Oral Embryology Workbook Answers 2024 PDF

**Oral Embryology** **Biomedical Sciences, Year 1** Diagram Description automatically generated **Image source: Thesleff 2014** **Student name:** **\ ** **INTRODUCTION** Use this workbook to support your **self-directed study**, reading and learning for the content covered in the lectures on...

**Oral Embryology** **Biomedical Sciences, Year 1** Diagram Description automatically generated **Image source: Thesleff 2014** **Student name:** **\ ** **INTRODUCTION** Use this workbook to support your **self-directed study**, reading and learning for the content covered in the lectures on Oral Embryology. Answers will not be provided, refer to the lecture materials, reading and resources to find the answers. It is not essential to complete. Bring your questions to the consolidation session. **Lecture series, Workbook questions and Glossary of Terms**: +-----------------------------------+-----------------------------------+ | **Lectures** | **Questions** | +===================================+===================================+ | 1. Embryology of the head, face | 1-4 | | and oral cavity | | +-----------------------------------+-----------------------------------+ | 2. Embryology of the oral | 5-7 | | tissues | | +-----------------------------------+-----------------------------------+ | 3. Embryology of the crown | 8-15 | +-----------------------------------+-----------------------------------+ | 4. Embryology of the root | 16-23 | +-----------------------------------+-----------------------------------+ | 5. Embryology of eruption and | 24-31 | | exfoliation | | +-----------------------------------+-----------------------------------+ | 6. Consolidation session | See Moodle | +-----------------------------------+-----------------------------------+ | 7. Glossary of terms | End of document | +-----------------------------------+-----------------------------------+ **READING and RESOURCES:** **Textbook Reading**: - **Chapter 1, 5, 9, 10** of: Nanci, A. & Ten Cate, A.R., 2018. ***Ten Cate\'s oral histology : development, structure, and function.*** 9th edition / Antonio Nanci, PhD (McGill), PhD Honoris cause (University of Messina). - **Chapter 21, 22, 23, 24** of: Berkovitz, B. K. B., Holland, G. R., & Moxham, B. J. (2018). ***Oral anatomy, histology and embryology,** 5^th^ Ed*. Edinburgh: Mosby/Elsevier. **Resources Online:** - **Atlas of tooth development and eruption** -- essential guide to tooth development timeline: - **Digital laboratory oral histology**, slides 16-40 - **University of Michigan virtual laboratory** - **Embryology overview** [Embryonic Development - Embryology (unsw.edu.au)](https://embryology.med.unsw.edu.au/embryology/index.php?title=Embryonic_Development) **Videos:** - **Development of the Face**: ​ https://www.youtube.com/watch?v=FhhWG3XzARY​ - **Oral Tissue Development -- bud, cap, bell** - **Bud and Cap stage of Tooth Development:** - **Bell Stage: Embryology of the Crown**  ​ - Amelogenesis in detail - **Overview of Embryology of the Root** ​ - **Embryology of the root in detail** [[v=dEHv4BYfbBY&t=1s]](https://www.youtube.com/watch?v=dEHv4BYfbBY&t=1s) **Core articles:** - **Overview of oral embryology:** Magreni, A. and May, J. G. (2015) Embryology of the oral structures, *Operative Techniques in Otolaryngology-Head and Neck Surgery, *26 (3), pp. 110-114. DOI: [[https://doi.org/10.1016/j.otot.2015.06.002]](https://doi.org/10.1016/j.otot.2015.06.002). - **Overview of tooth development** 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]](https://doi.org/10.1111/adj.12102)  - **Overview of Enamel development (amelogenesis)** 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.