]. Soc. Cosmet. Chem., 21,595-605 (August 19, 1970) Toothpastes--Cleaning and Abrasion j. B. WILKINSON, M.A., B.S.c., F.R.I.C., and B. R. PUGH, B.Sc., Ph.D.* Presented December 1, 1969, New York City Synopsis--It is generally recognized that the •najority of people need some form of abrasive in their TOOTHPASTES if they are to maintain satisfactory tooth cleanliness. Such ABRA- SIVES vary dramatically in their ability to a}brade dental mineral and also in their CLEAN- ING PERFORMANCES in toothpastes, thus making it necessary that sound test methods are available for measuring such characteristics. Abrasion of dental mineral is measured by a RADIOTRACER TECHNIQUE in which radioactive teeth are brushed with a toothpaste slurry and any abraded particles found sub- sequently in such a slurry are monitored by normal radiotracer techniques. Measurement of cleaning is made using high-precision photography, in which pictures are taken of subjects' teeth after they have used each test paste for two weeks. A second technique has been de- veloped in which the soil differences are examined by an oral photometer constructed for this purpose. For most abrasives, there is a direct relationship between the abrasivity towards dental enamel and the cleaning performance. This relationship can, however, be broken with an abrasive of correctly selected physical properties. The high cleaning and low abrasive quali- ties of such an abrasive are described. INTRODUCTION One of the primary objectives of a toothpaste is to clean teeth [ectively and safely. This relatively si•nple criterion arises because most individuals feel a need to maintain their teeth free frown unsightly stains and potentially harmful bacterial plaque. It must be recognized, how- ever, that individuals vary greatly in their ability to build up a visible stain on their teeth (1). Heavy stainers (so•ne 15-20% of the popula- tion) can build up a visible stain in as little ti•ne as one week, while at * Unilever Research Laboratory, 455 London Road, Isleworth, Middlesex, England. 595

596 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the other extreme, there are those who develop little or no visible stain. The heavy stainer thus needs a high-cleaning toothpaste but the light stainer is not so critical. With the vast majority of products now on sale, the cleaning t•unction is achieved by use of an abrasive powder and greater cleaning ability is invariably associated with greater abrasivity. If it were an easy matter for an individual to recognize his propensity to develop visible stain, then he might be advised which ot• the many brands of tooth- paste available to him would adequately clean his teeth. He could then be assured that the abrasivity of his chosen brand would be no greater than necessary to perform adequately, but it would seem not yet prac- ticable to cater to the individual. In this situation, a greater understanding of the act of cleaning by abrasion was clearly very desirable, particularly to examine whether or •lot higher cleaning inevitably meant higher abrasion. This, then, led to a tribological study to obtain knowledge of how dental surfaces are worn by abrasive particles and the relationship of the nature of wear to the hardness, shape, and size of the particles and to the properties ot• the substrate. At the same time, it was necessary to conduct work in the evaluation or assessment area so that in vitro results could be related to performance in vivo. TOOTH ABRASION Abrasion ot• dental mineral has been examined by many workers and the history of its development is traced in a paper by Pugh and his col- laborators (2). As described by these authors, the preferred technique is direct and reliable. Natural teeth are prepared with an even enamel or dentine surface exposed. They are then irradiated by neutron bom- bardment and wear is measured by established radiotracer techniques. This, we believe, has the closest possible relationship with the in vivo situation in that the teeth are brushed with a normal toothbrush and a slurry of toothpaste. The tooth is normal except insofar that it is radio- active, but it has been established that, under the right conditions of ir- radiation, this has virtually no effect upon the wear characteristics. Recent publications by Stookey and Muhler (3) and Wright Stevenson (4) have also described essentially identical techniques. Ex- peri•nentally, the technique consists of mounting the radioactive tooth specimen in a trough and brushing it with a toothbrush immersed in an aqueous slurry of toothpaste. The brush is driven mechanically in a reciprocating action and is weighted to simulate the pressure exerted