Depending on the reason why the crown came out; yes, the crown can be put back in. Sometimes a crown will come out because the cement was old and gave way. If this is the case a reputable dentist will inspect for any decay under the crown, take an x-ray, clean the crown, check the fit, and re-cement the crown back in.
However, sometimes a crown will come about because a cavity that formed around the edge got big enough that the crown could no longer hold on. Hope this helps.
My best to you!
William F. Scott IV, DMD