Tooth Development (Odontogenesis). Dentition Primary dentition – develops during prenatal period –20 teeth Permanent dentition – develops as the jaw grows

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Tooth Development (Odontogenesis) Slide 2 Dentition Primary dentition develops during prenatal period 20 teeth Permanent dentition develops as the jaw grows and matures 32 teeth period in between during the preteen years mixed dentition period Slide 3 THERE ARE MULTIPLE STAGES IN TOOTH DEVELOPMENT but three major ones actually initiation stage 6 th to 7 th week bud stage 8 th week cap stage 9 th to 10 th weeks bell stage 11 th to 12 th weeks apposition stage vaires per tooth maturation stage varies per tooth Slide 4 Tooth formation first signs of formation day 11 thickening of the epithelium where tooth formation will occur on the 1 st branchial arch signals earliest mesenchymal markers for tooth formation are the Lim-homeobox genes (Lhx-6 and Lhx- 7) expressed as early as day 9 in the neural crest cells of the tooth region positions of the teeth are controlled by signals from the oral epithelium role of FGF-8 and Pax-9 determine the position of the tooth germs more than 90 genes have been identified in the oral epithelium, dental epithelium and dental mesenchyme!! so exact signaling mechanisms remain unclear Slide 5 Tooth formation: Initial stages The initiation of tooth formation starts around the 37th day of gestation. Primary epithelial bands: Horseshoe-shaped bands that appear approximately around the 37th day of development, one for each jaw. -there are two subdivisions: vestibular lamina and dental lamina -the dental lamina develops a series of epithelial outgrowths - grow deep into the mesenchyme -develops in the future spot for the dental arches -will form the midline for these arches -arches then form posteriorly from this point -the ingrowths represent the future sites for each deciduous tooth -the vestibular lamina cells rapidly enlarge and then degenerate forms a cleft that becomes the vestibule of the oral cavity -involves the physiologic process of induction -induction of ectodermal tissues by the developing mesenchyme -mechanisms remain unknown -at the 6 th week the stomatodeum is lined with ectoderm outer portion is the oral epithelium -this gives rise to the primary epithelial bands -also is a developing mesenchyme which contains neural crest cells that have migrated to the area -a basement membrane separates the developing oral epithelium and mesenchyme Slide 6 Bud Stage marked by the incursion of epithelium into the mesenchyme period of extensive proliferation and growth of the dental lamina forms into buds or oral masses that penetrate into the mesenchyme each tooth bud is surrounded by the mesenchyme buds + mesenchyme develop into the tooth germ and the associated tissues of the tooth this developing tooth forms from both the ectoderm and mesenchyme and from neural crest cells that have migrated into the mesenchyme 1.Tooth bud 2.Oral epithelium 3.Mesenchyme Slide 7 Cap Stage characterized by continuation of the ingrowth of the oral epithelium into the mesenchyme. tooth bud of the dental lamina proliferates unequally in different parts of the bud forms a cap shaped tissue attached to the remaining dental lamina looks like a cap sitting on a ball of condensing mesenchyme occurs for the primary dentition (during the fetal period) this stage marks the beginning of histodifferentiation (differentiation of tissues) the tooth germ also begins to take on form start of morphodifferentiation a depression forms in the deepest part of each tooth bud and forms the cap or enamel organ (or dental organ) produces the future enamel (ectodermal origin) below this cap is a condensing mass of mesenchyme dental papilla produces the future dentin and pulp tissue (mesenchymal origin) the basement membrane separating the dental organ and the dental papilla becomes the future site for the dentinoenamel junction (DEJ) remaining mesenchyme surrounds the dental/enamel organ and condenses to form the dental sac or the dental follicle Slide 8 Cap stage -together the enamel organ + dental papilla + dental follicle is considered the developing tooth germ or tooth primordium -these primordium will be housed in the developing dental arches and will develop into the primary dentition Slide 9 Bell Stage Continuation of histodifferentiation and morphodifferentiation cap shape then assumes a more bell-like shape differentiation produces four types of cells within the enamel/dental organ 1. inner enamel epithelium 2. outer enamel epithelium 3. stellate reticulum 4. stratum intermedium during the bell stage the dental lamina is separated from the dental organ the dental papilla undergoes differentiation and produces two types of cells 1. outer cells of the DP forms the dentin-secreting cells (odontoblasts) 2. central cells of the DP forms the primordium of the pulp dental sac increases its collagen content and differentiates at a later stage than the EO and DP Slide 10 Differentiation