Embryology of Tooth Eruption and Exfoliation PDF

Embryology of tooth erup0on and exfolia0on Learning Outcomes  Describe the three phases of tooth erup0on  Describe how the dento-gingival junc0on originates  Describe the process of tooth exfolia0on  Outline the theories of tooth erup0on  Be able to link the processes to the develop...

Embryology of tooth erup0on and exfolia0on Learning Outcomes  Describe the three phases of tooth erup0on  Describe how the dento-gingival junc0on originates  Describe the process of tooth exfolia0on  Outline the theories of tooth erup0on  Be able to link the processes to the developmental 0meline of teeth and to erup0on and exfolia0on ages for each tooth 2 Select the single best answer: The erup0on process of teeth: a) Begins in early childhood around 6 months of age b) Begins before birth and con0nues throughout life c) Is completed when all teeth are present in the mouth d) Is completed once all the primary teeth erupt 3 Select the single best answer: The erup0on process of teeth: a) Begins in early childhood around 6 months of age – this is part of the ac0ve erup0on phase, there are erup0ve processes that start much earlier b) Begins before birth and con0nues throughout life c) Is completed when all teeth are present in the mouth – con0nues aFer the teeth have appeared in the mouth d) Is completed once all the primary teeth erupt – the permanent den00on erupts aFer the primary den00on 4 Erup0on of teeth  The erup0on process of teeth is a con0nuous process that occurs throughout life that begins during early embryological development  It involves three phases  It begins once the tooth crown development is complete during the bell stage and alongside root development so although the Grst tooth is visible in the oral cavity around 6 months of age, the process begins much earlier  It is a mul0-factorial process not en0rely understood where there are various theories that A histological sec0on of an erup0ng lower incisor and the developing permanent successor – what stage of explain how it occurs development is the successor based on its shape? Bell Stage 5 Lets re@ect on why we need to know this? Provides the physiological founda0on of oral health advice for:  ‘teething’ for parents  wobbly teeth for children and parents  ‘wisdom’ teeth erup0ng Be able to clinically dis0nguish normal and abnormal tooth erup0on and exfolia0on for example: Photo showing the lower  Iden0fy a supernumerary tooth jaw of a child with a  Iden0fy a missing tooth wobbly front tooth.  Refer for orthodon0cs 6 DeEni0ons  Erup0on is the physiological movement of teeth from their developmental posi0on in the alveolar bone through the soF 0ssues to its posi0on of func0on in the oral cavity. The process of erup0on has three phases.  Exfolia0on is the physiological resorp0on of primary teeth un0l they Gif showing eruption and are lost (they exfoliate). exfoliation of a mandibular permanent premolar and its primary predecessor respectively. 7 Embryological links to erup0on and exfolia0on  Begins during the bell stage  Ameloblasts, cells of the enamel organ, osteoclasts, odontoclasts and oral epithelium play a role  Underpinning knowledge explains the various theories on the mechanisms of the erup0ng tooth 8 Clinical links to erup0on and exfolia0on The developmental 0meline during embryology follows into life with the erup0on 0meline that is ESSENTIAL to iden0fy the presence and posi0on of:  Missing teeth  Supernumerary teeth  Crowding of teeth and orthodon0c referral Clinical image showing an ectopically erupting UL3 with an over-retained ULC 9 Workbook ac0vity  Complete Sec0on 1, Ques0on 1-2, to recap your exis0ng knowledge of embryology relevant for tooth erup0on. 10  Three phases of the erup0on process Histological Example. A outlines the phases of eruption, B shows the histological perspective of each 11 1. The pre-erup0ve phase  The movement of the developing tooth within the alveolar bone un0l crown forma0on is complete  This movement starts during the bell stage remodelling the bony crypt to allow more space for the developing tooth 12 2. Ac0ve erup0on phase  The movement of teeth through the alveolar bone (intraosseous) then the soM 0ssue (supraosseous) to the oral cavity This phase starts around the enamel  similar 0me as root forma0on and con0nues un0l the tooth reaches occlusion (remember root forma0on con0nues aFer this phase) 13 3. Post-erup0ve phase  The movement of teeth aMer ac0ve erup0on to maintain occlusion and compensate for occlusal and proximal tooth wear as well as growth  This movement occurs through out life such as when an opposing tooth is removed 14 Single best answer: The erup0on process of teeth… a) Starts during the bell stage of tooth development b) Starts aFer birth for all the primary teeth c) Starts once the