Odontogenesis Flashcards
What are the 3 phases of tooth development?
Initiation (Sites of future teeth are established by tooth germs which are formed from invaginations of the oral epithelium called dental lamina)
Morphogenesis (The shape of the crown is established)
Histogenesis (The formation of enamel and dentin as well as dental pulp and periodontium)
What is the embryological origin of the teeth and vestibule of the mouth?
Ectomesenchymal tissue from the neural crest forms the dental papilla
Ectoderm forms the enamelitself
What are the 2 types of lamina formed in the oral cavity? What do they form?
Dental lamina which form the teeth.
Vestibular lamina which form the gums and the rest of the oral cavity.
Which side of the mouth does the vestibular lamina form?
Buccally
Which side of the mouth does the dental lamina form?
Lingually
How are the laminae formed?
First there is a thickening of mesenchyme in the oral epithelium which thickens
by the 6th week the oral epithelium thickens and invaginates into the oral mesenchyme to form a primary epithelial band.
By the 7th week the primary epithelial band divides into 2 processes, a buccally located vestibular lamina and a lingually located dental lamina.
What are the stages of formation of the teeth from tooth germs?
Bud stage
Cap stage
Bell stage
They are differentiated based on themorphodifferentiation and histodifferentiation of their enamel organs (epithelial components)
What happens during the bud stage?
The enamel organ in the bud stage is a simple, spherical or ovoid, epithelial condensation that is poorly morphodifferentiated and histodifferentiated. It is surrounded by mesenchyme.
*The cells of the tooth bud have a higher RNA content than those of the overlying oral epithelium, a lower glycogen content and increased oxidative enzyme
activity.
What happens during the cap stage?
During the cap stage there is morphodifferentiation of the enamel organ to form a cap shaped structure.
Internal and external enamel epithelia are formed from peripheral cells (columnar cells) and a central portion is formed which consists of rounded cells (cuboidal cells).
In the 12th week the stellate reticulum starts to form from the central rounded cells. Intercellular spaces contain lots of glycosaminoglycans
What happens during the early bell stage?
Further morphodifferentiation and histodifferentiation takes place.
A high degree of histodifferentiation is achieved in the early bell stage. The enamel organ shows four distinct layers: external enamel epithelium, stellate reticulum, stratum intermedium and internal enamel
epithelium.
What week does the cap stage begin?
11th week of development
When does the early bell stage begin?
14th week of development
How would bone resorption issues affect the bell stage?
They would interfere with mitoses that take place leading to altered occlusal margins in the tooth. (increased internal epithelial folding is common)
What does the external enamel epithelium do during the bell stage?
The external enamel epithelium is thought to be involved in the maintenance of the shape of the enamel organ and in the exchange of substances between the enamel organ and the environment.
The point at which the external and internal enamel epithelium meet is the cervical loop
What happens in the stellate reticulum during the bell stage?
In addition to glycosaminoglycans, the cells also contain
alkaline phosphatase but have only small amounts of RNA and glycogen. The mesenchyme-like features of the stellate reticulum include the synthesis of collagens in the tissue.
The main function ascribed to the stellate reticulum is a mechanical one. This relates to the protection of the underlying dental tissues against physical disturbance and to the maintenance of tooth shape. It has been
suggested that the hydrostatic pressure generated within the stellate reticulum is in equilibrium with that of the dental papilla, allowing the proliferative pattern of the intervening internal enamel epithelium to determine
crown morphogenesis.
What does the ennermost cell layer do in the enamel organ?
The innermost cell layer of the enamel organ, the internal enamel epithelium, deposits and later modifies the enamel. The other components of the enamel organ, the stratum intermedium, the stellate reticulum and the external enamel epithelium, play important supportive roles.
What does the dental papilla seen in the cap stage mature into?
The Dentin and the pulp
What does the dental follicle seen in the cap stage develop into?
The cementum, the periodontal ligament, and the alveolar bone
Which structure from the cap stage eventually forms the enamel?
The enamel organ; the inner epithelium forms ameloblasts which elongate to form enamel.
Which structure from the cap stage forms the dentin?
The dental papilla cells differentiate into odontoblasts which form the dentin in the opposite direction to the enamel.
