Embryology of the Crown PDF

Embryology of the Crown Lauren Stockham Biomedical Sciences, Year 1 Intended learning outcomes A"er the session students should be able to: Describe the processes of amelogenesis and den?nogenesis during the embryology of the crown Describe the cell lifecycles of the ameloblast and odonto...

Embryology of the Crown Lauren Stockham Biomedical Sciences, Year 1 Intended learning outcomes A"er the session students should be able to: Describe the processes of amelogenesis and den?nogenesis during the embryology of the crown Describe the cell lifecycles of the ameloblast and odontoblast Link the processes to the developmental ?meline and clinical signiBcance GDC Learning Outcomes: 1.1.5, 1.1.6  Embryology of the crown: Recap stages of tooth formaDon of development the Dssues within the tooth crown Stages: FuncDons: Image source: Thesleff 2014 Embryology of the Crown During the bell stage the speciGc Dssues of the tooth crown start to form, each with its own process. Embryology of the Crown Clinical Significance: Amelogenesis Dentinogenesis Pulp formation Disruption in the Processes processes can affect the quality or quantity of the tooth tissues Tissues within Enamel Dentine Coronal pulp formed thus have the tooth crown impacts on a persons oral health. Amelogenesis overview Amelogenesis is the process of enamel forma?on. There are 4 main stages: E 1. Presecretory D 2. Secretory 3. TransiDon 4. MaturaDon Shape Each stage is deGned by the morphology and func?on of the ameloblasts - the cells that form This Photo by Unknown Author is licensed under CC BY-SA-NC enamel. Cross-section of a premolar tooth showing the hard tissues of the crown – enamel (E) and dentine (D). 4 Stages of Amelogenesis Transition – stop secreting, Secretory – secret retract Tome’s enamel matrix Maturation – Pre-secretory – cell process harden the matrix differentiation Ameloblast cell Dento- enamel junction Source: Adapted from Bartlett 2013  Odontoblasts start to secrete dentine first before ameloblasts start to secrete enamel. Dentinogenesis starts before amelogeneis 1. Pre-secretory stage of amelogenesis The pre-secretory stage of amelogenesis relates to denDnogenesis: Specialist cells that form dentine -Odontoblasts secrete1 pre-denDne matrix Ameloblast Pre-denDne matrix mineralises Goes hard. - Pre- the basement membrane breaks down ameloblast the denDne contacts the pre-ameloblasts Pre-ameloblasts diQerenDate into ameloblasts ready to start amelogenesis. Pre-dentine mineralising Odontoblast Amelogenesis and denDnogenesis conDnue in parallel during embryology of the crown. Source: Adapted from Bartlett 2013  Ameloblasts develop Tomes’ process - this process secretes enamel matrix The secretion mechanism links Enamel - highly specialised and to the structure of enamel in 2. Secretory stage structured histology. The ameloblasts secrete enamel matrix in a highly specialised way during the secretory Ameloblast stage: The ameloblasts develop a Tomes’ process (like a tail) The Tomes’ process is what secretes of the enamel matrix Enamel Tomes’ matrix Enamel matrix is a mix of organic - process Pre- proteins and inorganic - crystal minerals dentine The ameloblasts move away from the matrix forming denDne in the opposite direc?on to the odontoblasts Source: Adapted from Bartlett 2013 3. Transi?on stage Stop secretion of enamel due to retracting of the Tomes’ process Once the ameloblasts reach the full thickness of enamel, they change during the transiDon stage. Change their shape by retracDng the Tomes’ process Retract Tomes’ Change their func?on by stopping the process secreDon of enamel matrix and shi"ing to maturing it. As a result of the transiDon, no more new enamel can be formed, now or ever. Enamel is only formed at formation of crown Source: Adapted from Bartlett 2013  Organic proteins and inorganic crystals Maturing stage by Organic proteins allow for inorganic 4. Matura?on Stage special proteins crystals to grow and harden and solidify. At this point, amelogenesis is complete The ameloblasts mineralise/harden the secreted enamel matrix to 96% during the maturaDon phase: It uses specialised proteins to harden it The inorganic crystals grow in size Amelogenesis is complete. The ameloblasts funcDon shiPs to a protec?ve stage ready for erupDon. Source: Adapted from Bartlett 2013 Den?nogenesis overview DenDnogenesis is the process of den?ne forma?on. It starts before amelogenesis E D It conDnues throughout life It is similar to the secretory and maturaDon stages of amelogenesis with some disDnct diQerences Odontoblasts are the cells that form denDne and conDnue to live throughout the life of This Photo by Unknown Author is licensed under CC BY-SA-NC the tooth. Cross-section of a premolar tooth showing the hard tissues of the crown – enamel (E) and dentine (D). Den?nogenesis Ameloblasts travel outwards The process of denDnogenesis: Ameloblasts on one side and odontoblasts on the other of basement membrane towards the tooth surface starts at the