Shaju Jacob

Shaju_Jacob@imu.edu.my

Extension 2755

Senior Lecturer Dentistry

(Periodontology)

LEARNING OBJECTIVE

This presentation is a continuation from the previous

lecture on healthy periodontium, in this lecture

cementum and bone will be discussed.

At the end of this lecture you will be able to:

Describe clinical and macroscopic features of

cementum and bone

Describe the microscopic feature of cementum and

bone

Discuss its function and its importance

CEMENTUM

IN HEALTH

Definition: Cementum is calcified, avascular mesenchymal tissue that forms the outer covering of the anatomic root.

It is also called as substantia ossea.

It was first discovered microscopically demonstrated by two pupils of Purkinje in 1835.

CEMENTUM

It serves to invest and

attach the periodontal

fibers

To maintain the thickness of

root in apical region

INORGANIC:

Calcium and phosphate in the form of HYDROXYAPATITE

crystals

These crystals are 55nm wide,8nm thick

Highest fluoride content

Calcium and magnesium

TRACE AMOUNT:

Copper, Fluorine, Iron, Lead,

Potassium, Silicon, Sodium and Zinc

COMPOSITION

Non-Collagenous Protein:

Cementum is rich in glycoconjugates, which represent either glycolipids, glycoproteins or proteoglycans and harbors a variety of other proteins.

The predominant noncollagenous proteins are:

1) Bone sialoprotein 3) Osteonectin 2) Osteoponitin 4) Fibronectin, Tenasin

ORGANIC: Collagen:

Type I - 90%

Type III - 5%

CELLS OF CEMENTUM:

a) Cementoblast

b) Cementocytes

c) Cementoclast

CEMENTOCYTES CEMENTOBLASTS

Cemental Fibers

Sharpeys Fibers (extrinsic): These fibers are embedded

portions of the principal fibers

of the periodontal ligament and

are formed by fibroblasts.

Intrinsic Fibers: these are

fibers that belong to the

cemental matrix and are

produced by cementoblasts.

Structure of cementum

Under light microscope, two types of cementum are visible. Based on the presence or absence of cells they are classified as:

Acellular Cementum ( Primary cementum)

Cellular cementum ( Secondary cementum)

It will be seen under two headings:

Formation

Anatomical Characteristics

Formation of Acellular Extrinsic fiber cementum

The first cells that align along the newly

formed, but not yet mineralized, mantle

dentin surface exhibit fibroblastic

characteristics.

Mineralization of the mantle dentin takes

place

Intermingling of collagen fibers at cementum

and dentin interface.

Then fiber fringe extends towards PDL.

Initial acellular extrinsic fiber

cementum thus consists of a thin

mineralized layer with a short

fringe of collagen fibers

implanted perpendicular to the

root surface inserting in mantle

dentin

Cells on the root surface

secrete noncollagenous

matrix proteins that fill in the

spaces between the

collagen fibers and regulate

mineralization of the

forming cementum layer.

Bone sialoprotein

This activity continues until about

1520 um of cementum has been formed, at which time the intrinsic

fibrous fringe becomes connected to

the developing periodontal ligament

fiber bundles.

Anatomic characteristics of acellular

cementum

It is the first formed cementum and is therefore referred to as primary cementum.

It covers approximately the cervical third or half of the root. It does contain any cell.

This cementum is formed before tooth reaches the occlusal plane and its thickness ranges from 30 to 230 microns.

It is thinnest at the cementoenamel junction and thickest towards root apex.

Sharpeys fibers make up most of the structure of acellular cementum.

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

Formation cellular Intrinsic Fiber

Cementum

Cementoblasts start forming a less mineralized layer.

Matrix proteins that fill in the spaces between the collagen fibrils, regulate mineral deposition and impart cohesion to the mineralized layer.

A layer of unmineralized matrix, termed cementoid.

