Week 9 - Tooth Development Amelogenesis and Dentinogenesis Flashcards

1
Q

What is amelogenesis

A

the process of enamel formation in teeth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What synthesizes enamel

A

inner enamel epithelium cells which differentiate into ameloblasts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What happens prior to amelogenesis

A

Odontoblasts initiate dentine matrix formation prior to the beginning of amelogenesis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the 5 stages of amelogenesis

A
  1. Pre-secretory (active)
  2. Secretory (active)
  3. Transitional
  4. Maturational (active)
  5. Post-maturational
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What occurs in the pre-secretory stage of amelogenesis

A
  • Inner enamel epithelium differentiate into pre-ameloblasts
  • Pre-ameloblasts induce dental papilla cells to differentiate into pre-odontoblasts
  • Pre-odontoblasts release enzymes that degrade the basal lamina (separates enamel organ and dental papilla)
  • Odontoblasts begin to lay down dentin matrix
  • The first formed dentine induces the pre-ameloblasts to change into Ameloblasts
  • Ameloblasts first lay down enamel at the future cusp tips/incisal edges
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What occurs during the secretory stage of amelogenesis

A
  • tomes process forms (cone shaped process at the end of the ameloblast)
  • The Tomes process secretes enamel matrix protein
  • Enamel crystals that elongate around the tip of the tomes process form the prism core
  • Enamel Crystals extending from where the ameloblasts are joined to each other form at the prism boundary
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What occurs in the transition stage

A
  • Enamel secretion by the ameloblast stops
  • Ameloblasts reduce in height and the number of them reduce by 50%
  • All organelles of ameloblasts are reduced
  • Blood vessels invaginate into the enamel organ
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the composition of developing enamel

A
  • Amelogenins 90-95%
  • Non-amelogenins 5-10%
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What occurs in the maturation stage

A
  • Ameloblasts move minerals (Ca, PO4, CO2) into the matrix) and removes water and enamel matrix proteins
  • Enamel crystals increase in width and thickness and the crystals get closer together (reduction in the crystal space)
  • Amount of organelles in ameloblasts reduce
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What occurs in post maturation stage- amelogenesis

A
  • Ameloblasts become flat ended
  • A thin layer of protein separates ameloblast cells from enamel (primary enamel cuticle)
  • Remnants of enamel organ merge with flattened ameloblasts to form reduced enamel epithelium (REE)
  • Primary enamel cuticle + REE = Nasmyth’s membrane (protects enamel during eruption)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the primary enamel cuticle

A

thin layer of protein which separates ameloblast cells from enamel
It is the material extruded from the enamel during maturation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the reduced enamel epithelium (REE)

A

Remnants of the enamel organ which has merged with flattened ameloblasts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the Nasmyth’s membrane

A

Nasmythy’s membrane = primary enamel cuticle + reduced enamel epithelium

It protects the enamel during eruption

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is dentinogenesis

A

the process of the formation of dentin from odontoblasts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what cells produces dentin

A

ectomesenchyme dental papilla cells which differentiate into odontoblasts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the function of dentin

A
  • Forms a protective covering for dental pulp and provides support for overlying enamel
  • It also contains odontoblast processes and nerves
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are the physical properties of dentin

A
  • pale yellow colour
  • Tubular structure
  • Harder than bone and cementum but softer than enamel
  • Organic matrix and tubular structure provides greater compressive, tensile and flexural strength
  • Permeable (enamel is not permeable)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the chemical composition of dentin

A
  • The majority of dentin is composed of inorganic substances (70%) (mostly hydroxy apatite)
  • 20% organic (mostly collagen type 1)
  • 10% water
19
Q

When during tooth formation does dentinogenesis start

A

bell stage

20
Q

What are the stages of dentinogenesis

A
  1. Odontoblast differentiation
  2. Matrix Deposition
  3. Mineralization and modification
21
Q

Explain the step of differentiation of odontoblasts

A
  1. inner epithelium differentiate into pre-ameloblasts
  2. Pre-ameloblasts induce the peripheral layer of the dental papilla to differentiate into pre-odontoblasts
  3. The mitosis of one dental papilla cell produces a pre-odontoblast and undifferentiated mesenchymal cell
22
Q

What changes do dental papilla cells undergo to differentiate into pre-odontaoblasts

A
  • increase in size
  • Nucleus moves tot he basal part of the cell
  • golgi complex becomes prominent and positioned above nucleus
  • Rough ER increase in size
  • cell to cell junctions increase in number
  • Cell processes (extensions) extend towards the bottom of the inner enamel epithelium
23
Q

Explain the step of deposition of dentine martix

A
  • Dully developed odontoblasts produce dentin matrix

First formed dentine is called mantle dentine

Subsequently formed dentine is called circumpulpal dentine

Newly formed uncalcified dentine is called pre-dentine

24
Q

What is the mantle dentine

A

the first layer of dentine formed by odontoblasts

25
What is the circumpulpal dentine
mineralized dentine formed after the first layer
26
What is the pre-dentine
newly formed uncalcified dentine
27
What is the composition of dentine matrix
- collagen (type 1) fibrils - Dentine phosphoprotein
28
Explain the step of mineralization and modification in dentinogenesis
- odontoblasts form matrix vesicles which lie in the dentine - These matrix vesicles contains alkaline phosphatase and metalloproteinases - These matrix vesicles later rupture depositing calcium - this mineralizes the dentine, as it leads to crystal growth
29
What is the periodontium composed of
- cementum - periodontal ligament - Alveolar bone - gingiva and dento-gingival junction
30
What produces the periodontium
dental follicle - ectomesenchyme
31
What is cementogenesis
the process of the formation of cementum
32
What type of cells produce cementum
dental follicle cells which differentiate into cementoblasts
33
Where and when does cementogenesis occur
cervical margin after crown formation
34
What is the first step in cementogenesis
1. At the beginning of dentinogenesis HERS ( epithelial sheath) lose their continuity and dental follicle cells adjacent to the root dentine differentiate into cementoblasts
35
What is the second step in cementogenesis
- They secrete collagen fibrils into unmineralized dentine - secrete non-collagenous matrix - migrate towards the periodontal ligament secreting cementum matrix until the forming of periodontal fibers (extrinsic fibers) become incorporated to the cementum - cementoblasts become trapped in the forming of cementum and become cementocytes
36
What are the 2 types of cementum
1. Acellular cementum 2. Cellular Cementum
37
What is acellular cementum
cementum in the upper 2/3 of the root
38
What is cellular cementum
cementum in the lower 1/3 of the root
39
What is commonly found in acellular cementum and not cellular cementum
extrinsic fibres which are produced by fibroblasts and a few cementoblasts
40
What is commonly found in cellular cementum and not acellular cementum
cementoblasts which secrete intrinsic fibers these fibres have no role in attachment
41
Out of extrinsic and intrinsic fibers which helps with attachment
extrinsic
42
What are the 3 configurations of cemeto-enamel junctions
1. Cementum overlaps enamel for a short distance (60%) 2. Butt joint between enamel and dentine (30%) 3. Dentine between enamel and cementum is exposed (10%) - this leads to a high probability of caries in the dentine
43
What is the periodontal ligament
dense fibrous connective tissue which is situated between the cementum and the alveolar bone socket providing support and anchoring the teeth within the jaw bone
44
What forms the periodontal ligament
dental follicle