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TOOTH DEVELOPMENT SUMMARY OF DEVELOPMENTAL SEQUENCE 1. Mandibular & Maxillary arches formation 2. Formation of primary epithelial band 3. Vestibular lamina & dental lamina forms 4. Dental placode formation 5. Bud 6. Cap Enamel knot formation Cervical loop formation 7. Bell 8. Crown 9. Root EARLY ORAL DEVELOPMENT Week 6 - Formation of Primary Epithelial Band • Epithelium proliferates & thickens • Invagination of oral epithelium into mesenchyme • Form cleft/vestibule separates lip & jaw Week 7 - Vestibular Lamina & Dental Lamina forms • Epithelial cells of dental lamina invaginates • Division of primary epithelial band • Apoptosis of cells to form sulcus of vestibule DEFINITIONS Dental Placode dental laminathickenings/outgrowths into mesenchyme along the Mark sites of deciduous teeth Formation due to changes in mitotic spindle orientation and cleavage plane of dividing epithelial cells Dental Lamina Process/structure of epithelial cells connecting enamel organ to oral ectoderm BUD STAGE • Dental lamina extends at dental placodes into ectomesenchyme • 1st condensation of mesenchyme around epithelium • Late bud stage = Further condensation of mesenchyme cells Bud Stage Energy Sources: • High mRNA content • Lower glycogen content • Increased oxidative activity CAP STAGE Early Late • Bud flattens • Enamel organ bigger • Histo-differentiation • Dental papilla ball of condensed ectomesenchymal cells • IEE & Stellate reticulum • Ectomesenchyme cells form dental • Dental follicle limits dental papilla papilla • Vascular supply • Nerve supply • Formation of enamel knot TOOTH GERM • Enamel organ - epithelial ingrowths resembling 'cap' • Dental papilla (dentine + pulp) - ball of condensed ectomesenchymal cells • Dental follicle - condensed ectomesenchyme limiting dental papilla and surrounding enamel organ WHAT IS THE ENAMEL KNOT? (6 points) 1. Non-dividing condensed epithelial cells in IEE 2. Around cusp tip in late cap/early bell stage 3. Expresses signalling molecules for nearby epithelial cells to proliferate further around papilla via reciprocal epithelial mesenchymal signalling 4. Becomes cusp tip 5. Drives expression of homeobox genes and crown patterning 6. Transitory SECONDARY ENAMEL KNOTS • Shh required for asymmetric development of dental cap (lingual aspect) • Enamel knot cells apoptose • Signalling molecules produced by primary enamel knot induces secondary enamel knot formation at sites of cusps in molar teeth in context dependent manner • Expression of homeobox genes in underlying ectomesenchyme • FGF4 dictates spacing of enamel knots CELL LAYERS Outer Enamel Epithelium Outer cuboidal cells of enamel organ 1 cell layer High nuclear : cytoplasm ratio Non-secretory protective role Becomes part of the dentinogingival junction Stellate Reticulum Secrete hydrophilic GAGs to increase extracellular space Produces jelly-like ECM Cells interconnect via desmosomes Star-shaped Stratum Intermedium Flattened 2-3 cell thick Alkaline phosphatase activity Enamel formation/ signalling Inner Enamel Epithelium Next to dental papilla Short columnar 1 cell thick Differentiates into ameloblasts BELL STAGE Early Late • Crown pattern established • Dental lamina disintegrates • Increased germ size • Germ looses attachment to oral epithelium • Histo-differentiation of cell layers • Serres glands/epithelial pearls from dental lamina - forms odontogenic cysts/supernumerary teeth • IEE growth complete CROWN STAGE Bell to Crown Transition: 1. Dentinogenesis at central incisors 2. Undifferentiated papilla cells next to IEE turn into odontoblasts 3. Tall columnar cells, basal polarised nucleus, large increase synthetic organelles 4. Secretion of predentine Crown Stage: 1. Pre-dentine secreted, basement membrane breaks down so contact between IEE and predentine 2. IEE cells terminally differentiate into ameloblasts 3. Mineralised tissue deposition 4. At future cusp tip INNERVATION Vascular Nerve • Enters dental papilla at cap stage • Pioneer fibres during bud/cap stage at future root and form rich plexus in follicle • Increases in bell stage and then around germ decreases • Doesn't penetrate dental papilla until dentinogenesis • Enamel organ avascular so blood supply from dental papilla HOW DOES THE PERMANENT DENTITION ARISE? (3 points) 1. Successional lamina arises from proliferation/extension of dental lamina 2. Proliferate lingually of dental lamina at 5-10 mths 3. Lingual aspect of dental laminaTOOTH INDUCTION 1. Epithelium has instructional role over ectomesenchyme 2. Then vice versa during bud stage (ectomesenchyme instructive influence) 3. Molecular field formed during late bell stage (reciprocal induction) DENTAL PATTERNING THEORIES Field Theory = Local signalling factors tell mesenchyme to form tooth of specific shape during bud stage Clone Theory = Mesenchyme already programmed to become specific tooth shape prior to bud stage SIGNALLING FACTORS Osr2 Transcription factor Expressed in mesenchyme Regulation of gradient in jaw buccal to lingual Inhibits BMP4 & MSX1 pathways, restricting tooth formation lingually Vestibular lamina boundary buccally Shh Localised proliferation in ectoderm to form tooth bud Induces ectodermal thickenings in non-dental ectoderm Wnt-7b Negative regulator of Shh Inhibited by BMP4 Ectodin Regulates BMP4, Shh & Wnt pathway via LRP-4 receptor Defects cause supernumerary teeth WHAT STAGES IS BMP2 PRESENT IN? (3 points) 1. Initiation - primary epithelial band 2. Bud - dental epithelium 3. Cap - enamel knot ODONTOBLAST DIFFERENTIATION • Late bell stage • Undifferentiated papilla cells next to IEE in bell to crown transition • Ectomesenchyme • dentine retreating pulpally, odontoblast cell bodies on formative surface of QUICK FIRE QUESTIONS 1. What is the enamel organ derived from? 2. What does dental papilla form? 3. What does the dental follicle form? 4. Where does predentine deposition & cell differentiation begin? 5. How is dentine secreted? 6. What is dental papilla derived from? 7. What is the boundary between the lip and the jaw? 8. What separates the IEE and dental papilla? 9. What does ectomesenchyme consist of? 10. What is the cell type in the primary epithelial band? 11. Where are ameloblasts located? 12. Where are odontoblasts located? QUICK FIRE ANSWERS 1. Epithelial cells of dental lamina 2. Dentine & pulp 3. Periodontium (supporting tissues) 4. At future cusp tip 5. Predentine then mineralised into dentine 6. Ectomesenchyme 7. Vestibular lamina 8. Basal lamina 9. Mesenchyme + neural crest cells 10. Stratified cuboidal epithelial cells 11. Line surface of crown (outer surface of enamel) 12. Pulpal surface of dentineWHAT IS STAGES ARE A, B, C & D? Bonus: What is the arrow in image d pointing to?