Tooth Development III - Dentinogenesis Flashcards
What are Odontoblasts?
- Dentine forming cells
- Derived from Ectomesenchymal cells
- Tall, columnar shape and establish a continuous single layer with a clear epithelioid appearance
What are the two stages of Odontoblast differentiation?
- Epithelial-mesenchymal interactions
2. Odontoblastic cytodifferentiation
What are the Epithelial-Mesenchymal Interactions?
- Induction signals from the ectodermal epithelium cause changes in the composition of the basement membrane of the internal enamel epithelium
- Growth factors are expressed within the Internal Enamel Epithelium
Cytodiffereniation of Odonoblasts: What happens during this process?
- Differentiation of the odontoblasts begins with the Dental Papilla cells adjacent to the deepest invagnination(s) of the Internal Enamel Epithelium
- Differentiation starts a the cusp tip or incisal edge
Cytodiffereniation of Odonoblasts: What happens to the Papilla cells?
- Hypertrophy of the Pre-odontoblasts
- Nuclei move away from the enamel organ; towards the basal part of the cell
- Re-arrangement of the cytoskeleton
- Small cell processes extend from the odontoblast - directed towards the basement membrane of the Internal Enamel Epithelium
- Number of processes reduces and one large one dominates
Cytodifferentiation of Odontoblasts: How do the newly differentiated cells bind to one-another and communicate?
- Smaller processes remain and link Odontoblasts to each other and to underlying cells in the pulp
- Cell-to-cell junctions increase in number
- Tight/Gap/Desmosomes junctions occur and allow for some signalling that coordinate the activities of the Odontoblasts
Deposition of Dentine Matrix: How does this process occur?
- Once fully differentiated, Odontoblasts secrete its organic matrix
- Collagen type I is the most prevalent component
- Dentine Phosphoprotein (DPP) is the 2nd most abundant protein
What’s the function of Dentine Phosphoprotein?
- Role in mineralisation and in Epithelial-mesenchymal signalling
- Also secreted by Pre-ameloblasts
- Secreted form Odontoblastic process a short distance form the cell body
What’s the first layer of Dentine laid down?
Mantle Dentine
What’s Mantle Dentine?
- Only at periphery of the tooth in the Coronal region
- Type I collagen fibres that are laid down initially lie at right angles to the future Dentine-Enamel Junction
- Cell budding to form matrix vesicles occurs in mantle dentine
- Membrane-bound organelles containing ALKALINE PHOSPHATASE are formed leading to a concentration of phosphate ions within the vesicles and the development of crystals
- Less mineralised and consequently resilient
What’s the next layer of Dentine?
- Circumpulpal Dentine
What’s Circumpulpal Dentine?
- Bulk of Dentine
- Thin at initial stages of Dentinogenesis; becomes thicker continuously at the expense of the space initially occupied by pulp
- NOT A HOMOGENOUS LAYER
- Most prominent part of the dentine is formed by INTERTUBULAR DENTINE
- PERITUBULAR DENTINE is found around the lumen of the tubules
How is calcium controlled within Circumpulpal Dentine?
- Odontoblasts control the transport and release of calcium ions
- Calcium is concentrated in organelles at the distal end
- Deposited onto a template formed by collagen I fibrils; becoming a crystalline mineral
- Controlled by DPP
- DPP is highly anionic and thus can bind calcium
What happens if there are high levels of DPP?
- Crystal formation is inhibited
- Odontoblasts control mineralisation by controlling DPP concentration
What happens if a conformation change occurs with DPP?
- Allows DPP to bind more calcium ions; leading to the formation and growth of crystals
Where do the crystals appear first within Circumpulpal Dentine?
- Hole zone formed by quarter stacking of collagen
What’s DPP’s role in mineralisation?
- Transport of calcium ions to the mineralisation front
- Location of nucleation to specific regions on the collagen fibrils
- Stabilisation of the crystals
What’s the mineralisation front in Dentine?
- Area of mineralisation; boundary between unmineralised and mineralised Dentine
- Appears irregular
- Linear or spherical or a combination
- Calcospheres fuse, if not completely interglobular dentine will form
Later Dentines Formation: What’s Intratubular Dentine and how is it formed?
- Small crystals in amorphous matrix (glycoproteins, lipids, bone sialoprotein)
- The main Odontoblastic processes are surrounded by intratubular dentine
Later Dentines Formation: What’s Secondary Dentine and how is it formed?
- A programmed age change in Dentine
- Apoptosis of Odontoblasts as the pulp volume decreases
- Leads to a change in tubular direction
Later Dentines Formation: What’s Tertiary Dentine?
- Low grade stimuli to the pulp induce the proliferation of Tertiary dentine
- The tubules can be: Tubular/atubular/irregular
- The pulp doesn’t respond to stimuli by increasing the rate of deposition of secondary dentine but by inducing previously quiescent odontoblast-like cells to produce mineralised tissue
What’s Interglobular dentine?
- Dentine mineral is deposited as globules or calcospherites
- These can fuse to form a uniformly calcified tissue
HOWEVER
- Sometimes, (usually beneath mantle dentine/granular layer) the fusion is incomplete
- Give a TREE CANOPY APPEARANCE
What’s the Granular layer?
- Periphery of dentine in the root; presence of a dark granular zone
- In these areas the dental tubules in this area branch more profusely and loop back on themselves - creating air spaces in ground sections
- Layer is hypomineralised in comparison to circumpulpal dentine
What’s the Hyaline layer?
- Obscure origin
- Narrow band which is non-tubular and relatively structureless
- MAY serve as a bond between cementum and dentine
