Objectives: To develop improved mass-market tooth-whitening dentifrices it is essential to have robust in vitro performance models that correlate with in vivo results. This work aimed to improve the resolution of an in vitro stain removal model. The model, which involves brushing naturally stained extracted bovine teeth with dentifrice slurries, has previously been shown to predict clinically observed product differences. However, the variability of the natural substrate reduces the ability of the assay to resolve small differences between products, which impedes formulation optimisation studies. Methods: This model has been modified with the aim of providing a screening procedure that discriminates more clearly between two test products, using a 30-minute brushing cross-over protocol. Because the teeth are partially cleaned by the first treatment a simple cross-over analysis may not be appropriate. However, for a comparison between two products, A and B, certain assumptions do allow a within-tooth comparison of treatment effects to be performed. Results: Using this protocol and data treatment, a whitening toothpaste containing sodium triphosphate (STP) (A) removed more stain than a non-STP control (B) (p=0.009 using student t-test), reflecting clinical results. Values given are mean±s.e. (n=14): DL*(T1[A])=8.13±1.32; DL*(T2[B])=1.69±0.31, mean ratio=0.24. DL*(T1[B])=9.21±1.40; DL*T2[A]=4.19±0.59, mean ratio=0.70, (where T1 and T2 are treatments 1 and 2 respectively, and DL* is the change in whiteness using the L*a*b* scale). Conclusions: These results demonstrate that, with key assumptions, the resolving power of the new protocol is high, whilst its relevance to in vivo use conditions is preserved.

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