ULTRASTRUCTURE AND FUNCTIONS OF

CEMENTUM

Presented by

Saranya s

PG student

CONTENTS INTRODUCTION CEMENTOGENESIS PHYSICAL CHARACTERISTICS CHEMICAL COMPOSITION CELLS OF CEMENTUM CLASSIFICATION OF CEMENTUM FUNCTION TYPES OF JUNCTION CEMENTUM RESORPTION AND REPAIR CLINICAL SIGNIFICANCE CONCLUSION REFERENCES

INTRODUCTION

Cementum is the calcified, avascular mesenchymal tissue that

forms the outer covering of the anatomic root - Carranza

Cementum is the thin layer of calcified tissue

covering the dentin of the root and it is one

of the four structures that support the tooth

in the jaw - Berkovitz

Cementum:

Is a hard bone like tissue covering the anatomic roots of the teeth. GENCO

Cementum Development - Cementogenesis

Root formation commences when the enamel organ has reached its final size .

The inner and outer cell layers of the enamel epithelium, which delineate the enamel organ, proliferate from the cervical loop to form Hertwig’s epithelial root sheath.

Continuous cell mitotic activity at the apical termination of Hertwig’s root sheath leads to a coronoapical growth of this double cell layer.

Its most apical portion, that is, the diaphragm, separates the dental papilla from the dental follicle.

•where the Cementum is formed during root

development.

Pre - functional development

stage

• which takes place when the tooth is about to reach the occlusal level & continues

throughout life.

Functional development

stage

PRE – FUNCTIONAL STAGE…..Cementum formation in developing

teeth is preceded by the

deposition of dentin along the inner aspect of

Hertwig’s Epithelial Root Sheath (HERS).

Once the 1st layer of radicular mantle dentin has been laid down by maturing odontoblasts

& before mineralization of dentin reaches the

inner epithelial cells, HERS becomes

fragmented.

Cells from the dental follicle then

penetrate the HERS & occupy

the area next to the predentin.

This direct contact of dentin with the connective tissue of the dental follicle,

stimulates the undifferentiated ecto - mesenchymal cells to

differentiate into cementoblasts, which

begin to produce collagen fibers

The first Cementum deposited on the

superficial layer of mantle dentin(hyaline layer)contains enamel

matrix proteins.

FUNCTIONAL STAGE… Associated with the attachment of the root to the

surrounding bone and continues throughout life.

It is mainly during the functional development that adaptive and reparative processes are carried out by the biological responsiveness of cementum,

This in turn, influences the alterations in the distribution and appearance of the cementum varieties on the root surface with time.

FATE OF HERS

Breakdown of Hertwig’s epithelial root sheath involves degeneration or loss of its basal lamina on the cemental side

Loss of continuity of the basal lamina is followed by the appearance of collagen fibrils and cementoblasts between epithelial cells of the root sheath

Some sheath cells migrate away from the dentin toward the dental sac – become the epithelial rests of Malassez found in the PDL

The other sheath cells remain near the developing tooth, are incorporated into the cementum

Soon after the HERS breaks up undifferentiated mesenchymal cells from adjacent connective tissue differentiate into Cementoblasts.

These cells have numerous mitochondria, well formed golgi apparatus and large amount of granular endoplasmic reticulum.

Cementoblasts synthesize collagen and protein polysaccharides which make up the organic matrix of the cementum.

Development of cellular cementum – 2 stages

Early stage• Extrinsic fibres were

few and intrinsic fibres were randomly arranged

Later stage• Extrinsic fibres were

thicker and the intrinsic fibres appeared to encircle them

Development of acellular cementum

Epithelial cell rests showed a close relationship

Development of acellular cementum is associated with the secretion of enamel matrix proteins ( EMP) by HERS preceded by the mineralization of the first layer of dentin adjacent to the root

HERS also secrete BSP, osteopontin and fibrillar collagen.

Epithelial mesenchymal reaction leading to the development of cementoblasts.

Enamel proteins and amelogenin are reported to be involved in epithelial mesenchymal reaction.

PHYSICAL CHARACTERISTICS Cementum is light yellow in color &

distinguished from enamel by its lack of luster and its darker hue.

Lighter in color than dentin.

Hardness of fully mineralized cementum is less than that of dentin.

Permeability- Both Cellular & Acellular Cementum are permeable to a variety of materials, with that of Cellular being > Acellular Cementum.

Permeability of cementum ↓ with age.

- ( Blayney et al., 1941).

CHEMICAL COMPOSITION

INORGANIC PORTION(45-50%)

ORGANIC PORTION & WATER (50-55%)

Organic matrix composed of type I ( 90%) and type III (5%) collagens .

