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I. INTRODUCTION Gingiva KeratinizationII. GINGIVAL KERATINIZATION Process Control of keratinocyte differentiation Cytokeratins of oral mucosa Immuno chemical & electronmicroscopic pictureIII. KERATINIZED Vs NON KERATINIZED EPITHELIAIV. CLINICAL SIGNIFICANCE OF KERATINIZATION OF GINGIVA IN

HEALTH & DISEASE V. KERATINIZATION OF GINGIVA IN DISEASE Diseases & conditions with altered keratinization Clinical co relations of altered keratinization with diseaseVI. CLINICAL IMPLICATIONSVII. CONCLUSIONVIII. REFERENCES

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CONTENTS:

IntroducIntroduction tion

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GINGIVA

“Gingiva is the part of the oral mucosa that covers the alveolar processes of the jaws and surrounds the neck of the teeth. (Carranza 1o th ed)

““The fibrous investing tissue, covered by keratinized epithelium, which immediately surrounds a tooth and is contiguous with its periodontal ligament and with the mucosal tissues of the mouth.”.” A A P A A P 19921992

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Anatomically Free or Marginal

Gingiva. Attached Gingiva. Interdental Gingiva.

(Carranza 10th ed)

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Keratinization can be defined as expression & synthesis of keratin proteins in the basal layer of cell,their chemical composition in the upper layer & their interaction with keratohyalin granules & formation of filamentous matrix structure in the interior of corneocyte & strenghtening of the envelope.

(The process of keratinization of gingival epithelium. ;The Journal of western society of periodontology; 1979)

KERATINIZATION

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Also called as “CORNIFICATION” Differantiation process rather than degeneration Process of protein synthesis→Requires

energy→dependent on functional cells containing nucleus & organelles

Cell migrate from basal to superficial→biochemical & morphological events takeplace

Cytoplasmic proteins tranform into keratin filaments

Cytoplasm & nucleus both decompose.

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PARAKERATINI Z ATION: the stratum corneum retains pkynotic nuclei and the keratohyaline granules are dispersed, not giving rise to

stratum granulosum.NON-KERATINIZED EPITHELIUM neither granulosum nor corneum strata and superficial cells have viable nuclei.ORTHOKERATINIZATION: similar to that of skin with no nuclei in the stratum corneum

and a well-defined stratum granulosum.

  

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 Only some areas of the outer gingival epithelium are

orthokeratinized the other gingival areas are covered by parakeratinized or nonkeratinized epithelium.

In the gingival epithelium ,15% area is orthokeratinised other areas are covered by parakeratinised ;75%or nonkeratinised epithelium 10%

Diurnal cycle of keratinization activity is seen between 12pm to 4am

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The outer surface of the free & attached gingiva is covered by a keratinizing stratified squamous epithelium.

The principal cell type of the gingival epithelium, as well as of other stratified squamous is keratinocyte.

Keratinizing oral epithelium has four cell layers: Basal, Stratum basale, Spinous, Stratum spinosum Granular Stratum granulosum and Cornified,Stratum corneum

GINGIVA L KERATINI Z ATION

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  The basal layer is made up of cells that

synthesize DNA and undergo mitosis, thus providing new cells. Most of the new cells are generated in the basal layer.

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Cytoplasm of the basal cells contain widely dispersed tonofilaments, also referred to as Cytokeratins which are precurser of keratin’and in some way are attached to the attachment plaques.

ribosomes & rough endoplasmic reticulum are found-, indicative of protein synthesizing activity.

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( Orbans 10th ed)14

The intercellular spaces - are large & distended;

thus desmosomes are made more prominent &

these cells are given a prickly appearance.

The spinous (prickle) cells resemble a cockleburr or

sticker that has each spine ending at a desomosome.

Spinous cells are the most active in protein synthesis.

Contains numerous dense granules – keratinosome or

Odland bodies ( Orbans 10th ed)

2 Stratum spinosum

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ODLAND BODIES:

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Cells are larger and flatter.

Cells show increase in maturation.

nuclei shows signs of degeneration

and pyknosis.

