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: B 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? Early-late 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: Processes and patterns 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 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 Bone remodelling around it - resorption and deposition Happening in small space in embryos mouth As embryo grows, more space for teeth to erupt 12  Different rates of tooth movement - through bone much slower Through soft tissue - much faster 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 similar 0me as root forma0onMore space Enamel and con0nues un0l the tooth reaches occlusion (remember root forma0on con0nues aFer this phase) 13  Over eruption - recession, exposure of cementum 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: A 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 Single best answer: The erup0on process of teeth… a) Starts during the bell stage of tooth development b) Starts aFer before birth for all the primary teeth c) Starts once alongside the root forma0on of a tooth is complete which con0nues aFer the ac0ve erup0on phase d) Starts at the same 0me as the aFer crown forma0on begins is complete 16  Ac0ve erup0on phase in more detail Tooth moved into position and ready to start active phase Moved through bone and found pathway to move to soft tissues Diagrams showing the ac0ve erup0ve phase 17 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 Needs protection when moving through bone - osteoblasts and osteoclasts break down break, if no protection would also be able to break down the tooth 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 18 The erup0on pathway  The bone overlying the developing crown is resorbed by osteoclasts (and odontoclasts of predecessor teeth) Primary  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 - affects positioning of teeth 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 Single best answer  The reduced enamel epithelium: a) Forms a protec0ve layer over the tooth root crown during erup0on b) Forms from di\eren0ated ameloblasts and the outer enamel epithelium, stratum intermedium and any residual stellate re0culum during aFer amelogenesis c) Surrounds the developing tooth crown during erup0on d) Fuses with the oral epithelium to form the periodontal gingival adachment with the tooth 24 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 If the primary roots stopped exfoliating - direction of permanent tooth can change Can potentially have primary and secondary tooth present in mouth - unnecessary extraction A ground section of an exfoliating Encourage mobility as soon as they become slightly mobile - primary teeth 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 PDL doesn’t continue forming throughout life 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