Embryology of Oral Tissues - Student Notes PDF

Embryology of oral tissues Tutor: Lauren Stockham Module: Biomedical Sciences Year 1 Intended Learning Outcomes By the end of the session, students will be able to: Describe the stages of development of the teeth and oral mucosa Link the structures of the teeth and oral mucosa to their embr...

Embryology of oral tissues Tutor: Lauren Stockham Module: Biomedical Sciences Year 1 Intended Learning Outcomes By the end of the session, students will be able to: Describe the stages of development of the teeth and oral mucosa Link the structures of the teeth and oral mucosa to their embryonic origins Link the stages of development to the embryonic timeline Recognise the clinical significance of oral embryology GDC Learning Outcomes: 1.1.5, 1.1.6 WHY do we need to learn this? Identify healthy Identify abnormal Diagnose Prevent disease Manage disease and Materials and Preventive advice Maintain oral health healing medicaments If we understand how the oral tissues; teeth, gingiva and supporting structures; are formed, then we can support, maintain and restore oral health effectively.  More detail in Different Recap the Oral Tissues Dentitions and Histology lectures in Oral Dental Sciences. The teeth Enamel – surrounds the crown Dentine – bulk of the crown and root Cementum – surrounds the root Periodontal ligament – connects the root to the alveolar bone Pulp – inside of the tooth Alveolar bone – holds the teeth in place The oral mucosa – the soft tissue lining of This Photo by Unknown Author is licensed under CC BY https://philschatz.com/anatomy- the oral cavity, lamina propria and the book/resources/2409_Tooth.jpg gingiva. Embryonic origins and link to oral structures Ectoderm Neural crest cells Oral epithelial Ectomesenchyme cells cells Periodontal Ameloblasts Oral mucosa Lamina propria Pulp Cementum ligament Alveolar bone Odontoblasts Enamel Dentine Comparison of cell Oral epithelial cells are characteristics – Ectomesenchymal cells highly organised link to the are soft and jelly-like cells forming a compactly tissues formed. loosely arranged with structured tissue layer. intercellular substance.  Complexity of embryology of oral tissues The oral tissues form in the stomadeum of the embryo from a complex set of processes that include: Interactions between the epithelial cells (ectoderm) and the ectomesenchyme (neural crest cells) >300 genes determine the progress of development Signals between the cells and genes mediate the process The basis of our understanding so far comes from studying animal and human embryos, fetuses and infants. Morphological aspects - 150 years, Image of coding and signals Mechanisms regulating development - 50 years representing the complexity of processes in embryogenesis. There remains a lot to be discovered and understood. Research is continuing today with stem cells in tooth regeneration. Dental Lamina, Bud, Cap and Bell stage Stages and functions of oral tissue development  Stages of tooth development Stages: Functions: Image credit: Thesleff 2014 Stages of tooth development in 3D Video: Watch first without sound, a second time with sound, repeat as you require. Link to video: https://www.youtube.com/watch?v=t3hR2YGdqWk Initiation: The dental lamina, Week 6-7 The oral epithelial cells in the mandibular and maxilla prominences form the primary epithelial band. In week 7 this then divides into: The dental lamina The vestibular lamina The dental lamina extends to follow the outline of the developing dental arches. Link this back to the development of the face Image adapted: Magreni and May 2015 to visualise the where the dental lamina is Showing site of the dental lamina forming. developing in the future mandibular dental arch. Initiation: The vestibular lamina, Week 7 The vestibular lamina forms adjacent to the dental lamina. It will give rise to the vestibule (space between the teeth and lip) of the oral cavity. The basement membrane separates the two cell layers of oral epithelium and the ectomesenchyme – this membrane is key for facilitating messages/interactions during the tooth development process. Oral epithelial cells Basement membrane Future lip DL VL Underlying ectomesenchymal cells Image source: UnivNantes Vertical cross-section of the vestibular lamina (VL) and the dental lamina (DL) – now try and visualise this in your own mouth. Initiation: The dental lamina, Week 8 The dental lamina forms a series of epithelial swellings known as