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j. Cosmet. sci., 49, 275-283 (July/August 1998) Dental stain prevention by abrasive toothpastes: A new in vitro test and its correlation with clinical observations P. L. DAWSON, J. E. WALSH, T. MORRISON, and J. GRIGOR, Unilever Dental Research, Quarry Road East, Bebington, Wirral L63 3JW, United Kingdom. Accepted for publication July 15, 1998. Synopsis A new in vitro test based on the removal of a model film from polished hydroxyapatite discs has been developed to predict more precisely the stain prevention properties of toothpastes in vivo. It is argued that dental stain prevention, as opposed to removal, is the predominant function provided by abrasive pastes suitable for unrestricted home use. It is necessary, therefore, to focus on abrasive systems capable of efficient removal of the relatively soft and invisible up-to-24-hour-old salivary pellicle formed between brushings, rather than on hamer visible mature stain. A cleaning model of this film has therefore been developed. The abrasive effect on the model film of a typical silica xerogel has been examined, and the data compared with clinical observation of stain build-up. A good correlation was apparent. Stain prevention increased dramati- cally from zero to 4% w/w silica, after which higher levels had little or no beneficial effect, despite a continuing increase in potential dentine damage. INTRODUCTION It is well known (1) that the chemical nature of many of the foods and beverages that we consume can create a hostile environment in the mouth unless some form of regular cleaning, beyond that of natural salivary irrigation, is practiced. Acids and sugars, via bacterial plaque growth, promote physiological damage to teeth and gums in addition to tainting the breath, and residual colored compounds will cause unsightly discolor- ation of the tooth surfaces (2). These effects can be mitigated to a large extent via daily brushing with a dentifrice (3). The rapid removal of plaque and food residues during brushing is believed to be predominantly a mechanical bristle function, and thus related mainly to brush design and operator skill (4). The control of dental stain, however, requires, in addition, the presence of an abrasive agent (5). Since Roman times a wide variety of finely ground minerals have been essential ingredients of tooth-cleaning preparations (6). Today, finely divided amorphous silicas (SiO2), precipitated chalks (CaCO3), and calcium phosphates (e.g., dicalcium phosphate dihydrate) are normally used in toothpastes (7). 275