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DS1101 - S1 Y1 > Week 9 - Tooth Development Amelogenesis and Dentinogenesis > Flashcards

Week 9 - Tooth Development Amelogenesis and Dentinogenesis Flashcards

1
Q

What is amelogenesis

A

the process of enamel formation in teeth

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2
Q

What synthesizes enamel

A

inner enamel epithelium cells which differentiate into ameloblasts

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3
Q

What happens prior to amelogenesis

A

Odontoblasts initiate dentine matrix formation prior to the beginning of amelogenesis

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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
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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
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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
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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
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8
Q

What is the composition of developing enamel

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

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12
Q

What is the reduced enamel epithelium (REE)

A

Remnants of the enamel organ which has merged with flattened ameloblasts

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13
Q

What is the Nasmyth’s membrane

A

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

It protects the enamel during eruption

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14
Q

What is dentinogenesis

A

the process of the formation of dentin from odontoblasts

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15
Q

what cells produces dentin

A

ectomesenchyme dental papilla cells which differentiate into odontoblasts

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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
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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)
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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
Q

What is the circumpulpal dentine

A

mineralized dentine formed after the first layer

26
Q

What is the pre-dentine

A

newly formed uncalcified dentine

27
Q

What is the composition of dentine matrix

A
  • collagen (type 1) fibrils
  • Dentine phosphoprotein
28
Q

Explain the step of mineralization and modification in dentinogenesis

A
  • 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
Q

What is the periodontium composed of

A
  • cementum
  • periodontal ligament
  • Alveolar bone
  • gingiva and dento-gingival junction
30
Q

What produces the periodontium

A

dental follicle - ectomesenchyme

31
Q

What is cementogenesis

A

the process of the formation of cementum

32
Q

What type of cells produce cementum

A

dental follicle cells which differentiate into cementoblasts

33
Q

Where and when does cementogenesis occur

A

cervical margin after crown formation

34
Q

What is the first step in cementogenesis

A
  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
Q

What is the second step in cementogenesis

A

cementoblasts secrete non-collagenous matrix
- the first layer of cementum has extrinsic fibres which were within the dental follicle
- cementoblasts become trapped in the forming of cementum and become cementocytes

36
Q

What are the 2 types of cementum

A
  1. Acellular cementum
  2. Cellular Cementum
37
Q

What is acellular cementum

A

cementum in the upper 2/3 of the root

38
Q

What is cellular cementum

A

cementum in the lower 1/3 of the root

39
Q

What is commonly found in acellular cementum and not cellular cementum

A

extrinsic fibres
which are produced by fibroblasts and a few cementoblasts

40
Q

What is commonly found in cellular cementum and not acellular cementum

A

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

41
Q

What are the 3 configurations of cemeto-enamel junctions

A
  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
42
Q

What is the periodontal ligament

A

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

43
Q

What forms the periodontal ligament

A

dental follicle

DS1101 - S1 Y1 (50 decks)

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