What do i do if my guinea pig's tooth breaks after a fall?

You could wait and see if it grows back. Or I would take it to the vet soon. Yea, that, but you need to cut up its hay, feed it liquid through a sgrynge or eyedropper, and feed it lots of fruits and veggies. Give it extra TLC. a tooth normally takes from one to two weeks to fully gorw back. Good Luck!