Hydroxyapatite (HAP) powder serve as useful synthetic analogs for studying the adsorption and desorption chemistries involved in chromogen attachment, retention and curing during stain formation. By using HAP powders as substrate, a new method has been developed in our laboratory to screen chemical agents and formulations for their whitening chemistries. Objectives: The purpose of the present study was to evaluate the chemical stain prevention efficacy of various marketed dentifrices using the newly developed in vitro HAP powder model.  Methods: Two hundred mg of HAP powder (BIO-RAD Laboratories, Hercules, CA, U.S.A.)was exposed to 20 ml of dentifrice supernatant (25% w/w slurry), vortexed for one minute and centrifuged. After twice washing with deionized water, the powder was exposed to 20 ml of filtered tea solution (1 Lipton tea bag/50 ml water), vortexed for one minute and centrifuged. Finally, the powder was twice washed with deionized water, filtered and air-dried. The powders were photographed for visual evaluation as well as examined quantitatively by measuring the L, a, and b scores using SpectraScan PR650.  The dentifrices compared with the water control were Crest Dual Action Whitening^â(CDAW), Colgate Total Plus Whitening^â(CTW), Aquafresh Multi-Action Whitening^â(AMAW), Arm & Hammer Advanced Whitening^â(A&H) and Rembrandt Plus^â(RP). Results: Pre-treatment of HAP with various dentifrices produced significant differences in the levels of stain acquired by HAP powder as observed visually and measured quantitatively as follows DE: CDAW: 2.0a; AMAW: 4.5a; A&H: 16.8b; RP: 20.5b,c; CTW: 23.3c,d; and Water control: 27.1d; (a¹b @ p<0.05 students paired t). Conclusions:  The surface active agents having strong affinity for HAP were found to be very effective in inhibiting the adsorption of stain components. The active in CDAW, sodium hexametaphosphate, showed directionally better than AMAW dentifrice and significantly superior to all other tested dentifrices towards stain prevention efficacy.