Collagen fibrils are produced rapidly and deposited haphazardly during the initial phase; however, subsequently the bulk of fibrils organize as bundles oriented mostly parallel to the root surface.

cementoblasts start forming a

less mineralized variety of

cementum

As the process proceeds, some

cementoblasts become trapped in the

matrix they form. These entrapped cells,

with reduced secretory activity, are

called cementocytes and sit in lacunae.

Cellular

Cementum

Canaliculi of

cementocytes

Lacunae of

cementocyte

Some cementoblasts

become trapped in the matrix

to form cementocytes and sit

in lacunae.

Cementum

Cementocyte

Cementoid

Anatomic Characteristics of

Cellular cementum

It is the cementum is formed after the tooth

reaches the occlusal plane.

It is more irreglular and contains cells within

its matrix called cementocytes.

Cellular cementum is more on the apical half

of the root.

It is less calcified than acellular cementum.

Sharpeys fibers make up smaller portions and

are separated by collagen fibers.

Formation of cementum continues throughout the life, it is

the cellular cementum which continuously contributes to

the length of root.

Classification of Cementum:

Based on the findings Schroeder 1985 classified cementum:

Acellullar afibrillar cementum: (AAC):

Acellular extrinsic fiber cementum:(AEFC)

Cellular mixed stratified cementum; (CMSC):

Cellular intrinsic fiber cementum (CIFC):

Intermediate cementum:

1. Acellular Afibrillar

cementum

2. Acellular Extrinsic fiber

cementum

3. Cellular intrinsic fiber

cementum

4. Cellular Mixed stratified

cementum

Intermediate Cementum or hyaline layer of Hopewell Smith.

Periodontal

ligament

cementum

Intermediate

cementum

Dentin

Clinical Significance: hyaline layer contains epithelial derived enamel like

proteins and has an important role in the attachment of cementum to the

dentin surface.

60% to 65% Cementum overlapping the enamel

30% End-to-end relationship of enamel and cementum

5% to 10% space between enamel and cementum with dentin

CEMENTO ENAMEL JUNCTION:

Cementodentinal Junction:

The terminal apical areas of the

cementum where it joins the internal root

canal dentin is known as the

cementodentinal junction (CDJ).

When root canal treatment is performed

the obturating material should be at CDJ.

It remains stable without any increase or

decrease.

The CDJ is 2 to3 um wide.

Anchorage

Attachment

Adaptive and reparative function

Walling in filled canals

Repairing roots (horizontal fracture)

Sealing of necrotic pulps by occluding apical foramen

Protecting underlying dentin

FUNCTIONS:

ALVEOLAR

BONE IN

HEALTH

Bone is a mineralized connective tissue.

About 60% of its weight is inorganic material, about

25% organic material and about 15% water.

The mineral phase is carbonated hydroxyapatite,

distributed both within the spaces between and on the

surfaces of the collagen fibrils.

The cells through their capacity for osteosynthesis and

resorption, have a pivotal role in the maintenance of the

matrix.

Bone consists of two-thirds inorganic matter and one-third organic matrix.

INORGANIC MATTER:

Calcium & Phosphate,

Hydroxyl

Carbonate

Citrate

ORGANIC MATTER:

90% of collagen Type I

Non collagenous proteins;

Osteocalcin

Osteonectin

Bone morphogenetic protein

Phosphoproteins

Proteoglycans.

Organization of Adult Bone

Inner and outer

circumferential lamellae

Osteons (Haversian

lamella)

Cementing lines

Haversian canal

Blood vessels,

nerves,

mesenchymal

tissue, endosteum

Interstitial lamella

ALVEOLAR PROCESS

The alveolar process is the portion of the maxilla and mandible

that forms and supports the tooth sockets (alveoli). Develops in

response to presence or absence of teeth.

The alveolar process consists of the following:

1. An external plate of cortical bone formed by haversian bone

and compacted bone lamellae.

2. The inner socket wall of thin, compact bone called the

alveolar bone proper, which is seen as the lamina dura in radiographs.

3. Cancellous trabeculae, between these two compact layers,

which act as supporting alveolar bone.

