1. What is in an electric toothbrush?
Open up an old electric toothbrush and it is easy to see how it works. The figure below shows the cam / gear, housing, motor, battery, charging coil, and circuit board.
The first removable is the head brush, which is the primary brushing part. There is a semi-rotating head under the brush. When the cam mechanism inside the handle is driven by the motor, the semi-rotating head reciprocates from left to side.
The cam and gear sets are the most ingenious part of the electric toothbrush design. It converts the high-speed rotation of the toothbrush motor into reciprocating (back and forth) brushing exercises to clean the teeth more effectively.
The purple motor shaft rotates at a high speed, rotating the blue eccentric wheel, while the yellow rod converts the rotation to a low-speed back-and-forth vibration. The cam and gear devices are connected to the gear on the top of the motor, so the motor drives it directly. Below the motor, there is a rechargeable battery. Connecting to the housing is a simple circuit board for switch control. The shell is made of tough plastic, with the on-through switch set in a very soft piece of thin rubber. The purpose of the housing is to keep water and toothpaste away from circuits, motors, and batteries.
2. What is the difference between sonic toothbrush and ordinary electric toothbrush?
Sonic toothbrushes work like regular electric toothbrushes: they move back and forth over the surface of their teeth, wiping off plaque. The most obvious difference is the speed of motion: an acoustic toothbrush typically vibrates at about 260Hz (260 times per second), which is equivalent to 31,000 teeth brushing per minute, or ——, about 10 times faster than a regular electric toothbrush.
