Week 9 - Tooth Development Flashcards
How many teeth are there in a primary dentition
20
How many teeth are there in a permanent dentition
32
What is the anatomically distinct unit where each tooth develops from
tooth germ
Where do permanent molars develop in comparison to the deciduous
distal
where do permanent successors develop in comparison to the deciduous buds
lingual
What are the 2 tissues which teeth develop from
epithelium and ecto-mesenchyme
Where is epithelium derived from
ectoderm
where is ecto-mesenchyme derived form
neural crest cells
What in the tooth germ does the ectoderm eventually form
enamel organ
What does the enamel organ eventually form
enamel
What does the ectomesenchyme form in the tooth germ
dental follicle and dental papilla
what does the dental follicle form
cementum
periodontal ligament
alveolar bone
what does the dental papilla form
dental pulp
What comprises the tooth germ
enamel organ
dental follicle
dental papilla
What are the 3 stages of tooth development
- Bud stage
- Cap stage
- Bell stage
When does pre tooth development occur
6th week
What occurs in pre tooth development
primary epithelial band forms which corresponds to the position of the future upper and lower jaws
In week 7 of fetal development this primary epithelial band will bifurcate into a lingual process called the dental lamina and a buccal vestibular lamina.
What occurs in the bud stage
- The dental lamina proliferates and takes the shape of a bud which is referred to as the enamel organ
- During this there is also a dense condensation of ecto-mesenchymal cells around the bud
What occurs in the cap stage
- Concavity of the epithelium forms due to unequal rates of cell division, forming a cap shape
- Ectomesenchyme cells that surround the concavity is called the dental papilla
- Ectomesenchyme cell which surround the whole enamel organ is called the dental follicle
What happens in the late cap stage
- Central cells of the enamel organ becomes stellate reticulum
- cells which line the concavity becomes inner enamel epithelium
- outer cells become outer enamel epithelium
What occurs in the bell stage
- Week 14
-enamel organ grows to form a bell shape establishing the shape of the crown
-inner enamel epithelial cells differentiate into pre-ameloblasts (will form enamel) - dental papilla cells differentiate into odontoblasts (will form dentin)
- dental lamina between the oral epithelium and tooth germ separate
- dental lamina breaks down
- Remnants of dental lamina may remain in the adult mucosa (epithelial cell rests (pearls) of serres)
- Shape of the future crown is defined
What occurs during the late bell stage
- Dentine formation (always occurs before enamel formation)
- Cementum formation
- Enamel formation
outer enamel epithelium
inner enamel epithelium
dental papilla
ameloblasts
stellate reticulum
cervical loop
dental follicle
Stratum Intermedium
odontoblasts
Describe outer enamel epithelium
- cuboidal cells
- contact with each other via desmosomes and gap junctions
- function to maintain the shape of the enamel organ
- function to allow exchange of substances
Describe stellate reticulum
- star shaped cells
- they fill the inner space of the enamel organ and excrete fluid
- provides protection
describe stratum intermedium
- lies on top of the inner enamel epithelium
- contain alkaline phosphatase
- concerned with protein synthesis and its transport to and form the ameloblasts
Describe inner enamel epithelium
- columnar
- Rich is RNA
- links with stratum intermedium by desmosomes
- differentiates into pre-ameloblasts
- No alkaline phosphatase
Where does enamel and dentin formation begin
at the future cusp tips/incisal edges
What are 3 transitory structures
- Enamel knot
- Enamel cord
- Enamel niche
What are enamel knots
- These are localized thickening at the center of the inner enamel epithelium,
- characterized by bulges into the dental papilla
- It may be an important signaling center which helps direct tooth development
- Disappears in the bell stage
What are enamel cords
- a strand of cells seen at the early bell stage
- extends from the stratum intermedium to stellate reticulum
- its called enamel septum when it completely divides the stellate reticulum
- function is unknown
What are enamel niche
- The space in between the lateral and medial enamel strands (enamel strands are the dental lamina connecting the oral epithelium and the tooth germ)
- Function is unknown
When does root formation occur
after crown formation is complete
How do roots form
- Cells proliferates at the cervical loop creating Hertwig’s epithelial root sheath
- The HERS bends inwards towards the dental papilla to create the epithelial diaphragm
- HERS cells signal the differentiation of dental papilla cells adjacent to it into odontoblasts
- As odontoblasts secrete the root dentine the HERS cells disintegrate and move away
- With the disintegrated HERS dental follicle cells adjacent to the root dentin differentiate into cementoblasts
- Root elongation continue as more dentin and cementum are deposited
What is it called where HERS cells disintegrate but don’t move away from the root - and what can it cause
cell rest of Malassez which may lead to the development of cysts
What is hypodontia
the absence of fewer than 6 teeth (not including third molars)
What is oligodontia
the absence of 6 or more teeth (not including third molars)
What is anodontia
the complete absence of teeth