​ - **Cleft Lip and Palate:** Vyas T, Gupta P, Kumar S, Gupta R, Gupta T, Singh HP. Cleft of lip and palate: A review. J Family Med Prim Care. 2020 Jun 30;9(6):2621-2625. doi: 10.4103/jfmpc.jfmpc\_472\_20. PMID: 32984097; PMCID: PMC7491837. **Optional articles** - **Eruptive tooth movement** Craddock HL, Youngson CC. Eruptive tooth movement\--the current state of knowledge. Br Dent J. 2004 Oct 9;197(7):385-91. doi: 10.1038/sj.bdj.4811712. PMID: 15475894. - **Critical review on the theories of tooth eruption:** Marks, S.C., Jr. and Schroeder, H.E. (1996), Tooth eruption: Theories and facts. Anat. Rec., 245: 374-393. [https://doi.org/10.1002/(SICI)1097-0185(199606)245:2\3.0.CO;2-M](https://doi.org/10.1002/(SICI)1097-0185(199606)245:2%3c374::AID-AR18%3e3.0.CO;2-M) - **A recent review of eruption theories:** Rabea, A.A., 2018. Recent advances in understanding theories of eruption (evidence based review article). *Future Dental Journal*, *4*(2), pp.189-196. - **Overview of tooth regeneration** Baranova, J., Büchner, D., Götz, W., Schulze, M., & Tobiasch, E. (2020). Tooth Formation: Are the Hardest Tissues of Human Body Hard to Regenerate?. *International journal of molecular sciences*, *21*(11), 4031. **Embryology of the head, face, and oral cavity** 1. What are the 3 key embryonic origins that give rise to all tissues in the body? - ectoderm - endoderm - mesoderm 2. Define the neural crest cells, where they come from and what tissues derive from these? - Neural crest cells are highly specialised cells in the head and neck of the embryo that can also migrate to. They give rise to cranial sensory ganglia and nerves, peripheral nervous system, ectomesenchyme 3. Complete the table for each key structure during embryogenesis +-----------------+-----------------+-----------------+-----------------+ | Structure | Brief | Timeline during | Clinical | | | description | Embryogenesis | significance | | | | | (if any) | +=================+=================+=================+=================+ | Zygote, Morula | Zygote -- | Early | If zygote not | | and Blastocyst | fertilised egg | embryogenesis | fertilised, | | | and sperm | week 1 | will not | | | | | progress any | | | Morula -- 16 | | further. | | | cells in | | | | | process of | | | | | embryo | | | | | development | | | | | | | | | | Blastocyst -- | | | | | 70-100 cells in | | | | | process of | | | | | embryo | | | | | development | | | | | (early) | | | +-----------------+-----------------+-----------------+-----------------+ | Trilaminar disc | Embryoblast | Early | If doesn't | | | (inside the | embryogenesis | differentiate | | | embryo) that | Weeks 2-3 | then will not | | | has | | progress any | | | differentiated | | further as | | | into 3 layers | | these are the | | | -- ectoderm, | | building blocks | | | mesoderm and | | | | | endoderm from | | | | | the bilaminar | | | | | disc | | | +-----------------+-----------------+-----------------+-----------------+ | Neural tube and | Neural tube -- | Early | Issues with | | neuroectoderm | this will give | embryogenesis | this stage will | | | rise to the | Weeks 3-4 | affect neural | | | neural system | | development and | | | -- brain, | | likely any | | | spinal cord | | further | | | forms from the | | progress of the | | | neural plate | | embryo | | | | | | | | Neuroetoderm -- | | | | | differentiates | | | | | from the | | | | | ectoderm of the | | | | | trilaminar | | | | | disc, gives | | | | | rise to the | | | | | neural system | | | | | and the neural | | | | | crest cells -- | | | | | highly | | | | | specialised | | | +-----------------+-----------------+-----------------+-----------------+ | Stomodeum and | Stomodeum -- | Week 4 | Problems at | | the Branchial | primitive mouth | | this stage lead | | Arches | (early mouth) | | to significant | | | in the head of | | defects | | | the embryo | | | | | | | | | | Branchial | | | | | arches -- 6 in | | | | | total, bulges | | | | | of cells that | | | | | give rise to | | | | | all structures | | | | | in head and | | | | | face and neck. | | | | | Each branchial | | | | | arch has its | | | | | own nerve and | | | | | blood supply | | | +-----------------+-----------------+-----------------+-----------------+ | Face | Fusion of 5 | Week 4-5 | Problems at | | | processes -- | | this stage will | | | frontonasal, 2x | Week 7 | lead to facial | | | maxillary and | | clefts and | | | 2x mandibular | | deformities. | | | to outline the | | | | | face | | | | | | | | | | Optic and nasal | | | | | placodes form | | | | | from the medial | | | | | nasal and | | | | | lateral nasal | | | | | processes where | | | | | the future eye | | | | | and nose will | | | | | form | | | | | | | | | | The mandibular | | | | | and maxillary | | | | | process form | | | | | into the jaw | | | | | bones by week 7 | | | | | | | | | | The face of the | | | | | embryo is | | | | | visible by week | | | | | 7, the | | | | | structure will | | | | | continue to | | | | | develop further | | | | | and become more | | | | | distinguished | | | +-----------------+-----------------+-----------------+-----------------+ | Palate and | Primary palate | Week 6-7 | Unusual for | | secondary | forms at the | | problems with | | palate | same time as | Week 7-8 | primary palate. | | | the face from | | | | | the | | More commonly | | | fusion(expandin | | cleft palate | | | g) | | results from | | | of the | | poor/limited | | | frontonasal | | fusion of the | | | process and the | | palatine | | | medial nasal | | shelves. This | | | process. | | is completely | | | | | treatable at | | | Secondary | | birth. | | | palate forms | | | | | from the | | | | | palatine | | | | | shelves, rather | | | | | than them | | | | | expanding out, | | | | | they are the | | | | | only bones to | | | | | true | | | | | fusion/joining | | | | | together at the | | | | | midline with | | | | | the nasal | | | | | septum. This is | | | | | why problems | | | | | can occur | | | | | (cleft palate) | | | | | as it doesn't | | | | | quite fuse | | | | | fully leaving a | | | | | hole (cleft) | | | | | | | | | | An incisive | | | | | foramen is | | | | | formed -- | | | | | future | | | | | relevance for | | | | | nerve | | | | | innervation of | | | | | the palate. | | | +-----------------+-----------------+-----------------+-----------------+ | Tongue | The tongue | Week 4-7 | Tongue tie | | | develops from | | | | | multiple | | Dental Local | | | branchial | | anaesthesia | | | arches meaning | | only | | | it will have | | anaesthetises | | | multiple nerve | | the anterior | | | supplies and | | 2/3 of the | | | blood supplies | | tongue meaning | | | -- significant | | that they may | | | for local | | feel things at | | | anaesthesia. | | the posterior | | | The dental | | 1/3 -- this is | | | nerve block | | normal. It is | | | anesthetises | | not usually | | | the anterior | | required to be | | | 2/3 of the | | anaesthetised | | | tongue only. | | for dental | | | Not usually a | | procedures. | | | problem but | | | | | some patients | | | | | may still feel | | | | | things at the | | | | | back of the | | | | | tongue | | | | | (posterior 1/3) | | | | | this is normal. | | | | | | | | | | The anterior | | | | | 2/3 is from the | | | | | 1^st^ branchial | | | | | arch -- the 2x | | | | | lingual and | | | | | tuberculum | | | | | impar. | | | | | | | | | | The posterior | | | | | 1/3 of the | | | | | tongue forms | | | | | from the | | | | | 2/3/4^th^ | | | | | branchial | | | | | arches -- the | | | | | copula/hypobran | | | | | chial | | | | | eminence. | | | | | | | | | | The tongue is | | | | | initially | | | | | attached to the | | | | | floor of the | | | | | mouth, cell | | | | | death enables | | | | | it to separate | | | | | -- it this | | | | | doesn't occur, | | | | | the tongue | | | | | remains | | | | | attached | | | | | (tongue-tie) | | | | | will result | | | | | that can be | | | | | picked up and | | | | | remedied at | | | | | birth | | | | | particularly | | | | | when a baby is | | | | | struggling to | | | | | suckle/feed. | | | +-----------------+-----------------+-----------------+-----------------+ | Cleft lip and | A result of a | Week 7-8 | Identification | | palate | failure to fuse | | and management | | | completely or | | early is key to | | | partially of | | babies | | | the palatine | | development as | | | shelves and the | | it affects | | | nasal septum. | | feeding, | | | | | hearing, speech | | | Can be uni | | and | | | lateral (1 | | development. | | | sided), | | | | | bilateral (both | | MDT's involved | | | sides), include | | in management. | | | the lip, | | Treatment in | | | palate, or | | the UK is | | | both. | | excellent. | | | | | | | | Most common | | Life long | | | facial cleft -- | | dental care | | | 1 in 700 live | | depending on | | | births in the | | severity -- | | | UK | | totally | | | | | manageable but | | | | | are at an | | | | | increased risk | | | | | of oral | | | | | diseases. | +-----------------+-----------------+-----------------+-----------------+ 4. Fill in the table from the selections below related to the **branchial arches**: Branchial Arches Innervation Muscles Artery Cartilage or bones ------------------ ------------------------------------------- --------------------------------------------- ------------------- ----------------------------------------------------------------- I Trigeminal nerve (cranial nerve V) Muscles of mastication 1st aortic arch Merkel's cartilage -- give rise to mandible and maxillary bones II Facial nerve (cranial nerve VII) Muscles of facial expression 2nd aortic arch Reichert's cartilage -- gives rise to part of hyoid bone III Glossopharyngeal nerve (cranial nerve IX) Stylopharyngeal muscle (used in swallowing) 3rd aortic arch No cartilage, part of hyoid bone IV Vagus nerve (cranial nerve X) Laryngeal muscles 4^th^ aortic arch Cartilages of the larynx V transient VI Not required to know Terms to be placed in the table above: mandible maxilla glossopharyngeal nerve trigeminal nerve ------------------------------ -------------------- ------------------------ ------------------ muscles of facial expression aortic arch 1 aortic arch 3 hyoid bone aortic arch 2 Merkel's cartilage Reichert's cartilage hyoid bone muscles of mastication malleus incur **Embryology of the Oral Tissues** 1. Name the **three embryonic origins (tissue layers)** that give rise to all the structures in the human body? Give an example organ for each. - ectoderm - endoderm - mesoderm 2. **Label the diagram** below using the labels listed -- these are the structures that we will be learning about how they form:  *enamel,* *dentine,* *pulp,* *alveolar bone,* *gingiva,* *periodontal ligament,* *cementum,* *apical foramen,* *apex of the tooth* **\ ** 3. The following diagrams: **7a-7d** reflect the stages of the development of teeth. Name the **stage, label the cells indicated by the arrows and select the purpose**: a. **Stage: dental lamina** **Label cells:** oral epithelium (OE), ectomesenchyme (E) and basement membrane (BM) **Select the purpose/function of stage:** a. The enamel organ forms from the oral epithelium and the underlying ectomesenchyme forms the dental papilla surrounded by the dental follicle b. **The dental lamina starts to form where oral epithelium thickens in a band at the same time as the vestibular lamina** c. The enamel organ deepens to determine the shape of the tooth, the cells differentiate ready for odontogenesis to take place d. The oral epithelium of the dental lamina start to proliferate into the underlying ectomesenchyme at specific sites**[\ ]** b.  DL ---- BM OE E **Stage: bud stage** **Label cells:** oral epithelial cells of the bud (OE), underlying ectomesenchyme (E), basement membrane separating the oral epithelial cells and ectomesenchyme cells (BM), dental lamina (DL) **Select the purpose/function of stage:** a. The enamel organ forms from the oral epithelium and the underlying ectomesenchyme forms the dental papilla surrounded by the dental follicle b. The dental lamina starts to form where oral epithelium thickens in a band at the same time as the vestibular lamina c. The enamel organ deepens to determine the shape of the tooth, the cells differentiate ready for odontogenesis to take place d. **The oral epithelium of the dental lamina start to proliferate into the underlying ectomesenchyme at specific sites that represent the future position of each tooth** c. OE ---- EO DP BM DF E **Stage: cap stage** **Label cells**: dental follicle (DF), enamel organ (EO), dental papilla (DP), underlying ectomesenchyme (E), basement membrane separating the enamel organ from the dental papilla (BM), oral epithelium (OE) **Select the purpose/function of stage:** a. **The enamel organ forms from the oral epithelium and the underlying ectomesenchyme forms the dental papilla surrounded by the dental follicle** b. The dental lamina starts to form where oral epithelium thickens in a band at the same time as the vestibular lamina c. The enamel organ deepens to determine the shape of the tooth, the cells differentiate ready for odontogenesis to take place d. The oral epithelium of the dental lamina start to proliferate into the underlying ectomesenchyme at specific sites **[\ ]** d.  