In addition, the jaw bones consists of the basal bone, which is the

portion of the jaw located apically but unrelated to the tooth

ALVEOLAR PROCESS

Cortical plate.

Dense outer covering of the spongy bone.

Provides strength and protection.

Serves as attachment site for muscles.

Spongy bone.

Less dense and cancellous bone.

Makes up the central portion of the alveolar process

Compact and Spongy Bone

INTERDENTAL SEPTUM:

Interdental

septum consists of

cancellous bone

bordered by the

socket wall cribriform

plates of

approximating teeth

and the facial and

lingual cortical plates.

Lamina dura

Thin compact bone that lines the tooth socket.

Has many small

openings for

blood vessels

and nerve fibers.

CELLS AND INTERCELLULAR MATRIX:

OSTEOBLASTS OSTEOCLASTS

Mineralized matrix

Osteoid

Cell process

Osteoid

(or prebone)

SOCKET WALL:

The socket wall consists of dense, lamellated bone, some

of which is arranged in haversian systems, and bundle bone.

Bundle bone is the term given to bone adjacent to the

periodontal ligament that contains a great number of sharpeys

fibers.

Bundle bone is not unique to the jaws; it occurs through

the skeletal system wherever ligaments and muscles are

attached.

BONE MARROW:

In the embryo and newborn, the cavities of all bones are

occupied by red hematopoietic marrow.

The red marrow gradually undergoes a physiologic change

to the fatty or yellow inactive type of marrow.

Foci of red bone marrow are occasionally seen in the

jaws, like maxillary tuberosity, maxillary and mandibular molar

and premolar areas, and the mandibular symphysis and ramus

angle, which may be visible radiographically as zones of

radiolucency.

Periosteum

The tissue covering the outer surface of bone is termed

periosteum. It consists of;

1. Inner layer composed of osteoblasts surrounded

by osteoprogenitor cells.

2. Outer layer rich in blood vessels and nerves and

composed of collagen fibers and fibroblasts.

Bundles of periosteal collagen fibers penetrate the

bone, binding the periosteum to the bone.

Endosteum

The tissue lining the internal bone cavities is called

endosteum.

It consists of

1) Inner layer osteogenic layer

2) Outer layer fibrous layer.

Copyright 2007, Thomas G. Hollinger, Gainesville, Fl

Periosteum

Osteocyte in lacuna

Fibrous layer

of periosteum

Osteogenic or

cellular layer

of periosteum

Endosteum

(Osteoblasts)

Osteoblasts

REMODELLING:

It is the major pathway of bony changes in shape,

resistance to forces, repair of wounds, and calcium and phosphate

homeostasis in the body.

The interdependency of osteoblasts and osteoclasts in

remodeling is called coupling.

The bone matrix that is laid down by osteoblasts is

nonmineralized osteoid.

Bone resorption is a complex process morphologically

related to the appearance of eroded bone surfaces (Howships

lacunae) and large, multinucleated cells- Ostoclasts.

REMODELING OF ALVEOLAR BONE

Alveolar bone is the least stable of the periodontal

tissues because its structure is in a constant state of

flux.

A considerable amount of internal remodeling

takes place by means of resorption and formation, which

are regulated by local and systemic influences.

The remodelling of the alveolar bone affects its

height, contour, and density.

REFERENCES

Antonia Nanci, Ten Cates Oral Histology, 7th edition. Antonia Nanci and Dieter D Boohardt: Structure of

periodontal tissues in health and disease. Periodontology 2000 2003; 31: 12-31

Michael G. Newman , Henry Takei, Perry R. Klokkevold, Clinical Periodontology, 10 edi

Jan Lindhe, Karring, Lang, Clinical Periodontology and Implant Dentistry., 5th Edition.

Thomas G. Wilson Fundamentals of Periodontics, 2nd edition, Anatomy of Periodontium.

Bhaskar SN, Orbans Oral Histology and Embryology, 11 th edition