You do not necessarily have permission to use all of the photos and videos that you find from a Google search. To find images that you are sure you have permission to use in your assignments, you can use the image databases that the Library gives you access to - see the options below.
The Library gives you access to two databases with images that you can download to use in your assignments and presentations.
Stedman's Online has both photos and x-ray images of oral conditions and disorders. Select the Illustrations tab and then the Dental Dictionary tab to find images specific to your area.
Britannica ImageQuest has images of professionals providing dental care, as well as a few x-rays. It's organized differently from Stedman's so you'll have to try searching using terms like dental care to find results. This is a good place to find stock photos of patient interactions and dental tools.