Adam, I'm a Registered Dental Hygienist, retired, who worked in pediatric and general practice for thirteen years. I'd say that if the images are for the waiting room, most any type of format would work.
If they are for rooms in which dental work is done ("operatories"), those rooms need to be disinfected every single day. And after certain patients, most everything needs to be wiped down. From experience, I can tell you it's not the place (in my opinion) for anything that could not be framed behind glass and disinfected.
I haven't purchased anything but framed prints for my own home, so I don't have experience with acrylics, canvas, or metal. If any of those could be disinfected, they could be hung in an operatory. Otherwise, I certainly wouldn't want any of them back!