I have a set of bear teeth that I want to wear as a necklace. Is there anything I need to put on them, to protect them from becoming brittle or breaking? I don’t wanna run around with these around my neck and them fall apart or chip.
The teeth already have a some cracks and such.

You can add a protective coating by painting them with special lacker, varnish, or resins. Here’s a webpage that mentions such products (which are especially used for fossil materials):

http://www.flmnh.ufl.edu/natsci/vertpaleo/resources/prep.htm

However, if you’re going to use the teeth for a necklace, I think they won’t break if you are just careful, unless they’re deeply cracked.
After all, enamel (the outer shiny cover of the teeth) is the hardest body tissue.