Final answer:
The worst type of cement for a deep restoration is acidic cement. Resin cement and glass ionomer cement are recommended for deep restorations.
Step-by-step explanation:
The worst type of cement for a deep restoration is acidic cement. Acidic cement, also known as acid etch cement, is not suitable for deep restorations because it can erode the tooth structure and cause further damage. It is generally used for superficial restorations or bonding procedures. For deep restorations, it is recommended to use resin cement or glass ionomer cement as they provide better strength and durability.