First electric dental drill: Jan. 26, 1875

Dentistry takes a leap forward when George Green, a dentist in Kalamazoo, MI, receives a patent for a drill that's powered by an electromagnetic motor. For most of the 19th century, dentists had relied on foot pedals to drive their drills, instruments that allowed them to try to save teeth instead of just yanking them. In 1868, Green himself had created a pneumatic version of a drill run by a pedal-powered bellows. But his electric model is considered a turning point in modern dentistry.

Still, by today's standards, it's a crude device attached to what looks like a primitive vacuum cleaner on wheels. It's heavy and expensive. Not to mention that few dentists at the time have electricity in their offices to charge the motor's battery.

It will be another 30 years before most dentists make the switch from pedal-driven drills to electric ones. And it won't be until the 1950s before the invention of air-turbine dental drills, which are what is used today.

A point of comparison:  Modern dental drills can reach speeds of 800,000 revolutions per minute; the early ones, powered by pedals, spun at a rate of 15 revolutions per minute.