Royalty free images

I was wondering if anyone knew where I can find some royaltee free images of dentistry and such. I'm a page for a dental on call business and they don't have any images for me to use. Any help would be awesome, thanks guys!

i havnt looked but try http://www.istockphoto.com/index.php

or

http://www.fotosearch.co.uk/

gettyimages.com
fotolia.com

http://www.sxc.hu/
http://www.morguefile.com/