1. DEVELOPMENT OFTOOTHDr. Muznah SultanLecturerDepartment of OralBiology, DIDC-DUHS 2. CONTENTS1. Introduction2. Dental Lamina3. Vestibular Lamina4. Tooth development5. Developmental stages Bud stage Cap stage Bell stage Advanced bell stage6. Hertwigs epithelial root sheath and root formation7. Conclusion8. References 3. INTRODUCTION 4. Tooth formation occurs in the 6th week ofintrauterine life with the formation of primaryepithelial band.At about 7th week the primary epithelial banddivides into a lingual process called dental lamina &a buccal process called vestibular lamina. 5. DENTAL LAMINA 6. 2- 3 weeks after the rupture of buccopharyngeal membrane, certain areasof basal cells of oral ectoderm proliferate rapidly, leading to the formationof primary epithelial band The band invades the underlying ectomesenchyme along each of thehorse-shoe shaped future dental arches. 7. At about 7th week the primary epithelial band divides into an inner (lingual)process called Dental Lamina & an outer ( buccal) process called VestibularLamina The dental lamina serves as the primordium for the ectodermal portionof the deciduous teeth Later during the development of jaws, permanent molars arise directlyfrom the distal extension of the dental lamina 8. FATE OF DENTAL LAMINA It is evident that total activity of dental lamina exceeds over a period of atleast 5 yrs As the teeth continue to develop, they loose their connection with the dentallaminaThey later break up by mesenchymal invasion, which is at first incomplete and doesnot perforate the total thickness of the lamina 9. Fragmentation of the dental lamina progresses toward the developingenamel organ Any particular portion of the dental lamina functions for a much brieferperiod since only a relatively short time elapses after initiation of toothdevelopment before the dental lamina begins to degenerate 10. VESTIBULAR LAMINA Labial and buccal to the dental lamina in each dental arch, another epithelialthickening develops independently It is Vestibular Lamina also termed as lip furrow band Subsequently hollows and form the oral vestibule between the alveolar portionof the jaws and the lips and cheeks. 11. TOOTH DEVELOPMENT 12. At certain points along the dental lamina each representing the location of oneof the 10 mandibular & 10 maxillary teeth, ectodermal cells multiply rapidly &little knobs that grow into the underlying mesenchyme Each of these little down growths from the dental lamina represents thebeginning of the enamel organ of the tooth bud of a deciduous tooth First to appear are those of anterior mandibular region As the cell proliferation occurs each enamel organ takes a shape that resembles acap 13. DENTAL PAPILLAOn the inside of the cap, the ectomesenchymal cells increase in number.The tissue appears more dense than the surrounding mesenchyme andrepresents the beginning of the dental papillaB = Dental Papilla 14. DENTAL SAC/ DENTALFOLLICLESurrounding the combined enamel organ or dental papilla, the third part of thetooth bud forms. It is known as dental sac/follicle and it consists ofectomesenchymal cells and fibres that surrounds the dental papilla and the enamelorgan.C= Dental sac 15. Thus the tooth germ consists of ectodermalcomponent- the enamel organ, theectomesenchymal components- the dentalpapilla & the dental follicle The enamel is formed from the enamel organ,the dentin and the pulp from the dental papillaand the supporting tissues namely thecementum, periodontal ligament & the alveolarbone from the dental follicle During & after these developments the shapeof the enamel organ continues to change The depression occupied by the dental papilladeepens until the enamel organ assumes a shaperesembling a bell The dental lamina becomes longer, thinner &finally loses its connection with the epitheliumof the primitive oral cavity 16. DEVELOPMENTAL STAGES 17. MORPHOLOGICAL1. Dental lamina2. Bud stage3. Cap stage4. Early bell stage5. Advanced bell stage6. Formation of enamel and dentin matrixPHYSIOLOGICALInitiationProliferationHistodifferentiationMorphodifferentiationApposition 18. BUD STAGE / PROLIFERATION This is the initial stage of tooth formationwhere enamel organ resembles a small bud During the bud stage, the enamel organconsists of peripherally located lowcolumnar cells & centrally locatedpolygonal cells The surrounding mesenchymal cellsproliferate, which results in theircondensation in two areas The area of condensation immediatelybelow the enamel organ is the dentalpapilla The ectomesenchymal condensation thatsurrounds