Thanks for using JustAnswer. Hello, Dr. Cliff here. Dycal is a material that is used in fillings that are either getting close to the nerve or actually expose the nerve. The dycal is placed on the area where the nerve is present. The calcium hydroxide helps the tooth repair itself, in hopes that a root canal will not be needed. When the dycal is placed, the nerve will move away from the material. As it does this, new tooth is produced to fill in the area where the nerve is moving from. This continues until there is a nice new thick layer of new tooth present between the nerve and dycal. When this happens, the tooth will usually not require a root canal. So in closing, dycal serves as a protectant to the nerve to allow for new tooth to be produced to protect it.
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Best of Luck! Dr. Cliff