I wrote about this in yesterday’s post-braces report, but think it’s worth mentioning again.
At my last ortho appointment, I asked one of the technicians if she could sonic clean the retainers; the doctor has mentioned this last time I was there.
“No problem”, she said, and took the retainers.
When I was ready to leave after about 15 minutes, they were done and looked great! They use the machine they use to clean their instruments. I don’t know if all ortho offices will offer this, but it can’t hurt to ask.