root forma0on of a tooth is complete d) Starts at the same 0me as the crown forma0on begins 15 Ac0ve erup0on phase in more detail Diagrams showing the ac0ve erup0ve phase 17  Phase Active Eruption The role of the Reduced Enamel Epithelium Once amelogenesis is complete, the ameloblasts shrink and combine with the outer enamel epithelium, stratum intermedium and any residual stellate re0culum forming the reduced enamel epithelium It func0ons to:  Protect the developing tooth crown  Fuse with oral epithelium crea0ng an erup0on pathway  Form the dento-gingival junc0on – an essen0al seal Vertical cross-section of the cusp tip of an incisor during the pre-eruptive phase Needs protection because tooth needs to move through bone, bone is broken down my osteoclast. If no protection the crown of tooth could also be broken 18 down. The erup0on pathway  The bone overlying the developing crown is resorbed by osteoclasts (and odontoclasts of predecessor teeth)  This allows a pathway for movement that is ini0ated by complex signaling of the cells  The reduced enamel epithelium protects the tooth crown from the osteoclasts and the odontoclasts 19 The erup0on pathway  The reduced enamel epithelium fuses with oral epithelium to create an erup0on pathway  There are no blood vessels or nerves present yet  S0mula0on of and trauma occurs to ectomesenchyme to enable to fusion  This fusion forms a seal that prevents exposure of the underlying Fusion of the oral epithelium ectomesenchyme and haemorrhage and reduced enamel epithelium 20 Forma0on of the dento-gingival junc0on and sulcus  As the tooth breaks through the oral epithlium, the reduced enamel epithelium and oral epithelium (now combined) form the dento-gingival junc0on sealing the external oral cavity o\ from the rest of the body  It also forms a shallow trough that will create the gingival sulcus  This junc0on has clinical signiEcance for periodontal disease and the long A tooth erupting through the junc0onal epithelium of the gingiva gingiva and forming the dento- gingival junction 21 Rate of erup0ve movement  Movement through bone is slow = 1-10um/day  Movement through soF 0ssue is faster = 75um/day un0l occlusion reached  Muscular forces of the tongue, cheek, lips guide the tooth into posi0on  Sustained force of 4-5g is required – any habits that you can think of? *thumb sucking *dummy 22 Single best answer The reduced enamel epithelium: a) Forms a protec0ve layer over the tooth root during erup0on b) Forms from ameloblasts during amelogenesis c) Surrounds the developing tooth crown during erup0on d) Fuses with the oral epithelium to form the periodontal adachment with the tooth 23 Exfolia0on (shedding) of primary teeth  As the permanent successor teeth develop (posi0oned lingually), they increase in size and start the erup0ve phases  This signals the exfolia0on of the primary teeth where odontoclasts slowly resorb the roots of the primary teeth up to its crown that remains largely intact  Mas0catory forces also contribute to the exfolia0on process by applying pressure  The padern is usually the same thus any varia0ons are a key indicator of abnormali0es clinically A ground section of an exfoliating tooth and an erupting permanent 25 successor So how does the tooth actually erupt? We do not really know... There are various theories that adempt to explain this process. Research is ongoing in this area. 26 Root forma0on theory  The tooth crown is elevated by the thrust of root development  Refuted since erup0on occurs throughout life and root development does not Rocket launching analogy for root formation pressure 27 Bone re-modelling  It is unsure whether bone resorp0on and deposi0on cause teeth to erupt OR whether this is an e\ect  It is not the only mechanism, it is believed that it is modulated by the dental follicle Histological section of alveolar bone surrounding the developing tooth 28 Dental follicle theory  Signals between the dental follicle and the reduced enamel epithelium have been found to induce bone re-modelling  This may explain the consistency of erup0on 0mes as linked to the lifecycle of ameloblasts  A – enamel organ  B - dental papilla  C – dental follicle A histological section of a tooth in the bell 29 stage Periodontal ligament theory  The power of the forma0on of the periodontal ligament by Gbroblasts is thought to contribute to the movement in tooth erup0on  This is refuted similar to the root forma0on theory 30 Formation of the periodontal ligament Molecular determinants of tooth erup0on Various molecules are thought to be involved in the complex process of tooth erup0on each playing a di\erent role. There are also more recent theories under inves0ga0on including bite forces on the soF 0ssues and neuromuscular forces 31 Summary The erup0on and exfolia0on processes are complex and mul0-factorial, we have discussed:  The three phases of erup0on  The ac0ve phase in detail  How the phases link to embryological development  Outline of the theories of erup0on More detail and the clinical applica0on will be discussed further in Oral Biology. 