422 W. B. Davis and A. M. Rees-Jones Woodrough of St Bartholomew's Hospital, London for the considerable contribution toward the work and methods referred to in this paper. REFERENCES 1 Majors, P. A. and Wild, J. E. The evaluation of antiperspirant efficacy: influence of certain variables. J. Soc. Cosmet. Chem. 25 139 (1974). 2 Kuno, Y. Charles C. Thomas, Illinois. Human Perspiration (1956). 3 Quatrale, R. P., Stoner, K. L. and Felger, C. B. A method for the study of emotional sweating. J. $oc. Cosmet. Chem. 28 91 (1977). 4 Shelley, W. B. and Hurley, M. J. Studies on topical antiperspirant control of axillary hyperhidrosis. Acta Derm.-Vener. 55 241 (1975). 5 Park, W. M. and Reece, B. L. Fundamental Aspects of Medical Thermography (1976) British Institute of Radiology, London.

J. $oc. Cosmet. Chern. :19 423-431 (1978) Toothbrush wear, brushing forces and cleaning performance B. R. P UGH Unilever Research, Isleworth Laboratories, Middlesex, England Presented at the Symposium on 'Product Evaluation', 18 April 1978, at Eastbourne Synopsis How long a brush should last is largely determined by the magnitude of the forces used during tooth- brushing. Other factors are also implicated. These may include the method of brushing, the geometry of the teeth and whether the individual pre-wets the toothbrush in hot or cold water, thus affecting the mechanical properties of the filaments. Forces measured during toothbrushing range from 4 to 20 N independent of the manual strength or sex of the individual. Those individuals who consistently brush with forces below 6 N do not wear out brushes. Toothbrushes having various states of wear have been examined for their cleaning effectiveness in v#ro. No serious loss in ability to remove cosmetic stains from teeth could be observed until the brushes were severely worn. For the majority of the population, this is unlikely to lead to a noticeable increase in cosmetic stains on their teeth. INTRODUCTION Toothbrushes are widely used for keeping teeth free from soft deposits of dental plaque and food particles. They are also used with toothpastes for removing visible stains. Such stains occur as a result of the absorption of coloured materials from tobacco and some foods or drinks into the proteinaceous film (of salivary origin) covering tooth enamel in vivo (1). While the removal of plaque depends largely on the dexterity and motivation of the individual, cosmetic stains cannot be removed by the action of a toothbrush and water alone. A toothpaste is required for this task (2, 3). The effects of toothbrush design and toothbrushing technique on performance have been reported (4, 5). It is surprising, however, that since many people habitually use toothbrushes that are badly worn (6), little attempt has been made to examine this factor. McKendrick, McHugh and Barbend (7) reported that they could find no correlations between brush wear and either the Oral Hygiene Index or the Periodontal Index. Bergstrom (8) found that wear was correlated with the Hygiene Index. No studies have reported the effect of brush condition on the ability of a dentifrice to remove cosmetic stains. How much a toothbrush has worn probably depends on the mechanical properties of the filaments, the forces applied during brushing and the manner by which the teeth are brushed. Heath and Wilson (9) have reviewed the literature on the measurement of the forces applied to a brush during toothbrushing and concluded that only a limited number of variables had been examined. In some cases subjects were asked to brush in a specified manner that was different from their normal brushing habits, and thus the forces recorded were probably atypical. Most studies were designed to establish force 0037-9832/78/0700-0423 $02.00 ¸ 1978 Society of Cosmetic Chemists of Great Britain 423