How is a missing tooth replaced?

I am 13 years old and when I was little I tripped on a board walk in Florida. This injury caused two of my teeth to grow in fused together. One of the fused teeth made it but the other did not grow a root so it fell out. I have been missing it ever since. I am using a expander right now and am waiting for my last couple of baby teeth to come out and my orthodontist said he would replace the tooth. My teeth are in reasonable good shape so how is it replaced?