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CEMENTUM

DEFINITION Cementum is the calcified a vascular mesenchmal tissue that forms

the outer layer cover of the anatomic root

Types of cementum

There are two main types of cementum they are:- 1.A celluar cementum and

2.cellular cementum The two main source’s of collagen fibers in cementum are sharpey’s

fibers which are the embedded portion of principal fibers of the

Periodontal ligament and are formed by the fibroblasts

Fibers that belong to cementum matrix and are produced by cementoblasts

Cementoblasts also form the non collagenous components of the inter fibrillar ground substance such as proteoglycans, glycoproteins and phosphoproteins

Proteoglycans are the most likely to play a role in regulating cell-cell and cell-matrix interactions

COMPOSTION

The major proportion of the organic matrix of a cementum is composed of type one (90%) and type three about (5%) collagens

ACELLULAR CEMENTUM

It is the first cementum formed, covers approximately the cervical third or half of the root and does not contain cell’s

This cementum is formed before the tooth reaches the occlusal plane and it’s thickness ranges froms 30 to 230 um

Sharpey’s fibers are completely calcified, with the mineral crystals. Oriented parallel to the fibrils as dentin and bone except in a 10 -50 um wide zone near the cementodentinal junction where they are only partially calcified

•Acellular cementum also contains intrinsic collagen fibrils that are calcified and irregularly arranged or parallel to the surface

•CELLULAR CEMENTUM

•Celluar cementum formed after the tooth reaches the occlusal plane is more irregular and contain cell’s (cementocytes) in individual spaces (lacunae)

that communicate with each other through a system of anastomising canaliculi

Cellular cementum is less calcified than the acellular type

Sharpey’s fibers occupy a smaller portion of cellular cementum and are separated by other fibers that are arranged either parallel to the root surface

Both acellular and cellular cementum are aranged in lamellae separated by incremental lines parallel to long axis root this lines are called rest periods

PERMEABILITY OF CEMENTUM

In very young animal’s acellular cementum and cellular cementum are very permeable and permit the diffusion of dyes from the pulp and external root suface

THICKNESS OF CEMENTUMCementum deposition is a continuous process

that proceeds at varying rates

Cementum formation is most rapid in the apical regions where it compensates for tooth eruption, which it self compensate for attrition

The thickness of cementum on the coronal half of the root varies from 16-60um

It attains greatest thickness (upto 150-200 um) in the apical third and in the fraction areas

Abnormalities in the thickness of cementum may range from an absence of cellular cementum to an excessive deposition of cementum

The term hyper cementosis refers to a prominent thickening of cementum

Hyper cementosis occurs a generalisied thickening of the cementum

CEMENTUM RESORPTION AND REPAIR

Cementum resorption may be caused by local and systemic factors

Local condition causing cementum resorption include trauma from occlusion orthodontic movement pressure from malaligned erupting teeth cysts and tumors teeth with out junctional antagoinsts

Systemic condition citied as predisposing to or including cemental resorption include calcium deficiency hypothyroidism, hereditary fibrous osteodystrophy

EXPOSURE OF CEMENTUM TO ORAL ENVIRONMENT

Cementum becomes exposed to the oral environment in cases of gingival recession and as result of loss of attachment in pocket formation

CEMENTO ENAMEL JUNCTION

The cementum at and immediately subjacent to cemento enamel junction is of particular clinical importance in root scaling procedures

Three types of relationships involving the cementum may exists at cementoenamel junction

In about 60 -65% of cases, cementum over laps the enamel in about 30% an edge-edge but joint exists and 5-10% the cementum and enamel fail to meet

CEMENTO DENTINAL JUNCTION

The terminal apical area of cementum where it joins the internal root canal dentin is known as cemento dental junction

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