the tooth bud & the dentalpapilla is the tooth sac 19. The dental papilla as well as the dental sac are not well defined during the budstage, they become more defined during the subsequent cap & bell stages The cells of the dental papilla form the dentin and pulp while the dental sac formscementum & periodontal ligament 20. CAP STAGE / PROLIFERATION As the tooth bud continues to proliferate, it does not expand uniformly intoa large sphere Instead unequal growth in different parts of the tooth bud leads to the capstage which is characterized by a shallow invagination on the deep surface ofthe bud 21. OUTER & INNER ENAMELEPITHELIUM The peripheral cells of the cap stage arecuboidal , cover the convexity of the cap& are called the outer enamel epithelium The cells in the concavity of the capbecome tall columnar cells & representthe inner enamel epithelium 22. The outer enamel epithelium is separated from thedental sac, & the inner enamel epithelium from thedental papilla, by a delicate basement membrane 23. STELLATE RETICULUM Polygonal cells located between the outer and the inner enamel epithelium, beginto separate due to water being drawn into the enamel organ from the surroundingdental papilla As a result the polygonal cells become star shaped but maintain contact with eachother by their cytoplasmic process As the star shaped cells form a cellular network, they are called the stellatereticulum 24. The cells in the center of the enamel organ are densely packed and formthe enamel knot This knot projects toward the underlying dental papilla 25. At the same time a vertical extension of the enamel knot,called the enamel cord occurs 26. The function of enamel knot &cord may act as a reservoir of thedividing cells for the growingenamel organ The enamel knot act as asignaling centers as manyimportant growth factors areexpressed by the cells of theenamel knot & thus play animportant role in determining theshape of the tooth The ectomesenchymalcondensation i.e the dental papilla& the dental sac are pronouncedduring this stage of dentaldevelopment 27. BELL STAGE / HISTODIFFERENTIATION Due to continued uneven growth of theenamel organ it acquires a bell shape In bell stage crown shape is determined It was thought that the shape of the crownis due to pressure exerted by the growingdental papilla cells on the inner enamelepithelium This pressure however was shown to beopposed equally by the pressure exerted byfluid present in the stellate reticulum The folding of enamel organ to causedifferent crown shapes is shown to be dueto different rates of mitosis & difference incell differentiation time 28. INNER ENAMEL EPITHELIUM The inner enamel epithelium consists of a single layer of cells that differentiateprior to amelogenesis into tall columnar cells called ameloblasts These elongated cells are attached to one another by junctional complexeslaterally & to cells in the stratum intermedium by desmosomes The cells of the inner enamel epithelium exert a strong influence on theunderlying mesenchymal cells of the dental papilla, which later differentiate intoodontoblasts 29. STRATUM INTERMEDIUM A few layers of squamous cells form the stratum intermedium , between theinner enamel epithelium & the stellate reticulum These cells are closely attached by desmosomes & gap junctions This layer seems to be essential to enamel formation 30. STELLATE RETICULUM The stellate reticulum expands further due to continued accumulation of intra-cellularfluid These star shaped cells, having a large processes anastomose with those of adjacentcells As the enamel formation starts., the Stellate reticulum collapses to a narrow zonethereby reducing the distance between the outer & inner enamel epithelium 31. OUTER ENAMEL EPITHELIUM The cells of the outer enamel epithelium flatten to form low cuboidal cells The outer enamel epithelium is thrown into folds which are rich in capillarynetwork, this provides a source of nutrition for the enamel organ Before the inner enamel epithelium begins to produce enamel. Peripheral cellsof the dental papilla differentiate into odontoblasts These cuboidal cells later assumes a columnar form & produce dentin 32. DENTAL LAMINA Dental lamina is seem to extend lingually and is termed successional dentallamina as it gives rise to enamel organs of permanent successors of deciduousteeth The enamel organs of deciduous teeth in the bell stage show successional lamina& their permanent successor teeth in the bud stage 33. DENTAL SAC The dental sac exhibits a circulararrangement of fibres & resemblesa