Dental hard tissue formation Flashcards
Enamel derived from…
epithelial cells
What is the hexagonal cross-section structure of enamel crystal?
What is represented by the yellow ball?
Fluoride ion
What are the benefits of fluoride ion replacing OH-?
- Stabilises the lattice
- More acid resistant
- Therefore useful in prevention
What’s significance of the centre of the hexagon in the centre of the crystal?
Flips 90 degrees in alternating pattern
What is it called when another ion displaces the OH- ion?
When can too much fluoride be bad?
In children as is interferes with development - enamel will not form correctly.
Critical pH
The pH below which apatite dissolves
Critical pH for Hydroxyapatite and Fluroapatite
Hydroxyapatite - pH 5.5, Fluroapatite - pH 4.5
What is this graph representing?
Stephan curve; patient gives standardised glucose rinse, then saliva buffers and pH raises again.
Example of pathological mineralisation in the mouth
Stones in salivary glands (calcification)
Theories of mineralisation
- Alkaline phosphatase hypothesis
- Nucleation theories (homogenous/heterogenous)
- Matrix vesicles
Alkaline phosphatase hypothesis
Enzyme breaks down phosphatases
releasing inorganic phosphates (HPO4 2-)
Which reacts with Ca driving the reaction of precipitation
Why might the Alkaline phosphatase hypothesis be incorrect?
- (organic phosphates) Too low to be an effective source
- Other sites contain alkaline ph (e.g kidneys)
- Normal serum (phosphate) is sufficient
Homogenous nucleation
Formation of a crystal where it didn’t form before from a solution of ions (containing Ca and PO).
EXAMPLE: add copper sulfate crystals stir it goes blue increasing heat can mean saturation point is lower i.e can add more crystals - when starts to cool again, crystals begin to precipitate out of it again (e.g.adding sugar to tea cold = less sugar, hot = more sugar)
Why might the homogenous nucleation theory be incorrect?
Taking the same experiment as copper sulfate crystals - the same does not work from a supersaturated solution of CuSO4.
Heterogenous nucleation
Theory of epitaxy ( “template to grow on”)
(i.e hail stones are crystal structures from water that grow on the ‘template’ of dust)
- Organic matrix acts as the epitactic agent (template for growth)
Possible nucleators for heterogenous nucleation
Collagen
Proteoglycans
Lipids
Phosphoproteins
Matrix vesicles
Membrane package produced by cells containing high concentrations of Ca and PO ions.
Helps initiate mineralisation in a tissue.
What is the first formed hard tissue?
Dentine, then enamel, then cementum.
Dentine is derived from…
Ectomesenchymal cells
First four stages of tooth germ growth
Epithelial cells growth on top of a condensation of ectomesenchymal cells.
Final stages of tooth germ growth
Crown stage = when hard tissues start to appear
Dentine is formed by…
Odontoblasts (derived from papilla, ectomesenchymal)
When does dentine formation begin?
At the end of the bell stage (starting at the cusp)
Three stages of dentine formation
- Cytodifferentation - cells differentiation to odontoblasts
- Matrix formation
- Mineralisation
A
Dental follicle (
B
Dental papilla
C
Enamel organ
A
Outer enamel epithelium
B
Stellate Reticulum
C
Stratum intermedium
D
Inner enamel epithelium
E
Cervical loop
Initial communication from dental papillae to inner enamel epithelium
Number of cell divisions
inner epithelium cells communicates to the dental papillae
to divide and mature to odontoblasts
final signal from the dental papillae to the inner enamel epithelium
IEE cell to mature to ameloblasts
SI - Stratum intermedium
Basic steps of dentine formation (5 stages)
- DP tells cells to divide (cells migrate and line up against basal lamina)
- Cells enlarge in acellular space; two rows of cells (one row is the odontoblasts, other cells sit waiting until called upon = tertiary dentine).
- Odontoblast cells increase in synthetic/secretory organelles
- Organic matrix secreted as odontoblasts retreat = predentine (produces matrix vesicles etc for a template for mineralisation to occur).
- Mineralisation occurs = dentine formed.
mineralisation of dentine
Mantle dentine
“outer layer” very first formed layer.
Contains large collagen fibres, 90 degrees to ADJ.
Circumpulpal dentine
Rest of dentine, collagen fibrils (closely packed + interwoven)
What is the enamel’s 1-2% organic matrix made up of?
Enamel proteins (NOT collagen)
What happens to the pre-ameloblasts during odontoblast maturation?
The pre-ameloblasts nucleus polarises away from the odontoblasts.
What happens when the odontoblast process extend into the ameloblast layer?
enamel spindle
What happens as the basal lamina disintegrates?
Mature ameloblasts begins laying down enamel.
What is significant about the way ameloblasts lay down enamel in terms of their final shape
Pointed end
What components of
In which direction do the ameloblasts retreat to when laying down enamel?
Green arrow
What is the pointed part of the ameloblast known as?
Why is tomes process important?
Needed for prisms - needed for shape and thus acid etching etc.
What causes the prism core/sheath recurring pattern?
- Direction of retreat of ameloblasts
- tomes process
Amelogenesis summary
Starts after dentine formation begins
Secretion of organic matrix
Maturation by mineralisation
Removal/breakdown of organic matrix (function complete = allowed crystallisation to occur from heterogenous nucleation)
Enamel proteins examples
Amelogenins (90%)
Enamelins (roughly 2%)
Tuftelin - confined to ADJ
Amelogenins
Rich in proline and glutamine.
Hydrophobic
Thixotrophic
Function of enamel proteins
Aid nucleation of hydroxyapatite (epitactic matrix)
Orientate and stabilise crystal growth
Broken down and lost during maturation
Maturation of enamel requires…
Maturation of tomes process
Process changes to microscopically folded cell membrane
Enamel cuticle
After maturation is complete, this cuticle is the final ameloblast secretion (1um thick - like a basal lamina
From top to bottom, describe the stage of ameloblast development
Postmaturation
Maturation
Secretory
Presecretory
What is the fate of the reduced enamel epithelium function?
HERS: inductive influence
Root dentinogenesis and cementogenesis (indirect)
Cementoblast origin
Traditional view: Dental follicle
New evidence: Some derived from HERS cells. Undergo EMT to form cementoblasts.
How is cementum laid down?
- Cementoblasts migrate outwards depositing matrix (precementum: collagen + ECM)
- Mineralisation no matrix vesicles
- PDL collagen fibres become trapped in cementum and mineralise.
How is acellular cementum formed?
Enamel matrix proteins in the hyaline layer induces cementoblast differentiation from follicle, leading to cementum being laid down (cementogenesis) this is ACELLULAR cementum.
What would give rise to cementum on the enamel surface?
- If the reduced enamel epithelium breached then the follicle cells could be exposed to the enamel.
- This induces them to become cementoblasts.
- The proteins in enamel can induce cementogenesis.
Emdogain
Used to help treat and reverse the effects of periodontal disease, aiding reattachment.
Made from enamel matrix proteins.
Forms ACELLULAR cementum.
What produces reparative dentine?
The dental pulp (originally papilla) has the potential to differentiate new odontoblasts from stem cells and deposit reparative forms of dentine in response to dental caries.
