Cementum
Cementum is a thin
layer
of
calcified
connective
tissue
covering the external
surface of the roots of
the teeth, extending
from C.E.J. at the
cervical portion and
continues to the apex.
• It's like bone accept that cementum is Avascular.
• It's thickness varies according to age and site.
• It's usually much thicker in the apical part of the
root and in the interradicular area of multirooted
teeth than in the cervical region.
• Cementum deposition continue throughout the
life of the tooth, so it's thickness increase with
the age.
• The cementum usually act to provide a medium
for attachment of collagen fibers that bind the
tooth to alveolar bone.
Physical Characteristics
1-Color
It's light yellow in color, lighter than dentin color
2- Thickness
Acellular cementum (20-50 µm)
Cellular cementum (150-200 µm)
3- Permeability
Cellular C. is more permeable than acellular C.
Physical Characteristics
4- The fully mineralized cementum is softer and
more permeable than dentin.
5- Cementum is less readily resorbed than bone. so
the success of physiological and orthodontic
tooth movement relies upon resorption of bone
without resorption of the tooth.
Chemical Composition
45-50 % Inorganic
substances
consists of calcium&
phosphate in the
form of hydroxyapatite crystals
50-55% Organic
substances
collagen fibers
type I
embedded in a
ground
substance .
protein prolin
Polysaccharides
Cementum contains the greatest amount of fluoride in
all mineralized tissues
By/ Dr. Hesham Dameer
This mean matrix formation and
mineralization. The formation
of cementum following the
deposition of dentin along the
inner aspect of hertwig’s
epithelial root sheath. Once the
dentin formation is started, the
epithelial root sheath will loose
it's continuity, then the
undifferentiated mesenchymal
cells from the adjacent
connective tissue of the dental
follicle will be indirect contact
with the formed dentin, then
these
cells
started
to
differentiated
into
cementoblasts
(cementum
forming cells).
Cementogenesis
After degeneration
of the epithelial root
sheath
ectomesenchymal
cells from the inner
portion of the dental
follicle differentiate
and become
cementoblasts
cementoblasts.
Once the dentin formation is started, the epithelial root
sheath will loose it's continuity
then the undifferentiated mesenchymal cells from the
adjacent connective tissue of the dental follicle will be
indirect contact with the formed dentin
then these cells started to differentiated into cementoblasts
(cementum forming cells).
• The cementoblasts are protein synthetic
cells. so these cells characterized by
having abundant cytoplasmic organelles,
the main product of these cells are the
collagen fibers which form the main part
of the organic matrix in addition to the
ground substance.
After some cementum matrix (cementoid
which is uncalcified matrix) has been laid
down
which
usually
lined
by
cementoblast, the minerlization of it will
begin. that Ca and phosphate ions present
in tissue fluid are deposited into matrix as
unit cells of hydroxyl apatite crystals,
these crystals are arranged parallel to the
long axis of the collagen fibers.
Types of Cementum
There are 2 types of cementum
according to the presence of
cementocyte .
1-Acellular cementum:It's the first formed cementum,
so it named as primary
cementum, in anterior teeth it
cover completely the root
from C.E.J. to the apex, while
in multirooted teeth it's often
absent on apical 1/3 of the
root. It appear as a
homogenous layer in ground
section.
Types of Cementum
2- Cellular Cementum
Secondary cementum usually formed in the 2/3 of the
root covering a layer of a cellular cementum also
found in bifurcation area in multirooted teeth.
Under light microscope we found that cells
incorporated into this type of cementum which is
cementcyte which are similar to osteocyte in bone,
these cells lies in a spaces or lacunae the
cementocyte has numerous processes or canaliculi,
these processes are anastomosis with those of a
neighboring cells, these canaliculi are directed
toward the periodontal ligament, from which the
cells obtain their nutrition.
Cementocyte
• Both Cellular and Acellular cementum are
separated by Incremental lines which
indicated the periodic formation of it,
these lines are highly mineralized areas
with less collagen and more ground
substance than other portion of cementum.
Collagen fibers of cementum :The matix contain 2 groups of fibers :1-Intrinsic fibers :They usually present as part of cementnm matrix , it
formed by cementoblasts, and are arranged
parallel to the root surface.
2-Extrinsic fibers (sharpey’s fibers) :Which is the embeded parts of principle fibers of
P.D.L. into cementnm, they formed by fibroblasts
and arranged perpendicular to the root surface.
Cementodentinal junction
This junction is relatively smooth in permanent
teeth and scalloped in deciduous teeth, the
attachment of cementum to dentin in either case
is quite firm, because the collagen fibrils of
cementum and dentin interwine at their interface
in a very complex fashion, so its very difficult to
identified which fibrils are of cementumor
dentin in origin.
sometimes
cementum
the
by
Dentin
a
separated
layer
known
from
as
intermediate cementum, this layer don’t
exhibit characteristic feature of either dentin
or cementum.
The types of cementoenamel junction
1-cementum Overlap the enamel for a short distance
this occur in 60% of teeth.
this occurs when the enamel epith. early
degenerates at its cervical termination, permitting
C.T. to come indirect contact with the E. surface.
2-Cementum Meet the enamel edge to edge which
occur in 30%.
3-cementnm fail to meet enamel (Gap) it occur in
10% this occurs when Enamel epith. In the cervical
portion of the root is delayed in its separation from
dentin .
The types of cementoenamel
junction
Hypercementosis
its abnormal thickening of cementum.,
-if the overgrowth occur in functional teeth its
termed as hyperatrophy, like in teeth under
stress.
-If the overgrowth occur in nonfunctional teeth
it known as hyperplasia, as in case of
impacted teeth, or tooth antagonize missing
tooth.