Is made a remember for the two biological elements which audit on the root physiological formation: the dental pulp and the Hertwig's epithelial root sheath. Is discussed like on the practice clinic, we can find undamaged both elements, or we have only with the Hertwig's epithelial root sheath. We indicate a treatment when we have a vioble dental pulp, like different treatment if only we have the Hertwig's epithelial sheath. Is remembered rules which help to keep the health of the periodontal tissues, preventing to the same initiation and preventing too the immunologic reactions.