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14 Cards in this Set
- Front
- Back
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How are enamel and dentin formed?
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Reciprocal induction
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DENTINOGENESIS
The odontoblast |
-dentin formed by odontoblasts derived from undifferentiated cells of the dental papilla in response to growth factors from the internal dental epithelium
-cessation of mitotic activity of the IDE --> change in polarity --> cells of superficial dental papilla become preodontoblasts and then odontoblasts -have a nucleus polarized away from the IDE, increased cytoplasm that obliterates the acellular zone between the IDE and dental papilla |
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2 functional states of the odontoblast
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1) SECRETORY
-abundant cytoplasm, large basally located nucleus -cytoplasm taken up by RER, Golgi and secretory granules -junctional complexes, desmosomes connect odontoblasts 2) RESTING |
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DENTINOGENESIS
Dentin formation - Mantle dentin |
-first dentin formed
-organic matrix consists of ground substance and type I collagen deposited; several elongated apical processes emerge and matrix vesicles extruded from odontoblast cytoplasm (predentin deposited from neck area) -as matrix deposition continues, a single large odontoblast process remains behind and hydroxyapatite crystals are deposited --> crystals increase in size and mineralize -unmineralized (most recent) dentin matrix is predentin **the odontoblast retreats towards the dental pulp, leaving the odontoblast process w/i newly formed dentinal tubule -- in coronal dentin, tubules form S shape, in root are straight |
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DENTINOGENESIS
Dentin formation - Primary (circumpulpal) dentin, Secondary dentin, Tertiary (reparative) dentin |
PRIMARY (CIRCUMPULPAL) DENTIN
-constitutes dentin that encircles the pulp chamber -formed prior to completion of the apical foramen **majority of dentin in tooth is primary** SECONDARY DENTIN -forms after establishment of apical foramen -decreases root chamber and pulp TERTIARY (REPARATIVE) DENTIN -localized dentin in reponse to irritation or trauma -abnormal, disorganized, rapidly produced dentin |
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DENTINOGENESIS
Mineralization of Dentin |
-shows a pattern of globular calcification
-small, isolated crystalline nuclei continue to grow radially and eventually coalesce with neighboring calcosperites -interglobular dentin--> intervening uncalcified dentin adjacent to mantle dentin in areas of incomplete fusion |
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Amelogenesis
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-the process of enamel formation that begins at the early crown stage of tooth development
-presence of predentin is necessary for amelogenesis to occur -involves initial stage of deposition of partially mineralized enamel, then undergoes a subsequent stage of water and organic matrix removal and increased mineralization -enamel derived from internal dental epithelium and assited by the stratum intermedium and stallate reticulum -initiated at cusp tips and proceeds laterally along cusp inclines |
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AMELOGENESIS
Life Cycle of the Ameloblast - Overview |
-changes occur in the cells of the IDE beginning at the cusp tips down towards the cervical loop --> secretory function
-cells of IDE become tall columnar cells, nucleus is polarized towards the stellate reticulum -at this point, superficial dental papilla cells differentiate into odontoblasts which secrete predentin-->enamel matrix deposition by ameloblasts -ameloblasts migrate away from DEJ-->enamel matrix mineralizes and ameloblasts develop conical cellular projection--TOMES' PROCESS -enamel organ then collapses until only several layers of cells on top of layer of post-secretory ameloblasts--reduced enamel epithelium |
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AMELOGENESIS
Developmental Stages of the Ameloblast - Morphogenetic Stage |
-the IDE cells comprise a cuboidal or low columnar epithelium with round, central nucleus and Golgi body toward stratum intermedium
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AMELOGENESIS
Developmental Stages of the Ameloblast - Differentiation Stage |
-cells of IDE elongate, increase size in nucleus and Golgi; shift position so, nucleus towards stratum intermedium and Golgi encompasses much of central and apical cytoplasm
-junctional complexes at proximal and distal ends **NOW CONSIDERED PRE-AMELOBLASTS** |
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AMELOGENESIS
Developmental Stages of the Ameloblast - Secretory Stage |
-enamel matrix produced and deposited against mantle dentin, immediately mineralizes -- structureless
-ameloblast migrates towards stellate reticulum forming the TOMES' PROCESS -enamel matrix secreted from: 1) periphery of cell -- forms an encircling wall around a pit where Tomes' process fits 2) one surface of Tomes' process -- secretes enamel matrix into pit |
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AMELOGENESIS
Developmental Stages of the Ameloblast - Maturation Stage |
-occurs after enamel production is completeted
-ameloblast decreases in size and organelle content; water and organic components removed; inorganic material added to matrix |
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AMELOGENESIS
Developmental Stages of the Ameloblast - Protective Stage |
-closing of maturation
-ameloblasts secrete basal lamina against enamel surface and establish hemidesmosomes -ameloblasts protect the enamel from cellular influences of the follicular connective tissue |
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AMELOGENESIS
Maturation of Enamel |
-early enamel organic matrix comprised mostly of low molecular weight proteins -- AMELOGENINS
-no matrix vesicles involved (differs from dentin) -instead, crystallization begins w/i enamel matrix -hydroxyapatite crystals from dentin at DEJ initiate process by serving as nuclei -enamel proteins and water are removed and calcium is added as matrix matures |
