Sterilized. The CDC is explicit: handpieces and other intraoral devices that attach to air and water lines, including low-speed motors and prophy angles that aren't disposable, should be heat-sterilized between patients. Surface disinfection is not an acceptable substitute, because the inside of a handpiece can pull in and hold contaminated material you can't reach with a wipe.
Between patients
The routine most offices follow, in order:
- Flush the handpiece for 20 to 30 seconds with the bur in, discharging water and air into the sink or a high-volume evacuator, to clear the lines.
- Remove the bur. Wipe off visible debris on the outside.
- Clean and lubricate according to the manufacturer's instructions. Some models are lubricated before sterilization, some after, some both. Follow your model's sheet, not a general rule.
- Package it, sterilize it in a heat sterilizer, and leave it packaged until it's needed chairside.
Why they die early
Handpieces fail from skipped lubrication, from being run dry after sterilization, and from being pulled out of the sterilizer before the dry cycle finishes. Each manufacturer's instructions are the authority on their own product, and they're the thing a service rep will ask about first.