Cementum lec.

Cementum

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.

Acellular cementum (20-50 µm)

Cellular cementum (150-200 µm)
Physical Characteristics
2- Thickness
1-Color
It's light yellow in color, lighter than dentin color
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
50-55% Organic substances
consists of calcium& phosphate in the form of hydroxy-apatite crystals
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).


After degeneration of the epithelial root sheath ectomesenchymal cells from the inner portion of the dental follicle differentiate and become cementoblasts
Odontoblast
• cementoblasts.
Cementogenesis


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 the Dentin separated from cementum by a layer known 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.