AN INVITRO AND INVIVO STUDY OF TOOTHBRUSH BRISTLE SPLAYING

The extent to which a toothbrush is worn out, as evidenced by bristle splaying, is an important determinant of cleaning efficacy. In order f or this aspect of oral hygiene to be studied, an accelerated means of producing a life-like pattern of bristle splaying was investigated and compared with splaying induced by a human test-panel. Porcelain dentu re teeth were brushed under a static applied load in a slurry of denti frice, by means of a revolving ''figure 8'' motion, for up to 12,000 r evolutions. This was found to induce an increase in the degree of spla ying (as measured by ''wear index'') that was well-fitted (R2 = 0.96) by a second-order expression of the form: WI = WI(i) + R(i)t(j) - Ct(j )2 where WI = wear index, WI(i) = initial wear index, R(i) = initial r ate of increase in WI, t(j) = brushing time measured in either machine revolutions (t(r)) or weeks of human use (t(w)), and C = a separate c onstant for each brushing mode (machine or human panel). The rate of s playing was found to be strongly influenced by the quality of the bris tle filament, but not by small differences in toothbrush design. The s playing pattern induced by the machine could not be distinguished visu ally from that in a set of brushes used at home by human volunteers. A strong correlation was found between the splaying produced by machine -brushing and by a panel who brushed free-style at home for 13 weeks. The data fit a linear correlation function: t(r)(machine-brushing time ) = 38 + 320t(w) These results demonstrate that an accelerated brushin g method can mimic the human process involved in toothbrush splaying, that a quantitative relationship exists between the two, and that it i s sensitive to brush-construction factors known to affect splaying. Th is method is therefore suitable for use in investigations concerning t oothbrush durability and the effects of toothbrush design and use on v arious aspects of oral health.