DENTO-GINGIVAL UNIT

Dr. Khushbu Mishra

HKE’S S.N Dental College, Gulbarga

• Introduction• Junctional epithelium– Development of junctional epithelium– Structure– Epithelial attachment – Dynamic aspects of junctional epithelium– Expression of various molecules and their functions– Permeability – Functions– Regeneration – role of JE in initiation of pocket formation

• Junctional epithelium around implants• Supra-gingival fiber apparatus– Classification– Features and functions

• Biologic width• Conclusion

Introduction

• Teeth are trans-mucosal organs.

• This is a unique association in the human body where a hard tissue emerges through the soft tissue.

• Permanently wet, warm, nutrient rich oral cavity

Perfect habitat for microorganisms

forms complex ecological system

attaches to glycoprotein layer on solid/ non shedding surfaces

Tissue in vicinity are constantly challenged.

• The tooth-epithelial interface thus call for a specialized structural and functional adaptation

• Listgarten MA, 1970:Dento-gingival unit refers to the functional unit comprising of junctional epithelium and the gingival fibers

Junctional

Epithelium

Gingival GroupFibers

• Gingival apparatus maintains free gingival and functional epithelium in close approximation to tooth.

• The attachment of functional epithelium to tooth is reinforced with gingival fibers, which brace the gingiva against tooth surface.

• So that, gingival fibers along with junctional epithelium

functional unit

Dentogingival unit

History

• Gottlieb (1921) was the first to describe the junctional epithelium

• Schroeder and Listgarten (1977) clarified the anatomy and histology of the dentogingival junction in their monograph: ‘Fine structure of developing epithelial attachment of human teeth’.

• The oral epithelium around a tooth is divided into three functional compartments– gingival, sulcular, and junctional epithelium

• The gingival epithelium extends from the mucogingival junction to the gingival margin where crevicular/sulcular epithelium lines the sulcus

• At the base of the sulcus connection between gingiva and tooth is mediated with JUNCTIONAL EPITHELIUM

Three zones of the gingival epithelium

Crevicular (sulcular) epithelium

Oral epithelium

Junctional epithelium

Development of junctional epithelium

• Shortly before 1st contact a slow cell transformation

process develops• Beginning orally and ending at CEJ,

1 to 2 yrs ( Schroeder & Listgarten 1977)

3 to 4 yrs (Tencate 1998)

• REE gradually multilayer non keratinizing squamous

converts to epithelium

• During transformation process,

reduced ameloblasts undergo structural change

short columnar flattened cells that orient

parallel to enamel surface

Structure of junctional epithelium

• Anatomical aspects• Junctional epithelium and interstitial cells• Epithelial attachment

Anatomical aspects

• part of marginal free gingiva• Forms a collar• Interproximal area ---- fuse to form

epithelial lining of interdental col• The coronal termination of the

junctional epithelium corresponds

usually to the bottom of the

gingival sulcus.

JE and Interstitial cell

• JE is a collar-like band of nonkeratinised stratified squamous epithelium extending from cemento-enamel junction to bottom of gingival sulcus

• Coronally it is 15-30 cells thick and apically narrows to 1-3 cells

• Its length varies from 0.25 – 1.35mm

stratum basale ( towards CT)• Made up of 2 layers

stratum suprabasale

(facing tooth surface)• Organelles- lysosomal bodies, golgi fields, polyribosomes,

cisternae of RER are abundant.• All JE cells express unique set of cytokeratins 5, 13, 14, 19

& occasionally 8, 16, 18.• Cells are connected by Desmosomes.• Fluid filled intercellular spaces may vary in width.

EPITHELIAL ATTACHMENT APPARATUS

• The term epithelial attachment: refers to the attachment apparatus, i.e. internal basal lamina

& hemidesmosomes

that connects the junctional epithelium to the tooth surface.

• It consists of hemidesmosomes at the plasma membrane of the cells directly attached to the tooth (DAT cells) and a basal lamina-like extracellular matrix, termed the internal basal lamina, on the tooth surface

Structural and molecular composition of the epithelial attachment apparatus at DAT cell

N-nucleus of a DAT cell,

IF-cytoplasmic keratin filaments

The hemidesmosomes at the plasma membrane are associated with the a6b4 integrin that communicates with Ln-5= laminin 5 located mainly in the internal basal lamina, the extracellular domain (?) for B180 is a collagenous protein (perhaps type VIII), that has not yet been definitely characterized.