SL ----- OEE IEE SR DP DF CL DS **Stage: bell stage** **Label cells**: dental sac (DS), dental follicle (DF), stellate reticulum (SR), dental papilla (DP), cervical loop (CL), successional lamina (SL), outer enamel epithelium (OEE), inner enamel epithelium (IEE) **Select the purpose/function of stage:** a. The enamel organ forms from the oral epithelium and the underlying ectomesenchyme forms the dental papilla surrounded by the dental follicle b. The dental lamina starts to form where oral epithelium thickens in a band at the same time as the vestibular lamina c. **The enamel organ deepens to determine the shape of the tooth, the cells differentiate ready for odontogenesis to take place** d. The oral epithelium of the dental lamina start to proliferate into the underlying ectomesenchyme at specific sites **Embryology of the Crown** 4. Place the cells into the appropriate section of the flow chart representing the differentiation pathway: **Pulpal cells, inner enamel epithelium (IEE), outer enamel epithelium (OEE), ameloblasts, stellate reticulum, stratum intermedium, pre-ameloblasts, pre-odontoblasts and odontoblasts**   Enamel organ​ - Outer enamel epithelial cells​ - Stratum intermedium​ - Stellate reticulum​ - Inner enamel epithelial cells​ - Pre-ameloblasts​ - Ameloblasts​ Dental papilla​ - Pre-odontoblasts​ - Odontoblasts​ - Pupal cells​   5. Label the following diagram in relation to the histological development of teeth: *Dental lamina, dental papilla, dental sac, outer enamel epithelium, cervical loop, ectomesenchymal cells, inner enamel epithelium, stratum intermedium, stellate reticulum, permanent tooth's successional lamina* C1 - Outer enamel epithelium ------------------------------- C2 -- Stellate reticulum C3 -- Stratum intermedium C4 -- inner enamel epithelium C5 -- cervical loop D -- dental sac E -- ectomesenchyme cells A1 -- dental lamina --------------------------- A2 -- successional lamina B -- dental papilla 6. **Number these stages in order of when they occur during the embryology of the crown** Order Stages ------- -------------------------------------------------------------------------------------- 8 Enamel matrix is laid down 5 Pre-dentine is laid down 4 Dentinogenesis starts at the future cusp tips 12 The enamel matrix is mineralized 9 The dentine matrix is mineralized 10 Stellate reticulum cells deflate 11 Stellate reticulum and stratum intermedium cells disappear 6 Pre-ameloblasts are triggered by dentine matrix to differentiate into ameloblasts 3 Pre-odontoblasts are triggered by pre-ameloblasts to differentiate into odontoblasts 7 Amelogenesis starts at the future cusp tips 2 The inner enamel epithelial cells differentiate into pre-ameloblasts 1 The outer periphery cells of the dental papilla differentiate into pre-odontoblasts 7. **The lifecycle of the ameloblast is:** a. limited to the time the tooth erupts b. limited to the time crown formation is complete c. limited to the life of the tooth d. **limited to the completion of the bell stage** 8. **The lifecycle of the odontoblast:** a. is complete by the time the tooth erupts b. is complete by the crown has formed c. **continues throughout the life of the tooth** d. continues until the pulp formation is complete 9. D**escribe the two stages of amelogenesis.** 10. **The formation of the pulp:** a. Takes place during crown formation and is complete before the tooth erupts b. Takes place after crown formation and is complete after the tooth erupts c. **Takes place during crown formation and is complete when the root is fully formed** d. Takes place before crown formation and is complete before the tooth erupts 11. Complete the table below: Features Amelogenesis Dentinogenesis ------------------------------------------------ ---------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------- Cell Ameloblast odontolblast Location it begins At the future dej At the future DEJ Pattern of formation waves Direction in relation to dental papilla