dental placodes that will give rise to each tooth. These placodes are surrounded by ectomesenchyme cells. The interactions between the oral epithelial cells of the dental placode and the underlying ectomesenchyme cells via the basement membrane will initiate the next stage of tooth development. Showing the dental lamina and dental placode. Image adapted: Theself 2014. The Bud stage, Week 9-10 The oral epithelial cells of the dental placode proliferate to form a bud. The bud presses into the underlying ectomesenchyme forming the enamel organ. The enamel organ will give rise to a tooth with one enamel organ per tooth. Image source: UnivNantes The bud forming in the dental lamina that will eventually give rise to a tooth. The Cap stage, Week 11 The enamel organ changes shape by hollowing out at the bottom surface to resemble a cap. DF In the hollow, ectomesenchymal cells proliferate rapidly to form the dental papilla (DP). DP Surrounding the dental papilla and enamel organ, ectomesenchymal cells proliferate more to form the dental Image source: UnivNantes follicle (DF). The bud has turned into a cap shape allowing a hollow for the dental papilla (DP). The enamel organ is surrounded by the dental follicle (DF). Morphogenesis: the bud and the cap stage The transition between the bud and cap stages is signified by morphogenesis – the development of morphological characteristics – in this case the tooth crown’s morphology (shape) starts to form. The enamel knot is a key signaling center enabling morphogenesis of the cusp shape and outline. Morphogenesis continues up to the bell stage. Image: Theself 2014.  What tooth crown is visible? HINT: the The Bell stage first tooth to erupt is B also the first tooth to form. The enamel organ changes shape further by hollowing out and extending to map the full size and shape of the tooth crown (A) including the occlusal and cusp details. A The enamel organ separates from the dental lamina (B). The bell stage has 2 parts: Image source: UnivNantes The early bell stage The cap has turned into a bell shape and is separated from the dental lamina (B). The outline of the crown is now The late bell stage visible in vertical cross-section (A). Histo-differentiation: Bell stage Histodifferentiation (cell differentiation) takes place in the bell stage where the cells within the enamel organ and the dental papilla differentiate into different cell types ready to form the different tissue structures of the tooth. This will be discussed in further detail in Embryology of the Crown. Image: Theself 2014.  Early Bell Stage: cell differentiation pathway Enamel organ Dental papilla Outer enamel Stratum Stellate Inner enamel Pre- Pupal cells epithelial cells intermedium reticulum epithelial cells odontoblasts Key points: Pre- Odontoblasts What cells make up the enamel organ and the ameloblasts dental papilla? Link their characteristics to the structure of the respective tissues formed. What do you think the role of ameloblasts and Ameloblasts odontoblasts will be? HINT: Slide 5  Early Bell Stage: Enamel organ Image showing a histological vertical section of an enamel organ in the bell stage. Oral epithelial cells in the enamel organ differentiate into: Outer enamel epithelium (OEE) - cuboidal cells along the periphery – these will play a key role in the eruption process Stellate reticulum (SR) - star shape cells on the inside of the outer enamel epithelium – play a key role in facilitating amelogenesis OEE SR Stratum intermedium (SI) - flattened cells layer on SI the inside of the inner enamel epithelium – play a key IEE role in facilitating amelogenesis Inner enamel epithelium (IEE) - tall columnar cells along the inside – these will eventually differentiate This Photo by Unknown Author is licensed under CC BY-SA into ameloblasts http://www.wikidoc.org/images/6/66/Toothhistology11-17-05.jpg Early Bell Stage: Dental papilla Image showing a histological vertical section of an enamel organ in the bell stage. The ectomesenchyme cells in the dental papilla differentiate into: Odontoblasts (O) (from pre-odontoblasts) along the periphery of the dental papilla – these carry out dentinogenesis. Pulpal cells (P) in the centre of the dental papilla that will eventually become the pulp O P of the tooth This Photo by Unknown Author is licensed under CC BY-SA http://www.wikidoc.org/images/6/66/Toothhistology11-17-05.jpg Late bell stage Ameologensis After cellular differentiation the enamel organ is Dentinogenesis