Abstract
We conducted an in vivo study with weekly observations of the relationship between toothbrush bristle wear and brushing force, as well as an in vitro study of the relationship between bristle wear and the removal of experimental plaque. In the in vivo study, we found that the burshing forces em-ployed by the subjects tended to increase as the bristles became worn. The stronger the brushing force, the more the bristles of the outside ranks spread out, while the bristles of the center ranks charged very little regardless of brushing force. Scanning electron microscopic observations of the bristle tips of the center ranks revealed obvious wear of the bristle tips at 2 weeks, and by 4 weeks they had spread considerably. At the tips of the outside ranks, wear of the bristles was slight from the tip. We found that the hardness of the bristles decreased with the use of the toothbrush.
In the in vitro study, we found that the hardness of the bristles decreased with the number of brush-ing strokes and that the actual area cleansed de-creased as the toothbrush became older for all brushing force values. Measurements showed that brushes that had been used for some time removed less gold coating from the experimental apparatus than did newer ones, regardless of brushing force.
These results indicate that toothbrushes should be replaced every 3 or 4 weeks for maximum plaque removal effect.
