CEMENTUM

CementumCEMENTUM

CEMENTUM is calcified avascular mesenchymal tissue that forms the outer covering of anatomic root. Its provides anchorage mainly to principal fibres of periodontal ligament. Two surfaces of collagen fibres can be found in the cementum:

1 Sharpey’s fibres which are formed by the fibro blast .

2 Fibres belonging to the cementum matrix per se [intrinsic] produced by cementoblasts.

Two types of cementum were described earlier:

1 Acellular cementum / primary cementum

2 Cellular cementum/ secoundary cement

Acellular Cementum Cellular Cementum1 Forms during Root formation 1 Forms after eruption of tooth & in response

to functional demands2 Doesn,t contains any cell 2 Contains cementocytes

3 Seen at the coronal portion of the root 3 Seen more apically

4 Formation is slow 4 Deposition is more rapid

5 Arrangement of collagen fibres is more organized

5 Collagen fibres are irregularly arranged

CL ASSFICATION

Depending on location , morphology and histolological appearance ,shroeder and page have classified cementum as:

a. Acellular afibrillar cementum (AAC): It contains only the mineralized ground substance. It does not contain collagen fibers nor does it exhibit entrapped cementocytes. It is a product of cementoblasts and

is found almost exclusively on the enamel near the cementoenamel junction with a thickness of 1 to 15 m.

b. Acellular extrinsic fiber cementum (AEFC): By definition it is composed primarily of Sharpey’s fibers of periodontal ligament but does not contain cementocytes. Developmentally they come to occupy the coronal one half of the root surface. Its thickness is between 30 and 230 m.

c. Cellular mixed stratified cementum (CMSC): It harbours both intrinsic (cementoblasts derived) and extrinsic (fibroblast derived) fibers and may contain cells. In humans it is seen in the apical third of the roots, apices and furcation areas. Its thickness varies from 100 to 1000 p.m.

d. Cellular intrinsic fiber cementum (CIFC): It contains only intrinsic fibers secreted by cementoblasts and not by the periodontal ligament fibroblasts. In humans it fills the resorption iacunae.

e. Intermediate cementum (or) the hualine layer of Hope Well Smith: It is an ill-defined zone extending from pre-cemenfoenamel junction to the apical 1/3rd of the root. It appears to contain cellular remnants of Heriwigs Sheath embedded in calcified ground substance. The significance of this layer is that. it contains enamel like proteins, which helps in attachment of cementum to dentin. It has been observed by many that, when this layer is removed during root planing procedure, the resultant reparative cementum that is formed will not be attached firmly on the dentin.

DEVELOPMENT OF CEMENTUM

To understand the development of cementum one has to understand the root formation. Development of cementum and root of the teeth starts once the formation of enamel is completed.

Early development of cement

The outer and inner epithelial together form the epithelial root sheath of Hertwig ,which is responsible for determing the shape of the root .

The outer and inner epithelial layers become continuous in area of the cej and form a two layered sheath ,which grows in underlying mesenchyme.

The root sheath bends horizontally at level of future cement enamel junction forming the epithelial diaphragam ,following which the cervical opening becomes smaller.

Once the crown formation is complete the cells of the inner enamel epithelium loose their ability to form enamel epithelium ,but retain the ability to induce perimesenchymal cells differtiante into odontoblasts and to proceed with the formation of predentin and dentin .

The root sheath at this stage becomes discontinuous

After the dentin formation is completed ,certain changes occur in root sheath , the epithelial cells of root sheath produce a layer of on root dentin ,has hyaline layer of “ HOPE WELL SMITH or INTERMEDIATE CEMENTUM” .

The root sheath at this stage becomes discontinuous and enable the surrounding follicular mesenchyme to come in contact with the amelogein

These follicular cells then differentiate into cementoblast and deposit the organic matrix of cementum on the root surface.

LATER DEVELOPMENT OF CEMENTUM

C ementoblast are cuboidal cells that are arranged on the outer surface of the hyaline layer . These cells are responsible for the organic matrix .

These cells are responsible for the deposition of the organic matrix of cementum which consists of cementum which consists of proteoglycan ground substance ,intrinsic collagen fibres and is followed by subsequent mineralization of organic matrix .

Mineralization starts with the formation of a thin layer called cementoid . Mineral salts are derived from the tissue fluid containing calcium and phosphate ions and are deposited as hydroxiapatite crystals .

