A Clinically-Validated In Vitro Method for Evaluating Tooth Whitening

Objectives: The purpose was to develop a clinically-validated test method for screening in vitro the performance of peroxide-containing tooth whitening formulations.

Methods: The whiteness of human teeth with natural intrinsic stain was assessed by objective (L*a*b*) measurements using a spectrophotometer (Minolta CM-503i) and by subjective assessments using a shade guide (average of 3 independent, blinded examiners with Vitapan®-System). A total of 20 teeth, which were stratified according to intrinsic whiteness scores, were randomly assigned to 2 equivalent groups: (1) peroxide-containing Mentadent® Advanced White (M), which had been shown to whiten teeth by 2 shades in a 1-month clinical study, and (2) a regular peroxide-free toothpaste, Crest® Cavity Protection (C). Teeth were treated on a shaker with 10-minute applications of freshly-prepared slurry (1:2 by weight) of toothpaste in artificial saliva. After 30, 60, 120, and 240 cumulative minutes of treatment, teeth were reassessed for whiteness using both measurement methods.

Results: For M, ΔE (calculated from L*a*b* values) increased significantly after each interval according to the equation ΔE = 4 – (120/(x+30)), (x in minutes); for C, after a slight initial increase after 30 minutes, there was no significant change in ΔE. For M approximately 2 shades of whitening were achieved in 180 minutes, which strongly correlated (r2 = 0.99) to a corresponding change in ΔE of 3.4. For C there was no visible change in shade.

Conclusion: Exposure of human teeth with natural intrinsic stain to a peroxide toothpaste for 2 hours produced similar whitening to that achieved in the mouth with twice daily use for 1 month. Based on the equation for ΔE versus exposure time, greater whitening might be achieved with extended peroxide-toothpaste use.