If dental crown of your tooth came out, then you should call your dentist
asap and schedule an appointment with him. Don’t keep the loose dental crown in your mouth as you may accidentally swallow it. Dental crown can become loose and can come out because of decay below dental crown, lack of tooth structure to hold dental crown, if dental crown is ill fitting, more stresses and forces on dental crown or excess of sticky foods. Dental crown can also fall if permanent cement which is used by dentist is not of good quality or because of wear of dental crown which can cause percolation of fluids in dental crown and fall of dental crown.By the time, you get it fixed; you can avoid eating from that side of the mouth and keep that area clean to avoid any secondary infections.