Well, there's no point in stressing - it doesn't help you get through it and it makes things worse. What you are dealing with is normal things that parents/people have to deal with all the time. Hand, foot, mouth is a viral infection, nothing your child will be scarred for life from. The tooth is fixed, so your good there. See? They way I look at it is, it could always be worse. If this is all I have to deal with, then I have it pretty good.
It sounds like you may have some anxiety? I think stressing so hard that you break a tooth doesn't sound very healthy. You may want to find an outlet for your stress (hobby, girl time, etc.) or look into classes or therapy on how to better manage your stress.
I used to make everything worse by thinking negatively & obsessing & I am finally to the point where not much gets me upset anymore. I finally realized that sh!t is going to happen in life, and you may not be able to control that, but you CAN control how you react. Stressing is just bad for you, and your kids can feed off of it, too.