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UKCD Histo Tooth Dev
learning objective for tooth development
| Question | Answer |
|---|---|
| When does odontogenesis begin? | Between the 5th and 6th week of in utero development. |
| What are the two major events involved in the odontogenesis process? | Morphodifferentiation (determines the shape of the crown of the tooth) and cytodifferentiation that differentiates the special groups of cells required for the formation of dental tissues. |
| Name the phases of morphogenesis. | Bud, cap and bell stages. |
| What two specific cell populations are involved in morphogenesis? | Oral epithelial cells (give rise to enamel organ) and neural crest mesodermal cells cause the oral cells to proliferate and form the dental papilla |
| What cells would have to be absent for odontogenesis not to occur? | Neural crest mesoderm cells |
| What are the 2 laminae formed by proliferation of the oral ectoderm cells? | The vestibular and dental laminae |
| What does the vestibular lamina form? | The vestibule (the space between the lip and gingiva). |
| What two layers are exhibited in the cap stage? | Outer and inner dental epithelium. |
| Further differentiation of the cap results in the formation of what structure? | The enamel knot. |
| From which structure does the bud of the permanent tooth arise? | The dental lamina of the primary tooth. |
| What are the two components of the bell stage of tooth development? | The epithelial component and the mesenchymal component. |
| Name the four distinct layers of the epithelial component | 1. inner dental epithelium 2. stratum intermedium 3. stellate reticulum 4. outer dental epithelium |
| What organ will the inner dental epithelium become? | forms the enamel |
| What organ will the stratum intermedium become? | controls passage of materials into and out of the future ameloblasts |
| What organ will the stellate reticulum become? | forms a fluid-filled space into which the enamel layer can grow |
| What organ will the outer dental epithelium become? | fuses and is eventually shed |
| What are the two components of the mesenchymal aspect? | The dental papilla and the dental sac (follicle |
| In what stage does the cervical loop become prominent? | The bell stage. |
| What is the cervical loop? | The downward growing edge of the cap forming inner and outer dental epithelial cells |
| What continued down growth of the cervical loop form? | The anatomical crown of the tooth. |
| What is the function of the stratum intermedium? | This layer of cells is found behind the ameloblast layer and controls what passes between these cells and the capillaries that indent the ODE. |
| What is the function of the stellate reticulum? | It provides a fluid-filled space into which the enamel layer can grow to give the tooth its anatomical shape for the crown. |
| What do the cells of the IDE eventually become? | Ameloblasts (enamel forming cells). |
| What eventually happens to the cells of the ODE? | They fuse with the ameloblasts and stratum intermedium to become the reduced enamel epitheloium (REE) that is shed either during eruption or functional occlusion. |
| What are epithelial (Serre's) pearls. | The remnants of the epithelial cells that formed the dental lamina as it begins to break down |
| Why are epithelial pearls clinically important? | Persistent islands of epithelium can become focal points for the formation for certain oral pathologies. |
| hat are the 3 regions (features) of the tooth germ? | The dental organ, dental papilla and dental sac (follicle). |
| What does the dental organ region of the tooth germ give rise to in the adult tooth? | enamel |
| What does the dental papilla region of the tooth germ give rise to in the adult tooth? | dental pulp and dentin layers |
| What does the dental sac region of the tooth germ give rise to in the adult tooth? | cementum, PDL and alveolar bone socket. |
| What do the first series of cellular interactions in odontogenesis result in? | Morphodifferentiation (interaction between the oral ectoderm epithelial cells and the neural crest mesenchymal cells). |
| What do the second series of cellular interactions in odontogenesis result in? | The initiation of cytodifferentiation (differentiation of the cell types responsible for the formation of dentin and enamel). |
| What causes the cells of the peripheral region of the dental papilla to differentiateinto odontoblasts? | The development of the cells of the IDE into preameloblasts which secrete compounds into the underlying basal lamina that causes the peripheral pulp cells to become odontoblasts. |
| What causes the preameloblasts of the IDE layer to begin secreting enamel (amelogenin)? | Temporary contact odontoblast cell processes plus the initiation of dentin secretion. |
| What is the membrana perforata? | The old basal lamina under the IDE layer that breaks done to allow the odontoblast processes to contact the overlying preameloblasts. |
| In what region of the tooth does cytodifferentiation first occur? | The incisal aspect of the cusp |
| To which region does cytodifferntiation sequentially extend (ie. stop)? | It extends down to the cervix (future enamel-cementum jucntion). |
| What are the 5 functional stages in cytodifferentiation? | 1. Morphogenic (initiation) stage 2. Organizing stage 3. Formative (secretory) stage 4. Maturation stage 5. Protective stage |
| What occurs in the Morphogenic (initiation) stage? | dental pulp cells proliferate and IDE cells ready for transformation into preameloblasts. |
