sonic toothbrushes rely on sweeping motion alone to clean the teeth, the movement that they provide is often high in amplitude, meaning that the length of the sweeping movements that they make is large. One study found that using sonic toothbrush causes less abrasion to the gum when compared to the manual toothbrush. Ultrasonic 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 2.4 million 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 million 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. 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 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. Effectiveness In 2014, a Cochrane review demonstrated that power toothbrushes remove more plaque and reduce gingival inflammation more than manual toothbrushes. This review showed electric toothbrushes had greater effectiveness over manual ones. For