basement membrane – the future dento-enamel juncDon (DEJ) Dento- Odontoblasts secret pre-den?ne matrix largely 2. Enamel Matrix enamel of collagen junction 1. Dentine The pre-denDne matrix is mineralised/hardened in spheres to 70-75% inorganic Odontoblasts travel inwards Odontoblasts travel inwards, in the opposite towards the direc?on to the ameloblasts and eventually pulp end up at the border of the pulp. Diagram demonstrating the direction of travel of the ameloblasts and odontoblasts as indicated by the arrows. Odontoblasts Odontoblasts have a cytoplasmic extension Within dentinal tubules embedded into the predenDne and denDne called an odontoblast process. Clinical signiGcance: Odontoblasts live for the life of the tooth picks up sDmuli and sensaDons that trigger odontoblasts to form secondary and ter?ary den?ne Thus denDne is able to repair itself and form throughout life. Link to structure and Source: Wikimedia function of dentine. Odontoblast cell Coronal pulp forma?on During denDnogenesis, the ectomesenchyme cells in the central of the dental papilla form the pulp ?ssue in the crown – coronal pulp. Coronal pulp includes; Blood vessels, lymph Dssue, nerves, Gbroblasts, stem cells and collagen form. Image showing the developing tooth crown of a rodent, similar to humans. (SI – stratum intermedium, AM – ameloblasts, E – enamel matrix, D - denDne, PD - predenDne, O – odontoblasts, DP – dental pulp. Source: TreuDng et al 2018.  Link to Histology of PaSerns of forma?on Enamel and Dentine Amelogenesis and denDnogenesis start at the cusp ?ps and incisal edges of the future dento-enamel juncDon (DEJ). The cells conDnue to map out the full shape of the tooth crown as seen in images a-e. Repeated cycles of matrix secreDon and mineralisaDon occur creaDng incremental lines. These may be visible clinically if there is a disturbance during the process. Image showing the pacern of formaDon of enamel and denDne starDng at the cusp Dps (a) through to compleDon (e) (Brickley et al 2020) Timing of embryology of the crown Before tooth eruption After tooth eruption Enamel complete No more enamel forms Ameloblast adopts new Ameloblast lifecycle function to protect complete Primary dentine Secondary dentine complete forms slowly throughout Odontoblasts settle at life periphery of pulp Odontoblasts live at periphery of pulp Link this to the eruption timeline for teeth  What teeth are circled? Second molars Clinical signiBcance of ?ming How old is this patient? 8-9 Crowns still forming Image source: Bashar et al 2019 Orthopantomogram (OPG) radiograph showing the developing dentition.  Link to lectures on Disturbances in the processes developmental anomalies, staining and oral histology. Amelogenesis and denDnogenesis are very complex processes. Forming highly specialised tissues Disturbances can result in issues with 11 21 the quality or quanDty of enamel. These are called developmental anomalies. Examples include: Amelogenesis imperfecta Enamel hypomineralisaDon Low mineralisation Enamel hypomineralisaDon and hypoplasia, also Enamel hypoplasia Low tissue known as molar-incisor hypomineralisaDon (MIH) Image source: wikimedia Enamel forms before tooth erupts - ameloblasts so not live throughout live, unable to Fluorosis form new enamel, higher risk of oral diseases. Summary Up next: Embryology of Embryology of the the Crown Root. Process, patterns and Amelogenesis Dentinogenesis Pulp formation timings Cell functions and lifecycle Ameloblast Odontoblast Dental papilla Tissues formed and link to clinical Enamel Dentine Coronal pulp significance of disturbances in the process References ThesleQ I. (2014). Current understanding of the process of tooth formaDon: transfer from the laboratory to the clinic. Australian dental journal, 59 Suppl 1, 48–54. hcps://doi.org/10.1111/adj.12102 Bartlec JD. Dental enamel development: proteinases and their enamel matrix substrates. ISRN Dent. 2013 Sep 16;2013:684607. doi: 10.1155/2013/684607. PMID: 24159389; PMCID: PMC3789414. TreuDng, P.M., Morton, T.H. & Vogel, P. 2018, 7 - Oral Cavity and Teeth, Academic Press, San Diego. Wikimedia: hcp://upload.wikimedia.org/wikipedia/commons/d/dd/D_amelogenesis_imperf ecta.jpg Bashar AKM, Akter K, Chaudhary GK, et al. Primary molar with chronic periapical abscess showing atypical presentaDon of simultaneous extraoral and intraoral sinus tract with mulDple stomata. BMJ Case Reports CP 2019;12:e229039. Brickley, MB, Kahlon, B, D'Ortenzio, L. Using teeth as tools: InvesDgaDng the mother–infant dyad and developmental origins of health and disease hypothesis using vitamin D deGciency. Am J Phys Anthropol. 2020; 171: 342– 353. hcps://doi.org/10.1002/ajpa.23947 Lemmers, S. 2017, Stress, life history and dental development: a histological study of mandrills (Mandrillus sphinx). Thesis. Learning resources Reading list Workbook acDviDes Watch videos to recap Image source: Lemmers (2017). Watch video of the Bell stage: hcps://www.youtube.com/watch?v=74yika7GIpc Thank you! Image credit: Lauren Stockham