| What occurs in the Organizing stage? | dental pulp cells round up into odontoblasts and the IDE cells organize their cytoplasmic components for the transformation into prealmeloblasts. |
| What occurs in the Formative (secretory) stage? | odontoblasts begin dentin secretion (odontogeneisis) and the overlying pre-ameloblasts become secretory ameloblasts and begin secreting amelogen |
| What occurs in the Maturation stage? | transformation of immature enamel into mature enamel. Ameloblasts stop secreting enamel (loose their Tome’s process) and exhibit a ruffled border. Prismless enamel is formed at the end of this phase. |
| What occurs in the Protective stage? | The ruffled border secretes a cuticle for the maturative ameloblasts to anchor to. These cells plus the overlying stratum intermedium and ODE cells all form the reduced enamel epithelium. |
| What is a maturative ameloblast? | One whose Tome’s process has resorbed and exhibits a ruffled border . This cell membrane will then become the basal aspect again and anchor via hemidesmosomes to the newly secreted cuticle. |
| How does a mature ameloblast differ from a secretory ameloblast? | It lacks an active enamel-secreting face or Tome’s process. |
| What is a Tome's process? | A shovel-shaped slanted apical cell membrane that secretes amelogens into the surrounding environment that will mature into enamel. |
| What is a ruffled border? | A resorbed Tome’s process that secretes prismless enamel to “smooth off” the secretory surface |
| What is involved in enamel maturation? | The water and organic component of the newly secreted amelogens (enamelins) are replaced with calcium and phosphate ions. |
| List the similarities between dentin and enamel formation? | Similarities: secretory ends of odontoblasts and ameloblasts face the shared basal lamina; they both move away from the basal lamina as secretion begins; both layers communicate between cells via gap junctions. |
| 2339 What are the major differences between them? | odontoblasts produce CT-like material, ameloblasts produce no collagen; odontoblasts leave a long process in their matrix, ameloblasts do not; dentin initially (as in predentin) contains no HA salts, enamel matrix contains some as soon as it is deposited. |
| Where does root formation start? | After crown formation is complete and eruption begins. |
| What is the epithelial diaphragm? | The continuation of the cervical loop down into the root, points inward (and grows inward as well as downward) to define the eventual apical foramen as well as form the root sheath over each root defined by the inward growth of the epithelial diaphragm. |
| What does its downward growth leave behind and what does it form? | The epithelial root sheath (of Hertwig). This forms the overal shape (morphology) of the root. |
| What must be initiated before root formation can begin? and why? | Eruption. To make room within the bony crypt the tooth has developed in. |
| The cells of the IDE induce the pulp to differentiate into what cell type? | Odontoblasts |
| Do odontoblast stimulate the overlying IDE to become ameloblasts? | Yes |
| How is cementum formation initiated? | The epithelial root sheath breaks down allowing the surrounding CT cells to contact the dentin layer. Cementoblasts form and start to secrete cementum to cover the dentin. |
| What is an epithelial rest? | A remnant “island” of epithelial root sheath following its dissolution. |
| What cells are responsible for forming cementum? | Cementoblasts |
| What process is responsible for the formation of a multi-rooted tooth? | The inward growth of a projection from the epithelial diaphragm. |
| What is a bony compartment as opposed to a bony crypt? | A bony compartment is the space within the alveolar bone process in which the primary tooth develops. The term bony crypt refers to a similar space but contains the secondary tooth. |
| What are the three phases of eruption? | 1. Pre-eruptive phase; 2. Prefunctional eruptive phase; 3. Functional eruptive phase. |
| What occurs in the first phase to the bony compartment or crypt, the ameloblasts? | Marked bone remodelling of the bony compartment/crypt occurs. The ameloblasts of the reduced enamel epithelium become squamous-like at the cuspal areas. |
| List the 4 major events that occur during the pre-functional eruptive phase. | 1 Root formation begins 2 tooth moves toward oral cavity w/in compartment/crypt to make room for developing root 3 tip of crown of tooth penetrates fused epithelial layers entering oral cavity 4 tooth erupts until contacts opposing crown |
| What is the eruptive pathway? | An inverted triangle of tissue from the oral cavity to the eruptive location of the bony compartment/crypt. The blood and nerve supply degenerates in this region that will become the pathway for the erupting tooth. |
| What must be broken down for eruptive pathway to enlarge? | The roof of the bony compartment/crypt must be eroded by osteoclasts. Macrophages release hydrolytic enzymes breaking down overlying tissue in the eruptive pathway. |
| What two epithelial membranes fuse prior to eruption? | The reduced enamel epithelium covering the crown of the erupting tooth and the overlying oral epithelium. |
| From where does the periodontal membrane grow? | The PDL develops from a membrane of collagen fibers that begin to form at a growth center lateral to the lower end of the developing root. |
Created by:
wiechartm
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