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An electric toothbrush is a toothbrush that uses electric power usually supplied by a battery to move the brush head rapidly, either by back-and-forth oscillation, or by rotation-oscillation (where the brush heads alternates clockwise and counterclockwise rotation).
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The first electric toothbrush, the Broxodent, was conceived in Switzerland in 1954 by Dr. Philippe-Guy Woog. 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 AC 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 USA by E. R. Squibb and Sons Pharmaceuticals in 1959. After introduction, it was marketed in the USA 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 which 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 longer certified line-voltage appliances for bathroom use. Newer appliances had to use a step-down transformer to operate the actual toothbrush at low voltage (typically 12, 16 or 24 volts). Wiring standards in many countries require that outlets in bath areas must be protected by a RCD/GFCI device (e.g., required in USA since the 1970s on bathroom outlets in new construction).
By the 1990s there were problems with safety certification of Broxo's original design. Further, improved battery-operated toothbrushes were providing formidable competition. Broxo S. A. still produces and markets a low-voltage model, but its public visibility in the USA has been limited in the face of large competitors, such as Philips Sonicare and Braun Oral-B models.
Electric brushes can be classified into two categories according to the type of action that they employ: vibration or rotation-oscillation. When using vibrating toothbrush, a brushing technique similar to that used with a manual toothbrush is recommended, whereas with rotating-oscillating brushes the recommend cleaning technique is to simply move the brush slowly from tooth to tooth.
The newest developments in this field are ultrasonic toothbrushes, which use ultrasonic waves to clean the teeth. In order for a toothbrush to be considered "ultrasonic" it has to emit a wave at a minimum frequency of 20,000 hertz or 2,400,000 movements per minute. Typically, ultrasonic toothbrushes approved by the U.S. Food and Drug Administration (FDA) operate at a frequency of 1.6 MHz, which translates to 192,000,000 movements per minute. Most ultrasonic toothbrushes have an additional sonic vibration ranging from 9,000 to 40,000 movements per minute. Any toothbrush operating at a frequency or vibration less than 2,400,000 movements per minute (20,000 hertz) is a "sonic" toothbrush. It is called 'sonic' because its operating frequency, for example 31,000 movements per minute, is within the human hearing range of between roughly 20 hertz to about 20,000 hertz. The first ultrasonic toothbrush, first called the Ultima and later the Ultrasonex, was patented in the USA in 1992, the same year the FDA gave it approval for daily home use. Initially, the Ultima worked only on ultrasound, but a few years later, a motor was added to give the Ultrasonex brush additional sonic vibration. Today, most ultrasonic toothbrushes work simultaneously in the ultrasonic mode together with sonic.
Claims have been made that electric toothbrushes are more effective than manual ones as they are less dependent upon a patient's personal brushing technique. Some dentists also claim that they help kids with overcoming their fear of the dentist. 
Independent research finds that most electric toothbrushes are no more effective than manual brushes—assuming that people using a manual toothbrush brush effectively. The rotation-oscillation-models have been found to be marginally better than manual ones. The research concludes that the way brushing is done, including the amount of time spent, is more important than the choice of brush. For patients with limited manual dexterity or where difficulty exists in reaching rear teeth, however, dentists regard electric toothbrushes as being especially beneficial. A recent Cochrane review has bought to light new evidence that suggests the effectiveness of electric toothbrushes over manual ones. Plaque build-up and gingival inflammation was reduced by 11% and 6% respectively after one to three months of use and after three months of use, the reduction observed was greater - 21% reduction in plaque and 11 % reduction in gingival inflammation.
The effectiveness of an electric toothbrush depends not only on its type of action and on correct use, but also on the condition of the brush head. Most manufacturers recommend that heads be changed every three to six months at minimum, or as soon as the brush head has visibly deteriorated.
Power source and charging
Modern electric toothbrushes run on low voltage, 12v or less. A few units use a step-down transformer to power the brush, but most use a battery, usually but not always rechargeable and non-replaceable, fitted inside the handle, which is hermetically sealed to prevent water damage. While early NiCd battery toothbrushes used metal tabs to connect with the charging base, modern toothbrushes use contactless inductive charging: the brush unit and charger stand each contain a coil of wire; when placed in proximity, the powered coil from the stand transfers power by induction to the handle, charging the battery.
Many modern electric toothbrushes have a timer which buzzes, or briefly interrupts power, typically after two minutes, and sometimes every 30 seconds. This is associated with a customary recommendation to brush for two minutes, 30 seconds for each of the four quadrants of the mouth.
Some electric toothbrushes have LCD screens which show brushing time and sometimes smiley face icons or other images to encourage optimal brushing. These features could encourage people to brush more accurately.
Brushing teeth too hard causes enamel and gum damages. Most modern top-end electric toothbrushes come with pressure sensor, which prevents users from brushing too aggressively. There are two types of pressure sensors. Some sensors produce sound warning and some immediately stop movements of electric toothbrush when it's used too aggressively.
Most electric toothbrushes come with different cleaning modes and intensity levels. Cleaning modes are designed for special types of cleaning efficiency. Some of the most well known are Sensitive, Daily care, Whitening and Tongue cleaning.
- "Using A Rechargeable Electric Toothbrush" by Oral B
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- Dental and Oral Health (Adults) Don't Let a Disability Keep the Dentist Away — Daniel E. Jolly, Professor of Clinical Dentistry College of Dentistry The Ohio State University.