Sharpey’s fibers constitute the bulk of the cementum, mainly composed of type I collagen .

Type III collagen appears to coat the type I

collagen of sharpey’s fibers

Non-collagenous proteins present are bone sialoprotein, fibronectin, dentin sialoprotein, tenascin, osteopontin and osteonectin.

Promote cell attachment and cell migration.

Stimulate protein synthesis of gingival fibroblasts and periodontal ligament cells.

Play major role in the differentiation of cementoblast progenitor cells to cementoblasts

Cementum Attachment Protein (CAP)

Collagenous proteins 56kDa to 65kDa Promote the adhesion and spreading of

mesenchymal cells with osteoblasts and periodontal ligament fibroblasts.

Located in matrix of mature cementum & in cementoblast

Act as marker to differentiate from bone.

Cementum derived growth factor

Enhance the proliferation of the gingival fibroblasts and periodontal ligament cells

Cementum is rich in GAG, predominantly chondroitin sulphate additionally dermatan sulphate & hyaluronan.

Inorganic component of the cementum:

Hydroxyapatite (45% to 50%)

HA- bone(65%), enamel (97%), dentin (70%)

Thin and plate-like and similar to those in bone.

Average 55nm wide and 8 nm thick.

Also contains calcium, fluoride, magnesium, carbonate,

citrate.

CELLS OF CEMENTUM

 CEMENTOBLASTS

Origin :-

Are cemento – progenitor cells synthesising collagen & protein polysaccharide (proteoglycans) which make up the organic matrix of cementum.

Arise from the dental follicle proper which is ectomesenchymal in origin - a derivative of the cranial neural crest. (Tencate, 1971)

Differentiation:- The fibrogenic cells of the dental follicle are

either fibroblasts / mesenchymal cells.

Tend to become differentiate into cementoblasts as they invade, approach & align themselves along the external border of the dentin to form cementogenic layer.

Form a single / multicellular layer.

 

The components of multilayered cells are more flattened than that of single cells

Contain mitochondria, an extensive network of surrounding well developed Golgi system & ribosomes.

34

• Formed by cementoblasts derived from the dental follicle

Cellular Intrinsic Fibre Cementum

• Formed by the cementoblasts derived from the HERS

Acellular Extrinsic Fibre

Cementum

Cementoblasts forming CIFC

Cementoblasts forming AEFC

Express receptors for parathormone (parathormone Receptor Protein) which have a regulatory role in cementogenesis

Osteopontin and osteocalcin are expressed

Synthesize osteonectin

Do not show these receptors

Expresses only osteopontin

Synthesize osteonectin

In the differentiation of cementoblasts growth factors belonging to the TGFβ family including BMP, transcription factor- core binding factor α1( cbfa1), signaling molecule epidermal growth factor ( EGF) are involved.

EGF downregulates signals transduction from ligands such as TGF- α and EGF to control cell differentiation.

Prostaglandin E2 enhance differentiation of cementoblasts by activating protein kinase signaling pathway.

CAP,BSP and osteopontin help in the attachment of selected cells to the newly forming tissue.

CEMENTOCYTES The apical 1/2 or 1/3rdof the root is covered with cellular

cementum.

The number of cementocytes in the matrix is variable.

Cementum that is formed rapidly generally possesses wider lamellae & more cementocytes.

In the apical 1/3rd,cementoblasts trapped in rapidly calcifying cemental matrix, later, differentiate into cementocytes.

These locate in spaces termed lacunae & have numerous cytoplasmic processes coursing in canaliculi, that are preferentially directed towards the periodontal ligament.

This is how cementocytes derive their nutrition from periodontal ligament & contribute to the vitality of this mineralized tissue.

While adjacent canaliculi of neighboring cells communicate frequently, the processes remain independent.

Thus, the metabolites progress mostly by diffusion through the canaliculi of cellular cementum.

CEMENTOCLASTS They are multinucleated giant cells, which are

indistinguishable from osteoclasts.

Responsible for root resorption that leads to primary teeth exfoliation & also in the permanent dentition in mesial surfaces in compliance with mesial migration & may occur due to occlusal trauma & orthodontic therapy.

Types of Cementum

Embryologically Primary & Secondary

According to location on teeth ( Kronfield

1928).

- Radicular cementum- found on root surfaces.

- Coronal Cementum to Cementum that forms on the enamel covering the crown.

On the basis of cellularity (Gottlieb

1942).

- Acellular / Primary Cementum.

- Cellular / Secondary Cementum.

Schroder(1986) classifiction based on cellularity & organisation of collagen fibres

- Acellular afibrillar cementum.

