If your child allows you to push the tooth back into the socket after it’s been knocked out, that gives us the best possible chance to reattach it. Otherwise, the clock starts ticking as soon as the tooth comes out—when placed in a small cup of milk or saliva, about an hour can pass and we’ll still have a good chance at being able to successfully reinsert the tooth. After an hour, the likelihood of successful reattachment begins to decrease.