Week 9 - Tooth Development Amelogenesis and Dentinogenesis Flashcards
What is amelogenesis
the process of enamel formation in teeth
What synthesizes enamel
inner enamel epithelium cells which differentiate into ameloblasts
What happens prior to amelogenesis
Odontoblasts initiate dentine matrix formation prior to the beginning of amelogenesis
What are the 5 stages of amelogenesis
- Pre-secretory (active)
- Secretory (active)
- Transitional
- Maturational (active)
- Post-maturational
What occurs in the pre-secretory stage of amelogenesis
- 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
What occurs during the secretory stage of amelogenesis
- 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
What occurs in the transition stage
- 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
What is the composition of developing enamel
- Amelogenins 90-95%
- Non-amelogenins 5-10%
What occurs in the maturation stage
- 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
What occurs in post maturation stage- amelogenesis
- 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)
What is the primary enamel cuticle
thin layer of protein which separates ameloblast cells from enamel
It is the material extruded from the enamel during maturation
What is the reduced enamel epithelium (REE)
Remnants of the enamel organ which has merged with flattened ameloblasts
What is the Nasmyth’s membrane
Nasmythy’s membrane = primary enamel cuticle + reduced enamel epithelium
It protects the enamel during eruption
What is dentinogenesis
the process of the formation of dentin from odontoblasts
what cells produces dentin
ectomesenchyme dental papilla cells which differentiate into odontoblasts
What is the function of dentin
- Forms a protective covering for dental pulp and provides support for overlying enamel
- It also contains odontoblast processes and nerves
What are the physical properties of dentin
- 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)
What is the chemical composition of dentin
- The majority of dentin is composed of inorganic substances (70%) (mostly hydroxy apatite)
- 20% organic (mostly collagen type 1)
- 10% water
When during tooth formation does dentinogenesis start
bell stage
What are the stages of dentinogenesis
- Odontoblast differentiation
- Matrix Deposition
- Mineralization and modification
Explain the step of differentiation of odontoblasts
- inner epithelium differentiate into pre-ameloblasts
- Pre-ameloblasts induce the peripheral layer of the dental papilla to differentiate into pre-odontoblasts
- The mitosis of one dental papilla cell produces a pre-odontoblast and undifferentiated mesenchymal cell
What changes do dental papilla cells undergo to differentiate into pre-odontaoblasts
- 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
Explain the step of deposition of dentine martix
- 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
What is the mantle dentine
the first layer of dentine formed by odontoblasts
What is the circumpulpal dentine
mineralized dentine formed after the first layer
What is the pre-dentine
newly formed uncalcified dentine
What is the composition of dentine matrix
- collagen (type 1) fibrils
- Dentine phosphoprotein
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
What is the periodontium composed of
- cementum
- periodontal ligament
- Alveolar bone
- gingiva and dento-gingival junction
What produces the periodontium
dental follicle - ectomesenchyme
What is cementogenesis
the process of the formation of cementum
What type of cells produce cementum
dental follicle cells which differentiate into cementoblasts
Where and when does cementogenesis occur
cervical margin after crown formation
What is the first step in cementogenesis
- At the beginning of dentinogenesis HERS ( epithelial sheath) lose their continuity and dental follicle cells adjacent to the root dentine differentiate into cementoblasts
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
What are the 2 types of cementum
- Acellular cementum
- Cellular Cementum
What is acellular cementum
cementum in the upper 2/3 of the root
What is cellular cementum
cementum in the lower 1/3 of the root
What is commonly found in acellular cementum and not cellular cementum
extrinsic fibres
which are produced by fibroblasts and a few cementoblasts
What is commonly found in cellular cementum and not acellular cementum
cementoblasts which secrete intrinsic fibers
these fibres have no role in attachment
Out of extrinsic and intrinsic fibers which helps with attachment
extrinsic
What are the 3 configurations of cemeto-enamel junctions
- Cementum overlaps enamel for a short distance (60%)
- Butt joint between enamel and dentine (30%)
- Dentine between enamel and cementum is exposed (10%) - this leads to a high probability of caries in the dentine
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
What forms the periodontal ligament
dental follicle
