Week 9 - Tooth Development Amelogenesis and Dentinogenesis

Question 1

What is amelogenesis

Answer 1

the process of enamel formation in teeth

Question 2

What synthesizes enamel

Answer 2

inner enamel epithelium cells which differentiate into ameloblasts

Question 3

What happens prior to amelogenesis

Answer 3

Odontoblasts initiate dentine matrix formation prior to the beginning of amelogenesis

Question 4

What are the 5 stages of amelogenesis

Answer 4

1. Pre-secretory (active)
2. Secretory (active)
3. Transitional
4. Maturational (active)
5. Post-maturational

Question 5

What occurs in the pre-secretory stage of amelogenesis

Answer 5

• 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

Question 6

What occurs during the secretory stage of amelogenesis

Answer 6

• 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

Question 7

What occurs in the transition stage

Answer 7

• 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

Question 8

What is the composition of developing enamel

Answer 8

• Amelogenins 90-95%
• Non-amelogenins 5-10%

Question 9

What occurs in the maturation stage

Answer 9

• 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

Question 10

What occurs in post maturation stage- amelogenesis

Answer 10

• 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)

Question 11

What is the primary enamel cuticle

Answer 11

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

Question 12

What is the reduced enamel epithelium (REE)

Answer 12

Remnants of the enamel organ which has merged with flattened ameloblasts

Question 13

What is the Nasmyth’s membrane

Answer 13

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

It protects the enamel during eruption

Question 14

What is dentinogenesis

Answer 14

the process of the formation of dentin from odontoblasts

Question 15

what cells produces dentin

Answer 15

ectomesenchyme dental papilla cells which differentiate into odontoblasts

Question 16

What is the function of dentin

Answer 16

• Forms a protective covering for dental pulp and provides support for overlying enamel
• It also contains odontoblast processes and nerves

Question 17

What are the physical properties of dentin

Answer 17

• 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)

Question 18

What is the chemical composition of dentin

Answer 18

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

Question 19

When during tooth formation does dentinogenesis start

Answer 19

bell stage

Question 20

What are the stages of dentinogenesis

Answer 20

1. Odontoblast differentiation
2. Matrix Deposition
3. Mineralization and modification

Question 21

Explain the step of differentiation of odontoblasts

Answer 21

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

Question 22

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

Answer 22

• 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

Question 23

Explain the step of deposition of dentine martix

Answer 23

• 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

Question 24

What is the mantle dentine

Answer 24

the first layer of dentine formed by odontoblasts

Question 25

What is the circumpulpal dentine

Answer 25

mineralized dentine formed after the first layer

Question 26

What is the pre-dentine

Answer 26

newly formed uncalcified dentine

Question 27

What is the composition of dentine matrix

Answer 27

- collagen (type 1) fibrils - Dentine phosphoprotein

Question 28

Explain the step of mineralization and modification in dentinogenesis

Answer 28

- 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

Question 29

What is the periodontium composed of

Answer 29

- cementum - periodontal ligament - Alveolar bone - gingiva and dento-gingival junction

Question 30

What produces the periodontium

Answer 30

dental follicle - ectomesenchyme

Question 31

What is cementogenesis

Answer 31

the process of the formation of cementum

Question 32

What type of cells produce cementum

Answer 32

dental follicle cells which differentiate into cementoblasts

Question 33

Where and when does cementogenesis occur

Answer 33

cervical margin after crown formation

Question 34

What is the first step in cementogenesis

Answer 34

1. At the beginning of dentinogenesis HERS ( epithelial sheath) lose their continuity and dental follicle cells adjacent to the root dentine differentiate into cementoblasts

Question 35

What is the second step in cementogenesis

Answer 35

- 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

Question 36

What are the 2 types of cementum

Answer 36

1. Acellular cementum 2. Cellular Cementum

Question 37

What is acellular cementum

Answer 37

cementum in the upper 2/3 of the root

Question 38

What is cellular cementum

Answer 38

cementum in the lower 1/3 of the root

Question 39

What is commonly found in acellular cementum and not cellular cementum

Answer 39

extrinsic fibres which are produced by fibroblasts and a few cementoblasts

Question 40

What is commonly found in cellular cementum and not acellular cementum

Answer 40

cementoblasts which secrete intrinsic fibers these fibres have no role in attachment

Question 41

Out of extrinsic and intrinsic fibers which helps with attachment

Answer 41

extrinsic

Question 42

What are the 3 configurations of cemeto-enamel junctions

Answer 42

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

Question 43

What is the periodontal ligament

Answer 43

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

Question 44

What forms the periodontal ligament

Answer 44

dental follicle