IMPRESSION TRAYS / SPOONS
Most of North America is using disposable trays / spoons to avoid any potential contamination from AIDS, the H1N1 virus, and other viruses.
I was surprised by the German technician connected to the Braces online-Shop who is still using the steel autoclave-able  spoons / trays.
I had never seen these before and thought what an expense to throw-away these spoons, but did not know they were being reused.
When an impression is not correct, it would be easier to be able to reorder the  size of spoon needed rather than get another whole kit.
nanegor

Besides, as you say, the metal ones are autoclave-able. Or ultrasound-able. And from the clean shape and the separate packaging they come in, my shrewd guess is that is precisely what is being done to them prior to sending out. If you have any concerns (unwarranted, I daresay), you can put them in the dishwasher and/or rinse them with Alcohol. That will securely kill any bacteria or viruses there could possibly be - including HIV and H1N1.

All else is cultural - most Europeans just don't hold with the "use it perhaps once and throw it in the garbage" mentality that still prevails in the lower 48. This is also about saving valuable natural ressources such as crude oil (which is the raw material for plastic) and reducing garbage. Plus, many Europeans consider things that you can use more than once more intrinsically valuable and of much better quality than one-way stuff. That's also why drinks are sold in recyclable bottles around here, and no longer in cans. That's neither better nor worse, just different!

Cheers,
SC