cementum

CEMENTUM

By/ Dr. Hesham Dameer

Cementum is part of the peridontium

THE PERIODONTIUM

The peridontium consists of those tissues which surrounds , support the tooth and is composed of :

Gingiva Periodontal ligament Cementum Alveolar bone


GingivaThe gingiva is that part of the oral mucosa which surrounds the tooth and cover the alveolar bone .In light-skinned individuals the gingiva (G) can be readily distinguished from the adjacent dark red alveolar mucosa (AM) by its lighter pink color. Its apical border, that separates it from the adjacent alveolar mucosa, is the mucogingival junction (MGJ). A similar tissue relationship can be seen on the lingual aspect of the mandible

AM, alveolar mucosa .G, gingiva .MGJ, mucogingival junction

AM,alveolar mucosa .F, floor of the mouth .G, gingiva .MGJ, mucogingival junction

Periodontal ligament Dense connective fibers that connect the cementum covering the root of the tooth with the alveolar bone of the socket wall . Principal fibers of the periodontal ligament :The periodontal fibers of the periodontal ligament are primarily composed of bundles of type I collagen fibrils. They have been classified into several groups on the basis of their anatomic location:

The following constitute the principal fiber groups of the periodontal ligament:

1. Alveolar crest group 2. Horizontal group 3. Oblique group 4. Periapical group 5. Interradicular group


http://www.dental.pitt.edu/informatics/periohistology/en/glossary.html#Principal%20fibers

Cementum


Cementum is a hard connective tissue that covers the root of the tooth to furnish a medium into which the principle fibers of the periodontal ligament are terminally inserted .


It begins at the cervical portion of the tooth at the cemento-enamel junction and continues to the apex.

Cementum furnishes a medium for the attachment of collagen fibers that bind the tooth to surrounding structures.

Cementum


Acellular cementum (20-50 m)

Cellular cementum (150-200 m)

Physical Characteristics

2- Thickness

1-Color

Light yellowLighter 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

consists of calcium

phosphate in the form of hydroxy-apatite crystals

collagen fibers embedded in a ground substance .

protein

Polysaccharides

Cementum contains the greatest amount of fluoride in all mineralized tissues


• It takes place in two phases:• Matrix formation• Mineralization

There are 3 cell types responsible for the cementogenesis:• Cementoblasts• Cementocytes• Fibroblasts

• All of these cells are derived from the ectomesenchymal cells.

Cementogenesis


Cementogenesis

Cementum formation in the developing tooth is preceded by the deposition of dentin along the inner aspect of Hertwig‘s sheath . Once dentin formation is underway breaks occur in the epithelial root sheath allowing the newly formed dentin to come in direct contact with the connective tissue of the dental sac , the undifferentiated mesenchymal cells derived from the dental sac differentiate into cementoblasts . These cells have the ultrastructural characteristics typical of cells actively synthesis protein and polysaccharide .The main product of cementoblasts is collagen and ground substances , both constitute the organic component of cementum .The inorganic material of cementum is calcium phosphateHydroxy apatite .

cementoblasts.

Cementogenesis

Odontoblast


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

Growth of cementum is a rhythmic process and as a new cementoid is formed, the old one is calcified . A thin layer of cementoid can be observed on cemental surface which is covered by cementoblasts .The mineralization begins after forming the first layer of matrix.

The mineral crystals is deposited within and between the collagen fibers, the long axes of the crystals are arranged parallel to the long axis of the collagen fibers .

Sometimes crystals can be seen clustered into groups of nucleation centers as found in bone.

Cementogenesis

Cementoblasts

Cementodentinal junction

cementoid

Cementoblast is a protein forming and secreting cell.

D

Cem

ento

bla

st

Large open face nucleus

R E R

Golgi apparatus

Mitochondria

Alkaline phosphatase

Secretory granules

Collagen fibers + ground substance.

Cementum

Cementoid layer

Cem

ento

bla

sts

Maturation occur layer by layer for the collagen fibers

After reaching the full thickness the cementoblasts enter a quiescent stage.

During matrix formation fibroblasts form collagen fibers (sharpey`s fibers), which become embedded in the matrix to provide attachment of the root to the surrounding bone. Those fibers are also called perforating fibers.

.

