The number one reason for dental dental cap keep coming off is lack of retention, and tooth structure to hold the dental cap without the cement. If your bite on the crown is not adjusted, you are putting extra excessive forces on the crown while chewing, and the occlusion on the crown is wrong. Why does my crown keep coming out? Usually, this is due to an improper fit, a lack of cement, or a slight amount of tooth structure remaining that the crown can hold on to. If this happens, clean the crown and the front of the tooth. ... Causes of dental crowns falling off are many. Some are due to poor workmanship, some are due to the tooth itself.