Wow it is great that you are 24 and have not had a filling or root canal!!!
Do you brush and floss regularly?
Your teeth/mouth might be detoxing when you fast.
You might try Oil Pulling and or mixing a few drops of chinese Coptis in water and rinse and see if that helps.. that is what I do but I am older and sadly I've have lots of dental work.
Another posted mentioned MELT and I like both MELT and or Egoscue for alignment body work. Those are both great! And needful for all. But that does not really answer the fasting tooth connection.
You might Google Dr. Dawn Ewing (Houston TX) and the Tooth Body Connection Show and listen to some of her podcasts.
Will pray you get to the bottom of this as it seems to me that your body is trying to tell you something.