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 Hz 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.
Ultrasonic toothbrushes emit vibrations that are very high in frequency but low in amplitude. These vibrations break up bacterial chains that make up dental plaque and remove their methods of attachment to the tooth surface up to 5 mm below the gum line.[7]
Some ultrasonic toothbrushes, such as the Emmi-Dent, provide only ultrasonic motion. Other ultrasonic toothbrushes, such as the Ultreo and the Megasonex, provide additional sonic vibration ranging from 9,000 to 40,000 movements per minute, comparable to a sonic toothbrush, in order to provide additional sweeping motion which facilitates removal of food particles and bacterial chain remnants. The sonic vibration in these ultrasonic toothbrushes may be lower in amplitude than that found in a comparable sonic toothbrush because the bacterial chains do not need to be removed through sonic vibration, simply swept away, as they have already been broken up by the ultrasound.
Because of the similarity of the terms “ultrasonic” and “sonic”, there is some confusion in the marketplace and sonic toothbrushes are frequently mislabeled as ultrasonic ones. A toothbrush operating at a frequency or vibration of less than 2,400,000 movements per minute (20,000 Hz) 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 Hz to about 20,000 Hz. Only a toothbrush that emits ultrasound, or vibration at a frequency greater than the upper limit of human hearing, can be called an "ultrasonic" toothbrush.
Claims have been made that electric toothbrushes are more effective than manual ones as they are less dependent upon a user's personal brushing technique. Some dentists also claim that they help children with overcoming their fear of the dentist. Independent research finds that most electric toothbrushes are no more effective than manual brushes—assuming that people use a manual toothbrush brush effectively.[8][9] The rotation-oscillation-models have been found to be marginally better than manual ones.[8][10][11] 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.[12] A 2014 Cochrane review suggested 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.[13] In addition, ultrasound from a commercially available ultrasonic toothbrushhas been shown to break up dental plaque composed of chains of cariogenic Streptococcus mutans bacteria, destroying their cell walls and removing their methods of attachment to the enamel surface, at a distance of 5mm from the plaque.[7]
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.[14][unreliable source?] Most manufacturers recommend that heads be changed every three to six months at minimum, or as soon as the brush head has visibly deteriorated.