Outwards/away from Inwards/towards When is it complete? Prior to tooth eruption secondary dentine formation is complete when root formation is complete -- after eruption Source of vascular supply none pulp Outcome of cell after crown formation complete Reduces to protective enamel epithelium and will never function again as an ameloblast Continues throughout life **\ Embryology of root and supporting structures** 12. **Identify** in the diagram below **the structures associated with the tooth root** -- these are the structures that we will be learning about how they form: see diagram above page 10 -- have a go at drawing your own tooth to include all the structures 13. Using your knowledge of cells involved in tooth development so far, what cells do you think form the structures identified above: e. Cell: Odontoblasts - dentine f. Cell: Cementoblasts - cementum g. Cell: Fibroblasts -- periodontal ligament fibres h. Cell: Osteoblasts -- alveolar bone (osteoclasts remodel it) i. Cell: Ectomesenchyme -- pulpal tissue of the roots 14. Label the cells in this diagram indicated by the lines, and the stage below: Enamel ----------------------------- Stellate reticulum Outer enamel epithelium OEE Ameloblasts Stratum intermedium Dentine --------------------------------------------------------------------------- Odontoblasts Ectomesenchyme of the pulp Inner enamel epithelium IEE Cervical loop HERS (combined inner and outer enamel epithelium after the cervical loop) Dental sac is the pink lining (ectomesenchyme) around the structure  **Stage:**...root formation **Label cells:** Dentine (D), Enamel (E), ectomesenchyme of the pulp, epithelial root sheath (HERS), OEE, IEE, dental sac, cervical loop, dental sac, odontoblasts, stratum intermedium, stellate reticulum **Select the single best answer:** 15. Dentinogenesis of the tooth root: a. **Continues in a similar process to dentinogensis of the crown** b. Is triggered by contact with enamel matrix laid down by the ameloblasts c. Is triggered by contact with cementum matrix laid down by the ~~ameloblasts~~ d. Is ~~complete~~ at the time the tooth erupts 16. Cementogensis is : a. **carried out by the cementoblasts that originate from the ectomesenchyme of the dental sac and likely hertwigs epithelial root sheath** b. a process whereby cementum matrix is laid down and then mineralized by ~~osteoblasts~~ c. ~~completed~~ when the cementoblasts reach the apical foramen d. is a process that forms the cementum and ~~dentine~~ of the tooth root 17. The periodontal ligament: a. Forms from the collagen fibres that are deposited by ~~cementoblasts~~ b. Creates the attachment of the tooth from the ~~root dentine~~ to the alveolar bone c. Formation is ~~triggered by HERS mapping out the shape~~ of the root d. **Formation is carried out by fibroblasts that differentiated from the dental sac** 18. Match the following words to the statements: j. Epithlial rests of Malazzez, remnants of HERS that have not disintegrated may be observed in the **[periodontal ligament]** may play a role in regeneration and cysts. k. Alveolar bone originates from the ectomesenchyme cells surrounding the [ **dental sac**]. l. Enamel pearls are a result of a disruption in the processes where residual **[IEE cells]** near the CEJ differentiate into ameloblast. m. The formation of the root continues after [ **active eruption**] is complete. e. 19. Make notes on the stages of root formation For example -- make notes about each label, where it differentiated from, what cell forms it, what structure it forms etc Diagram is showing the root formation -- write down all you know about each cell/structure -------------------------------------------------------------------------------------------- Epithelial cells rests of malassez -- inactive IEE in the PDL -- purpose unsure PDL Cementoblasts, cementum Dentine, odontoblasts Alveolar bone, osteoblasts HERS Dental follicle cells pulp A map of the world Description automatically generated with low confidence **[\ ]** **Embryology of eruption and exfoliation** 5. **Label** the cells indicated by the arrow associated with the enamel organ in the advanced bell stage - these cells will play a role in eruption