Relationship between the plaque removal efficacy of a manual toothbrush and brushing force

This survey investigated the association between the efficacy of plaque removal and toothbrushing forces during a normal brushing regime. The 94 subjects participating in this study were requested not to brush 24 h prior to the experiment. Panelists brushed for 1 min with a manual toothbrush. Before and after brushing, plaque was assessed using the Turesky modification of the Quigley & Hein plaque index. A second 1-min exercise of brushing was carried out to assess the toothbrushing force. The mean plaque reduction was 39%, with vestibular surfaces being cleaned most effective (69%) and the lingual surfaces the least (21%). The mean brushing force was 330 g. No correlation was observed between efficacy and brushing force (r=0.14, p=0.16). The relationship between pre- and post-brushing plaque was stronger (r=0.68, p<0.001). Multiple regression analysis entering squared values of force as an independent variable into the equation, indicated that the relation between efficacy and force was not linear. A curve could be fitted to the plot (p=0.0004), demonstrating that up to a certain level of force, an increase of force is associated with an increase in efficacy (r=0.33, p<0.01). Beyond this point, application of higher forces resulted in reduced efficacy (r=-0.49, p=0.03). As was calculated in this particular test this 'transition' level of force was 407.4 g. The absence of a correlation between brushing force and plaque removal efficacy suggests that in a 'user model' brushing situation, other factors than brushing force are of major influence on the amount of plaque removed.