Cementum/Dental implant courses by Indian dental academy

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Introduction Cementum / simply cement is derived (from Latin CAEMETUM,

quarried stone) is a component of the tooth as well as the periodontium.

Definition: It is a mineralized dental tissue covering the anatomic roots of human teeth (ORBANS).

Definition (Glickman) : It is the calcified mesenchymal tissue that forms the outer covering of the anatomic roots.

It was first demonstrated microscopically in 1835 by Frankel and Raschkow, 2 pupils of Purkinic.

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It begins at the cervical portion of the teeth at the CEJ and continues to the apex.

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Cementum furnishes a medium for the attachment of collagen fibres that binds the tooth to the surrounding structures.

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It is a specialized connective tissue that shares some physical, chemical and structural characteristics with compact bone.

[Unlike bone however human cementum is AVASCULAR).

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DEVELOPMENT OF CEMENTUM / CEMENTOGENESIS Cementum is mesodermal in origin with dentin, alveolar bone, periodontal ligament.

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Cementum develops from dental follicle which surrounds the teeth germ.

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Development of cementum starts after crown formation is completed and before start of eruption.

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The outer and inner enamel epithelium after crown formation form a double layered sheath which proliferates from the cervical loop to form Hertwig’s epithelial roots sheath, which separates the D papilla from D. follicle.

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Cells of peripheral dental papilla differentiate along HERS into odontoblasts.

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These odontoblasts form a single layer of dentin, once the dentin formation begins breaks occur in the ERS allowing the newly formed dentin to come in direct contact with connective tissue of the dental follicle.

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Cells derived from this connective tissue are responsible for cementum formation.

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[Breakdown of HERS involves degeneration / loss of its basal lamina on the cemental side which is soon followed by the appearance of collagen fibres and cementoblasts] between the epithelial cells of the root sheath.

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Some sheath cells migrate away from the dentin towards the dental sac, which become the epithelial rests of malassez found in the periodontal ligament whereas others remain near the developing tooth and are incorporated into the cementum.

Precementum/Cementoid – is the unmineralized tissue begins at the CDJ. -

The cementoid layer ranges from 3 to 5µm in the A3rd (AC).

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It provides a compatible environment for CB and serves a protective function – resists cementoclasia.

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Composition – is predominantly collagen.

PHYSICAL PROPERTIES Cementum is LIGHT YELLOW in color and can be distinguished from enamel by: a) Its lack of luster and b) Its darker hue.

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Cementum is somewhat lighter in color than dentin. But clinically, it is not possible to distinguish cementum from dentin based on color alone.

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The density of completed mineralized cementum is found to be less than that of dentin.

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Cementum is very permeable (C and A.C.C.) and permit the diffusion of dyes from the pulp and from the external root surface.

[With

age,

the

permeability

of

cementum

diminishes].

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The thickness of cementum on half of the root varies from 16 to 60µm and it is the thickness of hair.

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It attains greater thickness up to 150 to 200µm in the apical 3 rd and in the bifurcation and trifurcation area.

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It is thicker in distal surface than mesial surface probably because of functional stimulation from mesial drift.

The average thickness of

– 95µm at age 20.

– 215 µm at age 60.

(I) INORGANIC SUBSTANCE -

Consists mainly of Ca and phosphate ions in the form of hydroxyapatite.

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Cementum has the highest fluoride content of all the mineralized tissue.

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Trace elements – Cu, Lead, Iron, Na, Mg, K, Zn.

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(II)

ORGANIC PORTION -

Primarily consists of Type I collagen fibres and protein polysaccharides (proteoglycans).

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Collagen of cementum indicated close similarities to the collagen of dentin and alveolar bone.

CHEMICAL COMPOSITION Cementum from fully formed permanent teeth contains about 45% to 50% - INORGANIC SUBSTANCES. 50% TO 55% - ORGANIC MATERIAL AND H20 1)

The ratio of O : InO and H 2O in cementum is difficult to determine because of 1. Age difference.