Cementogenesis


Remnants of the Hertwig`s root sheath, which disintegrate into the PDL are the Malassez cells.

intermediate cementum


Histological structure :

cementum cover the root dentin from cementoenamel junction to the root apex .

It is thinnest at this junction ( 20 – 50 μm ) but

becomes gradually thicker apicalward ranging from 150 – 200 μm ) or more .


Two forms of collagen are found in cementum :

* collagen fibrils * collagen bundles

The collagen fibrils are arranged in a very complex fashion and constitute the main bulk of the organic material of cementum.The collagen bundles represent the embedded portion of the principle fibers of the periodontal ligament, that is Sharpey´s fibers .

Two types of cells are functionally concerned with cementum :

* Cementoblasts

* Cementocytes

Cementoblasts line the root surface and when active, they contain numerous mitochondria, well developed Golgi complex, and open-faced nucleus. However, in resting cementoblasts, these cytologic features become less pronounced .


While cementum is being deposited, cementoblasts retreat leaving behind the formed cementum matrix. Occasionally, however, cementoblasts become entrapped in the forming matrix and then known cementocytes .

Cementocytes are seen located in lacunae in cementum matrix and typically have numerous processes lying in canaliculi . These processes may branch and frequently anastomose with those of the adjacent cementocytes . This indicates that these cells are not functionally separated from each other . Because cementum is avascular tissue, thus the processes of the cementocytes are oriented toward the periodontal ligament for nutrition .

As a result of continuous phasic deposition of cementum, resting lines known Salter lines appear in cementum .


Cementocytes

Cementocyte lacuna

CementocyteCementocyte canaliculi

Cementocyte process

Incremental Lines

• Incremental lines of Salter.

Incremental lines of Salter

Incremental lines of Salter

Dentin

Resting lines of Salter

Types of cementum : I) Based on cellular connotation :

1- Cementum containing cells :

a. Cellular cementum

b. Intermediate cementum

2- Acellular cementum

II) Based on fibrillar connotation :

1. Intrinsic fibers cementum

2. Extrinsic fibers cementum

3. Mixed fibers cementum

4. Afibrillar cementum

I) Based on cellular connotation : 1- Cementum containing cells : a. Cellular cementum is more frequently found on the

apical half of the root where cementum does contain cementocytes in its matrix .

b. Intermediate cementum Intermediate cementum is a thin, amorphous layer of hard tissue

approximately 10 micron thick. Is more frequently seen in the apical two thirds of the roots of

posterior teeth but rarely in incisors or primary teeth .

This type of cementum does not exhibit the characteristic features of either dentin or cementum, while in regard to its location, it is found intermediate between cementum and dentin .

In respect to the involved cells observed in intermediate cementum, there is argument about there derivation :

1- The cells of the epithelial root sheath of Hertwig are proposed to become entrapped while dentin or cementum is being rapidly deposited .

2- Other concept claims that odontoblasts are trapped on the outer dentin surface at the commencement of dentinogenesis which subsequently being enclosed by the forming cementum .

Cementogenesis

Cementoblasts


http://www.kck.usm.my/ppsg/histology/C_4.htm

Remnants of the Hertwig`s root sheath, which disintegrate into the PDL are the Malassez cells.



2- Acellular cementum :The matrix of this type of cementum does not involve

cementocytes . However, cementoblasts present on its outer surface and constitute an integral component of acellular cementum .

Acellular cementum may cover the root dentin from the cementoenamel junction to the root apex, but with frequent absence on the apical third of the root .

II) Based on fibrillar connotation : 1. Intrinsic fibers cementum : the fibers are derived

from the synthetic and secretory activity of cementoblasts .

2. extrinsic fibers cementum : in this form, the extrinsic fibers originate from the principal fibers of the periodontal ligament that is Sharpey´s fibers .

3. mixed fibers cementum : it contains both intrinsic and extrinsic fibers .

4. Afibrillar cementum : as enamel is completely formed and become fully calcified, it is seen covered by the reduced enamel epithelium which is of paramount importance in protecting enamel, however, the reduced enamel epithelium may retract from the cervical region of enamel . This allows for the adjacent mesenchymal cells to invade and intervene between enamel and its covering epithelium . The mesenchymal cells differentiate into cementoblasts and deposit a particular type of cementum, that is, afibrillar cementum, on enamel surface .


