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Ultrasonic toothbrush
An ultrasonic toothbrush is an electric toothbrush designed for daily home use that operates by generating ultrasound in order to aid in removing plaque and rendering plaque bacteria harmless. It typically operates on a frequency of 1.6 MHz, which translates to 96,000,000 pulses or 192,000,000 movements per minute. Ultrasound is defined as a series of acoustic pressure waves generated at a frequency beyond human hearing.〔(【引用サイトリンク】title=High Intensity Focused Ultrasound - Physics )〕
==Background==
Electric toothbrushes have been used by the public since the early 1950s. Today, they have evolved and based on the speed of their vibration, can be divided into three categories: electric, sonic and ultrasonic.
Electric toothbrushes vibrate in either an up/down direction, or in a circular motion, and sometimes in a combination of the two. Typically, the speed of their vibration is measured in movements per minute, where common electric toothbrushes vibrate at a speed of between a few thousand times a minute to approximately 10,000 to 12,000 times per minute. Sonic toothbrushes are called sonic because the speed or frequency of their vibration, as opposed to the sound of the motor, falls within the average range that is used by people in communication. The voiced speech of a typical adult male will have a fundamental frequency from 85 to 180 Hz (10,200 to 21,000 movements per minute), and that of a typical adult female from 165 to 255 Hz (19,800 to 30,600 movements per minute).〔Titze, I.R. (1994). Principles of Voice Production, Prentice Hall (currently published by NCVS.org) (pp. 188), ISBN 978-0-13-717893-3.〕〔Baken, R. J. (1987). Clinical Measurement of Speech and Voice. London: Taylor and Francis Ltd. (pp. 177), ISBN 1-5659-3869-0.〕 Ultrasonic toothbrushes work by generating an ultrasonic wave usually from an implanted piezo crystal, the frequency of which technically could begin at 20,000 Hz (2,400,000 movements per minute). The most common frequency however, around which many scientific studies have been conducted, is in the area of approximately 1.6 MHz, which translates to 96,000,000 waves or 192,000,000 movements per minute.
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