Objective: Compare the impact of new Aquafresh Pure White Stripsâ to commercially available peroxide based whitening treatments on enamel hardness. Methods: Enamel specimens were flattened and polished to enable surface hardness measurements. Baseline Vickers hardness measurements were acquired followed by initial pellicle formation onto the substrate. Groups of five (5) specimens were treated with whitening treatment slurry (with saliva). The whitening treatments consisted of the following: A) an OTC whitening gel containing 3% H2O2, B) an ADA approved 10% Carbamide Peroxide (CP) dental office dispensed whitening gel, C) a 10% CP dental office dispensed whitening gel, D) a 10% CP non-aqueous whitening gel, E) a 10% CP gel from Aquafresh Pure White Stripsâ , F) a 6% H2O2 gel from a commercially available whitening strip and G) a saliva control. The pH range for the treatments was between 4.5, for treatment A, to 7.6, treatment B. The enamel surfaces were exposed to the treatment twice a day for one hour. Specimens were stored in saliva between treatments. Additional surface hardness measurements were made after 14 and 28 treatments. Results: The average Vickers hardness numbers after 0, 14 and 28 treatments are as follows: A) 319, 322, 326 B) 335, 343, 335 C) 330, 327, 329 D) 331, 330, 321 E) 319, 314, 319 F) 327, 318, 332 G) 337, 336, 344. Standard deviations were on the order of 3% or less. Changes in surface hardness between 0 ® 14 treatments and 0 ® 28 treatments were not significantly different (p >0.05) between baseline and post-treatment time points for all groups. Conclusions: The in vitro data indicate that new Aquafresh Pure White Strips â will not impact surface hardness. Research supported by GlaxoSmithKline.