If there is nothing available to you and you still have the crown, gently rinse the crown out with water and place some toothpaste in the crown. Then, place the crown back onto the tooth, followed by biting gently on your teeth. There are over-the-counter cements available, but be very careful because these can result in further damage when you cannot clean the overflow of cement. Please see your dentist to prevent further damage. Never use any sharp instruments because you may cut into your gums.