LL = lamina lucida,

LD = lamina densa,

SLL = sub lamina lucida,

IBL = internal basal lamina.

HISTORICAL CONCEPTS OF ATTACHMENT

• Gottlieb (1921)

• Orban (1956)

• Waerhaug (1960)

• Schroeder and Listgarten (1971)

Gottlieb’s concept (1921)

• Soft tissue of gingiva is organically united to enamel surface.• He termed the epithelium contacting the tooth “epithelial

attachment”.

Orban’s concept (1953)

• He stated that the separation of the epithelial attachment cells from the tooth surface involved preparatory degenerative changes in the epithelium.

Waerhaug’s concept (1960)

• He presented the concept of epithelial cuff. This concept was based on insertion of thin blades between the surface of tooth and the gingiva

• Blades could be easily passed apically to the connective tissue attachment at CEJ without resistance.

• It was concluded that gingival tissue and tooth are closely adapted but not organically united.

Schroeder and Listgarten concept (1971)

• The previous controversy was resolved after evolution of transmission electron microscopy.

• Primary epithelial attachment refers to the epithelial attachment lamina released by the REE. It lies in direct contact with enamel and epithelial cells attached to it by hemi-desmosomes.

• When REE cells transform into JE cells the primary epithelial attachment becomes secondary epithelial attachment . It is made of epithelial attachment between basal lamina and hemi-desmosomes.

Epithelial attachment at molecular level

• The junctional epithelium faces both the gingival connective tissue (i.e., the lamina propria of the gingiva) and the tooth surface

JE

• Basement membrane – specialized extracellular matrices• Functions-

a. Compatmentalization

b. Filtration

(selective permeability barrier function)

c. Cell polarization, migration.

d. Cell adhesions

e. Cell differentiation.

• consists of lamina lucida

lamina densa

lamina fibroreticularis• Typical matrix constituents of basement membrane

1. Collagen types IV & VII

2. Laminin

3. Heparan sulfate proteoglycan

4. Fibronectin

5. Nidogen

6. Proteoglycan

7. perlecan

SCHEMATIC DEPICTION OF THE DETAIL OF THE INTERNAL BASAL LAMINA

It consists of two layers: the lamina lucida and lamina densa.

Hemidesmosomes (HD) originate from the lamina lucida, and tonofilaments splay out from each hemidesmosome.

• The internal basement membrane was initially described as an 80-120nm wide homogeneous layer. It directly faces the enamel, with an intervening laminated or non-laminated layer of cuticles (Listgarten, 1966) or afibrillar cementum (Kobayashi et al., 1976).

• There are numerous fine strands crossing the lamina densa of the internal basement membrane at the hemidesmosomes. These strands may have been the anchoring filaments of hemidesmosomes (Eady, 1994; Garrod, 1993).

• In the cytoplasm of the cells of the junctional epithelium, the tonofibrils are associated with hemidesmosomes.

• The internal basement membrane of the dentogingival border is uniquely specialized for mechanical strength, sealing off the periodontal tissues from the oral environment (Sawada & Inoue, 1996).

• The internal basement membrane takes the form of both thin and multilayered thick basement membranes

• Multilayered internal basement membrane may provide mechanical strength for firm attachment of the tooth to the gingiva and the sealing off of the periodontal tissues from the oral environment.

INTERNAL BASEMENT MEMBRANE

Internal basement membrane is composed of single broad lamina densa

Internal basement membrane is composed of multi-layers of lamina densa

• The finer level structure of the internal basement membrane is, the “cord” network. The basic texture of the lamina densa is made up of a 3-dimensional network formed by anastomosing, irregular, thread-like structures referred to as “cords” (Inoue, 1994; Sawada & Inoue, 2001).

Lamina densa is composed of fine network of irregular anastomosing cords

MECHANISM OF BINDING OF NORMAL TOOTH TO GINGIVA THROUGH CORD LIKE STRUCTURES IN

LAMINA DENSA

• The lamina densa of the internal basement membrane is closely associated with an additional layer referred to as the supplementary lamina densa found on the enamel side of the tooth.

• One part of the basement membrane, the supplementary lamina densa, is mineralized. This mineral deposit is continuous with that of the enamel of the tooth, and thus this deposit on the supplementary lamina densa forms an advancing edge of mineralization.

