Dr. Fatma Elturki

PERIODONTIUM

Periodontium Its defi nition and composition.Cementum Defi nition. Physical and chemical characteristics. Development of Cementum. Structure of cementum. Classifi cation of Cementum. Incremental lines of Salter Aging of Cementum. Clinical considerations. Function of cementum.Periodontal l igament Defi nition. Development of the PDL Histological structure. Age changes of PDL. Functions of the periodontal ligament.

OBJECTIVES

PERIODONTIUM

periodontium is an attachment apparatus of the teeth to the jaws bone.

The periodontium composed of:1.Cementum.2.Periodontal Ligament.3.Alveolar bone.4.Gingiva facing the tooth.

PERIODONTIUM

Cementum is a mineralized dental tissue covering the anatomical part of the root of the human teeth.

It begins at the cervical portion of the tooth at the cementoenamel junction and continues to the apex.

It serves as a medium for the attachment of collagen fibers that bind the tooth to the surrounding structures.

CEMENTUM

PHYSICAL CHARACTERISTICS

Cementum shares some physical, chemical and structural

characteristics with compact bone except that human cementum is

avascular and with no nerve supply.Thickness: the thickness of cementum at the cervical area is about (20-50µm) and it gradually increases in thickness till it reaches its maximum about (150-200u) at the apex and at the bifurcation of the root.

A

B

Color: cementum is light yellow in

color it is somewhat lighter

in color than dentin

Permeability: Cementum has been shown to be permeable to a variety of materials, where it is permeable from

the dentin side as well as from the periodontal ligament side.

Hardness : Relative softness and the thinness at the cervical portion means that cementum is readily removed by the abrasion when gingival recession exposes the root surface to the oral environment.

In fully formed permanent teeth, cementum contains: 45% to 50% (inorganic). 50% to 55% (organic).The inorganic substances consist mainly of calcium

and phosphate in the form of hydroxyapatite.The organic portion consists mainly of collagen and

non-collagenous protein forming the ground substance.

CHEMICAL COMPOSITION

DEVELOPMENT OF CEMENTUM

Cementum formation occurs along the entire root of the tooth.

Hertwig’s epithel ial root sheath (HERS) sends inductive signal to ectomesenchymal pulp cel ls to secrete predentin by differentiating into odontoblasts.

Once the dentin formation is started, the epithelial root sheath of Hertwig will lose its continuity, undiff erentiated mesenchymal cells from adjacent connective tissue of the tooth follicle will diff erentiate into cementoblasts.

Cementoblasts lay down cementum matrix (cementoid).

Mineralization occurs after some matrix production has taken place.

A-epithel ial root sheathB-dental papi l laC-odontoblastD-denti ne of rootE-predenti n layerF-cementoblastsG-cementumH-alveolar boneI- inner layer of dental fol l ic leJ-outer layer of dental fol l ic leK-intermediate layer of dental fol l ic le

The remnants of the epithelial root sheath of Hertwig migrate toward the dental sac and become the epithelial rests of Malassez found in the periodontal ligament of the fully developed tooth.

A-Epithelial rests of Malassez

B-cementum

1- Cells…The cells of the cementum are

cementoblasts and cementocytes.

A-Cementoblasts…Cementoblasts are

mesenchymal cells that form the cementum and are found lining the root surface, interposed between the periodontal fibers.

STRUCTURE OF CEMENTUM

Active cells are round, plump with basophilic cytoplasm and all the organelles associated with protein synthesis. Inactive Cells or resting cells have little cytoplasm and closed nucleus.

When acellular cementum is being formed, the cementoblasts resting behind the cementum matrix. When cellular cementum is being formed, the cementoblasts become trapped in lacunae with their own matrix and are then known as cementocytes.

B- CEMENTOCYTES

Lacuna of cementocyte

Canalicului

 cementocyte is a cell in the lacunae , frequently having long processes radiating from the cell body toward the periodontal surface of the cementum

2- The fi brous matrix …The collagen fibers of cementum matrix are of two sorts: Intrinsic fibers i t derived from cementoblasts. Run parallel

to the root surface.

