Ive broken a molar in half, the inside edge is very sharp and is causing significant pain. What should I do?

Call your dentist….but in the meantime get an emory board nail file (preferably new!) wash it off, and use it to gently file down the sharp edge. Also, the drug store sells wax intended to put on orthodontic wires to keep them from irritating the lips, you might be able to use this if you can get the tooth dry.  Hope this helps

Don't you think it would be a good idea to call your dentist?  It needs to be treated properly.