As you can see in the images above, electric handpieces have a series of shafts and gears which are coupled with numerous sets of bearings. Electric handpieces generally have 8 bearings in them, and when a bearing fails, unlike a pneumatic, an electric will continue to run. The failed bearing will cause increased friction and, consequently, increased heat. Additionally, the failure will “travel” up and down the line, throwing shafts and gears out of whack and their failure in turn. An exploded bearing can cause bits of debris to go flying around internally as well. Any change in sound, feel, vibration, or heat can indicate a bearing failure. If any of these conditions occur you need to STOP using the handpiece immediately and send it in for repair. Replacing bearings alone is many hundreds of dollars less expensive than replacing gears and shafts. Also, when running an electric, remember that the drive air and water serve to cool the handpiece – run electrics with as much air and water as you can stand, within the manufacturer’s recommendations.