ready to undergo crown formation (odontogenesis). Crown formation includes: Amelogenesis - formation of enamel by ameloblasts Dentinogenesis - formation of dentine by odontoblasts Image source: UnivNantes →More detail will be discussed in the next The enamel organ in the late bell stage undergoing session ‘Embryology of the Crown’. amelogenesis to form enamel and dentinogenesis to form dentine. Development of the oral mucosa The oral mucosa lines the oral cavity. Oral epithelial cells The oral epithelial cells in the vestibular lamina (VL) and lingual regions (LR) undergo proliferation, migration and differentiation according to the future function of the structure LR of the oral mucosa including: VL masticatory, lining and Ectomesenchyme specialized mucosa such as gingiva. The underlying ectomesenchymal cells give rise Vertical cross-section of the vestibular lamina (VL), to the lamina propria (connective tissue) and dental lamina and lingual region (LR). submucosa. Development of the Oral Mucosa cross-section Image credit: Michigan Histology and Virtual Microscopic Learning Reources, https://histology.medicine.umich.edu/resources/oral-cavity Histological slide showing a vertical cross-section of the developing oral cavity including the lip, tooth, oral mucosa and hard and soft palates. Timeline of eruption and Developmental anomalies Clinical significance Timeline of primary dentition development Late bell stage Bell stage complete Bell stage for permanent teeth Eruption Images adapted from: AlQahtani et al (2010)  More to come in Oral Developmental anomalies Dental Science and Year 2. Developmental anomalies may result from interruptions (environmental or genetic) in each stage of tooth development. Supernumerary (extra) teeth – extra bud Missing teeth – no initiation Shape of crown – the cap and early bell stage Quality of the crown – bell stage The impact can range from none to significant, This Photo by Unknown Author is licensed under CC BY https://static- 01.hindawi.com/articles/crid/volume-2013/614807/figures/614807.fig.001.jpg therefore additional care may be required. Clinical image showing two permanent teeth Link back to the origami folds – any wrong fold supernumeraries; an anomalie at the initiation or order of folds may affect the final size, shape stage. or quality of the developing tooth/teeth. Links to future learning: Histology of oral tissues (enamel, dentine, gingiva etc) – structure and function Histopathology of oral diseases – dental caries, periodontal diseases etc Developmental anomalies → Ultimately links to your day to day work as Clinical image showing a developmental anomaly an effective clinician known as enamel hypoplasia – note the appearance of enamel is not smooth. (Patel et al 2019) Summary Bud Overview of the process of the development of teeth and oral mucosa: the stages of tooth development the embryological origins Cap Timings of stages in relation to the embryonic timeline Clinical significance This provides the basis for the next session Bell where we will explore the late bell stage in more detail – the embryology of the crown. Images showing the bud cap and bell reflected in the spring season of flowers forming. Images credit: Lauren Stockham Learning resources: 1. Workbook activities 2. Oral embryology reading list and online resources 3. Videos Watch first without sound Watch a second time with sound https://www.youtube.com/watch?v=WjM3-ymWb3I Watch more as you need and pause along the way Image and video references Colors Paper, 2018. DIY Paper Flowers easy making tutorial (Origami Flower) – paper craft ideas. YouTube. Available online: https://youtu.be/nVauFzCx0rg Accessed 02/08/23. AlQahtani S J, Liversidge H M, Hector M P (2010). Atlas of tooth development and eruption. American Journal of Physical Anthropology 142(3):481-90. Thesleff, I. (2014), Current understanding of the process of tooth formation: transfer from the laboratory to the clinic. Aust Dent J, 59: 48-54. https://doi.org/10.1111/adj.12102 Patel, A., Aghababaie, S. & Parekh, S. Hypomineralisation or hypoplasia?. Br Dent J 227, 683–686 (2019). https://doi.org/10.1038/s41415-019-0782-9 UniNantes, 2016. Tooth Development – crown formation. YouTube. Online: https://www.youtube.com/watch?v=t3hR2YGdqWk Accessed 03/08/23. Analogy: Egg to Chick Process of egg to hatchling is complex just like the process for humans. Video link: https://www.youtube.com/watch?v=ozMPRSZ8Ykk Thank you! Image credit: Lauren Stockham