Odontogenesis - 1 & 2 Flashcards
Explain how the face develops -> What happens in the 4th to 7th week, in terms of face and palate development?
In utero
1) 4th week
- cranial neural crest cells migrate to the front of the head & form frontonasal process, mandibular process & maxillary process.
- the primitive oral cavity (stomodeum) is bounded by 5 facial swellings
2) 5th week
- mesenchyme from the frontonasal proliferate around the openings of nasal pits produce medial and lateral nasal processes.
- the optic placode & nasal placode/pit forms -> becomes eyes and nostrils
3) 6th week
- mandibular process merge. (failure to fuse -> mandibular cleft)
4) 7th week
- the oronasal cavity is completely filled by the developing tongue. then the maxillary process merge.
- the maxillary processes grow inward beneath the lateral nasal processes and towards the medial nasal processes of the upper lip.
Explain the process of the development of the jaw -> mandible
- Mandible initially develops intramembranously.
1) 6th week: - Mandible 1st appears as band dense fibrous tissue on anterolateral aspect of Meckel’s cartilage.
2) 7th week: - ossification centre appears in the band of dense fibrous tissue, near the future mental foramen
- Bone formation spreads rapidly from the centre -> spreads around inferior alveolar nerve & terminal branches
3) Later stage: - Continued bone formation, increases the size of the mandible, to surround the developing tooth germ
4) Meckel’s cartilage resorbs
5) As tooth germs reach bell stage - Developing bone becomes closely related to it and forms the alveolus
- Ramus of mandible is mapped out via condensation of fibrocellular tissue
6) Further ramus development - Backward spread of ossification from the body of ramus
7) 10th – 14th week: - 3 secondary cartilages develop within mandible
a) Largest = condylar cartilage (centre for mandible growth) - > lasts for 20 years old.
b) Second = Coronoid process
c) Third = in region of mandibular symphysis
8) Temperomandibular joint develops from mesenchyme - TMJ lies between developing mandibular condyle (below) & temporal bone (above)
- Both develop intramembranously
9) At birth: - No distinct chin
- 2 halves of mandible separated by mandibular symphysis
10) 2 years: - Ossification of symphysis is completed
- Growth of mandible occurs via bone remodelling
Explain the process of the development of the jaw -> maxilla
- develops intramembranously.
- 8th week: Centre of ossification appears
- Unlike the mandible, maxillary growth is not related to the appearance of secondary cartilages, because of the maxilla’s position in the developing skull
- Maxilla’s growth is influenced by the development of
o Orbital cavity
o Nasal cavity
o oral cavities - Growth of the maxilla occurs by bone remodelling & sutural growth.
- Premaxilla (Incisor-bearing part of the maxilla) -> develops from the frontonasal process
- Maxillary sinus -> outpocketing of the mucosa of the middle meatus of the nose at the beginning of the 4th month of intrauterine life.
When does the primary and permanent dentition develop?
- primary dentition -> develops during prenatal period
- Permenant dentition -> develops as the jaw grows and matures
what stage of odontogenesis does the tooth differentiate?
- bell stage.
What are the stages of tooth development?
- initiation stage – 6th to 7th week
- bud stage – 8th week *
- cap stage – 9th to 10th weeks *
- bell stage – 11th to 12th weeks *
- apposition stage – varies per tooth
- maturation stage – varies per tooth
Define the following: initiation, morphogenesis & histiogenesis.
1) initiation
- sites of the future teeth are establish by the appearance of tooth gems along an invagination of the oral epithelial -> called dental lamina
2) Morphogenesis
- shape of the tooth is determined by a combination of cell proliferation and cell movement.
3) Histiogenesis
- differentiation of cells (begun during morphogenesis), which give rise to dental tissues, both mineralized (enamel, dentin and cementum) and unmineralized (dental pulp, and periodentum).
Explain the bud stage.
- 8th week: a series of epithelial swellings develops on the deep surface of the dental lamina
o These epithelial swellings indicate early developing tooth germs.
Process
- Invagination of epithelium (forms buds) that invaginate into mesenchyme
o each tooth bud is surrounded by mesenchyme
- buds + mesenchyme develop into -> tooth germ + associated tissues of the tooth
- Enamel organ appears as simple, spherical/ ovoid epithelial condensation
Explain the cap stage.
1) At early cap stage – differentiation poor
- difference between between the round cells in the middle & periphery of enamel organ.
- Cells become arranged to form external & internal epithelia
2) At late cap stage – 12th week
- Central cells of enlarging enamel organ become separated, because they contain lots of glycosaminoglycans, which bring in water -> giving STELLATE RETICULUM
CELL DIFFERENTIATION:
o Cells of external enamel epithelium – stay cuboidal
o Cells of internal enamel epithelium – become more columnar
o Mesenchyme beneath internal enamel epithelium -> DENTAL PAPILLA
o Mesenchyme surrounding tooth germ -> DENTAL FOLLICLE/ SAC
Explain the bell stage.
- what are the main parts of the bell stage?
- what are the 4 main cells in the enamel organ?
- what 2 cells do dental papilla differentiate into?