32  EASTMAN DENTAL HOSPITAL EDUCATION CENTRE DENTAL HYGIENE & DENTAL THERAPY Embryology of Erup>on and Exfolia>on Teamwork Improving Kindness Safety Student name: 1  EASTMAN DENTAL HOSPITAL EDUCATION CENTRE DENTAL HYGIENE & DENTAL THERAPY INTRODUCTION This workbook is to be used in conjunc3on with your lecture and powerpoint on the Embryology of Erup3on and Exfolia3on. Sec>on 1: Ques3on 1-2 Sec>on 2: a) Ques3on 3-4 b) Ques3on 5-6 Sec>on 3: a) Ques3on 7 b) Ques3on 8 Sec>on 4: Ques3on 9 Sec>on 5: Glossary of Terms Learning resources and reading: Textbook Reading:  Chapter 10 of: Nanci, A. & Ten Cate, A.R., 2018. Ten Cate's oral histology: development, structure, and func:on. 9th edi3on / Antonio Nanci, PhD (McGill), PhD Honoris cause (University of Messina). Ar>cles:  Erup>ve tooth movement Craddock HL, Youngson CC. Erup3ve 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.  Cri>cal review on the theories of tooth erup>on: Marks, S.C., Jr. and Schroeder, H.E. (1996), Tooth erup3on: Theories and facts. Anat. Rec., 245: 374-393. hbps://doi.org/10.1002/(SICI)1097- 0185(199606)245:23.0.CO;2-M  A recent review of erup>on theories: Rabea, A.A., 2018. Recent advances in understanding theories of erup3on (evidence based review ar3cle). Future Dental Journal, 4(2), pp.189-196. hbps://doi.org/10.1016/j.fdj.2018.05.001 2  EASTMAN DENTAL HOSPITAL EDUCATION CENTRE DENTAL HYGIENE & DENTAL THERAPY Online:  Atlas of tooth development and erup3on – useful guide to erup3on 3meline: hbps://www.qmul.ac.uk/den3stry/atlas/  Digital laboratory oral histology, slides 31-33 hbp://www.uky.edu/~brmacp/oralhist/module3/lab/oh3main.htm Lecturer: Miss Lauren Stockham [email protected] 3  EASTMAN DENTAL HOSPITAL EDUCATION CENTRE DENTAL HYGIENE & DENTAL THERAPY Sec>on 1: Link embryological knowledge to the erup>on process of teeth: 1. Label the cells indicated by the arrow associated with the enamel organ in the advanced bell stage - these cells will play a role in erup3on too: Stellate re:culum, stratum intermedium, ameloblasts, outer enamel epithelium 2. 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 protec3ve layer with the remaining cells of the enamel organ c. Undergo apoptosis along with the disappearing stellate re3culum d. Use its Tome’s process to secrete enamel matrix e. Dikeren3ate into cementoblasts to form the root 4  EASTMAN DENTAL HOSPITAL EDUCATION CENTRE DENTAL HYGIENE & DENTAL THERAPY Sec>on 2a: Ques%ons during the session: 3. The erup>on process of teeth… a) Starts during the bell stage of tooth development b) Starts aler birth for all the primary teeth c) Starts once the root forma3on of a tooth is complete d) Starts at the same 3me as the crown forma3on begins 4. The reduced enamel epithelium… a) Forms a protec3ve layer over the tooth root during erup3on b) Forms from ameloblasts during amelogenesis c) Surrounds the developing tooth crown during erup3on d) Fuses with the oral epithelium to form the periodontal abachment with the tooth Sec>on 2b: Ques%ons post-session: 5. The three phases of erup>on include: a) Primary erup3on, permanent erup3on and exfolia3on b) Pre-erup3ve, ac3ve erup3ve and post-erup3ve c) Crown forma3on, root forma3on and erup3on d) Pre-erup3ve, intraosseous and supraosseous 6. The dento-gingival junc>on is important: a) to protect the crown with the reduced enamel epithelium b) to seal the oral cavity ok to the internal environment c) to enable erup3on of the tooth d) to form the gingival sulcus with the tooth root Addi>onal notes to support your learning: 5  EASTMAN DENTAL HOSPITAL EDUCATION CENTRE DENTAL HYGIENE & DENTAL THERAPY Sec>on 3: Consolida>ng your knowledge and understanding 7. Drawing on your knowledge obtained during the oral embryology sessions, iden3fy and describe the 4 stages of development happening in this diagram and label as many features as you can: Stages: … … Label features: … … 6  EASTMAN DENTAL HOSPITAL EDUCATION CENTRE DENTAL HYGIENE & DENTAL THERAPY Sec>on 3b: Clinical applica>on 8. Have a good look at the radiographic image below…is there anything that does not look normal in terms of the erup3on pabern of the teeth present? Make some notes on your thoughts and we will discuss. 7  EASTMAN DENTAL HOSPITAL EDUCATION CENTRE DENTAL HYGIENE & DENTAL THERAPY Sec>on 4: Addi>onal learning 9. To inves3gate the theories of erup3on further here are two useful ar3cles that I recommend reading and taking some notes: 8  EASTMAN DENTAL HOSPITAL EDUCATION CENTRE DENTAL HYGIENE & DENTAL THERAPY Sec>on 5: Glossary of Terms                          9