Antimicrobial can be a lot of things, a lot of it is trademarked.

This one:

pro-sys.com/…/antibacterial-adult-toothbrush/

Says it uses “StaClean™” So what does that mean?

Well…

prnewswire.co.uk/…/health-and-hygiene-announce-th…

“Something, something, duPont”? My best guess is that it’s a plastic that is non-porous so microbes can’t live in it.

This one says it’s infused with “Nano Silver”.

linhart.nyc/pages/nano-silver-toothbrush

Silver does have anti-microbial properties. “Nano Silver”? Who knows.

Really you’d have to read the fine print on each brush and do the research to be vaguely certain. :)