2. Difference in the prop of CC and A.C.C. 3. Contaminate of C samples by alien tissues.

2)

C is less radiopaque than E and D.

MINERALIZATION It is a highly odered and rhythmic process, that begins in the depth of the pre-cementum.

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Fine crystals are formed on, in and between the collagenase elements. Needle and plate shaped crystal formation, occurs.

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These (needle) crystals are arranged parallel to the fibrils and are smaller than those of E but similar to that of D and bone.

E. Pearls formation – is as a result from an atypical condition in which the R.S. adhere to the dentin and the IEF of the R.S. Seen in bifurcation and trifurcation areas when present more CERVICALLY – perio-procedures should be carried out.

ACCESSORY CANALS – At times premature discontinuities may take place in the R.S., here the OB are not formed because of the absence of IEF; so the connective tissue of the [DF migrates into the break and continues with RADICULAR PULP].

Undisturbed areas – Normal development and thus a channel is formed A.C. HISTOLOGY OF CEMENTUM Histologic sections of cementum show: a.

Cells, fibres, ground substances, resting lines.

b.

Cemento-enamel junction.

c.

Cemento-dentinal junction.

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CELLS: The cells associated with cementum are: 1. Cementoblasts.

2. Cementocytes.

3. Cementoclasts.

1. CEMENTOBLASTS – As soon as there is breakdown of HERS, the UMC from adjacent CT differentiate into cementoblasts.

These cells have i. Numerous mitochondria ii. Well-formed Golgi-apparatus. iii. Large amounts of granular endoplasmic reticulum.

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So. They actively synthesize COLLAGEN and PROTEIN POLYSACCHARIDES which make up the organic matrix of cementum.

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After, some cementum matrix is laid down, its mineralization begins.

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These cells are found lining the root surface.

2. CEMENTOCLASTS – found in HOWSHIPS LACUNAE. -

These are unilocular / multilocular cells.

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Function : 1. Resorption of cementocytes trapped in lacunae within their own matrix.

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3. CEMENTOCYTES CELLULAR

– CEMENTOBLASTS

1. These are active spider like

1. Are

cells.

arranged

in

single

primary layers adjacent to precementum using the RS.

2. Size – 8 to 15µm

2. Cuboidal in shape; when they are active they are plump.

3. They are round / oval with

3. Exhibit same processes which

numerous radiating

are long and few – they

processes. Body in lacunae

represent the secretory ends.

and processes – in canaliculi.

4. Acts as circulatory passages and

communicate

4. The projections penetrate into

with

the PC.

process of neighbouring cells.

5. SPARSE CYTOPLASM

5. Active CB – PULMP & –

BASOPHILIC CYTOPLASM

–

OPEN FACED NUCLI

–

ROUGH ER

Resting CB – CLOSED NUCLEUS –

LESS CYTOPLASM

The Fibrous Matrix -

The collagen fibres of cementum are of 2 types: i. Intrinsic fibres. ii. Extrinsic fibres.

Intrinsic fibres – Are those formed as a result of cementoblasts activity.

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Extrinsic fibres – Are periodontal ligament fibre bundles which are embedded into cementum. They are called Sharpey’s fibres (these fibres are usually seen in recently formed cementum) contain numerous collagen fibres.

INTRINSIC FIBRES

EXTRINSIC FIBRES

1. Fibres are thin.

1. Fibres are longer and thicker.

2. Diameter 1µm.

2. Diameter – 5 to 8µm.

3. Completely mineralized.

3. Completely mineralized.

4. Run parallel to the R.S.

/

partially

4. ⊥rt angle to the extension surface of tooth.

The Ground Substance -

The chemical mature of the PPS/GS of cementum is virtually unknown.

Resting Lines -

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

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These lines represent rest periods in cementum formation and are highly mineralized and have less collagen and more ground substance.

