In the case of conventional toothbrushes whose bristles have all needlelike tapering tips, the bristles near the tips become too thin and too flexible. In the case of toothbrushes whose bristle ends are all round or hemispherical, it is difficult to get into the spaces between teeth or boundary spaces...http://www.google.es/patents/US5991957?utm_source=gb-gplus-sharePatente US5991957 - Toothbrush