of the Enamel/Dental organ outer enamel epithelium (OEE) cuboidal shape protective barrier during enamel production may also be called the outer dental epithelium very little cytoplasm cells are separated from the dental follicle by a basement membrane inner enamel epithelium (IEE) short, columnar cells differentiates into the enamel secreting cells = ameloblasts separated from the dental papilla below it by a basement membrane also cells accumulate large amounts of glycogen may also be called the inner dental epithelium the IEE and OEE are continuous region where they connect curved rim of the EO = cervical loop stellate reticulum star-shaped cells in many layers center of the enamel organ forms a network = reticulum supports production of enamel stratum intermedium inner layer of compressed flat to cuboidal cells very high levels of the enzyme alkaline phosphatase supports production of enamel cervical loop IEE OEE Slide 11 Bell Stage -the cells in the center of the enamel organ begin to synthesize and secrete GAGs -this pulls water into the EO -increasing amount of fluid in the EO forces the central cells apart -however, they remain connected via cellular processes which makes them star shaped = stellate ret. B = inner dental epithelium (inner enamel epithelium) Slide 12 Bell stage early crown formation the dental papilla is separated from the enamel organ by a basement membrane immediately below this BM is a region called the acellular zone this is where the first enamel proteins will be laid down the dental lamina begins to break up into discrete islands of epithelial cells (epithelial pearls) separates the oral epithelium from the developing tooth these pearls may form cysts and delay eruption or they may develop into supernumerary teeth the IEE completes its folding and you can begin to identify the shape of the future crown pattern Slide 13 Tooth development so far Slide 14 Cap and Bell stages & Permanent teeth during the cap stage the development of the permanent dentition begins anterior teeth the primordia for these teeth appears as an extension off the developing dental lamina penetrates into the mesenchyme lingual to the primary primordium its site of origin is called the succesional dental lamina these permanent teeth are called succedaneous teeth (anterior teeth and the premolars) teeth that form with the primary tooth buds (primary predecessors) permanent molars are non- succedaneous - they are formed by posterior proliferation of the dental lamina. Slide 15 Appositional stage secretion of enamel, dentin and cementum these tissues are initially secreted as a matrix that is partially calcified serves as a framework for later calcification time period varies multiple inductions occur between the ectodermal tissues of the enamel organ and the mesenchymal tissues of the dental papillae and dental sac these inductions are crucial for the production of enamel, dentin and cementum these interactions are mediated by the basement membrane found in between these ectodermal and mesenchymal tissues Slide 16 Maturation stage characterized by the completion of calcification Slide 17 Ameloblasts and Odontoblasts ameloblasts the cells of the IEE assume a more columnar shape or they elongate differentiate into pre-ameloblasts this differentiation is characterized by the repolarization of these PAs movement of the nucleus away from the basement membrane this repolarization is critical to the differentiation of the PAs continued differentiation and maturation results in the formation of ameloblasts the pre-ABs induce the cells of the dental papilla to differentiate also odontoblasts differentiation by the mesenchyme of the dental papilla occurs after differentiation of pre-ABs begins results because the pre-ABs induce differentiation of the mesenchymal cells also also undergo repolarization mirror image of the pre-ABs (see Figure 6-12 and 6-13) after differentiation the ODs then start dentinogenesis begin to deposit predentin on the side of their basement membrane forms a layer immediately below the BM and above the cells (figure 6-13) therefore dentin formation begins before enamel synthesis explains why dentin is thicker than enamel Slide 18 At 1 the epithelium is separated from the dental papilla by an acellular zone. At 2 the cells of the inner dental epithelium have elongated, and the acellular zone begins to be eliminated as odontoblasts differentiate from ectomesenchymal cells in the tooth pulp. At 3 the odontoblasts retreat toward the center of the pulp, leaving behind formed dentin. At 4 the cells of the inner dental epithelium, now ameloblasts, begin to migrate outward and leave behind formed enamel. before dentin forms cells of the EO receive blood supply from vessels of the dental lamina as dentin forms, it cuts of this papillary source of blood/nutrients this causes a drastic reduction in the amount of nutrients that reach the EO but the ABs require extensive nutrients to form enamel stellate reticulum collapses and invagination of the OEE this brings