(Sawada & Inoue, 2003)

• In the mineralized portion of the lamina densa, mineral crystals were arranged in a network pattern which was comparable to the pattern of the cord network.

• This may facilitate more powerful gripping, and further demonstrates the elaborate mechanism by which firm binding of the mineral and organic phases is achieved.

DENTO-GINGIVAL BORDER OF TOOTH FROM DEMINERALIZED AND NON-DEMINERALIZED SAMPLES

DEMINERALIZED SECTION SHOWING THE EMPTY SPACE

OF SUBLAMINA DENSA

MINERALISED SECTION SHOWING MINERALISED

SUBLAMINA DENSA LUCIDA CONTINUOUS WITH ENAMEL

Dynamic aspects of junctional epithelium

• Cells and extracellular dynamics of JE – essential for its protective & regenerative function.

• Exfoliation must occur at extremely high rate ( Loe & Karring 1969)

• Since DAT cells are connected to basal lamina via hemidesmosomes, a remodelling of epithelial attachment must occur.

• Thus epithelial attachment normally is not static but dynamic.• Intercellular spaces of JE

provides pathway for fluid & transmigratory leukocytes

a variety of molecules + leukocytes ( host defense system)

Expression of various molecules and their function

• JE cells have surface or cell membrane molecules that play a role in cell matrix and cell-cell interactions. JE cells express numerous cell adhesion molecules (CAM’s), such as integrins and cadherins.

• Knowledge about structure and molecules involved in the

maintenance of cell-cell contact is particularly important in view of the pathological changes that the epithelium undergoes during its conversion to a pocket lining.

• Integrins – are cell surface receptors that mediate interactions between cell and extracellular matrix, and also contribute to cell to cell adhesion.

• The cadherins are responsible for tight contacts between cells.• E-cadherin, an epithelium specific cell adhesion molecule,

plays a crucial role in maintaining the structural integrity.• Intercellular adhesion molecule-1(ICAM-1 or CD-54) and

lymphocytic function antigen- 3(LFA-3) are additional cell adhesion molecules.

• Cells in contact with the internal basal lamina express the integrins.

• (CEACAM1)—a transmembrane cell-adhesion molecule that is expressed on leukocytes, epithelia, and blood vessel endothelia .

• high expression of interleukin-8 (IL-8), a chemotactic cytokine, is seen in the coronal-most cells of the junctional epithelium

• interleukin-1α (IL-1α), • interleukin-1β (IL-1β), • tumor necrosis factor-α (TNF-α)—are strongly expressed in

the coronal half of the junctional epithelium • N-acetyllactosamine—the type 2 chain H precursor of the

blood group A-specific carbohydrate, which is usually associated with the lowest level of cell differentiation.

• Antimicrobial molecules--- α and β defensins

cathelicidin family

calprotectin

DYNAMICS (TURNOVER RATE) OF JE

• The turnover rate of JE cells is exceptionally rapid. In non-human primates it is about 5 days (twice that of oral epithelium).

• The DAT cells express a high density of transferrin receptors supporting the idea of active metabolism and high turnover.

• DAT cells have an important role in tissue dynamics and reparative capacity of the JE.

• The existence of a dividing population of DAT cells in a suprabasal location in several layers from connective tissue is a unique feature of JE.

Mechanism of JE cells turnover

(1)The daughter cells are produced by dividing DAT cells and replace degenerating cells on the tooth surface.

(2) The daughter cells enter the exfoliation pathway and gradually migrate coronally between the basal cells and the DAT cells to eventually break off into the sulcus, or

(3)Epithelial cells move/migrate in the coronal direction along the tooth surface and are replaced by basal cells migrating round the apical termination of the junctional epithelium.

PERMEABILITY OF JUNCTIONAL EPITHELIUM

• The bi-directional arrows indicate that the junctional epithelium is the most permeable portion of the gingival epithelia. 

• Because of its permeability to bacterial products and other assorted antigens, the connective tissue adjacent to the junctional epithelium tends to become infiltrated with chronic inflammatory cells, primarily lymphocytes and plasma cells.

FUNCTIONS OF JUNCTIONAL EPITHELIUM

• Has attachment role and protective role.

• Permeability allows GCF and defence cells to pass across to protect underlying tissues from disease processes (periodontal disease).

• Helps maintain integrity of tooth/periodontium structure

• GCF contains gamma globulins and poly-morphonuclear leukocytes (PMNs) giving it immunological/phagocytic properties to combat disease processes.

