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Transcript of Cementum
It is calcified avascular mesenchymal tissue that forms the outer covering of anatomic root
Lighter than dentin
Less mineralized as compared to Enamel and Dentin
More mineralized as compared to alveolar bone
Human cementum is present in a thin layer.
More permeable than dentin
(45-50% by volume)
Calcium and phosphorus as Hydroxyapatite crystals
Has highest fluoride content out of all the mineralized tissues.
(50-55% by volume)
Type-I collagen 95%
Type-III collagen 5%
Composition of Cementum
Soon after Hertwig’s sheath break up, undifferentiated mesenchymal cells from adjacent tissue differentiate
into cementoblasts. Cementoblasts synthesize collagen and protein polysaccharides (Proteoglycans) whichmake up the organic matrix of cementum. These cells have numerous mitochondria, a well formed Golgiapparatus and large amount of granular endoplasmic reticulum.Cementocytes
The cells incorporated into cellular cementum are called cementocytes, and are similar to osteocytes.Cementocytes lie in spaces designated as lacunae. A typical Cementocyte has numerous cell processes orcanaliculi radiating from its cell body. These processes may branch and they frequently anastomose withthose of neighboring cells. The central cell mass may appear rounded, oval or squamoid. Diameter rangefrom 8 to 15 um. The cytoplasm is pale basophilic and the nucleus is centrally located. The cytoplasm of cementocytes in deeper layer of cementum contains few organelles. The endoplasmic reticulum appearsdilated and mitochondria are sparse. These characteristics indicate that cementocytes are eitherdegenerating or are marginally active cells. At a depth of 60um or more, cementocytes show definite signs of degeneration, such as cytoplasmic clumping and vesiculation. In the deeper layers cementocytes appear to beempty suggesting complete degeneration of cementocytes.Cementoclasts:Cementoclasts resemble osteoclasts.
These are multinucleated giant cells often located in the lacunae and are found on the surface of thecementum
They are responsible for extensive root resorption, during:
Mesial migration of tooth2.
This type of root resorption may lead to
Primary tooth exfoliation2.
Localized cemental resorption
Functions of Cementum:
Adaptive and reparative function.
Walling in filled canals.
Sealing of necrotic pulps by occluding apical foramen.
Protecting underlying dentin
Vitamin A,C D deficiency.
Hereditary fibrous osteodystrophy.
Pressure from malaligned eruptive teeth
Cysts and tumours
Teeth without functional antagonist
Replanted and transplanted teeth
Cells of Cementum.
Classification based upon time of formation
Formed before tooth reaches occlusal plane.
Covers cervical third or half of the root.
Does not contain cells.
Thickness is 30 to 230 um
Consist of abundant sharpey’s fibers arranged
irregularly or parallel to the root surface
Border with dentin is not clearly demarcated
Rate of development is relatively slow
Formed after tooth reaches occlusal plane
Contains cementocytes in lacunae which communicates through canaliculi
Sharpey’s fibres occupy smaller portion
Cementum deposition is a continuous process that proceeds at varying rates throughout life.
1. The thickness of cementum on the coronal half of the root varies from 16 to 60 µm or about the thickness of hair.
2.In the apical third and furcations the thickness is highest up to 150 to 200µm.
3. It is thicker in distal surfaces than in mesial surfaces probably because of functional stimulation from mesial drift over time
4. Between the ages of 11 and 70 the average thickness increases three fold with the greatest increase in the apical area. Average thickness of 95 µm at age 20 and 215 µm at age 60 have been reported.
Cementum formation occurs along the entire tooth Hertwigs epithelial root sheath (HERS)
Extension of the inner and outer dentalepithelium
HERS sends inductive signal to ectomesenchymal pulp cells to secrete predentin by differentiating into odontoblasts
HERS becomes interrupted
Ectomesenchymal cells from the inner portion of the dental follicle come in contact with predentin & differentiates into cementoblasts
Cementoblasts lay down cementum Hyaline layer of Hopewell-Smith (Intermediate Cementum)
First layer of cementum is actually formed by the inner cells of the HERS and isdeposited on the roots surface is called intermediate cementum or Hyaline layerof Hopewell-Smith.
Deposition occurs before the HERS disintegrates. Seals of the dentinal tubulesIntermediate cementum is situated between the granular dentin layer of Tomes andthe secondary cementum that is formed by the cementoblasts (which arise from the dental follicle)Approximately 10 mm thick and mineralizes greater than the adjacent dentin or the secondary cementum
Development of Cementum / Cementogenesis
Cells of Cementum
Cementoblasts synthesize collagen and protein polysaccharides (Proteoglycans) which make up the organic matrix of cementum.
These cells have numerous mitochondria, a well formed Golgiapparatus and large amount of granular endoplasmic reticulum.
Cementocytes lie in spaces designated as lacunae.
A typical Cementocyte has numerous cell processes or canaliculi radiating from its cell body.
These processes may branch and they frequently anastomose with those of neighboring cells.
The central cell mass may appear rounded, oval or squamoid.
THICKNESS OF CEMENTUM & ITS CLINICAL SIGNIFICANCE
Tyeps of Junctions and its clinical significance
These are multinucleated giant cells often located in the lacunae and are found on the surface of the cementum
1. Incremental lines of Salter
2. Cementodentinal junction
3. Cementoenamel junction
4. Sharpey's fibers
Structures of cementum
The collagen fibrils of cementum are of two kinds:
The first group is made up of the embedded parts of the principal fibers of the periodontal Ligament, which are known as sharpey's fibers (extrinsic group). They formed by the fibroblasts of the periodontal ligament.
The other group of collagen fibrils, which constitute the intrinsic group, are formed by the cementoblasts and are found between the sharpey's fibers arranged either randomly or parallel to the surface of the cement.
Types of collagen fibers of Cementum
In both acellular and cellular cement incremental lines run roughly parallel with the root surface.
These are formed by fiber-free amorphous substance and represent intervals between successive deposition of cementum and are called incremental Lines of Salter.
Histochemical study indicates that the incremental lines are highly mineralized areas with less collagen and more ground substance.
Incremental Lines of Salter
The dentin surface upon which cementum is deposited
is relatively smooth in permanent teeth.
The cementodentinal junction in deciduous teeth,
however, is sometimes scalloped
At the surface of the cement the principal fibers of the periodontal Ligament pass into its substance.
The fibers, which embedded in the cement, are known as sharpey's fibers.
In the acellular cementum sharpey's fibers are usually calcified.
In the cellular cementum each fiber commonly shows an uncalcified core with a calcified Periphery.
In dried ground sections they appear as dark lines as a result of their disintegration
Cementiclesare small-mineralized bodies, which may be found in the periodontal ligament.
They may be attached to the cementum or the alveolar bone, or occur free in the periodontal ligament.
When present, cementicles are generally found about all or most of the teeth.
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Done by : Dr. Lezan