Removing plaque from your teeth by tooth-brushing helps prevent gingivitis (gum inflammation). A review of forty-two studies has found that rotation oscillation electric toothbrushes (brush heads rotate in one direction and then the other) are better than manual toothbrushes at removing plaque and reducing gum inflammation. The Academy of General Dentistry recommends you brush your teeth at least three minutes twice a day.

Source: “Manual versus powered toothbrushing for oral health,” PG Robinson, et al., The Cochrane Database of Systematic Reviews, April 18, 2005.