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These lines indicate Rhythmic and Regular deposition of matrix.

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These are also known as INCREMENTAL LINES OF SALTER.

CEMENTO ENAMEL JUNCTION 3 types of r/n involving the cementum may exist at the cementoenamel junction.

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r/n which cementum may bear to enamel at the neck of the tooth.

1. 60% to 65% of cases – Cementum overlaps the enamel -

Overlap Type.

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Due

to

preparative

degeneration

of

REE,

cementocyte in contact with enamel lay cementum.

2. 30% of cases – Edge to edge -

Butt Type

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Cementum and enamel meet at a sharp point.

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3. 5% to 10% - Cementum and enamel fail to meet.

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GAP Type

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This is due to delayed degeneration of HERS.

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So here dentin may be covered by REE instead of cementum.

Primary Teeth

Deciduous

Intermediate C layer

CEMENTO DENTINAL JUNCTION -

The dentin surface upon which cementum is deposited is relatively smooth in permanent teeth in one of deciduous teeth it is scalloped.

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Sometimes dentin is separated from cementum by a zone known as the Intermediate cementum layer or Hopewell Smith layer. This is predominantly seen in the apical 2/3 rd of the roots of M’s and Pm’s and rarely in I’s and deciduous teeth.

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It is believed that this layer represents area where cells of HERS become trapped in a rapidly deposited dentin / cementum matrix. It is continuous / isolated.

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Size – 10µm thickness, thin layer of cal tissue, amorphous non cellular.

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CLASSIFICATION OF CEMENTUM [I] a. Acellular cementum b. Cellular cementum a)

It is the Ist

Acellular cementum –

formed cementum and covers approximately the c 2/3 / ½ of the root.

/ Primary cementum -

It does not contain cells.

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This cementum is formed before the tooth reaches the occlusal plane.

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Thickness ranges from 30 to 230µm.

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Sharpeys fibres make up most of the structure of ACC.

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ACC also contains other collagen fibrils they

are

calcified

and

irregularly

arranged / parallel to the surface. b) Cellular cementum –

It is formed after the tooth reaches the occlusal plane. Apical 2/3rd.

/ Secondary cementum -

It is more irregular and contains cells (cementocytes).

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Cellular cementum is less calcified than the acellular cementum.

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SF occupy a smaller portion of CC.

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Less mineralized and more permeable.

Cellular C 1. Osteocytes in lacunae with processes in canaliculi found.

Acellular C 1. No cells in cementum.

2. Rate of development is Faster.

2. Slow.

3. Incremental lines are Wide Apart.

3. Closer.

4. Precementum layer – Wide.

4. Narrower.

/

cementoid

[II] SCHOREDER CLASSIFICATION 1) Acellular afibrillar cementum.

2) Acellular extrinsic fibre cementum.

3) Cellular mixed stratified cementum.

4) Cellular intrinsic fibre cementum.

1)

AAC – It is a product of cementoblasts.

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Found in coronal cementum.

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Contains neither cells/ extrinsic / intrinsic CF apart from mineralized ground substances.

2)

AEFC – Contains densely packed bundles of SF and lacks cell.

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It is a product of FB and CB.

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Found in C3rd of roots.

3)

CMSC – It is a product of FB and CB. -

Found in A 3rd of roots and apices and furcation areas.

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Contains extrinsic, intrinsic fibres and cells.

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4)

CIFC – It is a product of CB. -

It fills the resorption lacunae.

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Contains cells but no collagen fibres.

[III] Based on fibres – cementum is classified into: 1. Intrinsic fiber cementum.

2. Extrinsic fiber cementum.

3. Mixed fiber.

FUNCTIONS OF CEMENTUM The principal function of cementum is assisting anchorage of the tooth.

