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Oral biology > OB12- Cementum > Flashcards

OB12- Cementum Flashcards

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1
Q

what is cementum?

A 
- Mineralised tissue
 - Ectomesenchymal
( From Dental Follicle )
- Covers tooth roots 
- Tooth support
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2
Q

What makes up cementum?

A

Mineral - 65%
Matrix - 23%
Water - 12%

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3
Q

what is the main role of epithelial cells?

A

To send a signal to the papilla cells to migrate, divide and form odontoblast laying down predentine that mineralises to dentine

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4
Q

what do both the follicle and papilla have?

A

a blood supply

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5
Q

In what circumstance can cement have live cells?

A
  • if it is less than 100 microns
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6
Q

In what circumstance can cement have dead cells?

A
  • more than 100 microns
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7
Q

what cells do bone have?

A

live cells

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8
Q

what is different about cement and bone?

A
  • 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
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9
Q

why is cement being resistant to resorption and bone being easily remodelled clinically important?

A

orthodonttic treeatment - appliance to apply small forces to tooth

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10
Q

what happens when cementum is 10%?

A

exposed dentine so potentially no attatchment and also hypersensitivity as tubules are exposed

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11
Q

what is root development driven by?

A

Hertwigs epithelial root sheath (HERS)

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12
Q

Describe what hers does.

A

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

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13
Q

what shapes the root?

A

root sheath

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14
Q

Describe features of hertwigs epithelial root sheath.

A
  • Apical development of the inner and outer enamel epithelium
  • Defines root morphology
  • Inductive influence:
    Root dentinogenesis
    Cementogenesis (indirect)
  • Proliferates (cell division) apically
  • Disintegrates cervically
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15
Q

What may HERS also form?

A

cementoblasts

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16
Q

Describe the stages of the formation of cementum.

A

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

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17
Q

what does the presence of enamel proteins on the surface of dentine do?

A

inducing signal

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18
Q

Where is the hyaline layer (of hopewell-smith)?

A

Between dentine and cementum

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19
Q

Describe the mineralisation of the hyaline layer.

A

highly mineralised

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20
Q

How thick is the hyaline layer?

A

10 microns

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21
Q

Where is the origin matrix of the hyaline layer from?

A

– epithelial cells ‐ enamel matrix proteins

– ? ectomesenchymal cells as well

22
Q

what is the role of the hyaline layer?

A

– Induces cementoblast formation

– cements cementum to tooth

23
Q

what is the traditional view of cementoblast origin?

A

derived from dental follicle

24
Q

What is the new evidence of the cementoblast origin?

A
  • at least some cementoblasts may be derived from HERS cells

- Undergo epithelial - mesenchymal transformation to form cementoblasts

25
Q

Describe cementogenesis.

A
  • Cementoblasts migrate outwards
    -Deposit matrix (pre -cementum) :
    > collagen
    > ground substance
    -Mineralisation no MV’s
    -PDL collagen fibres become trapped in cementum and mineralise
26
Q

what are the 2 types of cells in cementum?

A
  • cellular

- acellular

27
Q

Describe acellular cementum.

A
  • no cells
  • Slow deposition
  • Close incremental lines
  • Narrow precementum
28
Q

Describe cellular cementum.

A
  • cells in lacunae with canaliculi
  • rapid deposition
  • Incremental lines relatively far apart
  • Relatively wide precementum
29
Q

what are the 4 types of fibre classifications?

A
  • intrinsic fibre
  • extrinsic fibre
  • mixed fibre
  • afibrillar
30
Q

Describe intrinsic fibres.

A

– fibres from cementoblasts

– Small (1‐2 μm dia.), parallel to root surface

31
Q

Describe extrinsic fibres.

A

– incorporated PDL fibres
– Sharpey’s fibres, 5‐7μm diameter
– perpendicular or oblique to root surface

32
Q

What are mixed fibres?

A

both

33
Q

What is afibrillar

A

no fibres

34
Q

How else can cementum be classified?

A 
-primary cementum :
> first formed cement
> nearly always acellular 
-Secondary cementum 
> covers apical 2/3
35
Q

What are all the classifications of cementum?

A

-acellular extrinsic fibre cementum
-mixed fibre cementum :
>cellular
> acellular
-Cellular intrinsic fibre cementum
-Afibrillar cementum

Also: acellular intrinsic fibre cementum

36
Q

Describe the acellular extrinsic fibre cementum.

A
  • sharpeys fibres - from PDL
  • attachment
  • covers > 2/3 of the root from cervical margin towards apex
  • 50microns thick @ cervically
  • 200microns thick @ apically
37
Q

Describe mixed fibre cementum.

A
  • Bulk of cellular cementum characterised by:
    > cementocytes
    > incremental lines (of Salter)
  • both extrinsic (Sharpey) and intrinsic fibres
  • Can be acellular if slowly formed
38
Q

Describe cellular intrinsic fibre cementum.

A

-No attachment role
-Adaptive :
apical and inter-radicular regions

39
Q

Describe acellular afibrillar cementum.

A
  • 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
40
Q

Describe acellular intrinsic fibre cementum.

A
  • first formed cementum
  • collagen from cementoblast
  • slow formation
  • 15 - 20 microns thick
41
Q

Describe cementoblasts.

A
  • line the surface of cementum
  • between PDL fibre bundles
  • organelles reflect activity
  • they become trapped when cementum formed rapidly…..
42
Q

Describe cementocytes?

A
  • in lacunae
  • little cytoplasm
  • cell processes in canaliculi -project towards PDL
  • > 100microns from PDL , cementocytes die
43
Q

what is the function of primary/ acellular cementum?

A

anchorage

44
Q

what is the function of secondary/ cellular cementum?

A

-adaption:
>continued eruption
>mesial drift
-rapidly laid down

45
Q

what is hypercementosis?

A

difficult for extraction as root is much bigger than socket

46
Q

Describe the stages of the action of enamel matrix proteins.

A
  • hyaline layer
  • induces cementoblast differentiation from follicle
  • cementogenesis
  • acellular cementum
  • attachment
47
Q

what protects enamel from dental follicle?

A

Reduced enamel epithelium

48
Q

What happens if reduced enamel epithelium is breached?

A

follicle cells exposed to the epithelial product

49
Q

what happens after follicle cells are exposed to the epithelial product?

A

induction of follicle cells to cementoblasts

50
Q

what does the induction of follicle cells to cementoblasts cause?

A

cementogenesis

51
Q

what can induce cementogensis?

A

proteins in enamel

52
Q

what is the clinical application of cementogenesis?

A
  • Enamel matrix derivative applied to the root surface (emdogain -enamel protein in a syringe)
  • induces cementoblast differentiation
  • cementogensis
  • cementum
  • reattachment

Oral biology (29 decks)

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