Teeth-cleaning timer

Everyone should clean his teeth a tleast a couple of times a day. Dental research shows that cleaning one's teeth for three minutes at a time is best: longer periods may damage the gums, whereas the gums may not be massaged sufficiently, nor the plaque removed adequately, if the period is shorter. Some manufacturers have therefore started to build in timers in their electric toothbrushes that give a signal after three minutes.