- Continuation of histodifferentiation & morphodifferentiation
- Cap shape -> Bell shape
- Main parts:
o Enamel organ
o Dental papilla
o Dental follicle (surrounding) - Differentiation makes FOUR types of cells within enamel organ:
1) Inner enamel epithelium
2) outer enamel epithelium
3) Stellate reticulum
4) Stratum intermedium - Dental lamina becomes separated from dental organ
- Dental papilla undergoes differentiate & produces TWO types of cells
1) Outer cells of DP – forms odontoblasts
2) Central cells of the DP – forms the primordium of pulp
Explain the initiation stage and the formation of the dental lamina.
1) 6th week: the oral epithelium thickens and invaginates into the mesenchyme
o form a Primary epithelial band.
2) 7th week: the primary epithelial band divides into 2 processes:
a) Vestibular lamina (buccally located)
- contribute to vestibule of the mouth, delineating of lips and cheeks
b) Dental lamina (lingually located)
- contribute to development of teeth
What is the difference between dental lamina and enamel organ?
1) dental lamina = first signs of tooth development -> appears in 6th embryonic week.
- At that time, oral epithelium thickens & grows downward into the underlying connective tissue and does not create a visible ridge. This thickened oral epithelium is known as the dental lamina.
2) enamel organ
- aggregation of cells in the dental lamina
- each will become a tooth -> mapping the shape and size of tooth.
Explain what happens in the apposition stage.
- secretion of dentin, enamel & cementum
- these are secreted as matrix that is partially calcified.
- time period varies for each tooth3
Explain what happens in the maturation stage.
- completion of calcification of dentin, enamel &
cementum.
Explain the structural development of dentin.
- First deposited as layer of pre-dentin
- Unmineralised matrix secreted by odontoblasts (a mesh of collagen fibres)
- pre-dentin calcifies within 24 hours by hydroxyapatite.
- odontoblast processes elongate and are trapped in dental tubules.
- Forms from pulp -> surface & spread down cusp slope to cervical loop
- root dentin forms later
What is the difference between pre-dentin & dentin?
PRE-DENTIN
- mainly collagen & non-collagenous components
- elastic quality –> flexibility & prevents fracture
- yellowish colour
- Gradually mineralizes to form dentin
DENTIN
- Inorganic – hydroxyapatite in forms of small plates
- Organic – collagen type I, III, V
- collagen type I = act as scaffold for mineral in holes & pores of fibrils
- Tubules follow curves – flexibility & ability to withstand forces
What are ameloblasts?
- cells that produce enamel
- derived from cells of inner enamel epithelium
How do ameloblasts differentiation occur?
1) IEE differentiate into pre-ameloblasts
- Cells of the IEE become more columnar & elongated
- cells undergo repolarisation -> nucleus moves away from the membrane
2) Formation of ameloblast
- continued differentiation & maturation.
Note:
- occurs after dentine has been produced
- pre-Abs induce cells of dental papilla to differentiate
- dentine & enamel are deposited in opposite directions.
What are the life cycle stages of ameloblast?
1) Morphodifferentiation
- Shape changes
2) Histodifferentiation
- Cells change to become functional
3) Secretory (initial)
- Initial -> 1st layer of enamel deposited (30% inorganic)
- Tome’s process -> Replacement of organic by inorganic material
4) Maturation
- ruffle-ended: Absorb organic material & incorporate inorganic material via ameloblast
- smooth-ended: exit of protein fragments & water
5) Protective
- Atrophy of ameloblasts
What are the processes of amelogenesis?
There are 3 main stages
1) presecretory
- differentiation: morphodifferentiation (shape changes) & histodiffernetiation (microscopic)
- repolarisation: change polarity
- develop enamel synthesis apparatus
2) Secretory
- produces partially mineralised enamel (30% mineralised)
3) Maturation
- mineralise organic matter & removal of some organic matter -> 96% mineralisation.
- growth of crystals in width & thickness.
What direction does ameloblasts secrete enamel?
- Begins at first cusps tips
- Then sweeps down crow slopes
- Stops at CEJ (cemento-enamel junction)
What types of protein are in the enamel?
a) Amelogenins (bulk of proteins)
- accumulate during the secretory stage
b) non-ameloginins
- Enamelin (2%)
- Amelins/Ameloblastins (5-10%)
c) sulfated glycoproteins
d) Tuftelin (at DEJ)
e) enzymes
o Metalloproteinases (e.g. MMP20)
o Enamelysin (short-term breakdown)
o Serine proteinases (bulk degradation)
o Phosphatases
f) dentin sialoprotein
What is the developmental process of odontoblasts?
- pre-AB triggers the differentiation of mesenchymal cells to undergo repolarisation. There are also signalling molecules and growth factors secreted by IEE.
- odontoblasts then start dentinogenesis.
o deposit predentine on both sides of their basement membrane
o dentine depositition starts before enamel -> hence it’s thicker.
Explain the formation of mantle dentin.
- forms after OD differentiation
- ODs secrete Korff’s fibres (CNIII + fibronectin) in dental papilla
- Fibres extend towards IEE & fan out below epithelium
- As ODs increase in size & mature, it produce smaller CNI fibrils
- OD’s membrane extends processes into the ECM (inside dental papilla) & form enamel spindles
- also develops processes (Tome’s fiber) -> Left behind in the dental matrix as OD moves away from BM toward pulp
- Become fenestrated – increased exchange
