Tooth Development Flashcards
What are the 3 primary embryonic layers?
- Ectoderm
- Mesoderm
- Endoderm
Which one of the 3 primary embryonic layers is tooth enamel derived from?
ectoderm
Which one of the 4 primary embryonic layers are all the parts of the teeth and supporting structure apart from tooth enamel derived from?
Ectomesenchyme
What is the Ectomesenchyme?
neural crest tissue that develops beside the primitive nervous system (ectoderm)
What do teeth develop from?
germs
What is the first stage of tooth development?
initiation
What is a depression between the brain and the pericardium in an embryo which is the precursor to the mouth called?
stomodaeum
Approximately when does the primary epithelial band develop?
6 weeks
What does the primary epithelial band appear as?
thickening of epithelium at the embryonic mouth (stomodaeum)
What is the embryonic mouth called?
stomodaeum
What 2 parts does the primary epithelial band divide into?
- Vestibular lamina, which will form the buccal sulcus
- Dental lamina, from which the enamel organ develops
Approximately when does the dental lamina develop?
7 weeks
What shape is the dental lamina?
horse-shoe
What is the second stage in tooth development?
morphogenesis (bud stage)
What does morphogenesis mean?
generation of shape
When does the enamel organ - ‘bud’ stage 2 occur?
8-10 weeks
What happens at the ‘bud’ stage of dental development?
- Dental lamina invaginate and thickens into a ‘bud’ stage enamel organ
- An Ectomesenchymeal cell collection appears and this is the dental papilla
When does the enamel organ - ‘cap’ stage 3 occur?
11 weeks
What 2 epitheliums are present in the enamel ‘cap stage’?
- External enamel epithelium
- Internal enamel epithelium
- EEE and IEE meet at the cervical loop
What is the acculmation of ectomesencymal cells around the enamel organ called?
dental follicule
What is the fourth stage of tooth development?
bell stage
When does the enamel organ - ‘bell’ (cytodifferentiation) stage occur?
14 weeks
At what stage is the tooth shape starting to be defined?
bell stage
What are the 4 cell layers present in the ‘bell’ stage?
- Stratum intermedium
- Internal enamel epithelium
- External enamel epithelium
- Stellate reticulum
What is the function of stellate reticulum in the bell stage?
keeping storage of nutrients for tissues
comprises of glycoaminosglycans (attract water) which allows space for developing crown
At what time does an extension appear on the lingual side of the dental lamina - this is the dental lamina for the adult tooth?
12 weeks
At what time does the 1st permanent molar germ develop as a backwards extension of the dental lamina?
16 weeks
What is the fifth stage of tooth development?
matrix secretion (late bell)
At what time does matrix secretion (late bell stage) occur?
18 weeks
In what stage does the positioning of enamel and dentine begin?
late bell stage within matrix secretion
At what stage do cells become specialised?
late bell stage within matrix secretion
What do dental papilla cells (adjacent to the internal enamel epithelium) differentiate into?
odontoblasts
What do odontoblasts do?
lay down dentine matrix which is later mineralised (predefine)
What do ameloblasts do?
form enamel
What is the process of dentinogenesis?
Odontoblast differentiation from dental papilla cells near IEE
Deposition of dentine matrix (mainly collagen)
This unmineralised dentine is predentine
Mineralisation of dentine (hydroxyapatite)
What do IEE cells differentiate into?
ameloblasts
What are the 2 phases of formation of enamel?
1- Protein matrix deposition (30% mineralised matrix
2- Framework established, organic part removed, mineralisation is complete
What happens during the differentiation stage of amelogenesis?
IEE cells elongate becomes columnar and the nucleus moves to the basal end to become ameloblasts
What happens during the secretory stage of amelogenesis?
ameloblasts secrete and synthesise matrix proteins form the crystallites and rods (no mineralisation/hydroxyapatite)
What happens during the maturation phase?
proteins are removed, mineral content is increased
What happens during protection stage in ameloblasts?
ameloblasts regress (become smaller) to form a protective layer around enamel involved in eruption and epithelial attachment
What is the 5th stage in tooth development?
root formation
What must be completed before the root begins to form?
crown
Where do the EEE and IEE meet?
cervical loop
What does migration of the cervical loop map out?
crown shape
What is the root shape defined by in root formation?
The length, curvature, thickness, and number of roots are all dependent on the inner root sheath cells.
What is the apical growth (proliferation of cervical root cells) of cervical root known as?
hertwig’s epithelial root sheath
What does the Hertwig’s epithelial root sheath induce?
formation of root dentine
What is ‘debris of Malassez’?
epithelial cells on the PDL that are remains of HERS -may develop into cyst
What are cementoblasts?
differentiated ectomesenchymal cells from the follicle
What is the type of tissue, origin and product of the enamel organ?
epithelium, ectoderm, enamel
What is the type of tissue, origin and product of the dental papilla?
ectomesenchyme, neural crest, dentine, pulp
What is the type of tissue, origin and product of the dental follicle?
ectomesenchyme, neural crest, cementum, PDL, alv bone
What are the possible characteristics of dental development disorders?
shape, size, structure, number, presence, eruption
What is hypodontia
absence of some teeth
What is supernumerary ‘mesio-dens’?
presence of extra tooth between two teeth
What is germination?
two teeth in one space
What is fusion?
similar to germination but more defined
What is dentinogenesis imperfecta?
incorrect formation of dentine
What type of shape are stratum intermedium and stellate reticulum cells?
stratum intermedium - spindle shaped
stellate reticulum - star shaped
What do dental follicle cells differentiate into?
oestoblasts (alv bone)
fibroblasts (PDL)
cemenotoblasts (cementum)
What are the dental follicle cells?
cells surrounding the sides of the enamel organ (dental lamina is at the bottom)
What is the role of the epithelial cell rests of malassez?
remnants of hertwigs epithelial root sheath, that allow dental follicle cells to come into contact with the root dentine and to differentiate into cementoblasts