Embryology of the Root PDF

Embryology; Root  Embryology of the root = Formation of the tooth root and supporting structures Dentinogenesis Pulp formation Cementogenesis Fo...

Embryology; Root  Embryology of the root = Formation of the tooth root and supporting structures Dentinogenesis Pulp formation Cementogenesis Formation of PDL Osteogenesis Periodontal Root dentine Radicular pulp Cementum Alveolar bone ligament Overview of root embryology Starts at base of developed crown, the future cemento-enamel Embryology of the root and junction (CEJ). supporting structures Continues to apical foramen and continues after active tooth beings once embryology of eruption. the crown is complete. Hertwig’s epithelial root sheath (HERS) Forms from cervical loop/margin and maps out the shape of the root (for protection). Consists of inner and outer enamel epithelium however it does not differentiate any further. Surrounded by dental follicle (sac), and enclose dental papilla as pulp continues to form. Determine specific shape of each tooth, single or multi rooted, and creates in-folds for multi rooted teeth as it extends apically. Dentinogenesis of the root Hertwig’s epithelial root sheath signals for the continuation of dentinogenesis. Odontoblasts continue to form dentine along the epithelial root sheath, consistent with the crown and to the apical foramen. The dentinogenesis process is the same as in the crown. Formation of supporting structures is signalled after dentinogenesis of the root has started. Pre-dentine contacts and triggers Hertwig’s epithelial root sheath to disintegrate. Cells of the dental sac then contact the pre-dentine to instigate differentiation of cementoblasts and fibroblasts to start forming cementum and periodontal ligament. Cementogenesis Conducted by cementoblasts that originate from dental sac cells. Formation of cementum that covers the root surface, key role in attachment of the tooth to the alveolar bone. Cementum matrix is laid down, and then part mineralised and continues throughout life (similar to dentine and bone). Collagen fibres within cementum matrix embed into root dentine to form cemento-dentine junction (CDJ). Some cementoblasts embed within cementum matrix to form cementocytes. Periodontal ligament formation Cells within dental sac differentiate into fibroblasts. Fibroblasts form the periodontal ligament at the same time as cementogenesis. Collagen fibres from forming periodontal ligament embed into cementum and alveolar bone to form the tooth’s clinical attachment - (Sharpey’s fibres). Starts at the cervical loop (base of the crown), future cemento- enamel junction (CEJ), and continues for the full length of tooth. Alveolar bone Ectomesenchymal cells surrounding the dental sac differentiate into osteoblasts and osteoclasts. These form alveolar bone in a similar way to other types of bone. Sharpey’s fibres form part of the connection from alveolar bone to the cementum through the periodontal ligament. Radicular pulp formation in root canals Apical foramen forms at the base of the root. Enables pathway for blood, nerve, lymph vessel to supply to tooth. Pulpal root canals are spaces where the radicular pulp continues to form. Initally very wide, but over time (years) slowly narrow. Clinical implications: Accessory root canals If the epithelial root sheath breaks before the dentine is formed along the root, the adjacent Odontoblasts are unable to form dentine. Results in a defect in the dentinal tubule through to the pulp - creates accessory root canal. Clinical significance for periodontal and root canal treatments. Epithelial rests of Malassez As the epithelial root sheath disintegrates, remnants may be left adjacent to the root surface. These are evident later on in the periodontal ligament. Clinical significance linked to periodontal cysts and potential role in periodontal repair and regeneration. Enamel pearls Results from remnants of the inner enamel epithelium (differentiate into ameloblasts) to form enamel pearls. Usually at cemento-enamel junction and in furcation areas. Clinical significance is linked to periodontal disease.