Before it can be reliably translated, we need evidence of what stérilisation à nue is. Since we are dealing with botoxers et autres injectors of hyaluronic acid (about whom there was a horrifying documentary on French TV recently, with much said about lamentable hygiene) it might indeed be sterilization of unpackaged instruments, so unpackaged sterilization.

For which I find some references (mostly Canadian), along with 'bare sterilization'.

"Sterilization and Unpackaged Items
An unpackaged cycle (sometimes called flash sterilization) is a method for sterilizing patient care items for immediate use. Unpackaged sterilization should only be used under certain conditions; • Thorough cleaning and drying of instruments preceded unpackaged cycle; • Mechanical parameters are checked and an internal chemical indicator is used for each cycle; • Care is taken to avoid thermal injury to staff or patients; • Items are transported aseptically to the point of use to maintain sterility. When sterile items are left open to the air, they can quickly become contaminated. Therefore, critical instruments that are sterilized unpackaged should be used immediately and not be stored."
https://oralhealthbc.ca/wp-content/uploads/2022/08/06.02.004...

"Recommendation for semi-critical (nonsurgical) instruments used: we recommend unpackaged sterilization in autoclaves as a minimum. Critical (surgical) instruments used must be packaged according to regulations and marked for sterilization in the autoclave"
http://www.sunshine-dental.de/IFU/GebrauchsAufbereitungshinw...

"Highly dangerous oral instruments in bare sterilization and general container packaging should be used immediately after sterilization"
https://www.dentalinbox.com/operational-specifications-for-d...


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Note added at 2 hrs (2023-03-24 16:18:35 GMT)
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Or, as given as an alternative above, flash sterilization:

Flash Sterilization
The process by which unwrapped instruments are sterilized for immediate use when an emergency situation arises"
https://www.slideshare.net/lahcmultimedia/chapter-14-point-o...

"An unwrapped cycle (sometimes called flash sterilization) is a method for sterilizing unwrapped patient-care items for immediate use."
https://www.thefreedictionary.com/flash sterilization