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Brush your teeth too vigorously and you can end up with bleeding gums,
damaged teeth, or both. So Unilever has filed a patent on a toothbrush that
tells aggressive brushers when to ease off (W0 99/5935). A cavity runs along the
inside of the handle of the otherwise ordinary nylon brush, and is filled with a
piezochromic material which changes colour after a few seconds of excessive
pressure. Having given its visible warning, the handle gradually reverts to its
original colour. Alternatively, says Unilever, small plates of piezochromic
material can be interleaved with the brush bristles so that the head turns
stripy when your teeth are at risk.