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Dental Anatomy.1
Tooth Development
| Question | Answer |
|---|---|
| Odontogenesis | Tooth development |
| What are the stages of tooth development? | Initiation, Bud, Cap, Bell, Apposition & Maturation |
| When does the primary dentition develop? | During both the embryonic & fetal periods. |
| When is the permanent dentition formed? | Most of it is formed during the fetal period but tooth development continues for years after birth until the 2nd or 3rd molars are formed. |
| What takes place during the initiation stage? | INDUCTION (6th - 7th wk)mesenchymal tissues must influence the ectodermal tissues in order for initiation of odontogenesis to occur. |
| What does the outer portion of the ectoderm that lines the primitive mouth give rise to (become)? | The oral epithelium. (two bands of tissue--the future arches) |
| What forms deep in the oral epithelium by neural crest cells that have migrated to the area? | Ectomesenchyme |
| What separates the oral epithelium & the ectomesenchyme? | The basement membrane. |
| What is the new layer of epithelium that is formed as the oral epithelium grows deeper into the ectomesenchyme? And where does it start to form? | Dental lamina -- it starts to form in the midline of both arches & progresses posteriorly. |
| What is the second stage of odontogenesis? | BUD STAGE (8th wk) |
| What is the main process involved in the bud stage? | PROLIFERATION(growth) of the dental lamina into buds that penetrate into the ectomesenchyme. |
| What structural changes occur during the bud stage? | None, there is only proliferation (or growth) of the tissues during this stage. |
| What is the third stage of odontogenesis called? | Cap stage (9th - 10th wk) |
| What main processes are involved in the cap stage? | Proliferation, differentiation, Morphogenesis |
| What is the predominant physiological process during the cap stage? | morphogenesis |
| What forms in the deepest part of each tooth bud of dental lamina? | Enamel organ (or a cap) |
| What is the role of the enamel organ? | It will produce enamel. |
| What type of product is enamel? (endoderm, ectoderm, mesoderm?) | It is an ectodermal product -- because the enamel organ was originally derived from ectoderm. |
| Dental papilla? | A dense, ectomesenchyme tissue within the concavity of the cap of the enamel organ. |
| What will the dental papilla produce in the future? | Dentin & pulp tissue for the inner portion of the tooth. |
| What type of product are dentin & pulp tissue? | mesenchymal -- because the dental appilla is originally derived from ectomesenchyme which is influenced by neural crest cells. |
| What structure is between the enamel organ & dental papilla? | The basement membrane. |
| What does the basement membrane become? | The dentinoenamel junction. |
| What happens to the remaining ectomesenchyme surrrounding the outside of the cap (enamel organ)? | It condenses and takes on a capsulelike appearence it's called -- DENTAL SAC |
| What will the dental sac produce in the future? | The periodontium-- the supporting tissues of the tooth: cementum, periodontal ligament & alveolar bone |
| What type of product are the supporting dental tissues? | Mesenchymal -- the dental sac is originally derived from ectomesenchyme. |
| Tooth germ? And when is it present? | The enamel organ, dental papilla, & dental sac. (These embryological structures are all formed by the end of the cap stage) |
| What is the fourth stage of odontogenesis? | Bell Stage (11 - 12th wk) |
| What processes are involved in the bell stage? | continuation of proliferation, differentiation, & morphogenesis |
| What is the most prodominant process of the bell stage? | DIFFERENTIATION -- ENAMEL ORGAN now has four different types of cells -- so the enamel organ takes on a bell shape -- dental papilla (W/I the concavity of the enamel organ) now consists of two types of tissues or layers |
| Name the 4 types of cells found in the enamel organ during the bell stage. | *Inner enamel epithelium *Outher enamel epithelium * stellate reticulum *stratum intermedium |
| OEE | *outer cuboidal cells of the enamel organ *protective barrier of the enamel organ during enamel production |
| IEE | *innermost tall columnar cell of the enamel organ * will differentiate into ameloblasts that form enamel matrix |
| Stellate reticulum | *star-shaped network of cells *more outer middle layer of the enamel organ *support the production of enamel |
| Stratum intermedium | *compressed layer of flat to cuboidal cells *more inner middle layer of the enamel organ *support the production of enamel. |
| Outer cells of the dental papilla | *layer of the dental papilla *will differentiate into dentin-secreting cells (odontoblasts) |
| Central(or Inner) cells of the dental papilla | differentiates into pulp tissue |
| Dental sac during the bell stage. | *increasing amt of collagen fibers forming around the enamel organ * will differentiate into cementum, periodontal ligament, & alveolar bone |
| What is the fifth stage of odontogenesis? | Apposition |
| What happens during the apposition stage? | Enamel, dentin, & cementum are secreted in successive layers. SECRETED AS A MATRIX |
| Matrix | an extracellular substance that is partially calcified yet serves as a framework for later calcification. |
| What processes are involved in the apposition stage? | Induction & proliferation |
| What is the 6th stage of odontogenesis? | Maturation -- when the dental tissues fully mineralize to their mature levels. |
