Welcome to Justanswer.I will do my best to answer your question.I am not a great typist,be patient and feel free to ask if anything is unclear.If the tooth under the crown is still sound..There is no reason why the tooth cannot be reprepped and a new crown made.Implants are not simple fixes like many people think that they are.They require surgery,several months of waiting, and a big expense..There are alternatives to implants if the tooth actually needs to be extracted depending on the condition of your other teeth.The old crown most likely will not be able to be used but it is possible depending on how acurately you were able to seat the crown with temporary cement.The reason the crown does not fit the space anymore is because the adjacent teeth shifted..there was probably some time period that the tooth was out.My guess is the tooth can be saved by just redoing the crown.