When biting is too great for all - porcelain - crowns, or when gaps from missing teeth must be filled in, metal alloy must be placed under the porcelain for strength. This is the porcelain fused to metal crown technique. Again, the teeth are prepared for a full coverage restoration. After the impression is taken, a metal coping is made for the prepared tooth. This is then covered with porcelain. These crowns do not have the translucency of pure porcelain crowns. Therefore, the aesthetics may be slightly compromised in some situations. However, good ceramists can usually overcome the limitations, thereby creating lifelike restorations. When teeth are loose due to periodontal bone loss, this technique is used. Here the teeth are splinted together, by joining the metal structure of the crowns.