C ytoplasm is predominantly occupied by

the tonofilaments & tonofibrils.

C ells contain large no’s of small granules –

keratohyalin granules- these

granules help to form the matrix for the

numerous keratin fibers found in the

superficial layers ( Orbans 10th ed)17

Thus,corneocytes are mainly formed by bundles of keratin tonofilaments embedded in an amorphous matrix of filaggrin and surrounded by a resistant envelope under the cell membrane.

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BIOCHEMICAL PROPERTIES:

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Cells are very flat ,devoid of nuclei, full of

keratin filaments surrounded by a matrix

may be termed epithelial squamae & are

dehydrated.

does not synthesize protein.

These cells are shed (the process of

desquamation), necessitating constant

turnover of epithelial cells.

Str corn. provides the mechanical protective

function to the mucosa.

Varies in thickness (upto 20 cells).

Keratinocytes increase in volume in each

successive layer. ( Lindhe 5th ed)20

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FACTOR PROLIIFERATION DIFFERENTIATION

EGF ↑

KGF ↑↑

RETINOIDS ↑ ↓

CALCIUM ↑

TGF-α ↑

TGF-β ↓ ↑

α/β INTEGRINS+ LIGAND

↓

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EPIDERMAL GROWTH FACTOR & TRANSFORMING GROWTH FACTOR

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KERATINOCYTE GROWTH FACTOR

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RETINOIC ACID

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CALCIUM

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Non keratinized Keratinized

1.basal◦ Cuoidal ,columnar cells◦ Separate tonofilaments◦ Organelles◦ Site of cell division

2.prickle◦ Large ovoid cells◦ Dispersed tonofilaments◦ Organelles◦ Membrane coated granules-

upper layers◦ filaments ↑

3.intermediate.◦ Sligtly flattened cells◦ Dispersed tonofilaments &

glycogen 4.Superficial

◦ Same as intermediate layer◦ Nuclei are persistant

1.basal◦ Cuoidal ,columnar cells◦ Bundles of tonofilaments◦ Organelles◦ Site of cell division

2.prickle◦ Large ovoid cells◦ Conspicous tonofilament

bundles◦ Organelles◦ Membrane coated granules-

upper layers◦ filaments ↑

3.granular◦ flattened cells-contain

keratohyalin granules◦ Thickening of cell memb-granule

fuse with cell membrane 4. corneum

◦ F lattened &◦ Dehydrated cells◦ All organelles are lost◦ P acked with fibrillar material◦ Nuceus if present-pyknotic

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Immunohistochemistry, gel electrophoresis, and immunoblot techniques suggest that, keratin proteins are composed of different polypeptide subunits characterized by their isoelectric points and molecular weights.

Numbered →their molecular weights.

IMMUNOHISTOCHEMISTRY

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Cytokeratin proteins( CK ) They are composed of different polypeptide subunits

&numbered in a sequence contrary to their molecular weights.

eg. K19- mol wt. 40 kDa – present at basal cells

2 gene family Type I Acidic No. 9-20

high tissue specificity they are always in pairs - type I is smaller than type II by about

8kDa

TYPE IIBasic No.1-8

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Keratin K1, K2and K10 to K12 -Specific for epidermal type differentiation.

-Expressed with high intensity in orthokeratinized areas & less intensity in parakeratinized areas. K6 and K16

-Characteristic of highly proliferative epithelia. K5 and K14

-Stratification specific cytokeratines -Both are present in outer epithelia. K19 -Absent in orthokeratinized areas.

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ELECTRON MICROSCOP

Y

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Keratinocytes are interconnected by structures on the cell periphery called desmosomes.

They consist of two dense attachment plates into which tonofibrils insert and an intermediate,electron-dense line in the extracellular compartment

Tonofilaments →morphologic expression of the cytoskeleton of keratin proteins→ radiate in brush like fashion from the attachment plaques in the cytoplasm of the cells

cytoplasmic projections resembling microvillie extend into the intercellular space and often interdigitate

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The main function of the gingival epithelium is to protect the deep structures while allowing a selective interchange with the oral environment. This is achieved by proliferation and differentiation of keratinocyte

The gingiva is exposed to heavy mechanical stresses during mastication.moreover the epithelial attachment of tooth is relatively weak & susceptible to injury ;can cause permanent damage.

