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

424 B. R. Pugh patterns that could give guidance in designing laboratory brushing machines for measur- ing the abrasivity of toothpastes. None were concerned with the effect of brushing forces on the wear of a brush. In the investigation to be described here, the importance of brush condition on cos- metic cleaning was examined. Brushing forces were also examined to establish their role in the process of brush senescence. Methods for measuring cosmetic cleaning in vivo are both time-consuming and tedious (3, 10). Simple laboratory tests using plastics, paints, metals, etc. are generally unsatis- factory owing to the difficulty of matching their tribological properties to those for naturally stained protein films in vivo. Alternatively, naturally stained extracted teeth can be used. The optical reflectances of such teeth change only slowly when they are brushed with a slurry of a toothpaste and there are wide variations between the individual rates of change. These problems can be overcome by (a) constructing mosaics containing ten to fifteen teeth, (b) comparing the rates of increase in reflectance for two treatments on each mosaic (whether a reference and a test toothpaste or a reference and worn tooth- brush) and (c) absorbing a black dye into the protein film in order to magnify the changes in reflectance. Several authors measured the forces applied during toothbrushing using brushes with specially constructed handles containing the transducer elements (9). A more direct approach of cementing strain gauges onto the handles of commercial brushes is preferred as the bulky handles used in the former approach could conceivably have inhibited subjects from brushing naturally. Bergstrom (8) assessed the condition of toothbrushes by measuring the angle of permanent deformation of individual filaments. This approach was rejected by us because it could not be correlated with the perceived amount of wear. Instead, a simple scale has been developed in which samples of worn commercial brushes were ranked in order of the severity of wear. EXPERIMENTAL BRUSH WEAR A large number of worn commercial brushes were obtained from people who had used them normally at home. These brushes were Wisdom, Oral B 40 and Gibbs short-head varieties. For each type of brush, six were selected to cover a wide range of senescence. Two new brushes of each type were added to the numbers, making twenty-four brushes in total. Fifteen judges were selected at random and each independently was asked to sort the brushes into groups which represented perceptually important differences in patterns of wear, without restriction on either the number of groups or the number of brushes within a group. In addition, the judges assigned percentage scores to the severity of wear for each group based on the arbitrary notation that 100•o represented a completely worn out brush (in their estimation). BRUSH WEAR AND BRUSHING FORCES il'l FiFo Forty-seven panellists were recruited from office and laboratory personnel. Each was given a Gibbs short-head medium brush and asked to use it normally at home. At intervals over an eight week period, panellists returned their brushes for inspection.