Development of the Root and Periodontium PDF

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WARNING This material has been reproduced and communicated to you by or on behalf of Charles Sturt University in accordance with section 113P of the Copyright Act 1968 (Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. Do not remove this notice Development of the root and periodontium Dr Michelle Kang BDS (Otago), DClinDent (Oral Med), MRACDS (Oral Med) Acknowledgement of Country We would like to acknowledge the Wiradjuri, Ngunawal, Gundungarra and Biripai (or Biripi) peoples of Australia, who are the traditional owners and custodians of the lands on which CSU's campuses are located, and pay respect to their Elders both past and present. 3 DOH 115 session 2 planned outline Introduction to oral embryology Orofacial embryology Odontogenesis - early tooth development Amelogenesis Dentinogenesis Development of the root and periodontium Revision/catch up session Mid-session break Surface anatomy of the oral cavity Oral Mucosa Salivary glands The temporomandibular joint and introduction to occlusion Functional anatomy of the oral cavity Revision/catch up session 4 Learning outcomes Be able to use discipline-specific terminology to describe and identify the macroscopic and microscopic features of the teeth, oral tissues and related structures and their functions Be able to apply the knowledge of anatomy, histology, and embryology to explain, discuss, and identify the macroscopic and microscopic features, functions and development of oral and related tissues 5 Contents Root development: overview Epithelial root sheath of Hertwig Cementogenesis and root dentinogenesis Periodontal ligament (PDL) Neurovascular development Alveolar bone development Alveolar bone and cementum: comparison Clinical considerations 6 Root development: overview 7 https://www.youtube.com/watch?v=SCP38MrccsI (from 7:30 to 8:51) 8  Root development: overview Interaction between: 1. Dental follicle (dental sac) 2. Dental papilla 3. Epithelial root sheath of Hertwig (derived from cervical loop region of enamel organ) Davis, E. M. (2018). A Review of the Epithelial Cell Rests of Malassez on the Bicentennial of Their Description. Journal of Veterinary Dentistry, 35(4), 290-298. 9 Root development: overview Root development starts after crown development has commenced Once crown formation is complete, the external and internal enamel epithelium at the cervical loop of the enamel organ extends downwards -> forms a double-layered epithelial root sheath of Hertwig Epithelial root sheath proliferates -> forms shape of future root 10 Root development: overview Berkovitz, B. K. B., Holland, G. R., & Moxham, B. J. (2009). Oral anatomy, When a permanent tooth erupts in the histology and embryology (Fourth mouth, the amount of root present varies edition.). Mosby. (up to ½ of final root length) A wide open root apex is present, surrounded by a thin dentine Chakraborty, A., Dey, B., Dhar, R., & Sardar, P. (2012). Healing of apical Time for root development completion rarefaction of three nonvital open apex after tooth eruption: anterior teeth using a white portland cement Permanent tooth: around 3 more years apical plug. Contemporary Deciduous tooth: around 1.5 more clinical dentistry, 3(Suppl years 2), S177. 11 Epithelial root sheath of Hertwig 12 Epithelial root sheath of Hertwig Epithelial root sheath grows to enclose the dental papilla, except for an opening at the base (primary apical foramen) Berkovitz, B. K. B., Holland, G. R., & Moxham, B. J. (2009). Oral anatomy, histology and embryology (Fourth edition.). Mosby. 13 Epithelial root sheath of Hertwig Continuous sheet of tissue, between the dental papilla (internally) and dental follicle (externally). Separated from both by a basement membrane Epithelial root sheath: no stellate reticulum or stratum intermedium layer between the 2 epithelial layers (unlike the cervical loop region in the crown enamel organ) Occasional presence of stellate reticulum and stratum intermedium in the root -> may give rise to areas of enamel on the root surface (e.g. enamel pearls) Dental follicle (lies external to the root sheath) forms cementum, periodontal ligament and likely alveolar bone 14 Epithelial root sheath of Hertwig Cells of the internal layer of the epithelial root sheath -> induce the peripheral cells of the dental papilla to differentiate into odontoblasts Once dentinogenesis has commenced, the root sheath epithelial cells lose their continuity -> become separated from the surface of the developing root dentine Dental follicle cells differentiate into cementoblast-like cells -> cementogenesis commences Primary (acellular) cementum formed Berkovitz, B. K. B., Holland, G. R., & Moxham, B. J. (2009). Oral 15 anatomy, histology and embryology (Fourth edition.). Mosby. Epithelial root sheath of Hertwig Epithelial remnants are retained, and form epithelial rests of Malassez seen in the periodontal ligament (PDL) Note: Epithelial rests of Serres are epithelial remnants in gingiva (epithelial remnants when the dental lamina connection between stomodeum and enamel organ degenerates) Berkovitz, B. K. B., Holland, G. R., & Moxham, B. J. (2009). Oral 16 anatomy, histology and embryology (Fourth edition.). Mosby. Cementogenesis and root dentinogenesis 17 Cementogenesis and root dentinogenesis Cementogenesis is initiated at the cervical margin -> extends apically, as the root grows downwards Epithelial root sheath of Hertwig induces the adjacent dental papilla cells to differentiate -> into odontoblasts As these odontoblasts retreat inwards, they synthesis and secrete the root predentine matrix (ground substance, collagen fibrils) Mineralisation of the first-formed dentine occurs, spreads both inwards towards the pulp and also outwards toward the PDL 18 Cementogenesis Cells of the inner layer of the dental follicle differentiate into cementoblasts -> these form initial layer of primary (acellular) cementum on the surface of root dentine Primary (acellular) cementum Collagen: derived from periodontal ligament, passing into the cementum approximately perpendicular to the