Extrinsic fibers i t derived from fibroblasts of PDL. These are in the same direction of the PDL principal fibers i.e. perpendicular to the root surface. They are known as Sharpey’s fibers

STRUCTURE OF CEMENTUM

A-cementoblastsB-cementoidC-cementocytes in cellular cementumD-Sharpey’s fiber

Under the light microscope two types of cementum can be diff erentiated:

STRUCTURE OF CEMENTUM

Acellular cementum cellular cementumThe diff erence between the two types is the

presence or absence of the cells (cementocytes)

The cementum is usually covered by a zone of cementoid tissue 3-5µm wide in acellular cementum and wider in cellular cementum. This cementoid tissue is lined by cementoblasts.

Cementum may be classifi ed in the following ways: By cellularity:Acellular cementum : Cementum without any cells in its matrix. It is clear and structureless it directly overlies the granular layer of Tomes. It covers root dentin starting from the CEJ to the apex, but it is often missing at apical third of the root, where the cementum may be entirely of the cellular type. Cellular cementum : It has the same structure as the acellular cementum but contains cells (cementocyte). It is present in the apical area and overlying acel lular cementum. Also common in inter-radicular areas.

CLASSIFICATION OF CEMENTUM

Extrinsic fi ber  cementum: Cementum that contains primarily extrinsic fi bers, i.e. Sharpey's fi bers that are continuous with the principal fi bers of the periodontal ligament. These fi bers are play a major role in tooth anchorage.

CLASSIFICATION OF CEMENTUM

Intrinsic fiber cementum:  Cementum that contains primarily intrinsic fibers, i.e. fibers produced by cementoblasts.   This form of cementum is located predominantly at sites undergoing repair, following surface resorption.  It plays no role in tooth anchorage.

Mixed fiber cementum:  Cementum that contains a mixture of extrinsic and intrinsic fiber cementum.

By the origin of the matrix fibers:

Acellular cementumCellular cementum

Hyaline layer (of Hopewell Smith)

Granular layer of tomes

Dentin with tubules

Cementum is classified according two factors:I. Time of formation (primary or secondary).II. Presence or absence of cells within its matrix

(acellular & cellular), and origin of collagenous fibers of the matrix (intrinsic fibers and extrinsic fibers).

Thus cementum classified into:1. Acellular extrinsic fiber cementum (primary

cementum)2. Cellular intrinsic fiber cementum (secondary

cementum).3. Mixed fiber cementum where layers of acellular and

cellular cementum alternate in apparently random manner.

4. Acellular afibrillar cementum.

COMBINED CLASSIFICATION

Sometimes dentin is separated from cementum by a zone known as the intermediate cementum layer.

It is not resemble either dentin or cementum usually it is present in the apical two thirds of the roots of molars and premolars, rarely seen in incisors or deciduous teeth.

It is believed that this layer represents areas where cells of Hertwig's epithelial root sheath become trapped in a rapidly deposited dentin or cementum matrix.

Sometimes the intermediate cementum is found as a continuous layer and sometimes it is found only in isolated areas.

INTERMEDIATE CEMENTUM HYALINE LAYER OF HOPEWELL-SMITH

A-acellular cementum. B-hyaline layer. C -granular layer of Tomes. D-dentine

Both cellular, and acellular cementum are separated by incremental l ines into layers, which indicate periodic formation.

Histo-chemical studies indicate that incremental l ines highly mineralized areas with less collagen and more ground substance than other portions of cementum.

The incremental l ines are roughly parallel to the long axis of the root.

The cellular cementum is formed at a faster rate than the acellular cementum and the incremental l ines therefore located further apart than in acellular cementum.

INCREMENTAL LINES OF SALTER

The relation between cementum and enamel at the cervical region of teeth is variable:

In 60% Cementum overlaps enamel.

Cementum just meets enamel in 30%.

10% Have a small gap between cementum and enamel.

CEMENTOENAMEL JUNCTION

Aging of Cementum1. Smooth surface becomes irregular duo to

calcification of ligament fiber bundles where they are attached to cementum

2. Continues deposition of cementum occurs with age in the apical area.[Good: maintains tooth length; bad: obstructs the foramen]

3. Cementum resorption. Active for a period of time and then stops for cementum deposition creating reversal lines

4. Resorption of root dentin occurs with aging which is covered by cemental repair

It is an abnormal thickening of the cementum.