- Acelluar extrinsic fiber cementum.

- Acellular intrinsic fiber cementum.(1990)

- Cellular intrinsic fiber cementum.

- Cellular mixed stratified cementum

-Intermediate cementum

Based on the origin of the

collagen matrix

- Extrinsic.

- Intrinsic.

- Mixed.

ACELLULAR CEMENTUM

Refers to cementum lacking embedded cells. First formed cementum, covers approximately the

cervical ⅓ or ½ of the root & does not contain cells.

Formed before tooth reaches the occlusal plane.

Thickness ranges from 30 – 230µm.

- Schroeder, (1986).

Sharpey’s fibers make up most of the structure of acellular cementum, which has a principle role in supporting the tooth.

Most fibers are inserted at angles into the root surface.

They are completely calcified with mineral crystals oriented parallel to the fibrils, except in a 10 – 50 µm wide zone near the CEJ, where they are only partially calcified.

Also contains intrinsic collagen fibrils that are calcified and are irregularly arranged / parallel to the surface.

- Schroder, (1980).

CELLULAR CEMENTUM

Is formed after tooth reaches the occlusal plane.

Is more irregular & contain cells (cementocytes) in individual spaces (lacunae).

Less calcified than acellular cementum.

Sharpey’s fibers occupy a smaller portion of cellular cementum.

They are separated by other fibers that are arranged either parallel to the root surface or at random.

Thickness of cellular cementum is greater than acellular.

Both cellular & acellular cementum are arranged in lamellae separated by incremental lines, parallel to the long axis of the root.

These lines represent rest periods in cementum formation & are more mineralized than the adjacent cementum (Romanos 1992) & termed the ‘Incremental lines of Salter’.

Incremental lines ofSalter in cementum

DIFFERENCES BETWEEN ACELLULAR & CELLULAR CEMENTUM…..

Acellular Cementum

Cellular Cementum

Formation Forms before tooth reaches occlusal plane

After tooth reaches occlusal plane

Cells Does not contain any cells Contains cementocytes

Location Coronal portion of root Apical portion of root

Rate of formation

Slow Rapid

Incremental lines

More & close Sparse & wide

Acellular Cementum

Cellular Cementum

Precementum

Absent Present

Calcification More calcified Less calcified

Sharpey’s fibers

More Less

Regularity of fibers

Regular Irregular

Thickness 20 – 50µm near the cervical region &150 – 200µm near the apex.

Thickness of 1 – several mm.

ACELLULAR AFIBRILLAR CEMENTUM (AFC)

• Contains neither cells, nor extrinsic / intrinsic fibers, apart from a mineralized ground substance.

• It is a product of cementoblasts, found deposited on the enamel over small areas of the dental crown just coronal to the CEJ.

• Thickness is about 1 - 15 µm.

ACELLULAR EXTRINSIC FIBER CEMENTUM (AEFC):- Composed almost entirely of densely packed

bundle of Sharpey's fiber and no cells.

A product of fibroblasts and cementoblasts,

Found on the cervical ⅓ of roots, but may extend further apically..

Cementoblasts that produce AEFC differentiate in close proximity to the advancing root edge.

Thickness is between about 30 - 230 µm & continues to grow in thickness (1.5 - 3 µm / year) as long as the adjacent periodontal ligament remains undisturbed.

During root development, the first formed cementoblasts align along the newly formed, but not yet mineralized, mantle dentin surface & exhibit fibroblastic characteristics.

Deposit collagen fibrils within it so that dentin & cementum fibers intermingle.

Initially AEFC consists of mineralized layer with a short fringe of collagen fibers implanted perpendicular to the root surface.

Cementoblasts then migrate away from the surface but continue to deposit collagen so that a fine fiber bundle lengthens & thickens.

These cells also secrete non – collagenous matrix proteins that fill in the spaces between the collagen fibers.

Only after the first 15 – 20 µm have formed, the intrinsic fibrous fringe become connected to the PDL. fiber bundles.

The overall degree of mineralization of this cementum is about 45 – 60%.

AEFC has the potential to adapt to functionally dictated alterations such as mesial tooth drift.

CELLULAR MIXED STRATIFIED CEMENTUM (CMSC):

Contains both collagen fibers & calcified matrix.

It is the co – product of cementoblasts & fibroblasts and consists of both extrinsic & intrinsic fibers.

Appears primarily in the apical third of the roots & in furcation areas.

Consists of AEFC and CIFC that alternate & appear to be deposited in irregular sequence upon one another.

- Schroeder, (1993).

Deposit 0.1 – 0.5 µm / year.

