OB12- Cementum Flashcards
what is cementum?
- Mineralised tissue - Ectomesenchymal ( From Dental Follicle ) - Covers tooth roots - Tooth support
What makes up cementum?
Mineral - 65%
Matrix - 23%
Water - 12%
what is the main role of epithelial cells?
To send a signal to the papilla cells to migrate, divide and form odontoblast laying down predentine that mineralises to dentine
what do both the follicle and papilla have?
a blood supply
In what circumstance can cement have live cells?
- if it is less than 100 microns
In what circumstance can cement have dead cells?
- more than 100 microns
what cells do bone have?
live cells
what is different about cement and bone?
- cement has no blood vessels and bone does
- cement has no nerves and bone does
- Cement is resistant to resorption and bone is easily remodelled
why is cement being resistant to resorption and bone being easily remodelled clinically important?
orthodonttic treeatment - appliance to apply small forces to tooth
what happens when cementum is 10%?
exposed dentine so potentially no attatchment and also hypersensitivity as tubules are exposed
what is root development driven by?
Hertwigs epithelial root sheath (HERS)
Describe what hers does.
HERS doesn’t cover the root just a belt of cells at developing part of the root – once its done it job – induced root and cementum formation its breaks away
what shapes the root?
root sheath
Describe features of hertwigs epithelial root sheath.
- Apical development of the inner and outer enamel epithelium
- Defines root morphology
- Inductive influence:
Root dentinogenesis
Cementogenesis (indirect) - Proliferates (cell division) apically
- Disintegrates cervically
What may HERS also form?
cementoblasts
Describe the stages of the formation of cementum.
1) HERS induces odontoblast formation
2) Pre- dentine then dentine form HERS basal lamina breaks down
3) HERS cells secrete enamel matrix proteins (amelogenins) on to predentine surface
4) Enamel matrix proteins mineralise to form the hyaline layer (of Hopewell smith)
5) HERS disintegrates
6) Induction of follicle cells: migrate to root surface and form cementoblasts
7) Cementoblasts secrete cementum matrix and retreat outwards
8) Cementum matrix mineralises entrapping PDL fibres
9) Remnants of HERS form cell rests of malassez in PDL - cystic potential
what does the presence of enamel proteins on the surface of dentine do?
inducing signal
Where is the hyaline layer (of hopewell-smith)?
Between dentine and cementum
Describe the mineralisation of the hyaline layer.
highly mineralised
How thick is the hyaline layer?
10 microns
Where is the origin matrix of the hyaline layer from?
– epithelial cells ‐ enamel matrix proteins
– ? ectomesenchymal cells as well
what is the role of the hyaline layer?
– Induces cementoblast formation
– cements cementum to tooth
what is the traditional view of cementoblast origin?
derived from dental follicle
What is the new evidence of the cementoblast origin?
- at least some cementoblasts may be derived from HERS cells
- Undergo epithelial - mesenchymal transformation to form cementoblasts
Describe cementogenesis.
- Cementoblasts migrate outwards
-Deposit matrix (pre -cementum) :
> collagen
> ground substance
-Mineralisation no MV’s
-PDL collagen fibres become trapped in cementum and mineralise
what are the 2 types of cells in cementum?
- cellular
- acellular
Describe acellular cementum.
- no cells
- Slow deposition
- Close incremental lines
- Narrow precementum
Describe cellular cementum.
- cells in lacunae with canaliculi
- rapid deposition
- Incremental lines relatively far apart
- Relatively wide precementum
what are the 4 types of fibre classifications?
- intrinsic fibre
- extrinsic fibre
- mixed fibre
- afibrillar
Describe intrinsic fibres.
– fibres from cementoblasts
– Small (1‐2 μm dia.), parallel to root surface
Describe extrinsic fibres.
– incorporated PDL fibres
– Sharpey’s fibres, 5‐7μm diameter
– perpendicular or oblique to root surface
What are mixed fibres?
both
What is afibrillar
no fibres
How else can cementum be classified?
-primary cementum : > first formed cement > nearly always acellular -Secondary cementum > covers apical 2/3
What are all the classifications of cementum?
-acellular extrinsic fibre cementum
-mixed fibre cementum :
>cellular
> acellular
-Cellular intrinsic fibre cementum
-Afibrillar cementum
Also: acellular intrinsic fibre cementum
Describe the acellular extrinsic fibre cementum.
- sharpeys fibres - from PDL
- attachment
- covers > 2/3 of the root from cervical margin towards apex
- 50microns thick @ cervically
- 200microns thick @ apically
Describe mixed fibre cementum.
- Bulk of cellular cementum characterised by:
> cementocytes
> incremental lines (of Salter) - both extrinsic (Sharpey) and intrinsic fibres
- Can be acellular if slowly formed
Describe cellular intrinsic fibre cementum.
-No attachment role
-Adaptive :
apical and inter-radicular regions
Describe acellular afibrillar cementum.
- On enamel surface
- Due to localised disruption of REE
- DF cells to come into contact with enamel - induced
- mineralised GS
- Importance of the REE
- no function
Describe acellular intrinsic fibre cementum.
- first formed cementum
- collagen from cementoblast
- slow formation
- 15 - 20 microns thick
Describe cementoblasts.
- line the surface of cementum
- between PDL fibre bundles
- organelles reflect activity
- they become trapped when cementum formed rapidly…..
Describe cementocytes?
- in lacunae
- little cytoplasm
- cell processes in canaliculi -project towards PDL
- > 100microns from PDL , cementocytes die
what is the function of primary/ acellular cementum?
anchorage
what is the function of secondary/ cellular cementum?
-adaption:
>continued eruption
>mesial drift
-rapidly laid down
what is hypercementosis?
difficult for extraction as root is much bigger than socket
Describe the stages of the action of enamel matrix proteins.
- hyaline layer
- induces cementoblast differentiation from follicle
- cementogenesis
- acellular cementum
- attachment
what protects enamel from dental follicle?
Reduced enamel epithelium
What happens if reduced enamel epithelium is breached?
follicle cells exposed to the epithelial product
what happens after follicle cells are exposed to the epithelial product?
induction of follicle cells to cementoblasts
what does the induction of follicle cells to cementoblasts cause?
cementogenesis
what can induce cementogensis?
proteins in enamel
what is the clinical application of cementogenesis?
- Enamel matrix derivative applied to the root surface (emdogain -enamel protein in a syringe)
- induces cementoblast differentiation
- cementogensis
- cementum
- reattachment
