Embryology of the Root GN PDF

Embryology of the Root and Suppor5ng Structures Lauren Stockham Biomedical Sciences, Year 1 Intended learning outcomes A"er this session students should be able to: Describe the processes involved in the embryology of the root Describe the establishment of a@achment of the tooth to its supp...

Embryology of the Root and Suppor5ng Structures Lauren Stockham Biomedical Sciences, Year 1 Intended learning outcomes A"er this session students should be able to: Describe the processes involved in the embryology of the root Describe the establishment of a@achment of the tooth to its suppor5ng structures Link the processes to the developmental 5meline and clinical signiBcance GDC Learning Outcomes: 1.1.5, 1.1.6  Embryology of the root: Recap stages of tooth formaCon of development the tooth root and supporCng structures Stages: FuncCons: Image source: Thesleff 2014  Embryology of the root and suppor5ng structures ADer the bell stage and embryology of the crown, the speciHc Cssues of the tooth root and supporCng 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  The same time the root is forming, the surrounding bone is also forming Adj to osteoblasts in centre, where actomesenchyme cells Overview of embryology of the root of dental papilla will be forming dental pulp of root - radicular pulp The embryology of the root and supporCng 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 junc5on (CEJ) and conCnues to the apical foramen. It conCnues aDer ac5ve tooth erup5on 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 Cme 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. b Also known as cervical margin At base of crown It consists of the inner and outer enamel epithelium although does not diUerenCate any further. It is surrounded by the dental follicle (sac) and encompasses the dental papilla as the pulp conCnues to form. For protection The cervical loop that elongates and bends to form Hertwig’s Epithelial Root Sheath. Hertwig’s epithelial root sheath Knows moropholy of different teeth - how many roots In folds are created to form multiple roots The epithelial root sheath is able to determine the speciHc shape of each tooths’ root, whether single root or mul5-rooted. It creates in-folds for mulCple 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). Den5nogenesis of the root DenCne formaCon of the root: Hertwig’s epithelial root sheath signals the conCnuaCon of denintogenesis The odontoblasts conCnue to form denCne along the root sheath consistent with the crown Ensured consistency with crown This process conCnues 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 DenCnogenesis of the root starCng at the cervical loop conCnuous with the denCne of the crown. Den5nogenesis of the root The formaCon of the supporCng structures is signalled a"er denCnogenesis of the root has started: The pre-denCne contacts and triggers the epithelial root sheath to As not needed anymore disintegrate The cells of the dental sac contact the pre-denCne insCgaCng the diReren5a5on of the cementoblasts and Hbroblasts to start forming cementum and the periodontal DisintegraCon of the epithelial root sheath a"er ligament. contact with pre-denCne during denCnogenesis of the root.  No cells 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 conCnues throughout life, similar to denCne and bone. Cementum is a hard tissue - is mineralised Cross-secCon of the periodonCum showing the relaConship between root denCne, cementum, periodontal ligament and alveolar bone. Cementogenesis Cementum plays a key role in the a@achment of the tooth to the alveolar socket. During cementogenesis: Collagen Bbres in the cementum matrix embed into the root den5ne forming the cemento-denCne juncCon (CDJ) Collagen Hbres from the forming periodontal ligament embed within the cementum supporCng aZachment to the Sharpey’s fibres alveolar bone Some cementoblasts embed within the Cross-secCon of the periodonCum showing cementum matrix to form cementocytes the relaConship between root denCne, Not form cementum anymore but living within cementum tissue cementum, periodontal ligament and alveolar bone. Periodontal ligament forma5on Cells within the dental sac diUerenCate into Bbroblast cells to form the periodontal ligament alongside cementogenesis. At same time as cementogenesis Collagen Hbres from the periodontal ligament embed into cementum and alveolar bone forming the tooth’s clinical a@achment. -Base of crown This process starts at the cervical loop, the future cemento-enamel juncCon, and conCnues Developing tooth root showing the aZachment of Hbroblasts to form the future periodontal ligament. for the full length of the root. Alveolar bone Forming around tooth Sharpeys fibres - part of connection from alveolar bone to the cementum through the peridoontal ligament Ectomesenchymal cells surrounding the dental sac will diUerenCate 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 aZachment (Omi and Mishina 2022)  What teeth are circled? Clinical signiBcance of 5ming Developing successors Note that the 36 is erupted but the roots are still developing – what does this tell about the significance of root formation? Present in mouth but roots still developing 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 conCnues to form in the root. IniCally they canals are very wide and open and slowly narrow over Cme (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.  No adjacent odontoblasts to form the dentine - creates space/defect in dentine tubule Accessory root canals If the conCnuity of the epithelial root sheath breaks before the denCne is able to form along the root, the adjacent odontoblasts are not able to form denCne resulCng in a defect in the denCnal tubule through to the pulp. This creates an accessory root canal. This has clinical signiBcance for root canal treatments and periodontal treatments 3D image showing accessory root canals (Ahmed et al 2018). resulCng in possible perio-endo lesions. Epithelial rests of Malassez As the epithelial root sheath disintegrates, remnants may be le" adjacent to the root surface. These are evident later on in the periodontal ligament known as Epithelial Rests of Malassez. Clinical signiBcance has been linked to periodontal cysts, and a potenCal role in Histological view of developing tooth root periodontal repair and regeneraCon. showing epithelial rests of malassez (ERM) (Source: Davis 2018). Anomalies: Enamel pearls May result from remanets of the inner enamel epithelium that can diUerenCate into ameloblasts to form enamel pearls parCcularly at the Cemento-enamel juncCon and in furcaCon areas. Clinical signiBcance in the treatment of periodontal disease. This Photo by Unknown Author is licensed under CC BY-SA-NC Enamel pearl in furcaCon area of fused roots of a molar tooth. Ques5on: 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 diUerenCate from inner enamel epithelium So why not in the root? Ameloblasts not present? Think back to the cell diUerenCaCon 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 supporCng structures: DenCnogenesis of the root denCne Radicular pulp formaCon in root canals Cementogenesis Periodontal ligament formaCon Alveolar bone formaCon Image Source: Stock images Clinical implicaCons and Cming. AcCve erupCon of a volcano. Up next: Embryology of ErupCon and exfoliaCon Learning Resources Reading list Workbook Watch this detailed descripCon of the processes hZps://www.youtube.com/watch? v=dEHv4BYfBY&t=1s References ThesleU I. (2014). Current understanding of the process of tooth formaCon: transfer from the laboratory to the clinic. Australian dental journal, 59 Suppl 1, 48–54. hZps://doi.org/10.1111/adj.12102 Ahmed, HMA, Neelakantan, P, Dummer, PMH. A new system for classifying accessory canal morphology. Interna5onal Endodon5c 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. hZps://doi.org/10.1002/dvg.23490 Davis, E.M. (2018). A Review of the Epithelial Cell Rests of Malassez on the Bicentennial of Their DescripCon. Journal of Veterinary Den5stry, 35, 290 - 298. Bashar AKM, Akter K, Chaudhary GK, et al. Primary molar with chronic periapical abscess showing atypical presentaCon of simultaneous extraoral and intraoral sinus tract with mulCple stomata. BMJ Case Reports CP 2019;12:e229039.