Thus keratinization of gingiva may afford relative protection.

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The Involucrin becomes cross linked (by the enzyme transglutaminase) to form a thin (l0nm), highly resistant, electron dense, cornified envelop just beneath the plasma membrane.

The keratin is also strongly cross-linked by disulphide bonds, contributing to the mechanical and chemical resistance of the layer.

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The keratinized gingiva on the facial aspect of teeth extend from gingival margin to MGJ. It is often claimed that presence of zone of atleast 2mm of keratinized gingiva is necessary for the maintainance of gingival health.(Gottsegon 1954,Naber 1954,Glickman 1992,Corn 1973,Schuluger 1977).

Lang & Loe(1992) support this whereas others authors (Miyasatto 1977,Grey & Besmimoulin 1980, Doffman et al 1980) suggests that there is no requirement for minimal width-provided accumalation of plaque is inhibited.

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Width of the attached gingiva

Maxilla Mandible

Incisors premolars Incisors

3.5 to 4.5mm 1.9 mm 3.3 to 3.9mm 1.8 mm

premolar

ATTACHED GINGIVA

Resistance to products of inflammation. Gives support to the marginal gingiva Helps to withstand functional stress Resistance to tensional stresses. Provides solid base for movable alveolar

mucosa To dissipate the pull on the gingival margin

created by the muscles of the adjacent alveolar mucosa. ( Sullivan et al 1968)

Helps to prevent soft tissue recession and attachment loss

Helps in connective tissue attachment

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Keratinization serves as an epithelial barrier so with decreased keratinization infection susceptibility is increased.(Scheman;1989)

There is increased susceptibility to masticatory force damage due to decreased resistance to functional & tensional stresses.

SEQULAE:

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Rapid turnover of cells of keratinized epithelium

Keratinized layer is dehydrated to form hexagonal disks or squames

Squames are cont. lost by desquamation & replaced by cells of underlying layers

Rapid clearance-limits colonization & invasion of epithelial surface by pathogenic micro organisms Including common oral fungus candida albicans

Thus with↓keratinization↑chances of infection are there

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The immunohistochemical patterns of the different keratin types, envelope proteins, and filaggrin, change under normal or pathologic stimuli, modifying the keratinization process THIS COULD BE OF DIAGNOSTIC VALUE.

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Oral dysplasia is a premalignant lesion but some cases respond to treatment or revert spontaneously and therefore it is desirable

to define molecular changes that would allow pathologists to identify the highest risk lesions.

Moreover K8,k18 &K19 – found in highly proliferative epithelia is seen in oral leukoplakia & SCC.(Su et al, 1996)- they can be used for diagnosis

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The desmosomes attachment plaques contain the polypeptides desmoplakin I and II.

Monoclonal antibodies to these polypeptides can be used to detect an epithelial tumor by immunofluoroscent microscopy.

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Accelarated turnover of cells is seen. K6, K16 and K17 were detected

suprabasally in psoriatic epidermis As keratins K6, K16 and K17 are expressed

in keratinocyte hyperproliferation, Thus it signifies the same.

PSORIASIS

Leigh et al; 1995

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Hyperkeratotic lesions - lichen planus and fibromas showed aberrations in their Ck profile.

extended expression of keratinization marker Ck 10, Ck 14 and Ck 16 in the suprabasal compartment.

The stratification markers Cks 4 and 13 showed a decreased expression.

Help to to characterize benign mucosal lesions with dysplasia and might be helpful for distinguishing these lesions from potentially malignant ones.

BENIGN LESIONS OF THE ORAL MUCOSA

Volden et al 199951

parakeratotic epithelium markers (K4 and K13) were detected but showed reduced expression in orthokeratoses( K1 and K10), particularly in the presence of lymphocytes.

study showed an alteration in the pattern of differentiation-specific keratins, although involvement of the lymphocytic infiltrate (Interferon γ )in OLP resulted in further gene modulation.

