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Cementum
By
Professor of Oral BiologyFaculty of Oral and Dental Medicine
Cairo University
Cementum is a specialized calcified dental tissue covering the anatomical root of human teeth.
Cementum serves as a medium of attachment of the colagen fibers that bind the tooth to the surrounding structures.
Cementum resembles bone in some of its physical and chemical structures , however, it is :
Avascular
Not innervated
Unnable to remodel
Acellular cementum (20-50 m)
Cellular cementum (150-200 m)
Physical Characteristics
2- Thickness
1-Color
Light yellow
Lighter in color than dentin,
darker than enamel
3- Permeability
Permeable from dentin and PDL sides.
Cellular C is more permeable than acellular C.
Chemical Composition
45-50 % Inorganic
substances50-55% Organic
substances
Hydroxyapatite
crystals Collagen
Polysaccharides
Cementum contains the greatest amount of
fluoride in all mineralized tissues.
Less harder than dentin&
much less harder than
enamel
Histological Structure
•Large cuboidal cells
•Found on the surface of both
celular and acellular
cementum.
•They produce collagen fibers
(intrinsic fibers) and ground
substance of cementum.
Cementoblasts
Cementoblast is a protein forming and secreting cell.
Large open face nucleus
R E R
Golgi apparatus
Mitochondria
Alkaline phosphatase
Secretory granules
They are incorporated in
cellular cementum
Spider shape appearance
They have numerrous
irregular processes.
Most processes are
directed towards PDL.
Cementocytes
Dentin PDL
The cell body is located in a space called lacuna and
their processes are present in canaliculi
Cementocytes in deeper layers of cementum undergo
degeneration and gradually lose their organelles and
die
Dentin PDL
In ground section, cementocytes spaces
appear as dark spaces
Cementocyte And Osteocyte
Dentin side
PDL side
Lacuna
Canaliculi
Osteocyte
A- The embedded part of PDL fibers( Sharpys fibers, this
is formed by PDL fibroblasts and called extrensic
fibers.
B- Other fibers are formed by osteoblast and are called
intrinsic fibers.
Extrensic fibers are short and dense arranged
perpendicular to root surface.
Intrinsic fibers are arranged parallel to the root surface.
Collagen fibers of cementum are derived
from two sources:
Types Of Cementum
1- Acellular ementum 2- Cellular cementum
3- Intermediate cementum 4- Afibirllar cementum
Acellular Cementum
Thickness is 20-50 µm.
It is clear and structureless
Incremental lines of Salter are parallel to the surface.
Sharpey’s fibers space can be seen in it .
The bulk of collagen fibers are derived from Sharpys fibers , so it is called acellular extrinsicfiber cementum.
This the only type found in incisors and extend to the apical foramen.
It is found in the coronal part of the root of the premolars and molars roots.
Cellular Cementum
•It is found at the apical third and the furcation area of premolars and molars.
Thickness increase gradually till root apex reaching 150- 200 µm
It is formed faster than acelular cementum.
It is more permeable than acelular cementum.
•It is formed mainly of intrinsic fibers ( Intrinsic fiber
cementum).
•It contains cementocytes ( Imprisoned cementoblasts).
In decalcified sections, the lacnae appears as minute space containing the cementocytes
In ground section, the lacunae of cementocytesappear black as they are filled with air after desentigration of the cells during preparation
Some cementoblasts become entrapped in the forming
matrix and then known as cementocytes
Incremental Lines Of Salter
They are hypermineralized area with less collagen
fibers and more ground substance
In acellular C, less
distance between IL
In cellular C,more
distance between IL
• IL are faint lines run parallel to the root surface
Intermediate Cementum
Premature
degeneration of
epith. Root sheath
of Hertwig ( after
odontoblasts
differentiation and
before dentin
formation)
It occur at apical 2/3 of premolars and molars
roots and rare in incisors and deciduous teeth
Contains entrapped
epithelial cells&
intrinsic fibers
Cemento Dentinal Junction
It is not distinctive, because the Fibers of dentin and cementumintermingle at the interface
CD
Cemento Dentinal Junction
Smooth in permanent
teeth
Scalloped in deciduous
teeth
Cemento Enamel Junction
30% cementum
meets the enamel
in a sharp line
10% cementum and enamel
doesn’t meet because of
delayed separation of epith
root sheath of Hertwig (area
of dentin not covered by C).
60%
cementum
overlaps E
(afibrillar
cementum)
Afibrillar Cementum
The enamel at cervical
area not covered by
reduced dental
epithelium before
tooth eruption
The connective tissue of
the dental sac lay down
cementum on the
exposed enamel
Functions Of Cementum
1- It occludes sensitive dentin
2- Acts as a medium for attachment of collagen fibers of PDL (Sharpey’s fibers).
3- The continuous formation of cementum keeps the attachment apparatus intact.
4- Cementum depositionepically compensate for the attrition.
5- It is a major reparativetissue ( 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
Cem
en
tob
last
Large open face nucleus
R E R
Golgi apparatus
Mitochondria
Alkaline phosphatase
Secretory granules
Collagen fibers +
ground substance.
Cementum
Cementoid layer
Ce
me
nto
bla
sts
Resorption of cementum
•Normal phenomena in deciduous
teeth .
Certain factors as trauma or
sustained pressure can result in
resorption of cementum.
Age Changes Of The Cementum
DD
Localised
1- Hypercementosis.
May affect one tooth or all teeth Hypercementosis
ThicknessCementum formation is continuous throughout life in a very slow rate Especially in apically and in the furcation area.The rate of formation may vary from time to time .
Hypercementosis
hyperplasia
Hypercementosis
hypertrophy
Increase number of
Sharpey’s fibers
Decrease number of
Sharpey’s fibers
Types Of Hypercementosis
2- Permeability
From
periodontal
side, but remain
at the
superficial
recently formed
layers
From dentin
side
remains at
apical area
ONLY
Cementicles
Calcified oval or round nodules found in the PDL, single or in groups.
They may be free or attached or impedded in cementum.
The origin may be calcified epith. Cells (Rests of Mallasez).