Hypercementosis may aff ect one tooth or may be generalized in all teeth, also it is either l imited to a small area of the root or through the whole root length.

When the increase in thickness of cementum occurs in a good functioning tooth and it can be considered as a response for the improvement of the functional qualities through increasing the root surface areas and thus permitting more periodontal fi bers to be attached to the tooth, this is termed cementum hypertrophy . But if the growth occurs in non functioning teeth or the increase in cementum occurs in embedded teeth this is called cementum hyperplasia .

HYPERCEMENTOSIS

• Calcified ovoid or round nodule found in the PDL.

• Single or multiple near the cemental surface.

• Free in l igament; attached or embedded in cementum.

• common in aging and at sites of trauma.

Origin: Nidus of epithelial cell that are composed of calcium phosphate and collagen to the same amount as cementum.

CEMENTICLES

CLINICAL CONSIDERATIONS

Cementum is more resistant to resorption than is bone, & it is for this reason that orthodontic tooth movement is made possible.

Cementum resorption can occur after trauma or excessive occlusal forces. In most cases of repair, there is a tendency to re-establish the former outline of the root surface by cementum. This is called anatomic repair.

However, if only a thin layer of cementum is deposited on the surface of a deep resorption, the root outline is not reconstructed, & a bay like recess remains.

In such areas the periodontal space is restored to its normal width by formation of a bony projection, so that a proper functional relationship will result. the outline of the alveolar bone in these cases follows that of the root surface. This is called functional repair.

cementum is similar to bone but has no nerves. Therefore it is non-sensitive to pain. Scaling produces no pain, but if cementum is removed, dentin is exposed causes sensitivity.

Cementum furnishes a medium for the attachment of collagen fibers of the periodontal ligament to the" alveolar bone. The continuous deposition of cementum is of considerable functional importance, as the most superficial layer of cementum ages, a new layer of cementum must be deposited to keep the attachment apparatus intact.

In the same time deposition of the cementum at the apical part of the root can compensate, to some extent for the loss of tooth substance that may occur from occlusal wear. Cementum serves as a major reparative tissue for root surfaces damage as fracture or resorption can be repaired by deposition of new cementum.

FUNCTION OF CEMENTUM

Periodontal ligament

The periodontal ligament is a soft, fibrous specialized connective tissue which is present in the periodontal space, which is situated between the cementum of root of the tooth and the bone forming the socket wall.

PERIODONTAL LIGAMENT

It is continuous with the connective tissue of the gingiva and communicates through vascular channels in the bone with marrow spaces.

At the apical foramen it is continuous with the dental pulp.

The width of periodontal ligament is not uniform it ranges from 0.15-0.21

mm. The periodontal ligaments of primary teeth are wider than those

found in permanent teeth.

After separation of HERS, the cells of dental foll icle migrate to the external surface of the newly formed root dentin. These migrated foll icular cells diff erentiate into cementoblast that deposit cementum , other cells diff erentiate into fi broblasts which synthesize the fi bers and ground substance of periodontal l igament. The fi bers of periodontal l igament become embedded in the developed cementum and alveolar bone. As the tooth erupts the fi bers of the periodontal l igament are oriented in the characteristic fashion.

DEVELOPMENT OF THE PDL

The outer layer of dental follicle (perifollicular mesenchyme)

The inner layer of

dental follicle

dental follicle

Developing tooth

PERIODONTAL LIGAMENT (PDL)

At first the developing fiber bundles of the PDL are thin and not

well oriented.

They are all

directed obliquel

y

Only after the teeth come into occlusion do the fiber bundles of PDL become well organized in terms of thickness and

orientation

Similar to all connective tissue the PDL consists of :

HISTOLOGICAL STRUCTURE

Cells

Extracellular

substances

Fibers

Resorptive

Progenitor Defensive

Synthetic Ground Substance

BVlymphatic

Nerve

I- THE CELLSSynthetic

cells

Resorptive cells

Progenitor cells

Defensive cells

fibroblasts, osteoblasts & cementoblasts.