The disintegrated hertwigs root sheath slowly moves away from the root surface and remain in the periodontal ligament forms from the dental follicle soon after root formation begins

As the cementum continues to increase in thicknes more fibres become incorporated into the cementum a nd eventually called as “SHARPEY”S FIBRES “ ,when periodontal ligament become established .

Aleveolar bone forms around the periodontal ligament. Thus space of periodontal ligament become narrower.

Functions

a. Primary function of cementum is to provide anchorage to the tooth in its alveolus. This is achieved through the collagen fiber bundles of the periodontal ligament, whose ends are embedded in cementum.

b. Cementum also plays an important role in maintaining occlusai ielationsps. whenever the incisal and occlusal surfaces are abraded due to attrition, the tooth supra erupts in order to compensate for the loss and deposition of new cementum occurs at the apical root area.

COMPOSITION

The cementum is composed of both inorganic (46%) and organic matter. The organic matrix is chiefly composed of 90 percent Type I collagen. 5 percent Type III collagen and non-collagenous proteins like enamel proteins, adhesion molecules like tenacin and fibronectin, glycosaminoglycans like chondroitin sulfate, dermatans sulfate & heparan sulfate which constitute the remaining organic matrix.

Thickness of Cementum

Formation of cementum is a continuous process, the formative rate of which varies throughout life. It is most rapid at the apical regions. At the coronal half the thickness varies from 16 to 60 p.m (almost the thickness of hair) and at the apical third it varies from 150 to 200 p.m. it is thicker in the distal surfaces

as compared to the mesial surfaces and this can be explained by functioral stimulation following mesial migration.

Hypercementosis or cemental hyperplasia is a rominent thickening of the cementum. It can be localized or generalizd. It may ppçggpzed thic1cenjpgf the cemen±unj.ith nodular eniargemnt a pgor as spike like projections (cemental spikes). The etiology of hypercementosis is not very well understood.TI1spike like projections could be as a result of excessive tension from orthodontic appliancçor occlusal forces. The generalized type may be associated with a variety of situations like, teeth without antagonists, in teeth with chronic pulpal and periapical infections. J7Yypercementosis of the entire dentition may be seen in patients with Paget’s disease.

Cementoenamel Junction

At the cementoenamel junction three types of relationships may exist. In about 6o -65 percent of cases the cementum overlaps the enamel, in about 30 percert of cases end-to-end_relationship of enamel and cementum is seen and to 10 percent the cementum and enamel fail to meet.

Cemental Resorption and Repair

Cemental resorption may be caused by local, systemic idiopathic factors. Local conditions that contribute to cemental resorption are, trauma from occlusion, orthodontic tooth movement, pressure from erupting teeth, cysts and tumors, teeth without functional antagonist, per apical disease and periodontal disease,systemic conditions that may predispose to cemental resportion are calcium deficieny, hypothyroidism and pagets disease.

Remodellin g of cementum requires the presence of viable connective tissue and occur even in non-vital teeth.

Cernentum is not exposed to the oral environment because it is covered by alveolar bone and gingival . In cases of gingival recession and as a consequence of loss of attachment in pocket formation, cementum can become exposed to the oral environment. Once exposed organic substances, inorganic ions and bacteria pentrate the sufficiently permeable cementum. Caries of the cementum may also develop.

PATHOLOGIES ASSOSIATED WITH CEMENTUM

1. HYPERCEMENTOSIS2. BENIGN CEMENTOBLASTOMA3. PERIAPICAL CEMENTAL DYSPLASIA4. HYPOCEMENTOPHOSPHATASIA5. PAGET’S DISEASE

SUMMARY

1. Cementum is a calcified avascular mesenchymal tissue that forms the outer covering of the anatomic root2. Acellular cementum forms during root formation and is seen at the coronal portion of the root, whereas cellular) cementum forms after eruption of the tooth and is seen apically on the root.3. The cementum consists of 46 percent inorganic matter and the rest 90 percent omanic being Type I collagen and the remaining consists of non-collagenous proteins.4. Three types of relationships of cementum may exist at the cementoenamel junction. In 60 to 65 percent of cases cementum overlaps the enamel, in 30 percent edge-to- edge butt joint exists and in 5 to 10 percent the cementum and enamel do not meet.

BIBILIOGRAPHY

1. A.R. TENCATE

2. JAN LINDE

3. S.N.ORBAN’S

4. NEWMAN, TAKEI, FERMIN, A. CARRANZA