Thus, the pattern of keratin gene expression may be altered in response to frictional/smoking stimuli or immune-mediated mechanisms

ORAL NON-DYSPLASTIC KERATOSES AND LICHEN PLANUS

Bloor et al 200052

Terminal differentiation markers, typical of cornified epithelia (CK 1, 9, 10 and 11), were detected supra basally in the snuff user's keratosis but not in the normal control epithelium.

The results show that use of oral snuff causes some alterations in the CK expression pattern of the affected epithelium. Whether the alterations are indicative of a premalignant change is, however, uncertain.

Effect of snuff and smoking on cytokeratin expression in oral

mucosa

Luomanen et al ;1997

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The mitotic index in patients with diabetes was slightly lower, keratinization in the gingival tissues for both groups was essentially identical.

COMPARISON OF KERATINOCYTE PROLIFERATION IN DIABETIC AND NON-

DIABETIC INFLAMED GINGIVA

Gükhan Açikgoz ;2004

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The pattern of keratin expression of the epithelium of pocket lining was found to be essentially similar to normal JE.

PATTERN OF CYTOKERATIN EXPRESSION IN THE EPITHELIUM OF INFLAMMED HUMAN GINGIVA &

PERIODONTAL POCKET

Mackenzie ;1993

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dyshesive, dyskeratotic epithelial syndrome caused by an abnormality in desmosomes and gap junctions, involves the mucosae, skin, hair, eyes, and lungs.

gingival sections showed a dyshesive epithelium with atrophy, dyskeratosis, lack of keratinization, and unusual cytoplasmic inclusions.

patients with hereditary mucoepithelial dysplasia have numerous skin problems and are susceptible to recurrent infection .

HEREDITARY MUCOEPITHELIAL DYSPLASIA

Scheman;198956

Conclusion

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Keratinization of gingiva is indespensable

to maintain its state of health.Expression of cytokeratins is tissue specific

and even strata specific & any alteration in this suspects breach from its state of normalcy.

It is desirable to define these molecular changes that would allow pathologists to

identify the highest risk lesions & thus it holds promising future in diagnosis….

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1. Clinical peridontology 8, 9,10th edition – Carranza F.A., Michael G. Newman.

2. Oral Histology, Development, structure and function – A.R. Tencate, 5th

edition

3. Periodontics ;Elly and masson.

4. Orbans Oral Histology and Embryology – S.N. Bhaskar, 10th edition.

5. Clinical Periodontology and Implant Dentistry – Jan Lindhe, 4th edition. 6. Relation between width of attached gingiva & health. JP 19727. Oral cells & tissues .Garant8. Comparison of Keratinocyte Proliferation in Diabetic and Non-Diabetic

Inflamed Gingiva ;JP July 2004, Vol. 75, No. 7, Pages 989-9949. Hereditary mucoepithelial dysplasia. Case report and review of the literature

J Am Acad Dermatol. 1989 Aug;21(2 Pt 2):351-710. Patterns of cytokeratin expression in the epithelia of inflamed human

gingiva and periodontal pockets J Periodontal Res. 1993 Jan;28(1):49-59

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REFERENCES:

11. Differentiation-dependent expression of keratins in human oral epithelia J Invest Dermatol. 1986 Mar;86(3):249-54

12.Effect of snuff on cytokeratin expression in oral vestibular sulcus epithelium J Oral Pathol Med. 1997 Mar;26(3):110-6

13.Expression of intermediate filament proteins in benign lesions of the oral mucosa Eur Arch Otorhinolaryngol. 1999;256(10):514-9

14.Keratins (K16 and K17) as markers of keratinocyte hyperproliferation in psoriasis in vivo and in vitro Br J Dermatol. 1995 Oct;133(4):501-11

15.Gene expression of differentiation-specific keratins (K4, K13, K1 and K10) in oral non-dysplastic keratoses and lichen planus J Oral Pathol Med. 2000 Sep;29(8):376-84

16.The process of keratinization of gingival epithelium. The Journal of western society of periodontology; vol 27; no.3 pg: 72-85 1979

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