Fibroblasts, osteoclasts & cementoclasts.

undifferentiated mesenchymal

cells

macrophage, lymphocytes &mast cells

epithelial cells remnants of the

epithelial root sheath of

Hertwig

II- The fibers

*The fibers of the periodontal ligament are mainly collagen.

They are divided into:A) The principal fibers.B) The oxytalan fibers.

*Elastic fibers are restricted almost entirely to the walls of blood vessels.

1- principle fi ber bundle of the PDL:i. The alveolar crest group.ii. The horizontal group.iii. The oblique group.iv. The apical group.v. The interradicular group.

A- THE PRINCIPAL FIBERS

At the end, all the principle collagen fiber bundles of the PDL are embedded in cementum or bone. The embedded portion is referred to as Sharpey’s fiber.

A- THE PRINCIPAL FIBERS

2- Gingival ligament:- They are found in the lamina propria of the gingiva:I. Dentogingival group.II. Alveologingival group.III. Circular group.IV. Dentoperiosteal group.V. Transseptal fi ber

system.

A- THE PRINCIPAL FIBERS

These are immature elastic (pre-elastic) fi bers.

They need special stains to be demonstrated.

They tend to run in an axial direction, one end being embedded in bone or cementum and the other in the wall of blood vessels.

At the apical region they form a complex network.

The function of the oxytalan fi bers has been suggested that they supporte the blood vessels of the periodontal ligament during mastication i.e., it prevents the sudden closure of the blood vessels under masticatory forces.

B- OXYTALAN FIBERS

INTERSTITIAL TISSUE

The ground substance fi lls the spaces between cells, fibers,

They are areas containing some of the blood vessels, lymphatics and nerves and surrounded by loose connective tissue.

Ground Substance

Main blood supply is from superior and inferior alveolar arteries . The blood vessels are derived from the fol lowing:

1. BRANCHES FROM APICAL VESSELS Vessels supplying the pulp.

2. BRANCHES FROM INTRA-ALVEOLAR VESSELS:- Vessels run horizontally and penetrate the alveolar bone to enter into the periodontal l igament.

3. BRANCHES FROM GINGIVAL VESSELS : - The arterioles and capil laries ramify and form a rich network. Rich vascular plexus is found at the apex and in cervical part of l igament.

BLOOD SUPPLY

Lymphatics:A network of lymphatic vessels follows the path of

blood vessels. Usually the flow is from the ligament toward and into the adjacent alveolar bone.

(A) Subepithelial capillary network of the gingiva, (B) Capillary network of the periodontal ligament, (C) Supraperiosteal arterial, and (D) Arterials penetrating the interdental alveolar bone.

NERVE SUPPLY

Nerves found in ligament pass through foramina in alveolar bone.

The nerves are the branches of second and third division of fifth cranial nerve (trigeminal nerve) and follow same path as blood vessels.

These nerve fibers provide sense of touch, pressure, pain and proprioception during mastication.

THE AGE CHANGES OF PERIODONTAL LIGAMENT

*The periodontal ligament through aging shows: vascularity cells thickness

*They may contain cementicles.

FUNCTIONS OF THE PERIODONTAL LIGAMENT

The periodontal ligament has the following functions:Supportive: Periodontal ligament forms a

functional system, which provides an attachment for the tooth to the bone of the jaw, while at the same time permitting the teeth to withstand the considerable forces of mastication.

Sensory: The periodontal ligament having the mechanoreceptor contributes to the sensation of touch and pressure on the teeth. So the proprioceptive reflex protects the tooth in case of sudden overload. It causes inhibition of the activity of the masticatory muscles. Opening the mouth at once relieves the pressure.

Nutritive: The blood vessels in the periodontal ligament provide nutrient supply required by the cells of the ligament and to the cementocytes and the most superficial osteocytes.

Formative: The cells' present in the periodontal ligament as the fibroblasts are responsible for the formation of new periodontal ligament fibers and dissolution of the old fibers as the continued adaptive readjustment of the suspensory ligament demands. Another formative function is fulfi lled by the cementoblasts and osteoblasts which are essential in building up cementum and bone.

Protective: The protective function of the periodontal ligament is achieved by: a- The principal fibers. b- The blood vessels, c- The nerves.

FUNCTIONS OF THE PERIODONTAL LIGAMENT

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