too: *Stellate reticulum, stratum intermedium, ameloblasts, outer enamel epithelium* Labelled from top ------------------- OEE SI SR IEE  6. Using your knowledge of the ameloblast cell lifecycle, the role once **amleogenesis is complete** of the ameloblast is to: a. Mineralise the secreted enamel matrix b. **Reduce in size and from a protective layer with the remaining cells of the enamel organ** c. Undergo ~~apoptosis~~ along with the disappearing stellate reticulum d. Use its Tome's process to secrete enamel matrix - no as this occurs during amelogenesis not once it is complete e. Differentiate ~~into cementoblasts~~ to form the root **\ ** 7. **The eruption process of teeth...** **a)     Starts during the bell stage of tooth development** b)     Starts ~~after birth~~ for all the primary teeth c)     Starts once the root formation of a tooth is ~~complete~~ d)     Starts at ~~the same time~~ as the crown formation begins 8. **The reduced enamel epithelium...** a. Forms a protective layer over the tooth ~~root~~ during eruption b. Forms from ameloblasts ~~during~~ amelogenesis c. **Surrounds the developing tooth crown during eruption** d. Fuses with the oral epithelium to form the ~~periodontal attachment~~ with the tooth **Section 2b: *Questions post-session:*** 9. **The three phases of eruption include:** a. Primary eruption, permanent eruption and exfoliation b. **Pre-eruptive, active eruptive and post-eruptive** c. Crown formation, root formation and eruption d. Pre-eruptive, intraosseous and supraosseous 10. **The dento-gingival junction is important:** a. to protect the crown with the reduced enamel epithelium b. **to seal the oral cavity off to the internal environment** c. to enable eruption of the tooth d. to form the gingival sulcus with the ~~tooth root~~ 11. Drawing on your knowledge obtained during the oral embryology sessions, identify and describe the 4 stages of development happening in this diagram and label as many features as you can: Active eruption -- can see the cusp tip has pierced through the gingiva -------------------------------------------------------------------------------------------------------------------------------------------- Formation of the dento-gingival junction as the tooth erupts -- this is why **not** to probe erupting teeth you may interrupt this process Reduced enamel epithelium is protecting the erupting tooth from osteoclast activity Developing permanent successor in the bell stage Root formation continues of the tooth in active eruption Diagram Description automatically generated **\ ** 12. Have a good look at the radiographic image below...is there anything that does not look normal in terms of the eruption pattern of the teeth present? Make some notes on your thoughts and we will discuss. +-----------------------------------------------------------------------+ | **Horizontal bitewing left** | | | | **Upper teeth -- 23, 24, 25, 26 with DO amalgam, 27** | | | | **Lower teeth -- 33, 34 (deep occlusal pit), 75, 36** | | | | **It is strange that all permanent teeth appear to be fully erupted | | (completed active eruption) except for the remaining primary tooth | | indicating this patient is older eg adult, there does not appear to | | be a permanent successor in the furcation of the 75 indicating that | | it may be missing or in an odd position. Would need an OPG or PA to | | confirm presence/position of 35.** | | | | **The 75 is out of occlusion and does not appear to have a clear | | lamina dura between the roots and alveolar bone. Both these indicate | | that it is likely ankylosis of the 75. Refer to dentist/ortho for | | opinion ? monitor, ? xla (will be difficult if ankylosed) ? other.** | +-----------------------------------------------------------------------+ **[\ ]** **Glossary of terms** Fill in the table and add to it throughout your learning especially in embryology. It may also be useful for other areas of your learning helping to familiarise with dental terminology. I highly recommend you complete this yourself -- it will help with your understanding -- you can do it! Terminology Definitions Alternative terminology ------------- ------------- -------------------------