An electric toothbrush is a toothbrush that makes rapid automatic bristle motions, either back-and-forth oscillation or rotation-oscillation (where the brush head alternates clockwise and counterclockwise rotation), in order to clean teeth. Motions at sonic speeds or below are made by a motor. In the case of ultrasonic toothbrushes, ultrasonic motions are produced by a piezoelectric crystal. A modern electric toothbrush is usually powered by a rechargeable battery charged through inductive charging when the brush sits in the charging base between uses. Electric toothbrushes can be classified according to the frequency (speed) of their movements as power, sonic or ultrasonic toothbrushes, depending on whether they make movements that are below, in or above the audible range (20–20,000 Hz or 2400–2,400,000 movements per minute), respectively. History The earliest example of an electric toothbrush was first produced by Tomlinson Moseley. Sold as the Motodent, a patent was filed by his company, Motodent Inc. on December 13, 1937. In Switzerland in 1954 Dr. Philippe Guy Woog invented the Broxodent. Woog's electric toothbrushes were originally manufactured in Switzerland (later in France) for Broxo S.A. The device plugged into a standard wall outlet and ran on line voltage. Electric toothbrushes were initially created for patients with limited motor skills and for orthodontic patients (such as those with braces). The Broxo Electric Toothbrush was introduced in the US by E. R. Squibb and Sons Pharmaceuticals in 1960. After introduction, it was marketed in the US by Squibb under the names Broxo-Dent or Broxodent. In the 1980s Squibb transferred distribution of the Broxodent line to the Somerset Labs division of Bristol-Myers Squibb. The General Electric automatic toothbrush was introduced in the early 1960s; it was cordless, with rechargeable NiCad batteries and although portable, was rather bulky, about the size of a two-D-cell flashlight handle. NiCad batteries of this period suffered from the memory effect. The GE automatic toothbrush came with a charging stand that held the hand piece upright; most units were kept in the charger, which is not the best way to get maximum service life from a NiCad battery. Also, early NiCad batteries tended to have a short lifespan. The batteries were sealed inside the GE device, and the whole unit had to be discarded when the batteries failed. The use of an AC line voltage appliance in a bathroom environment was problematic. By the early 1990s Underwriter Laboratories (UL) and Canadian Standards Association (CSA) no