Chapter 7: Root Formation (Rhizagenesis) PDF

Chapiter VII Root Formation (Rhizagenesis) ROOT FORMATION (Hertwig’s epithelial root sheath) Dentin formation Cementum formation Alveolar Bone formation Periodontal ligament formation  Root formation Importantly, the tooth root is an essential element...

Chapiter VII Root Formation (Rhizagenesis) ROOT FORMATION (Hertwig’s epithelial root sheath) Dentin formation Cementum formation Alveolar Bone formation Periodontal ligament formation  Root formation Importantly, the tooth root is an essential element in the function of the dentition because it anchors teeth to the maxilla or mandible. Accordingly, the loss of roots leads to diminished bone support and, hence, perturbed tooth function. In addition, during mastication and resting states, the root helps transmit and balance occlusal forces through PDLs to the jaw bones and serves as a passageway for the neurovascular bundle that supplies blood flow, nutrition and sensation to our teeth. The development of the roots begins after enamel & dentin formation has reached the future cementoenamel junction. Root formation (Hertwig’s epithelial root sheath) The main tissues that contribute to root formation are the Hertwig’s epithelial root sheath (HERS), dental papilla, and dental follicle Root formation (Hertwig’s epithelial root sheath) The cervical loop The main tissues that contribute to root formation are the Hertwig’s epithelial root sheath (HERS), dental papilla, and dental follicle  Root formation (Hertwig’s epithelial root sheath) Upon completion of crown formation, the cervical loop cells continue to proliferate and become the HERS. The HERS extends toward the apex of the future root, enclosing the dental papilla, while continuously interacting with the surrounding ectomesenchymal cells. Ectomesenchymal cells of the dental papilla adjacent to the inner layer of the HERS undergo differentiation into odontoblasts and form the root dentin.  Root formation (Hertwig’s epithelial root sheath) The HERS is also important for cementum and PDL formation: As root formation progresses, the dental follicle cells come in contact with the HERS while the HERS itself becomes perforated into a mesh network structure. This allows the dental follicle cells to come in contact with the root dentin surface and induces them to differentiate into cementoblasts, which produce cementum matrix proteins, and fibroblasts, which produce the PDL. In addition, some HERS- derived cells differentiate into cementocytes. Further on, the HERS rapidly disintegrates and becomes small clusters of epithelial cells, known as the epithelial cell rests of Malassez (ERM). Dentin formation Dentin is a pale-yellow substance that is the major component of the tooth hard structure overing the dental pulp. At the beginning of root development, the two layers of the HERS form before the appearance of root dentin. Cementum formation The tooth root is covered by cementum on its surface and is stabilized by periodontal ligament fibers, which are embedded in both the cementum and alveolar bone. Cementum formation Alveolar Bone Formation Alveolar bone is formed by intramembranous bone formation during the formation of the mandible and maxilla. Alveolar bone actually consists of two components: alveolar process of the two jaws, the maxilla, and mandible alveolar bone proper. Alveolar Bone Formation Alveolar process: This bony structure forms to house the developing tooth buds and, once erupted, the roots of the teeth. It provides structural support for the dentition. Alveolar bone proper: is the portion of bone that lines the tooth socket. It provides an attachment site for the periodontal ligament and its associated tooth.  Periodontium Formation Periodontal ligaments are derived from the dental follicle. The initiation of dental ligament formation begins at the stage when HERS interruption is detectable Cementum formation After interacting with the HERS, pro- fibroblasts migrate to the root surface and alveolar bone surface. The tiny and short collagen fibers attach to the root surface and grow into the periodontal space. The fibers embedded in the cementum are called Sharpey’s fibers. The arrangement of these fibers at the early root developmental stage is disordered. Later, the fibroblasts, pre-fibroblasts and stem cells in the dental follicle are activated and the fibers grow thick and well-organized. These strong fibers are important for linking the root and alveolar bone and to stabilize the tooth in the alveolar bone securely for the function of mastication.