Objectives: To assess the potential of two new two-phase whitening toothpastes, containing calcium, phosphate, fluoride, and baking soda, to scratch enamel. Methods: Enamel specimens were prepared by polishing the surface of human enamel cores with 1200-grit diamond paper (Buehler Inst Co). As a means of demonstrating changes to the enamel surface based upon treatment, fifteen polished cores were brushed twice for five minutes with an aluminum oxide containing toothpaste (Colgate Platinumâ) using an electric brush (Crest® Spin-brush) applied at 75 g force. Brushed cores were then characterized for the presence and extent of abrasive-induced scratches by SEM. The fifteen cores were divided into 3 treatment groups of five each and given two additional five minute treatments with either one of the two experimental toothpastes or the aluminum oxide toothpaste control. The two experimental toothpastes differed by the use of two commercially available sources of polishing silica abrasive (Sylodent 756, W. R. Grace & Co, or Zeodent 165, J. M. Huber Co.) Following this additional treatment, the cores were reexamined by SEM. Results: SEM photographs show that the microscopic score marks on enamel cores brushed with an abrasive whitening toothpaste change after further brushings with the same paste, as new score marks obliterate the old ones. When brushed with the dual-phase formulas, however, the original score marks remain essentially unaltered, and no new ones appear. Conclusion: The dual-phase calcium-containing bicarbonate toothpastes do not scratch enamel.