Cementoenamel Junction (CEJ)

• 3 patterns may be present• 1) In approximately 60% of teeth cementum overlapping the cervical end of

enamel for a very narrow area at the CEJ . This occurs as a result of premature degeneration or retraction of the reduced enamel epithelium at the cervical region of enamel . This allows for the adjacent mesenchymal cells to invade and intervene between enamel and its covering epithelium . The mesenchymal cells differentiate into cementoblasts and deposit a particular type of cementum, that is, afibrillar cementum, on enamel surface .

• 2) 30% of all teeth, cementum meets the cervical end of enamel in a knife edge-to-edge pattern .

• 3) In approximately 10% of teeth, cementum does not meet enamel where a zone of root dentin appears devoid of cementum . This can result in dental hypersensitivity as the gingiva recedes exposing the underlying root dentin

Relation of Cementum to Enamel at the Cementoenamel Junction (CEJ)

In 60% of the teeth cementum Overlaps enamelIn 30% of the teeth cementum just Meets enamelIn 10% of the teeth there is a small Gap between cementum and enamel

Edge to edge 30%


Cementum do not meet enamel 10%


Cementum overlaps enamel 60%


The dentin surface upon which cementum is deposited is relatively smooth in permanent teeth.

The cementodentinal junction in deciduous teeth, however, is sometimes scalloped.

Cementodentinal junction

Permanent teeth

Deciduous teethBy/ Dr. Hesham Dameer

Functions of cementum :

1. Cementum furnishes a medium for the incorporation of the principal periodontal fibers, thereby securing the binding of the tooth root to the alveolar bone proper .

2. Cementum serves as a reparative tissue in case of root fracture or resorption .

3. Functional adaptation :

* When the superficial layer of cementum functionally ages, a subsequent layer is deposited thus restoring the integrity of the attachment apparatus .

* Another feature of functional adaptation is the excessive formation of cementum on the apical root surface to compensate for the occlusal and incisal wear and restore the normal occlusion .


Histological cross-section through a periodontal ligament . The periodontal ligament fibers (F) originate from the cementum. and insert into bundle bone (BB), so named because it contains numerous Sharpey's fibers (SF). Neurovascular channels (NV) that house blood vessels, lymphatics and nerves in a loose connective tissue sheath course throughout the periodontal ligament. The ligament also contains cell rests of Malassez (M).


http://www.dental.pitt.edu/informatics/periohistology/en/glossary.html#Cell%20rests%20of%20Malassez

1) Hypercementosis:It is an abnormal thickening of cementum, may be diffuse

or circumscribed.

It may affect all teeth of the dentition, be confined to a single tooth, or even affect only Parts of one tooth.

If the overgrowth occurs in functional teeth and improves the functional qualities of the cementum, it is termed cementum hypertrophy.

If the overgrowth occurs in nonfunctional teeth, it is termed cementum hyperplasia .

Age changes of cementum

Hyperplastic cementum covering the enamel drops termed excementosis

the enamel drops

Generalized hypercementosis

Localized hypercementosis

In Localized hypertrophy prong like extension of cementum may be formed. This condition frequently is found in teeth that are exposed to great stress (ortho) (compensatory cementum). This extension of cementum provide a larger surface area for the attaching fibers; thus a firmer anchorage of the tooth to the surrounding alveolar bone is assured.

Age changes of cementum

Root resorption and forming Reparatory cementum

Root resorption – lost D. has been replaced by cellularcementum, on the top of which acellular C. has formed

Hypercementosis


2) Decrease permeability : by aging the permeability of cementum decreses gradually , the permiability from the periodontal ligament side is lost except in the most recent formed layers of cementum .

3) Cementicles : they are ovoid or round calcified structure that exhibits by dystrophic calcification of the degenerated periodontal tissue or the epithelial rests of Malssez . They nidus favoring the deposition of concentric layers of calcosherites around the degenerated or hemorrhagetic areas .Cementicles may be: 1. Free in the periodontal ligament. 2. Attached the cementum and form excementosis.

3. Embedded in the cementum during its growth by age.

Periodontal ligament

Cementum

Bone

Free Cementicles

Free Cementicles

Periodontal ligament

Attached Cementicles

THE END

My best wishes for you

Dr. HESHAM Dameer

cementum

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