Embryology of the Root PDF

Embryology of the Root and Supporting Structures Lauren Stockham Biomedical Sciences, Year 1 Intended learning outcomes After this session students should be able to: Describe the processes involved in the embryology of the root Describe the establishment of attachment of the tooth to its s...

Embryology of the Root and Supporting Structures Lauren Stockham Biomedical Sciences, Year 1 Intended learning outcomes After this session students should be able to: Describe the processes involved in the embryology of the root Describe the establishment of attachment of the tooth to its supporting structures Link the processes to the developmental timeline and clinical significance GDC Learning Outcomes: 1.1.5, 1.1.6  Embryology of the root: Recap stages of tooth formation of development the tooth root and supporting structures Stages: Functions: Image source: Thesleff 2014  Embryology of the root and supporting structures After the bell stage and embryology of the crown, the specific tissues of the tooth root and supporting structures start to form. Embryology of the Root Processes Formation of the Dentinogenesis Pulp formation Cementogenesis Periodontal Osteogenesis ligament Tissues of the root and Periodontal Root dentine Radicular pulp Cementum Alveolar bone ligament supporting structures Overview of embryology of the root The embryology of the root and supporting structures begins once the embryology of the crown is complete. It starts at the base of the developed crown, the site of the future cemento- enamel junction (CEJ) and continues to the apical foramen. It continues after active tooth eruption is complete. Diagram showing the developing tooth root (Matalova et al 2015). 3D video of processes involved in embryology of the root Watch once without sound, a second time with sound https://www.youtube.com/watch?v=5Mi4AX50LO0 Hertwig’s epithelial root sheath Hertwig’s epithelial root sheath (HERS) forms from the cervical loop and maps out the shape of the root. It consists of the inner and outer enamel epithelium although does not differentiate any further. It is surrounded by the dental follicle (sac) and encompasses the dental papilla as the pulp continues to form. The cervical loop that elongates and bends to form Hertwig’s Epithelial Root Sheath. Hertwig’s epithelial root sheath The epithelial root sheath is able to determine the specific shape of each tooths’ root, whether single root or multi-rooted. It creates in-folds for multiple roots as it extends to the apical foramen. Diagram showing the infolds of the epithelial root sheath to create multiple roots (Li et al 2017). Dentinogenesis of the root Dentine formation of the root: Hertwig’s epithelial root sheath signals the continuation of denintogenesis The odontoblasts continue to form dentine along the root sheath consistent with the crown This process continues to the apical foramen The process is the same as in the crown The radicular pulp forms from the dental papilla within the root canals Dentinogenesis of the root starting at the cervical loop continuous with the dentine of the crown. Dentinogenesis of the root The formation of the supporting structures is signalled after dentinogenesis of the root has started: The pre-dentine contacts and triggers the epithelial root sheath to disintegrate The cells of the dental sac contact the pre-dentine instigating the differentiation of the cementoblasts and fibroblasts to start forming cementum and the periodontal Disintegration of the epithelial root sheath after ligament. contact with pre-dentine during dentinogenesis of the root. Cementogenesis Cementogenesis is the process of forming cementum that covers the root surface. It is conducted by cementoblasts that originate from cells of the dental sac. A cementum matrix is laid down, then part mineralised and continues throughout life, similar to dentine and bone. Cross-section of the periodontium showing the relationship between root dentine, cementum, periodontal ligament and alveolar bone. Cementogenesis Cementum plays a key role in the attachment of the tooth to the alveolar socket. During cementogenesis: Collagen fibres in the cementum matrix embed into the root dentine forming the cemento-dentine junction (CDJ) Collagen fibres from the forming periodontal ligament embed within the cementum supporting attachment to the alveolar bone Some cementoblasts embed within the Cross-section of the periodontium showing cementum matrix to form cementocytes the relationship between root dentine, cementum, periodontal ligament and alveolar bone. Periodontal ligament formation Cells within the dental sac differentiate into fibroblast cells to form the periodontal ligament alongside cementogenesis. Collagen fibres from the periodontal ligament embed into cementum and alveolar bone forming the tooth’s clinical attachment. This process starts at the cervical loop, the future cemento-enamel junction, and continues Developing tooth root showing the attachment of fibroblasts to form the future periodontal ligament. for the full length of the root. Alveolar bone Ectomesenchymal cells surrounding the dental sac will differentiate into osetoblasts and osteoclasts to form alveolar bone in a similar way that osteoblasts form other types of bone.  