In the development of tooth the tooth germ passes through various stages. The actual mineralization or deposition of enamel and dentin starts only in the advanced bell stage. The enamel dentin deposition starts from the incisal or cuspal tips of the tooth and then proceeds cervically. Once it reaches the Cervical Loop or the future cervical line of the tooth, then the root formation begins and gradually moves apically. The root does not have enamel but only has dentin deposited by Odontoblasts and cementum deposited by Cementoblasts. Root formation begins in the Advanced Bell Stage with the formation of Hertwigs Epithelial Root Sheath. It is a 2 cell layered sheath which originates from the Cervical Loop and grows into the underlying ectomesenchyme separating the Dental Papilla and Dental Sac. The Hertwigs Epithelial Root Sheath is formed by the extension of Inner Enamel Epithelium and Outer Enamel Epithelium. There is no Stellate Reticulum or Stratum Intermedium. The outer cells are cuboidal in shape similar to the Outer Enamel Epithelium. The inner cells are also cuboidal hence not like the tall columnar Ameloblasts and so don’t have the ability to deposit enamel. Hertwigs Epithelial Root Sheath sends signal to the Dental Papilla. The cells, on receiving the signal differentiate into Odontoblasts. These cells then start depositing dentin. Once dentin deposition starts the function of Hertwigs Epithelial Root Sheath ends. Hence, the function of Hertwigs Epithelial Root Sheath is just to differentiate the cells of the Dental Papilla to Odontoblasts. Once the function of Hertwigs Epithelial Root Sheath is over, its cells start undergoing degeneration. The degeneration of Hertwigs Epithelial Root Sheath is not complete and leaves remnants of cells called the Cell Rests of Malassez. These are dormant cells with no function but may give rise to pathologies like tumors or cysts. In a fully developed tooth in the jaw, they are found in the periodontal ligament towards the cementum. As the degeneration of Hertwigs Epithelial Root Sheath occurs the Dental Sac come in direct contact with the dentin. This contact of the peripheral cells of dental sac with dentin, differentiates them in to Cementoblasts. these Cementoblasts in turn start depositing cementum. These histological steps in, Enamel Organ, Dental Papilla and Dental Sac during root formation, remains same in all teeth. Though The morphology or shape of Hertwigs Epithelial Root Sheath differs in single and multirooted teeth. The Hertwigs Epithelial Root Sheath bends and grows horizontally to form the epithelial diaphragm. This epithelial diphragm does not meet in the middle and so reduces the size of the cervical opening to form the apical foramen. In a single rooted tooth the cervical opening is one. But in multi-rooted tooth the epithelial diaphragm grows in extensions to form 2 or 3 cervical openings which give rise to multiple roots.