by Chris Woodford. Last updated: June 18, 2013.
Do your friends reach for the sunglasses when you smile? If not, maybe it's time you invested in an electric toothbrush. These battery powered teeth scrubbers move their heads back and forth up to 7000 times a minute, shifting twice as much plaque (rotting, sugary food debris) as ordinary, manual toothbrushes. That's called good oral hygiene and it means you won't have to go to the dentist quite so often. The cleaner you keep your teeth (and the gums that support them), the longer they'll last you. Just remember, once your adult teeth are gone, you don't get replacements! Ever wondered how an electric toothbrush works? Let's take a closer look!
Photo: Use it properly, and a sonic toothbrush like this can get your teeth cleaner than a manual toothbrush—or an ordinary electric one.
What's inside an electric toothbrush?
Take an old electric toothbrush apart and it's easy to see how it works. I had one that didn't work anymore, so I had a quick look inside before taking it to the recycling center. Here's what I found:
The first thing you notice is the removable brush. This is the bit that does all the hard work. It has a semi-rotating head at the top so, as the mechanism inside the brush handle rotates back and forth the brush turns from side to side. Directly underneath the brush there's a cam and gear unit, which looks like this:
The cam and gear unit is the clever part of an electric toothbrush. It converts the high-speed rotary (spinning) motion of the brush's electric motor into reciprocating (back-and-forth) brushing motion that cleans your teeth more effectively. The cam and gear works a bit like this very simplified animation. The green wheel, driven by the motor, is always rotating clockwise at high speed, but the black lever is pivoted on rubber. So, as the green wheel turns, the black lever pulls first one way and then the other, moving the brush up and down.
(You can read more about cams in our article on cranks and cams.)
The cam and gear unit is connected to a gear built into the top of the motor, so the motor drives it directly. Underneath the motor, there's a rechargeable battery. Attached to the inner plastic case, there's a simple electric circuit board that controls the on/off switch on the outer case. The outer case is made of tough plastic and the on-off switch is set into it in a piece of thin, very flexible rubber. The purpose of the outer case is to keep water and toothpaste away from the circuit, motor, and battery—which would quickly rust if you got them wet. (If you're curious to know how an electric toothbrush can recharge itself standing on a plastic base, take a look at our article on induction chargers.) And that's pretty much all there is to it—a bit of clever, effective engineering technology that keeps your teeth in tip-top shape!