Refer to bone embryology Diagram showing the developing alveolar bone around developing and histology for more details tooth and its role in attachment (Omi and Mishina 2022) Clinical significance of timing What teeth are circled? Note that the 36 is erupted but the roots are still developing – what does this tell about the significance of root formation? Image source: Bashar et al 2019 Orthopantomogram (OPG) radiograph showing the developing dentition. Apical foramen and root canals Link to pulp inflammation, tooth eruption and calcification timelines. The apical foramen forms at the base of the root (not necessarily in the centre) enabling the main pathway for blood vessels, nerves and lymph vessels to supply the pulp of the tooth. Pulpal root canals are spaces where the radicular Root pulp continues to form in the root. Initially they canals are very wide and open and slowly narrow over time (years). Apical foramen The wide-open canals partly explains why it may be possible for a young tooth to survive pulpal injury. Diagrams showing pulpal root canals and apical foramen. Accessory root canals If the continuity of the epithelial root sheath breaks before the dentine is able to form along the root, the adjacent odontoblasts are not able to form dentine resulting in a defect in the dentinal tubule through to the pulp. This creates an accessory root canal. This has clinical significance for root canal treatments and periodontal treatments 3D image showing accessory root canals (Ahmed et al 2018). resulting in possible perio-endo lesions. 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 known as Epithelial Rests of Malassez. Clinical significance has been linked to periodontal cysts, and a potential role in Histological view of developing tooth root periodontal repair and regeneration. showing epithelial rests of malassez (ERM) (Source: Davis 2018). Anomalies: Enamel pearls May result from remanets of the inner enamel epithelium that can differentiate into ameloblasts to form enamel pearls particularly at the Cemento-enamel junction and in furcation areas. Clinical significance in the treatment of periodontal disease. This Photo by Unknown Author is licensed under CC BY-SA-NC Enamel pearl in furcation area of fused roots of a molar tooth. Question: Why doesn’t enamel form on the tooth root? (apart from enamel pearls) Hertwigs epithelial root sheath consists of outer and inner enamel epithelium In embryology of the crown, ameloblasts differentiate from inner enamel epithelium So why not in the root? Think back to the cell differentiation of the enamel organ and all the layers, compare to the layers present in the epithelial root sheath. Summary Embryology of the root and its supporting structures: Dentinogenesis of the root dentine Radicular pulp formation in root canals Cementogenesis Periodontal ligament formation Alveolar bone formation Image Source: Stock images Clinical implications and timing. Active eruption of a volcano. Up next: Embryology of Eruption and exfoliation Learning Resources Reading list Workbook Watch this detailed description of the processes https://www.youtube.com/watch? v=dEHv4BYfbBY&t=1s References Thesleff I. (2014). Current understanding of the process of tooth formation: transfer from the laboratory to the clinic. Australian dental journal, 59 Suppl 1, 48–54. https://doi.org/10.1111/adj.12102 Ahmed, HMA, Neelakantan, P, Dummer, PMH. A new system for classifying accessory canal morphology. International Endodontic Journal, 51, 164– 176, 2018. Matalová, E., Lungová, V. & Sharpe, P. 2015, Chapter 26 - Development of Tooth and Associated Structures, Academic Press, Boston. Omi, M., & Mishina, Y. (2022). Roles of osteoclasts in alveolar bone remodeling. genesis, e23490. https://doi.org/10.1002/dvg.23490 Davis, E.M. (2018). A Review of the Epithelial Cell Rests of Malassez on the Bicentennial of Their Description. Journal of Veterinary Dentistry, 35, 290 - 298. Bashar AKM, Akter K, Chaudhary GK, et al. Primary molar with chronic periapical abscess showing atypical presentation of simultaneous extraoral and intraoral sinus tract with multiple stomata. BMJ Case Reports CP 2019;12:e229039.