Origin of teeth • Teeth have a dual origin: • Ectodermal; • Mesodermal: • Ectomesenchymal.
EPITHELIUM-ECTOMESEMCHYME INTERACTION IN THE TOOTH DEVELOPMENT • Combine tissue type (neural crest cells + mesenchyme) is called ectomesenchyme. • In tooth development, an interaction occurs between oral ectoderm and ectomesenchyme to initiate the process. • Cellular interactions, between epithelium+ectomesenchyme:Formation of dentine, enamel and cementum as well as crown;
The processes involved in tooth development • Morphogenesis is stimulated by molecular signals that control: • Cell growth; • Migration; • Cell fate and differentiation. • For every developmental event a complex and intricate cascade of gene expression take place to direct the cells to the right place and onto the proper differentiation pathway; • Many of these pathways all result from epithelial-mesenchymal interactions in which essentially the same molecular mediators are implicated.
Embryonic terms to considerInduction • First process to occur during embryogenesis; • Interaction between developing embryonic cells.
Morphogenesis • May also be called morphodifferentiation; • Development of form and specific tissues; • Results from migration of embryonic cells and inductive interactions between these cells.
Specification of the embryo through segmentation; • Patterningisboth a spatialandtemporaleventasexemplifiedbyregionaldevelopment of incisors, canines, premolars, andmolars, whichoccursatdifferenttimesandinvolvestheclassicalprocesses of induction, competence, anddifferentiation. • Process of specialization of embryonic cells. Patterning Differentiation
interstitial growth • Growth deep within a tissue of organ; • As opposed to appositional growth – growth at the periphery through the addition of additional cell layers;
Stages of development • Initiation; • Proliferation; • Histodifferentiation; • Morphodifferentiation; • Apposition; • Maturation; • Eruption.
Iniciation of tooth development • The newly formed stomadeum is lined by a primitive two- or three-cell-thick layered epithelium covering an embryonic connective tissue that, because neural crest cells have migrated in it, is termed ectomesenchyme; • The ectomesenchyme consists of a few spindle-shaped cells separated by a gelatinous ground substance.
PHASE 1-initiation phase • Formation of primary epithelial thickening, dental lamina, tooth bud & the cap, bell stage cannot take place in absence of dentally active ectomesenchyme which becomes concentrated in regions of presumptive tooth development; • Inner epithelium of enamel organ induces ectomesenchyme of dental papilla to become orientated towards the intervening basal lamina and differentiate into odontoblasts.
Iniciation of tooth development • Thickening of the epithelium.
Stages of the initiation • Primary epithelial band; • Vestibular lamina; • Dental lamina.
Primary epithelial band • A continuous band of thickened epithelium forms around the mouth in the presumptive upper and lower jaws; • This bands are roughly horseshoe shaped and correspond in position of the future dental arches of the jaws; • Each band of epithelium quickly gives rise to two subdivisions: • The vestibular lamina and • The dental lamina just behind it.
Upper epithelial band tongue lower epithelial band
Upper and lower epithelial bands
The reason for epithelial thickening • The formation of these thickened epithelial bands is the result not so much of increased proliferative activity within the epeithelium as of a change in orientation of the mitotic spindle and clevage plane of dividing cells.
Sagittal section through the head of an embryo. A. Primary epithelial bands; B. The same structure at higher magnification; C The change in plane of clevage.
Development of the epithelial proliferation Upper epithelial band Lower Epithelial band
Vestibular Lamina • Thefirstsubdivision of theprimaryepithelialbandisvestibularlamina; • The vestibule forms as a result of the proliferation of the vestibular lamina into ectomesenchyme; • Itscellsrapidlyenlargeandthendegenerate to form a cleftthatbecomesthevestibulebetweenthecheekandtooth-bearingarea.
Dental lamina • The othersubdivision of theprimaryepithelialbandisdentallamina; • Dental lamina is located orally to the vestibularlamina; • Withinthedentallamina, continuedandlocalizedproliferativeactivityleads to theformation of a series of epithelialoutgrowths intotheectomesenchymeatsitescorresponding to thepositions of thefuturedeciduousteeth.
Dental lamina, Vestibular lamina Dental lamina • Vestibular proliferationleads to the formation of the vestibular lamina; • Oral proliferation leads to the formation of the dental lamina. Vestibular lamina
tongue Vestibular lamina Dental lamina
Next development ofdentallamina • Begin localized proliferations; • Early in the medial part - incisors; • Then in the lateral part - canines and molars; • In the upper and lower dental laminaareformed 10 proliferations; • The process is called “the formation of tooth bud” • This is the beginning of the toothdevelopment;
Initiation of toothdevelopment • Teethdevelopfromtwotyps of cells: • Oralepithelialcells; • Mesenchymalcellsfromthedentalpapilla; • Neuralcrestcells – ectomesenchymalcells; • Epithelialcellsare flat on the surface of theepitheliumand cylindrical immediately above to thebasallamina; • Theunderlyingectomesenchymalcellsaccumulatearoundtheepithelialautgrowths.
Theflatandcylindrical epithelialcells, basal lamina immediately below, andectomesenchymalcells Flat cells Cylindrical cells
Proliferation • The proliferation is: • Multiplication of cells; • Increases the amount of tooth bud; • The proliferation is observed: • Intheepithelium; • Intheectomesenchym.
Certaincells of thebasallayerbegin to proliferateat a morerapidratethendotheadjacentcells. Theseproliferatingcellscontaintheentiregrowthpotential of theteeth .
Toothedevelopmentproceedsinthreestages: • Dentalbud; • Dentalcap; • Dentalbell. • Thesetermsarediscriptive of themorphologybutwehave to describethesignificantfuctionalchangesthatoccurduringdevelopment, suchasmorphogenesisandhistodifferentiation; • Becausedevelopmentis a continuousprocess, cleardistinctionbrtweenthetransitionstagesisnotpossible.
Dentalbud • 1. Dental bud; • 2. Oral epithelium; • 3. Ectomesenchyme.
Histodifferentiation • Histological appearance of different cellswith: • Different form; • Different size; • Differentfunction; • Than are formed differentlayers of cells : • Intheepithelium; • Intheectomesenchym.
Morphogenesiswithmorphodifferentiation • The differentiated cells shall be arranged under differentlayers; • Each layer acquires a separate function; • Each layer takes part in creating the structures of the tooth, in determining the shape and size of thetooth.
Elements of thetooth germ • Enamelorgan - epithelial; • Dentalpapilla: • Мesenchymal; • Ectomesenchymal; • Dentalfollicle: • Мesenchymal; • Ectomesenchymal.
Budstage of toothdevelopment • Proliferation of epithelial cells; • Mitotic cell division; • Increasing the cells number; • Increasing the size of the cells; • Still no cells differentiation.
Budstage • Thebudstageisrepresentedbythefirst epithelialincursionintotheectomesenchyme of thejaw; • Theepithelialcellsshowlittleifanychangeinshapeorfunction; • Thesupportingectomesenchymalcellsarepacked closely and around theepithelialbud.
Ectomesenchylalcells arriving directly from neural crests • Stem cells involved in the formation of thetooth bud; • This is pluripotent cell capable to become virtually any cell.