• Such molecules pass readily across JE to underlying tissues.

• JE may contain neutrophils & other inflammatory cells indicating disease & state of health of periodontium.

• The junctional epithelium plays a crucial role since it essentially seals off periodontal tissues from the oral environment.

• Its integrity is thus essential for maintaining a healthy periodontium.

• Periodontal disease sets in when the structure of the junctional

epithelium starts to fail, an excellent example of how structure determines function.

JE in antimicrobial defense(1) JE cells exfoliate because of rapid

cell division

(2) Funnelling of junctional epithelial cells towards the sulcus hinder bacterial colonization.

(3) Active antimicrobial substances are produced in junctional epithelial cells.

(4) Epithelial cells activated by microbial substances secrete chemokines, that attract and activate professional defense cells, PMN.

• Role of JE in pocket formation

Role of JE in the initiation of pocket formation

• Conversion of the JE to pocket epithelium is regarded as a hallmark in the development of periodontitis.

• Schroeder – 1996 pointed to a biologically relevant and clinically important question that still awaits resolution: ‘what happens to the JE under conditions of sub-gingival microbial attack i.e. in context with pocket formation and deepening?’

• Schluger et al 1977: Pocket formation is attributed to a loss of cellular continuity in the coronal most portion of the JE

• Thus the initiation of pocket formation may be attributed to the detachment of the DAT cells from the tooth surface or to the development of intraepithelial split.

• Takata and Donath (1988) observed degenerative changes in the second or third layer of the DAT cells in the coronal most portion of the JE cells facing the biofilm.

• Schroeder and Listgarten 1977: An increased number of mononuclear leukocytes (T and B cells, macrophages) together with PMNs are considered as factors contributing to the disintegration of the JE.

The degeneration and detachment of DAT cells exposes tooth surface and creates a sub-gingival niche suitable for the colonization of anaerobic gram-negative bacteria and apical growth of dental plaque.

• Hintermann et al 2002: Gingipains degrade the epithelial cell-cell junctional complexes and cells exposed to proteinases derived from P.gingivalis showed reduced adhesion to extracellular matrix.

• Destruction of cell-cell and cell to ECM perturbs the structural and functional integrity of the JE.

• Regeneration of JE

• Injury to JE may occur due to intentional or accidental trauma. • Accidental trauma can occur during probing, flossing or tooth

margin preparations for restorations.• Intentional trauma occurs during periodontal surgeries where

the JE is completely lost. • Many studies have been done to investigate the renewal of JE.

These include studies done on renewal of JE on tooth and implant surface after mechanical detachment by probing.

• Studies have been done on mechanical trauma during flossing and on regeneration of JE after gingivectomy procedure which completely removes JE.

• Taylor and Campbell 1972: A new and complete attachment indistinguishable from that in control was established 5 days after complete separation of the JE from the tooth surface.

• Frank et al 1972: A study demonstrated that newly differentiated attachment apparatus with normal hemidesmosomal attachment is possible following surgery. This new attachment apparatus was seen on cementum as well as dentin.

• Listgarten 1972:Hemidesmosomes appeared to form prior to the basal lamina. The basal lamina is initially formed in close proximity to the hemidesmosomes at both the tooth and connective tissue interface. At 4 to 7 weeks, the basal lamina appeared complete. Studies have shown that regeneration of JE after procedure usually occurs within 20 days.

• JE AROUND IMPLANTS

• The junctional epithelium around implants always originates from epithelial cells of the oral mucosa, as opposed to the junctional epithelium around teeth which originates from the reduced enamel epithelium.

• Despite different origins of the 2 epithelia, a functional adaptation occurs when oral epithelia form an epithelial attachment around implants.

NATURAL TOOTH

• Epithelium tapers towards the depth

• Large number of cell organelles

• Fibers are arranged perpendicular

IMPLANT

•Epithelium is thicker•Few organelles•Fibers are arranged parallely•Numerous kerato-hyalin granules

NATURAL TOOTH IMPLANT

GINGIVAL FIBERS

THE SUPRAGINGIVAL FIBER APPARATUS

• The gingival lamina propria consists mainly of a dense network of collagen fiber bundles that account for about 55.43% of the connective tissue volume. This network is called the supragingival fiber apparatus.

• On the basis of their preferential orientation, architectural arrangement and sites of insertion, these bundles have been classified.

• These fiber bundles are densely populated by fibroblasts and consist mainly of collagen Type I and III.

