Embryology of the Crown PDF

Embryology of the Crown Lauren Stockham Biomedical Sciences, Year 1 Intended learning outcomes After the session students should be able to: Describe the processes of amelogenesis and dentinogenesis during the embryology of the crown Describe the cell lifecycles of the ameloblast and odon...

Embryology of the Crown Lauren Stockham Biomedical Sciences, Year 1 Intended learning outcomes After the session students should be able to: Describe the processes of amelogenesis and dentinogenesis during the embryology of the crown Describe the cell lifecycles of the ameloblast and odontoblast Link the processes to the developmental timeline and clinical significance GDC Learning Outcomes: 1.1.5, 1.1.6  Embryology of the crown: Recap stages of tooth formation of development the tissues within the tooth crown Stages: Functions: Image source: Thesleff 2014 Embryology of the Crown During the bell stage the specific tissues of the tooth crown start to form, each with its own process. Embryology of the Crown Clinical Significance: Disruption in the Processes Amelogenesis Dentinogenesis Pulp formation 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 formation. There are 4 main stages: E 1. Presecretory D 2. Secretory 3. Transition 4. Maturation Each stage is defined by the morphology and function 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 1. Pre-secretory stage of amelogenesis The pre-secretory stage of amelogenesis relates to dentinogenesis: Odontoblasts secrete pre-dentine matrix Ameloblast Pre-dentine matrix mineralises Pre- the basement membrane breaks down ameloblast the dentine contacts the pre-ameloblasts Pre-ameloblasts differentiate into ameloblasts ready to start amelogenesis. Pre-dentine mineralising Odontoblast Amelogenesis and dentinogenesis continue in parallel during embryology of the crown. Source: Adapted from Bartlett 2013  The secretion mechanism links to the structure of enamel in 2. Secretory stage 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 dentine in the opposite direction to the odontoblasts Source: Adapted from Bartlett 2013 3. Transition stage Once the ameloblasts reach the full thickness of enamel, they change during the transition stage. Change their shape by retracting the Tomes’ process Retract Tomes’ Change their function by stopping the process secretion of enamel matrix and shifting to maturing it. As a result of the transition, no more new enamel can be formed, now or ever. Source: Adapted from Bartlett 2013 4. Maturation Stage The ameloblasts mineralise/harden the secreted enamel matrix to 96% during the maturation phase: It uses specialised proteins to harden it The inorganic crystals grow in size Amelogenesis is complete. The ameloblasts function shifts to a protective stage ready for eruption. Source: Adapted from Bartlett 2013 Dentinogenesis overview Dentinogenesis is the process of dentine formation. It starts before amelogenesis E D It continues throughout life It is similar to the secretory and maturation stages of amelogenesis with some distinct differences Odontoblasts are the cells that form dentine and continue 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). Dentinogenesis Ameloblasts travel outwards The process of dentinogenesis: towards the tooth surface starts at the basement membrane – the future dento-enamel junction (DEJ) Dento- Odontoblasts secret pre-dentine matrix largely 2. Enamel Matrix enamel of collagen 1. Dentine junction The pre-dentine matrix is mineralised/hardened in spheres to 70-75% inorganic Odontoblasts travel inwards Odontoblasts travel inwards, in the opposite towards the direction 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 embedded into the predentine and dentine called an odontoblast process. Clinical significance: Odontoblasts live for the life of the tooth picks up stimuli and sensations that trigger odontoblasts to form secondary and tertiary dentine Thus dentine is able to repair itself and form throughout life. Link to structure and Source: Wikimedia function of dentine. Odontoblast cell Coronal pulp formation During dentinogenesis, the ectomesenchyme cells in the central of the dental papilla form the pulp tissue in the crown – coronal pulp. Blood vessels, lymph tissue, nerves, fibroblasts, 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 - dentine, PD - predentine, O – odontoblasts, DP – dental pulp. Source: Treuting et al 2018.  Link to Histology of Patterns of formation Enamel and Dentine Amelogenesis and dentinogenesis start at the cusp tips and incisal edges of the future dento-enamel junction (DEJ). The cells continue to map out the full shape of the tooth crown as seen in images a-e. Repeated cycles of matrix secretion and mineralisation occur creating incremental lines. These may be visible clinically if there is a disturbance during the process. Image showing the pattern of formation of enamel and dentine starting at the cusp tips (a) through to completion (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 Clinical significance of timing What teeth are circled? How old is this patient? 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 dentinogenesis are very complex processes. Disturbances can result in issues with the quality or quantity of enamel. These are called developmental anomalies. Examples include: Amelogenesis imperfecta Enamel hypomineralisation Enamel hypomineralisation and hypoplasia, also Enamel hypoplasia known as molar-incisor hypomineralisation (MIH) Image source: wikimedia Fluorosis 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 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 Bartlett 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. Treuting, P.M., Morton, T.H. & Vogel, P. 2018, 7 - Oral Cavity and Teeth, Academic Press, San Diego. Wikimedia: http://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 presentation of simultaneous extraoral and intraoral sinus tract with multiple stomata. BMJ Case Reports CP 2019;12:e229039. Brickley, MB, Kahlon, B, D'Ortenzio, L. Using teeth as tools: Investigating the mother–infant dyad and developmental origins of health and disease hypothesis using vitamin D deficiency. Am J Phys Anthropol. 2020; 171: 342– 353. https://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 activities Watch videos to recap Image source: Lemmers (2017). Watch video of the Bell stage: https://www.youtube.com/watch?v=74yika7GIpc Thank you! Image credit: Lauren Stockham