1. The primary function is to furnish a medium for attachment of collagen fibers that bind the tooth to alveolar bone.

2. Cementum serves as the major reparative tissue for root surfaces.

Damage to roots such as #’s and resorption can be repaired by deposition of new cementum.

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Continuous deposition of C is of functional importance therefore SA for the attachment of fibres increases.

3. Less of occlusal surface substances is compensated by continuous deposition of cement at apical portion.

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4. Keeps the attachment apparatus intact because of increased mesial drift a new layer gets deposited and helps in relocation and readaptation.

CLINICAL CONSIDERATIONS 1. Cementum is more resistant to resorption than is bone and it is for this reason ortho tooth movement is made possible.

2. Transverse # of the root may occur because of trauma and this may heal by deposition of new cementum.

3. Cementum resorption can occur after trauma / excessive occlusal wear.

4. Because of continuous cementum deposition around the apex, the total length of tooth is maintained in spite of the loss of E from occlusal wear. This deposition of cementum leads to a constriction of apical foramen and alteration in number, size and shape of apical foramena. The over all affect is that in older teeth the complexity of apical foramina is increased. This should be kept in mind during endodontic treatment.

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C. RESORPTION AND REPAIR : The cementum of erupted as well as unerupted teeth is subjected to resorption. Very common and may occur without any apparent etiology.

1. Idiopathic : TFO; or movement maligned teeth; cysts, tumors no adjacent, pa disease.

2. Systemic : Ca deficiency; hypothyroidism, p disease hereditary fibrous osteodystroy.

3. R may extend into D as well as P, but is usually painless.

4. C resp is not continuous and may alternate with periods of repair.

5. C repair can occur in devitalized as well as in vital teeth.

Anatomic repair and functional repair Root surface changes: 1. Structural changes (pathological granules) – in heavily infected RC they are at DCJ. 2. Areas of demineralization – RS caries progress round rather into the tooth (proteolysis of S.F. brings about fragmental / cavitation).

Active Lesion : yellowish / light brown soft and leathery consistency.

Inactive : Darker with smooth surface (on probing) harder in consistency.

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HYPERCEMENTOSIS [Cementum hypoplasia] care while extraction -

Refers to as prominent, thickening of cementum.

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It may be 1) Localized Circumscribed – surrounding root like a collar.

2) Diffused

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It might affect: i. All teeth of the dentition. ii. Single tooth. iii. Part of a tooth surface.

Causes: 1. In the teeth with Pa inflammation caz of pulpal involvement – extensive hyperplasia.

2. Accelerated growth of the teeth structure – in the absence of an antagonist.

3. Mechanical stimulation / orthodontic forces / heavy occlusal forces lead to excessive tension which results in spike like hypercementosis (SPUR/ PRONG – LIKE EXTENSION).

4. Entire dentition – hypercementosis in patients with Pagets diseases (Loss of lamina dura).

5. Cemental repair.

6. Ankylosis : is fusion of C and AB with obliteration of PDL occurs due to:

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1. Cemental resorption.

2. After chronic Pa inflammation.

3. It results in resorption of the root and its gradual replacement by bony tissue.

4. When titanium implants are place in the jaw healing results in bone tenned in direct apposition to the implant with any intervening CT. -

Ex cementosis (knob – like extensions of hypercementosis).

CEMENTOMA : Are masses of cementum; situated apically  may / may not be attached. They are considered to be either odontogenic neoplasms / developmental malformations. Seen in mandible > maxilla.

CEMENTICLES : Are globular masses of cementum arranged in connective lamellae. They lie free on PDL attached to the cementum; developed from calcified epithelial cells and SF’s.

Conclusion Cementum is the part of tooth supporting apparatus and any alteration in the normal form and function of this structure may result in disruption of normal psychological function of the tooth.

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CONTENTS 1. Introduction 2. Development 3. Physical properties 4. Chemical composition 5. Histology of cementum 6. Classification of cementum 7. Functions 8. Clinical considerations 9. Conclusion

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