CELLULAR INTRINSIC FIBER CEMENTUM (CIFC):

Contains cells but no extrinsic (Sharpey's) fibers.

A more rapidly formed & less mineralized variety of cementum.

(CIFC) is deposited on unmineralized dentin surface near the advancing root edge.

Formed by cementoblasts & fills resorption lacunae (resorptive cementum.)

Can easily repair a resorptive defect of the root due to its capacity to grow faster than any other form of cementum.

ACELLULAR INTRINSIC FIBER CEMENTUM (AIFC): An acellular variant of cellular intrinsic fiber

cementum that is also deposited during adaptive responses to external forces (i.e.,) slow deposition rate.

cells are not engulfed in their matrix - Bosshardt & Schreoder, (1990) .

Extrinsic Fiber• Derived

from the sharpey’s fibers

Intrinsic Fiber• Derived

from the cemento-blasts

Mixed Fiber• Both

extrinsic and intrinsic fibres present

BASED ON THE NATURE AND ORIGIN OF THE ORGANIC

MATRIX

Extrinsic fibers – Sharpey’s fibres continue into the cementum in the same direction as the principle fibers of the PDL

Intrinsic fibres run parallel to the root surface and at right angles to extrinsic fibres

THICKNESS OF CEMENTUM & ITS CLINICAL SIGNIFICANCE…..

Cementum deposition is a continuous process that proceeds at varying rates throughout life.

coronal half of the root varies from 16µm to 60µm

Apical third to furcations - 150µm – 200µm.

It is thicker on the distal surface than on the mesial, consequent to functional stimulation from mesial drift over time (Polson.A et al 1990).

Is more rapid in the apical region where it compensates for attrition (passive eruption).

Between the ages of 11 & 70, the average thickness ↑ 3 fold, with the greatest ↑ in the apical area.

Functions:

Anchorage

Adaptation

Repair

Anchorage:

Primary function is to give attachment to collagen fibers of the periodontal ligament.

It is a highly responsive mineralized tissue maintaining the integrity of the root, helping to maintain the tooth in its functional position in the mouth.

Adaptation: Cementum may be viewed as a tissue that makes the

functional adaptation of teeth possible.

Deposition of cementum in the apical area can

compensate for loss of tooth substance from the occlusal

wear.

As the most superficial layer of cementum ages, a new

layer of cementum will be deposited to keep the

attachment apparatus intact.

Repair: Serves as a major reparative tissue for root surfaces.

Damage to roots like fractures and resorptions can be

repaired by new cementum.

Protects the root dentin.

TYPES OF JUNCTION

CEMENTOENAMEL JUNCTION (Noyes etal 1938)

Cementum overlaps enamel

CEMENTODENTINAL JUNCTION

The terminal apical area of the cementum where it joins the internal root canal dentin

There is no change in the width of CDJ with age

CDJ is 2-3µm wide

It is often reported that an intermediate layer exists between cementum and dentine and this layer is involved in anchoring periodontal fibres to dentine – Intermediate cementum/Innermost cementum layer/Superficial layer of root dentin.

After periodontal surgery, the cementum regenerate, but shows a space between regenerated cementum and dentine indicating the absence of a true union.

CEMENTUM RESORPTION AND REPAIR

Permanent teeth do not undergo physiologic resorption as do primary teeth.

Cementum is less susceptible to resorption than bone.

70% of all resorption areas were confined to the cementum without

involving the dentin.

Resorption is carried out by multinucleated odontoclasts.

More fluoride content in cementum than bone and the surface of the cementum is covered by a layer of tightly packed collagen fibres, therefore the mineralized surface is inaccessible – makes it less susceptible for resorption.

Appears microscopically as bay like concavities in the root surface

Multinucleated giant cells and large mononuclear macrophages are found adjacent to cementum undergoing resorption.

Resorptive process may extend into the underlying dentin and even into the pulp, but it is usually painless.

Resorption is not continuous and may alternate with periods of repair and deposition of new cementum.

The newly formed cementum is demarcated from the root by a deeply staining irregular line – Reversal line.

Reversal lines contain a few collagen fibers

Contains highly accumulated proteoglycans with glycosaminoglycans.

Embedded fibres of the PDL reestablish a functional relationship in the new cementum.

LOCAL FACTORS CAUSING CEMENTUM RESORPTION:

Trauma from occlusion Orthodontic movement Pressure from malaligned erupting teeth Cysts and tumors Teeth without functional antagonists Embedded teeth Replanted and Transplanted teeth Periapical disease Periodontal disease

Systemic factors causing Cementum

Resorption:

Calcium deficiency

Hypothyroidism

Hereditary fibrous osteodystrophy

Paget’s disease

CEMENTUM – CLINICAL SIGNIFICANCE

HYPERCEMENTOSIS / CEMENTUM HYPERPLASIA:

Prominent thickening of the cementum. Localized to one tooth or affect the

entire dentition. An age related phenomenon.