Why are cells of the stellate reticulum shaped like stars?
Cells within the stellate reticulum produce glycosaminoglycans which increase the osmolarity of the central chamber and these cells are connected to each other by gap junctions. So when water enters the central chamber it expands pulling the cells apart.
When are cervical roots formed?
During the bell stage
What structures form the cervical loops?
They are formed by the junction between internal and external enamel epithelium which extends to form the cervical sheath and then the root of the tooth.
What is morphodifferentiation during the bell stage? what happens simultaneously to this stage?
The establishment of the shape of the crown
Histodifferentiation occurs simultaneously.
What happens during histodifferentiation?
The Odontoblasts are formed from the dental papilla and the ameloblasts are formed from the enamel organ’s inner epithelium.
When happens to the dental lamina during the late bell stage?
It disintegrates and degenerates. Separating the tooth germ from the oral epithelium.
What adverse outcome could arise from the disintegrated dental lamina?
The remaining cells can form odontogenic cysts and tumours
The cells can also form extra teeth
What tooth development stage do we see mineralization of the matrix? What else happens during this stage?
Advanced bell stage.
During this stage the tooth is mineralized while organic material is also degraded.
Ameloblasts eventually also fuse with the outer enamel epithelium and form the reduced enamel epithelium.
What structure is formed by the fusion of the internal and external enamel epithelia? What does this become?
Hertwig’s root sheath which becomes the tooth’s root.
Inner layer of root sheath cells become odontoblasts which secrete dentin. The root sheath disintegrates and cells from the follicle interact with the newly formed dentin and these cells form cementum and the periodontal ligaments.
Some cells remain and become the epithelial rests of malassez
What triggers differentiation of dental papillary cells into odontoblasts?
Differentiation of dental papillary cells into odontoblasts is a result of signalling from the differentiating inner enamel epithelium.
How is the formation of dentin related to the formation of enamel?
The establishment of a layer of dentin is necessary for the production of enamel matrix and thus inner enamel epithelium stimulates dental papilla cells to differentiate into a layer of dentin and then the layer of dentin triggers inner enamel epithelial cells to form enamel.
Which phase of amelogenesis is the Tomes’ process produced?
During the secretory phase
What happens during the 3 phases of amelogenesis?
Presecretory: Ameloblasts are formed from inner enamel epithelium
Secretory: Ameloblasts produce extracellular matrix proteins
Maturation: The enamel becomes mineralized by producing inorganic hydroxyapatite and breaking down the organic material
How does the Tomes’ process allow for the production of enamel?
It is responsible for the release of extracellular matrix proteins into the enamel. Initial layer produced is then mineralized immediately (this layer is made up of mantle dentin and this layer does not contain enamel rods.)
The Tomes’ process extends distally after the formation of the initial layer. The distal part of the Tomes’ process produces the rods and the proximal part produces inter rod enamel.
Enamel sheath is produced between the rod and inter rod enamel groupings.
Finally, the distal portion of the Tomes’ process disappears and a layer of rodless enamel is formed creating a sandwich of enamel with rods between to layers of rodless enamel.
What are the stages of the maturation phase of enamel formation? What happens during these phases?
Transitional phase: Ameloblasts decrease in size and undergo apoptosis. The layer of ameloblasts is reduced.
Maturation proper phase: Inorganic material replaces organic material. A ruffled border is formed by the reduced ameoblasts in a cyclical way (creation, loss, recreation of this border). Ruffle ended ameloblasts have tight junctions on apical border, whereas smooth ended ameloblasts have leaky junctions.
Tight junctioned ameloblasts produce lysosymes, serine proteases and metalloproteinases which break down the proteins in the enamel matrix. These broken down proteins then diffuse into the smooth ended ameloblasts.
Calcium binding proteins and calcium ATPases help increase calcium levels in the enamel matrix thus mineralizing it.
This occurs in waves travelling from the least mature part of the crown to the most mature.
When do periodontal tissues start to develop?
After the tooth’s root has calcified
When does the initiation stage of tooth development begin?
in the 6th to 7th week of gestation
When does the bud stage of tooth development occur?
In the 8th week