| What is the role of the basement membrane? | *It serves as a boundary between the cells of the enamel organ & the dental papilla *It also conveys communications between between enamel organ, dental papilla & dental sac allowing these tissue interations |
| List the events in the production of enamel & coronal dentin. | *The formation of preameloblasts, *odontoblasts, *dentin matrix, *ameloblasts *dentinoenamel junction *enamel matrix |
| Cellular repolarization | It is the movement of all the nuclei in the IEE cells to the position farthest away from the basment membrane. This changes IEE cells into preameloblasts. |
| What is the role of preameloblasts? | They will induce dental papilla cells to differentiate into odontoblasts. |
| Repolarization of odontoblasts. | The nuclei of the odontoblasts move from the center to a position in the cell farthest from the basment membrane. |
| dentinogenesis | Odontoblast make dentin matrix (or predentin) on their side of the basement membrane. |
| Why is the dentin layer in any location in a developing tooth slightly thicker than the corresponding layer of enamel matrix? | Because the odontoblasts start making dentin before the ameloblast start making enamal. |
| What makes the preameloblast differentiate into ameloblasts? | The basment membrane disintegrates so the preameloblasts come into contact with dentin that the odontoblasts produced this induces the preameloblast to differentiate into ameloblasts. |
| Amelogenesis? | Ameloblasts lay down enamel matrix on their side of the now disintegrating basement membrane. |
| Tomes' process | A tapered portion of each ameloblast where enamel matrix is secreted from. It faces the disintegrating basement membrane. |
| Dentineonamel Junction (DEJ) | Mineralization of the disintegrating basement membrane marks the inner junction between the dentin & enamel tissues |
| Attached cellular extensions in the length of the predentin that odontoblasts leave. | Odontoblastic process |
| Where are odontoblastic processes contained? | Dentinal tubule --a mineralized cylinder |
| What happen to the cell bodies of odontoblasts? | The will remain within pulp tissue. |
| What will become of cell bodies of the ameloblasts? | They will be involved in the eruption and mineralization proces but will be lost after eruption. |
| When does root deveopment take place? | After the crown is completely shaped & the tooth is starting to eruptinto the oral cavity. |
| What structure is responsible for root development? | Cervical loop |
| Cervical loop? | *is the most cervical portion of the enamel organ, *a bilayer rim that consists only of IEE & OEE |
| HERS | Hertwig's epithelial root sheath *a membrane that shapes the root & induces dentin formation in the root area so that it is continueous with coronal dentin. |
| Where does HERS come from? | *it is formed by the cervical loop from dental papilla tissue (the cerv. loop grows deeper into the ectomesenchyme of the dental sac, elongating & moving away from the newly completed crown to enclose more of the dental papilla tissue and forms HERS) |
| Why isn't there enamel in the root? | HERS induces odontolastic differentioation but doesn't induce enamel-forming ameloblasts. |
| Why doesn't HERS induce ameloblasts? | Because HERS consists only of the OEE & IEE it does not contain Stratm intermedium & Stellate reticulum. |
| What happens to the root sheath after root dentin formation is complete? | HERS is disintegrated and the basement membrane that seperates the the IEE & odontoblasts of the root area. |
| What happens to the cell bodies of HERS? | These groups of epithelial cells become located in the mature periodontal ligament. (they can become cystic later and cause problems) |
| Enamel pearls? | Small spherical enamel projections on the root surface from misplaced ameloblasts. (usually in CEJ area or fucation area if present) |
| What happens when undifferentiated cells of the dental sac come in contact with newly formed surface of root dentin? | The undifferentiated cells are induced to become immature CEMENTOBLASTS & cementogenesis begins. |
| Cementogenesis? | cementoblasts move to cover the root dentin & lay down a cementum matrix(also called cementoid) |
| Cementocytes? | Cementoblasts that become entrapped by the cementum the produce. |
| Cementum? | Calcification of cementocytes that are surrounded by the cemntoid (the cementum matrix) |
| DEJ | Dentinoenamel junction -- Junction between the dentin & enamel formed by the mineralization of the disintegrating basement membrane. |
| Periodontal ligament? | (PDL) is the ligament surrounding the teeth that supports & attaches the teeth to the bony surface of teh alveoli. |
| How is the PDL developed? | Collagen fibers are formed for the ectomesenchyme of the dental sac. |
| Where are the collagen fibers of the PDL located? | One end of the fiber bundles is inserted into the outer portion of the cementum & the surrounding alveolar bone to support the tooth. |
| Alveolar bone? | Tooth sockets formed by the mineralization of the ectomesenchyme of the dental sac. |
| Concrescence? | The roots of 2 or more teeth join as a result of excessive cementum deposition. |
| Describe the development of a root with more than one root branch. | The cervical loop of the enamel organ elongates & horizontal epithelial extensions develop which divides the usual single cervical opening into two or three openings. |
Created by:
riosalado