• Collagen Type I represents mainly dense fibers; Type III is related to loose connective tissue, subepithelially and around blood vessels.

• Mast cells are also regular residents, whereas lymphocytes, monocytes and macrophages vary in number with the need for and degree of protective activity.

CLASSIFICATION OF GINGIVAL FIBER GROUPS

based on their orientation,

sites of insertion,

the structures that they connect

PRIMARY FIBERS:• Alveologingival fibers• Circular fibers.• Dentogingival fibers

• Alveologingival fibers—extend from the periosteum of the alveolar crest into the gingival connective tissue. These fiber bundles attach the gingiva to the bone. (The periosteum is a dense membrane composed of fibrous connective tissue that closely wraps around the outer surface of the alveolar bone.)

• Circular fibers—encircle the tooth in a ring-like manner coronal to the alveolar crest and are not attached to the cementum of the tooth. These fiber bundles connect adjacent teeth to one another.

• Dentogingival fibers— are embedded in the cementum near the CEJ and fan out into the gingival connective tissue. These fibers attach the gingiva to teeth.

SECONDARY FIBERS

• Periostogingival fibers.• Intergingival fibers• Intercircular fibers• Interpapillary fibers• Transgingival fibers• Transseptal

Functions of the Gingival Fiber Bundles

1. Brace the free gingiva firmly against the tooth and reinforce the attachment of the JE to the tooth.

2. Provide the free gingiva with the rigidity needed to withstand the frictional forces that result during mastication.

3. Unite the free gingiva with the cementum of the root and alveolar bone.

4. Connect adjacent teeth to one another to control tooth positioning within the dental arch.

THE SUPRAGINGIVAL FIBER APPARATUS

• The formation and insertion of transseptal and dentogingival fibers is not specific to certain anatomic surfaces, but is functionally rather than anatomically determined.

• The supragingival fiber apparatus not only attaches the gingiva to teeth and bone but also provides a dense framework that accounts for the rigidity and biomechanical resistance of the gingiva.

• The fiber apparatus also controls the positioning of teeth within the dental arch and also protects the very sophisticated cellular defenses located at the dentogingival interface.

SUPRAGINGIVAL FIBERS AROUND IMPLANTS

BIOLOGIC WIDTH

• BIOLOGIC WIDTH is defined as the dimension of the soft tissue which is attached to the portion of the tooth coronal to the crest of the alveolar bone

• It is important from the restorative point of view because its violation leads to complications like gingival enlargement alveolar bone loss and improper fit of the restoration.

• Gargiulo et al (1961) in their study described the dimensions and relations of dentogingival junction in humans. The average histological width of connective tissue attachment was 1.07mm. The mean average length of epithelial attachment was 0.97mm with the range of 0.71mm-1.35mm.

• The average combined histological width of connective tissue attachment and junctional epithelium was 2.04mm, which is referred to as the BIOLOGIC WIDTH.

CONCLUSION

• DENTOGINGIVAL UNIT is important because of its anatomical location.

• It is the site of host-bacterial interaction in initiation of periodontal disease.

• There is a constant presence of bacteria and their products in the gingival sulcus which makes this an important structural component of periodontal defense mechanism.

• The conversion of the junctional epithelium to pocket epithelium is regarded as hallmark in the development of periodontitis.

Future scope

• To find out the therapeutic strategies that halt the disease progression at this important tooth-tissue interface.

References

• DD Bosshardt and NP Lang. The Junctional Epithelium: from health to disease. J Dent Res 2005, 84 (1): 9-20

• Moon-Il Cho & Philias R. Garant. Development and general structure of the periodontium. Periodontology 2000, Vol. 24, 2000, 9–27.

• Mark Bartold, Laurence J. Walsh & A. Sampath Narayanan. Molecular and cell biology of the gingiva.P. Periodontology 2000, Vol. 24, 2000, 28–55.

• Thomas M Hassell. Tissues and cells of the periodontium. Periodontology 2000, Vol. 3, 1993, 9-38

• Huberte . Schroede & R M Listgarten. The gingival tissues: The architecture of periodontal Protection. Periodontology 2000, Vol. 13, 1997, 91-120.

• Takashi Sawada1 and Sadayuki Inoue. Ultrastructure of Dentogingival Border of Normal and Replanted Tooth and Dental Implant, chapter 11 www.intechopen.com/books/implantdentistry

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