and level of hydrogen peroxide penetration into the pulp cavity, and evaluate relationships between penetration level and color change. Methods: 80 extracted canines were sectioned above the CEJ and pulp tissue removed. Tooth thickness was measured from the outer labial surface to the outer boundary of the pulp cavity at the cross-sectioned root 3mm below the CEJ using a digital caliper. Baseline color was measured spectrophotometrically; acetate buffer was added into the cavity. Teeth were mounted and exposed to two different bleaching regimens (conventional versus sealed bleaching technique). After exposure to 38% hydrogen peroxide gel for one hour, buffer was removed from the cavity and placed into a volumetric flask. Hydrogen peroxide amount was estimated spectrophotometrically using leucocrystal violet and horseradish peroxidase. Specimen color was re-measured 2 hours post-bleaching. Color change was measured per Commission Internationale de l'Eclairage methodology. Linear regression was used to evaluate factors affecting color change, including bleaching technique. Results: The conventional and sealed bleaching groups showed no difference at baseline with respect to tooth thickness or any of the L*a*b color measures (p>0.51); however there was significantly greater hydrogen peroxide penetration in the conventional bleaching group (p<0.0001). Linear modeling of the change in lightness (ΔL) showed that the increase in lightness tended to be greater for teeth with lower initial L* values (r=-0.32, p=0.004). After adjustment for initial L*, there was no evidence that ΔL differed with hydrogen penetration levels (p=0.53) or bleaching technique (mean group difference in ΔL= 0.36; p=0.27). Conclusion: Both groups showed significant increases in lightness exceeding 2 units and therefore discernible to the naked eye (p<0.0001); however, mean ΔL did not differ significantly with bleaching method or hydrogen peroxide penetration.