Excessive proliferation of cementum may occur

in neoplastic and non-neoplastic conditions like

benign cementoblastoma, cementifying

fibroma, periapical cemental dysplasia,

florid cemento-osseous dysplasia and

other fibro - osseous lesions

o Occurs as a generalized thickening of the cementum, with nodular enlargement of the apical third of the root.

o It also appears in the form of spike like excrescences (cemental spikes) created by either the coalescence of cementicles that adhere to the root or the calcification of periodontal fibers at the sites of insertion into the cementum. ( Lester, 1969)

If the over growth improves the functional qualities of the cementum; it is termed as ‘cemental hypertrophy’.

If the overgrowth occurs in non - functional teeth / if it is not correlated with increased function, it is termed ‘Hyperplasia’.

Sometimes, embedded calcified round bodies are found in localized areas of hyperplastic cementum.& are designated excementosis, & develop around degenerated epithelial rests.

The spike like type of hypercementosis generally results from excessive tension from orthodontic appliances or occlusal forces.

Hypercementosis of the entire dentition may occur in patients with Paget's disease.

Systemic disturbances that may lead to hypercementosis may include:

1. Acromegaly

2. Arthritis

3. Calcinosis

4. Rheumatic fever

5. Thyroid goiter

Does not require treatment.This may complicate if an affected tooth

requires extraction.

CEMENTAL APLASIA Hypophosphatasia A rare condition in which there is a reduction in

the activity of tissue non-specific alkaline phosphatase

Characterized by reduction in the formation of cementum, affects both cellular and acellular cementum

The attachment of PDL is affected, results in the premature loss of teeth

Fusion of the cementum and alveolar bone with obliteration of the periodontal ligament.

Ankylosis occurs in teeth with cemental resorption, which suggests that it may represent a form of abnormal repair.

ANKYLOSIS

Ankylosis also may develop after chronic periapical inflammation, tooth replantation and occlusal trauma and around embedded teeth.

Ankylosis results in resorption of the root and its gradual replacement by bone tissue. For this reason, reimplanted teeth that ankylose will lose their roots after 4 to 5 years and exfoliate.

As the PDL is replaced with bone, the proprioception is lost

Because the receptors are deleted or do not function correctly

Physiologic drifting and eruption of teeth can no longer occur.

So the ability of the periodontium to adapt to the altered force levels is greatly reduced

Radiographically resorption lacunae are filled with bone and PDL space is missing

CEMENTICLES

Calcified bodies in the PDL. that are adherent to or detached from the root surface.

Its diameter rarely exceeds 0.2 mm.

Develop from calcified epithelial rests, around small spicules of cementum / alveolar bone traumatically displaced into PDL.,

From calcified Sharpey’s fibers and thrombosed vessels within the PDL.

CEMENTAL TEARS: Detachment of fragments of

cementum from the root surface is known as ‘Cemental tear’, which may be complete or incomplete.

Detached cementum may be reunited by new cementum formation or may be completely resorbed / undergo partial resorption followed by the addition of new cementum & embedding of collagen fibers.

CEMENTOMA

These are masses of cementum generally situated apical to teeth to which they may or may not be attached.

They are considered either odontogenic neoplasms / developmental malformations.

Occurs more frequently in females than males.

Seen more commonly in mandible as compared to maxilla.

Radiographically, the lesion appears as a discrete, dense, radio-opaque mass in which isolated radiolucent markings may be seen.

CONCLUSION Cementum is the mineralized dental tissue

covering the anatomic roots of human teeth, which forms the integral part of the periodontium that supports the tooth in the socket.

The normal periodontium is a unique and complex structure that has distinct functions and capable of adaptation, repair and regeneration.

REFERENCES

Carranza’s Clinical Periodontology, 10th edition, Newman, Takai,Klokkevold,Carranza. Pgs 75-79

Oral Anatomy, Histology and Embryology, 4th edition,. B.K.B. Berkovitz, G.R. Holland, B.J Moxham, pgs 169 -178

Orban’s Oral Histology and embryology, 12th edition, pgs 137-154

Ten Cate’s Oral Histology, Development, structure and function, 7th edition, Antonio Nanci, pgs 239-253.

Dental cementum: the dynamic tissue covering of the root. Periodontology 2000. Vol. 13, 1997, 41-75