surface Also secretion of non-collagenous proteins (e.g. osteopontin, cementum-attached protein, bone sialoprotein), cytokines, growth hormones Cementoblasts: little contribution to extracellular matrix of the tissue Berkovitz, B. K. B., Holland, G. R., & Moxham, B. J. (2009). Oral 19 anatomy, histology and embryology (Fourth edition.). Mosby. Cementogenesis Primary (acellular) cementum Slow increase in thickness Approx 2μm throughout life Established continuity between principal collagen fibres of the PDL and those at the surface of the root dentine Required for tooth to be supported within the socket Continued slow mineralisation of collagen at the root surface Usually no evidence of a precementum layer Berkovitz, B. K. B., Holland, G. R., & Moxham, B. J. (2009). Oral 20 anatomy, histology and embryology (Fourth edition.). Mosby. Cementogenesis Primary (acellular) cementum Cementogenesis occurs rhythmically: periods of activity alternating with quiescent periods Structural lines may be visible within the tissue Incremental lines= associated with decreased activity periods Berkovitz, B. K. B., Holland, G. R., & Moxham, B. J. (2009). Oral anatomy, histology and embryology (Fourth edition.). Mosby. 21 Cementogenesis Secondary (cellular) cementum Following the formation of primary/acellular cementum in the cervical portion of the root, secondary (cellular) cementum appears in the apical region of the root (at around the time of tooth eruption) Cementoblasts: form distinct layer of cuboidal cells -> secrete collagen parallel to the surface, forming the cementum matrix Berkovitz, B. K. B., Holland, G. R., & Moxham, B. J. (2009). Oral 22 anatomy, histology and embryology (Fourth edition.). Mosby. Cementogenesis Secondary (cellular) cementum Once cementogenesis has begun, cells of the remaining dental follicle becomes obliquely orientated along the root surface -> becomes the fibroblasts of the periodontal ligament These fibroblasts secrete collagen of the PDL -> becomes embedded as Sharpey’s fibres, into the primary (acellular) cementum and into the developing alveolar bone Berkovitz, B. K. B., Holland, G. R., & Moxham, B. J. (2009). Oral 23 anatomy, histology and embryology (Fourth edition.). Mosby. Cementogenesis Secondary (cellular) cementum Formation of an unmineralized precementum layer (approx. 5μm thick) on the surface of cellular cementum Mineralisation of the deeper layer of precementum occurs Cementoblasts incorporated into the forming matrix -> converted into cementocytes Generation of new cementoblasts from stem cells/precursors within the PDL Incremental lines more widely spaced compared to primary acellular cementum (due to increased rate of formation) Berkovitz, B. K. B., Holland, G. R., & Moxham, B. J. (2009). Oral 24 anatomy, histology and embryology (Fourth edition.). Mosby. Periodontal ligament 25 Periodontal ligament: cell development With onset of root formation, the dental follicle cells show an increase in cytoplasmic organelles (especially those associated with protein synthesis and secretion) -> extracellular spaces fill with collagen and ground substance Dental follicle cells give rise to: cementoblasts, fibroblasts, osteoblasts of the periodontal ligament Increase in number of these cells during root and PDL formation Osteoclasts also appears in the developing PDL, at the alveolar bone surface -> allows bone to remodel, in association with tooth eruption and bone growth 26 Neurovascular development 27 Neurovascular development With root formation and tooth eruption, nerves adjacent to the bone grow into the PDL (usually accompanying blood vessels) Initial nerves: autonomic Sensory innervation: established later, fully organized after tooth eruption Blood vessels- derived from different sources: Enter from periapical area -> pass upwards within the ligament -> forms anastomoses with vessels entering from the adjacent developing alveolar bone As the tooth erupts -> receives vessels from adjacent gingiva 28 Alveolar bone development 29 Alveolar bone development Mandible and maxilla alveolar bone-> intramembranous bone formation Centre of ossification forms where osteoblasts lay down embryonic/woven bone Alveolus is separated from the developing enamel organ by the dental follicle To accommodate space for the growing tooth germs: Alveolar bone lamellae: undergoes resorption on the inner wall of the alveolus Alveolus outer wall: bone is deposited by osteoblasts -> teeth lie in a trough of bone 30 Alveolar bone development Teeth are later separated from each other by development of interdental septa Woven bone is later converted to adult lamellar bone With tooth eruption, the bone overlying the tooth undergoes resorption -> provides eruption pathway 31 Alveolar bone vs cementum 32 Alveolar bone and cementum: comparison Alveolar bone Secondary cellular cementum Composition Inorganic component Inorganic component - Small hydroxyapatite crystals - Small hydroxyapatite crystals Organic components Organic components - Type I collagen fibres (mostly) - Type I collagen fibres (mostly) - Noncollagenous content - Noncollagenous content (cementum has e.g. unique cementum attachment protein) Mineralisation Lag phase in mineralisation Lag phase in mineralisation - Surface is lined by layer of unmineralized - Surface is lined by layer of unmineralized matrix matrix Cells 3 cell types 3 cell types - Osteocytes - Cementocytes - Osteoblasts - Cementoblasts - Osteoclasts - Odontoclasts 33 Alveolar bone and cementum: comparison Alveolar bone Secondary cellular cementum Remodeling/ Continuous bone remodeling throughout Resorption= rarer, more localised resorption life Neurovascular Has blood vessels, nerves, marrow spaces Nil 34 Clinical considerations Enamel pearls Isolated enamel spheres, occasionally found on root surface More common in root bifurcation area Speculated that in the affected region, stellate reticulum and stratum intermedium develop between the internal and external enamel epithelia 35 Further reading Berkovitz, B. K. B., Holland, G. R., & Moxham, B. J. (2009). Oral anatomy, histology and embryology (Fourth edition.). Mosby. 36 End of lecture