capsule around the enamelorgan The fibres of the dental sac formthe periodontal ligament fibresthat span between the root & thebone The junction between the innerenamel epithelium & odontoblastsoutlines the future dentino-enameljunction 34. ADVANCED BELL STAGE/MORPHODIFFERENTIATION Characterized by thecommencement of mineralization &root formation The boundary between the innerenamel epithelium & odontoblastsoutline the future dentinoenameljunction Formation of dentin occurs first as alayer along the future dentinoenameljunction in the region of future cusps &proceeds pulpally & apically After the first layer of dentin isformed, the ameloblasts lay downenamel over the dentin in the futureincisal & cuspal areas 35. The enamel formation then proceedscoronally & cervically in all the regionsfrom the dentinoenamel junctiontoward the surface The cervical portion of enamel organgives rise to Hertwig Epithelial RootSheath (HERS) This HERS outlines the future root &thus responsible for the size, shape ,length & number of roots 36. CLINICALCONSIDERATIONS 37. HUTCHINSONS INCISORMULBERRY MOLARS 38. FUSION The phenomenon of toothfusion arises through union of twonormally separated tooth germs, anddepending upon the stage ofdevelopment of the teeth at the timeof union, it may be either complete orincomplete. However, fusion can also be theunion of a normal tooth bud to asupernumerary tooth germ. In thesecases, the number of teeth is fewer ifthe anomalous tooth is counted as onetooth. 39. GEMINATIONGemination arises when twoteeth develop from one toothbud and, as a result, thepatient has an extra tooth 40. FORMATION OF ENAMEL & DENTIN MATIX( APPOSITION) Apposition is the deposition of the matrix of the hard enamelstructures Appositional growth of the enamel & dentin is a layer likedeposition of an extracellular matrix. This type of growth istherefore additive Appositional growth is characterised by regular & rhythmicdeposition of the extracellular matrix, which is of itselfincapable of further growth 41. ROOT FORMATION 42. The development of roots begin afterenamel & dentin formation has reachedthe future cementoenamel junction The enamel organ plays an importantrole in root development by formingHERS, which models the shape of theroot HERS consists of outer & inner enamelepithelium only As the first layer of the dentin has beenlaid down, the epithelial root sheathloses its structural continuity and isclose relation to the surface of the root 43. Its remnants persists as anepithelial network of strands orclumps near the external surfaceof the root These epithelial remnants arefound in the periodontalligament of erupted teeth and arecalled as rests of mallasez 44. Prior to the beginning of root formation,the root sheath forms the epithelialdiaphragm The outer & the inner enamel epitheliumbend at the future cementoenameljunction into a horizontal plane,narrowing the wide cervical opening The proliferation of the cells of theepithelial diaphragm is accompanied bythe proliferation of the cells of theconnective tissues of the pulp, adjacent tothe diaphragm The free end of diaphragm does notgrow into the connective tissue but theepithelium proliferates coronal to theepithelial diaphragm 45. Connective tissue of the dental sacsurrounding the root sheathproliferates & invades the continuousdouble epithelial layer dividing it intonetwork of epithelial strands The rapid sequence of proliferation &destruction of Hertwigs root sheathexplains the fact that it cannot be seenas a continuous layer on the surface ofdeveloping root In the last stages of the rootdevelopment, the proliferation of theepithelium in the diaphragm lagsbehind that of the pulpal connectivetissue The wide apical foramen is reducedfirst to the width of the diaphragmaticopening itself & later is furthernarrowed by opposition of dentin &cementum to the apex of the root 46. CLINICAL CONSIDERATIONS 47. DILACERATION Dilaceration refers to an angulation or asharp bend or curve anywhere along theroot portion of a tooth Condition probably occurs subsequentto trauma or any other defect ofdevelopment which alters the angulationof the tooth germ during root formation Can easily be detected by radiographs Care should be taken during extractionsince these teeth are more prone tofracture 48. CONCRESCENCEConcrescence is a condition ofteeth wherethe cementum overlying the rootsof at least two teeth join together.The cause can sometimes beattributed to trauma or crowdingof teeth.Radiographic diagnosis ismandatory before attemptingtooth extraction