JUNCTIONAL EPITHELIUM

Nabin chaudharyBDS 2011

Junctions in oral mucosa• Junctions in the oral mucosa are

lines or surfaces, where two

different types of mucosa meet each

other.

• Within the oral mucosa there are

three junctions:

• Mucocutaneous junction – the site

of transition between skin and

mucous membrane.

• Mucogingival junction – between

gingiva and alveolar mucosa

• Dentogingival junction – between

tooth and free gingiva

Gingiva• Gingiva is that portion of the

oral mucosa that covers the tooth-bearing part of the alveolar bone and the cervical neck of the tooth

• Masticatory mucosa

• Morphologically gingiva is

divided into:

1. Attached gingiva

2. Free gingiva

3. The interdental papilla.

Dentogingival junction

• Defined as the oral epithelium that extends from the mucogingival junction to the gingival margin where crevicular/sulcular epithelium lines the sulcus

• Sulcular epithelium+junctional epithelium=dentogingival junction

• Gingival sulcus has a depth of 0.5-3mm(avg.1.8mm)

• Any depth greater than 3mm,considered pathologic,a sulcus this depth is known as a periodontal pocket

Epithelial components of gingiva

• The gingival epithelium is

subdivided into 3 sections:

• the oral epithelium (OE),

• the sulcular epithelium (SE),

and

• the junctional epithelium

(JE).

Junctional epithelium

• Junctional epithelium is the

stratified non-keratinizing

epithelium, that surrounds the

tooth like a collar with a cross-

section resembling a thin wedge.

• The epithelium of the gingiva

which gets attached to the tooth

is called junctional or

attatchment epithelium.

• Forms the floor of sulcus and attaches gingiva to tooth surface

• The union between this epithelium and tooth is referred to as epithelial attachment. It is bounded CORONALLY by the free gingival groove and APICALLY by the mucogingival junction

• Resembles REE in its structure in that they have a basal layer and few layers of flattened cells

Arrangement of cells in attachment epithelium

Junctional epithelium is unique as it possess 2 basement membranes – the internal and external basal lamina

Enamel

Lamina propria

Internal Basal Lamina External Basal LaminaHemidesmosomes

• The junctional epithelium has 2

basal laminas, one that faces the

tooth (internal basal lamina)

and one that faces the

connective tissue (external

basal lamina).

• The proliferative cell layer

responsible for most cell

divisions is located in contact

with the connective tissue, i.e.

next to the external basal

lamina.

• Cells of JE immediately adjacent to tooth attach to tooth by hemidesmosomes & basal lamina i.e. Internal Basal lamina

• Combination is known as the epithelial attachment,adhesive forces betn this zone are molecular in nature and act across a distance smaller than 4onm(400Ang)

• On opposite surface – JE in contact with lamina propria of gingiva & attached by hemidesmosomes and basal lamina i.e. External Basal Lamina

• IBL differs from EBL in that they lack laminin,anchoring fibrils and type IV collagen

• Cells of JE are attached to eachother primarily by desmosomes,and also by tight and gap junctions

Cont…

• Coronally: 15-30 layers thick. Apically: narrows to 3-4 layers thick

• Extends upto 2mm on the surface of the tooth

• Contains fewer tonofilaments and desmosomal junctions

• Cytokeratins present are CK5,CK14,CK19(simple epithelia has CK8,CK18)

• Shows no sign of differentiation to form a keratinized surface epithelium

• highest turnover rate of 5-6 days

• Highly permeable and it has large intercellular spaces,so that neutrophils have an easy passage in and out of the epithelium

• Also permits the easy flow of crevicular(gingival) fluid

• The junctional epithelium is more permeable than the oral or sulcular epithelium.

Significance of JE

• Has attachment role and protective role• Helps maintain integrity of tooth / periodontium structure.• Permeability allows GCF and defence cells to pass across to

protect underlying tissues from disease processes (periodonal disease)

• GCF contains g globulins and polymorphonucleocytes (PNMs) giving it immunological / phagocytic properties to combat disease processes

• The lysosomes of the junctional epithelium may have a phagocytic function

• Langerhans cells migrate to sulcular and oral epithelium when infection or inflammation is present

• These defence rxns to the bacteria in the gingival sulcus constitute barriers against the invasion of bacteria and the penetration of toxins

• A diagnosis of gingivitis implies that the actual level of the junctional epithelial attachment has not migrated apically, but is still on the enamel or on the cementoenamel junction

• A diagnosis of periodontitis implies that the junctional epithelium has migrated apically two, three, or more millimeters from its original level at the cementoenamel junction

Development of junctional junnction

• Junctional epithelium is derived from Reduced Enamel Epithelium(REE)

• Ameloblast after formation of enamel matrix they leave a thin membrane on the surface of enamel PRIMARY ENAMEL CUTICLE.

• Ameloblasts cells becomes flat cuboid cells – REE• As tooth erupts and crown penetrates overlying oral

epithelium a fusion occurs between REE and oral epithelium so that epithelium continuity is never lost

• Remnants of PEC after eruption– NASMYTH’S MEMBRANE.

• Tip of crown emerged, the REE termed as PRIMARY ATTCHEMENT EPITHELIUM

• As Tooth erupts,REE grows shorter and forms gingival sulcus.

• The replacement of primary attachment epithelium by cells derived from gingival epithelium is called secondary attachment epithelium

Shift of dentogingival junction• Position of gingiva on the surface of the tooth changes with time

• active eruption refers to the bodily movement of the developing

tooth through the overlying jawbone and oral mucosa into the

oral cavity.

• Active eruption normally stops when the erupting tooth comes

in contact with its antagonist in the opposite jaw.

• Passive eruption refers to the uncovering of the anatomic

crown because of apical recession of the surrounding tissues,

rather than bodily movement.

• Passive eruption has been

classified into 4 stages• stage 1: bottom of the

gingival sulcus remains on enamel & apical end of attachment epithelium at CEJ

• The junctional epithelium is located entirely over the enamel.

• Persists in primary teeth for 1 yr of age before shedding and in permanent teeth upto 20-30 yrs

• stage 2: bottom of GS on the enamel & apical end of attachment epithelum is shifted to the surface of cementum

• The junctional epithelium is located in part over the enamel and in part over the cementum

• Apical migration of sulcus is the result of detachment of basal cells and reestablishmrent of their epithelial attachment at a more apical level

• Dissolution of fibre bundles that were anchored in cervical parts of cementum,caused by enzymes formed by epithelial cells,by plaque metabolites or immunologic rxns

• Persists upto 40 yrs or later

• Stage 3: Bottom of the GS at

CEJ & epithelial attachment

entirely on the cementum

• The entire junctional

epithelium is located over

cementum, with its coronal

end at the cemento-enamel

junction

• Stage 4: Recession of gingiva(The entire junctional epithelium is located apical to the cemento-enamel junction)

• 1st and 2nd stages (passive eruption),anatomic crown is larger than clinical crown

• 3rd and 4th represent recession

• In 3rd stage,anatomic and clinical crowns are equal

• In 4th stage, clinical crown is larger than anatomic crown

Dynamics of migration of tissues of dentoepithelial junction

Enamel Cuticle• When the ameloblasts are replaced by oral epithelium a secondary

cuticle is formed

• Amorphous material between JE and underlying hard tissue

• Not visible in demineralised sections

• Cuticle also seen between JE and underlying cementum

• Secondary Enamel cuticle and cemental cuticle=dental cuticle

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