Cementum

Cementum

Acellular cementum (20-50 m)

Cellular cementum (150-200 m)
Physical Characteristics
2- Thickness
1-Color
Light yellow

Lighter in color than dentin

3- Permeability
Permeable from dentin and PDL sides.
Cellular C is more permeable than acellular C.

Chemical Composition

45-50 % Inorganic substances
50-55% Organic substances
Hydroxyapatite crystals
Collagen
protein
Polysaccharides
Trace elements
Cementum contains the greatest amount of fluoride in all mineralized tissues

Cementum Structure

Acellular cementum

Cellular cementum



Cementoid layer
Malassez

Cementocytes

Acellular Cementum

Thickness is 20-50 µ.

It is clear and structureless
Covers the coronal half of the root.
Incremental lines of Salter are parallel to the surface.
Sharpey’s fibers space can be seen in it .
Alternating layers of
a cellular and cellular cementum could be seen.

Cellular Cementum

Lacunae of cementocytes
Cementocytes

PDL side

Dentin side

Cementocytes

Incremental lines of Salter

Cementocyte And Osteocyte

Dentin side

PDL side


Lacuna
Canaliculi

Osteocyte

Cementocyte And Osteocyte

Periodontal ligament side

Dentin side
Lacuna
Canaliculi

Osteocyte

Cellular Cementum



Dentin side
PDL side
Viable superficial cementocytes

Degenerated deep layer’s cementocytes

Cementoid
The uncalcified matrix of cementum is called cementoid.
It is lined by cementoblast.
Connective tissue fibers from the PDL are embedded in the cementum and serve to attach tooth to surrounding bone (Bone bundle)
These embedded fibers are known as Sharpey`s fibers.

Acellular- Cellular

Acellular
Cementoblast are absent
Covers the root from CEJ to the apex
Predominates in the coronal half of the root
Sometimes found on the surface of cellular cementum
Cellular
Cementoblasts are seen
Seen in apical 3rd of root
Predominates in the apical half of root
Frequently seen on the surface of acellular cementum


Incremental Lines Of Salter

They are hypermineralized area with less collagen fibers and more ground substance

In acellular C
In cellular C

Cemento Dentinal Junction

C
D

Smooth in permanent teeth

Scalloped in deciduous teeth

Touching:

30% cementum meets the enamel in a sharp line
Gapping:10% cementum and enamel doesn’t meet because of delayed separation of epith root sheath of Hertwig (area of dentin not covered by C).
Overlapping:60% cementum overlaps E (afibrillar cementum)
Cemento Enamel Junction

3-Intermediate cementum

Sometimes dentin is separated from the cementum by a zone known as intermediate cementum.
This layer is seen mostly in apical 2/3rd of Molars and Premolars.
This layer represents areas where cells of Hertwig`s epithelial root sheat become trapped in a rapidly deposited dentin or cementum matrix.
It is rarely seen in primary and anterior teeth.

4-Afibrillar cementum (No fibril)

Cementoblasts contact enamel surface produce afibrillar cementum
Afibrillar cementum contacts connective tissue cells and forms fibrillar cementum.


Types Of Cementum
1- Acellular cementum

2- Cellular cementum

3- Intermediate cementum

4- Afibirllar cementum

Functions Of Cementum

1- Acts as a medium for attachment of collagen fibers of PDL (Sharpey’s fibers) that bind tooth to alveolar bone.

2- The continuous formation of cementum keeps the attachment apparatus intact (undamaged).

Cementoid T

Cementoblast

3- Cementum deposition apically compensate (balance) for the attrition.

4- It is a major reparative tissue and protect dentin.
( as in case of fracture or resorption of root)

Cementogenesis

1- Matrix formation
2- Maturation
Collagen fiber type I
Ground substance
Hydroxy apatite crystals

1- Matrix formation

Cementum is formed during root formation

Future C E J

Epith. Diaph.

H E R

D
Cementoblasts

Cementoblast is a protein forming and secreting cell.

D

Cementoblast

Large open face nucleus
R E R

Golgi apparatus

Mitochondria


Alkaline phosphatase
Secretory granules

Collagen fibers + ground substance.

Cementum

Cementoid layer

Cementoblasts

Age Changes Of The Cementum




D
D


Localised

1- Hypercementosis.

Is abnormal thickening of cementum. May affect one tooth or all teeth

Hypercementosis

Hypercementosis hyperplasia
Hypercementosis hypertrophy
Increase number of Sharpey’s fibers
Decrease number of Sharpey’s fibers

Types Of Hypercementosis

Types Of Hypercementosis

2- Permeability

From periodontal side, but remain at the superficial recently formed layers

From dentin side remains at apical area ONLY

Clinical considerations

Cementum is more resistant to resorption than bone because cementum is avascular; bone is vascular.
Cemental resorption is repaired by formation of cellular or acellular cementum or by both.This is called anatomic repair.
Thin layer of cementum is deposited on the surface of a deep resorption.in such areas, the periodental space is restored to its normal width by formation of a bony protection.This is called functional repair.