If a tooth has a large or very deep defect under the gum, e.g. due to caries or a fracture, a ceramic dental crown is required. In the case of large defects, there is not enough support for fillings and the tooth would be at risk of fracture. In this case, the dental crown encloses the tooth and gives it new support. In the case of deep defects, it is not possible to ensure drainage, which is essential for the stability of a filling. The cement used to secure the dental crown is insensitive to moisture.