cementum 2014

Cementum

By

Professor of Oral BiologyFaculty of Oral and Dental Medicine

Cairo University

Cementum is a specialized calcified dental tissue covering the anatomical root of human teeth.

Cementum serves as a medium of attachment of the colagen fibers that bind the tooth to the surrounding structures.

Cementum resembles bone in some of its physical and chemical structures , however, it is :

Avascular

Not innervated

Unnable to remodel

Acellular cementum (20-50 m)

Cellular cementum (150-200 m)

Physical Characteristics

2- Thickness

1-Color

Light yellow

Lighter in color than dentin,

darker than enamel

3- Permeability

Permeable from dentin and PDL sides.

Cellular C is more permeable than acellular C.

Chemical Composition

45-50 % Inorganic

substances50-55% Organic

substances

Hydroxyapatite

crystals Collagen

Polysaccharides

Cementum contains the greatest amount of

fluoride in all mineralized tissues.

Less harder than dentin&

much less harder than

enamel

Histological Structure

•Large cuboidal cells

•Found on the surface of both

celular and acellular

cementum.

•They produce collagen fibers

(intrinsic fibers) and ground

substance of cementum.

Cementoblasts

Cementoblast is a protein forming and secreting cell.

Large open face nucleus

R E R

Golgi apparatus

Mitochondria

Alkaline phosphatase

Secretory granules

They are incorporated in

cellular cementum

Spider shape appearance

They have numerrous

irregular processes.

Most processes are

directed towards PDL.

Cementocytes

Dentin PDL

The cell body is located in a space called lacuna and

their processes are present in canaliculi

Cementocytes in deeper layers of cementum undergo

degeneration and gradually lose their organelles and

die

Dentin PDL

In ground section, cementocytes spaces

appear as dark spaces

Cementocyte And Osteocyte

Dentin side

PDL side

Lacuna

Canaliculi

Osteocyte

A- The embedded part of PDL fibers( Sharpys fibers, this

is formed by PDL fibroblasts and called extrensic

fibers.

B- Other fibers are formed by osteoblast and are called

intrinsic fibers.

Extrensic fibers are short and dense arranged

perpendicular to root surface.

Intrinsic fibers are arranged parallel to the root surface.

Collagen fibers of cementum are derived

from two sources:

Types Of Cementum

1- Acellular ementum 2- Cellular cementum

3- Intermediate cementum 4- Afibirllar cementum

Acellular Cementum

Thickness is 20-50 µm.

It is clear and structureless

Incremental lines of Salter are parallel to the surface.

Sharpey’s fibers space can be seen in it .

The bulk of collagen fibers are derived from Sharpys fibers , so it is called acellular extrinsicfiber cementum.

This the only type found in incisors and extend to the apical foramen.

It is found in the coronal part of the root of the premolars and molars roots.

Cellular Cementum

•It is found at the apical third and the furcation area of premolars and molars.

Thickness increase gradually till root apex reaching 150- 200 µm

It is formed faster than acelular cementum.

It is more permeable than acelular cementum.

•It is formed mainly of intrinsic fibers ( Intrinsic fiber

cementum).

•It contains cementocytes ( Imprisoned cementoblasts).

In decalcified sections, the lacnae appears as minute space containing the cementocytes

In ground section, the lacunae of cementocytesappear black as they are filled with air after desentigration of the cells during preparation

Some cementoblasts become entrapped in the forming

matrix and then known as cementocytes

Incremental Lines Of Salter

They are hypermineralized area with less collagen

fibers and more ground substance

In acellular C, less

distance between IL

In cellular C,more

distance between IL

• IL are faint lines run parallel to the root surface

Intermediate Cementum

Premature

degeneration of

epith. Root sheath

of Hertwig ( after

odontoblasts

differentiation and

before dentin

formation)

It occur at apical 2/3 of premolars and molars

roots and rare in incisors and deciduous teeth

Contains entrapped

epithelial cells&

intrinsic fibers

Cemento Dentinal Junction

It is not distinctive, because the Fibers of dentin and cementumintermingle at the interface

CD

Cemento Dentinal Junction

Smooth in permanent

teeth

Scalloped in deciduous

teeth

Cemento Enamel Junction

30% cementum

meets the enamel

in a sharp line

10% cementum and enamel

doesn’t meet because of

delayed separation of epith

root sheath of Hertwig (area

of dentin not covered by C).

60%

cementum

overlaps E

(afibrillar

cementum)

Afibrillar Cementum

The enamel at cervical

area not covered by

reduced dental

epithelium before

tooth eruption

The connective tissue of

the dental sac lay down

cementum on the

exposed enamel

Functions Of Cementum

1- It occludes sensitive dentin

2- Acts as a medium for attachment of collagen fibers of PDL (Sharpey’s fibers).

3- The continuous formation of cementum keeps the attachment apparatus intact.

4- Cementum depositionepically compensate for the attrition.

5- It is a major reparativetissue ( as in case of fracture or resorption of root)

Cementogenesis

1- Matrix formation 2- Maturation

Collagen

fiber type I

Ground

substance

Hydroxy apatite

crystals

1- Matrix formation

Cementum is formed during root formation

Future C E J Epith. Diaph.

H E R

D

Cementoblasts

Cementoblast is a protein forming and secreting cell.

D

Cem

en

tob

last

Large open face nucleus

R E R

Golgi apparatus

Mitochondria

Alkaline phosphatase

Secretory granules

Collagen fibers +

ground substance.

Cementum

Cementoid layer

Ce

me

nto

bla

sts

Resorption of cementum

•Normal phenomena in deciduous

teeth .

Certain factors as trauma or

sustained pressure can result in

resorption of cementum.

Age Changes Of The Cementum

DD

Localised

1- Hypercementosis.

May affect one tooth or all teeth Hypercementosis

ThicknessCementum formation is continuous throughout life in a very slow rate Especially in apically and in the furcation area.The rate of formation may vary from time to time .

Hypercementosis

hyperplasia

Hypercementosis

hypertrophy

Increase number of

Sharpey’s fibers

Decrease number of

Sharpey’s fibers

Types Of Hypercementosis

2- Permeability

From

periodontal

side, but remain

at the

superficial

recently formed

layers

From dentin

side

remains at

apical area

ONLY

Cementicles

Calcified oval or round nodules found in the PDL, single or in groups.

They may be free or attached or impedded in cementum.

The origin may be calcified epith. Cells (Rests of Mallasez).