You have not mentioned which tooth got knocked out. If it has single root then I presume that it is front tooth. Now instead of the milk tooth, adult tooth will come in that place and this will start coming at the age of 6-7 years depending upon which tooth has to come. By getting the xray done your dentist will tell you the position of adult tooth. Till the adult tooth comes, for aesethic and functional purposes, temporary replacement can be planned. This you can discuss with your dentist because without clinical examination this cannot be commented upon. For more info on human dentition you can read the following article from this link in our website which will tell you the age at which teeth comes.
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