Oral Histology, Embryology and Genetics Spring 2008

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Oral Histology, Embryology and GeneticsOral Histology, Embryology and Genetics

Spring 2008Spring 2008

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Course SyllabusCourse Syllabus

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Oral MucosaOral Mucosa

Mucous Membrane: Moist lining of the gastrointestinal tract, nasal passages andother body cavities that communicate with the exterior

In the oral cavity the lining is called as oral mucous membrane or oral mucosa

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Functions of the Oral MucosaFunctions of the Oral Mucosa

1. Protection: Barrier for mechanical trauma and microbiological insults

2. Sensation: Temperature (heat and cold), touch, pain, taste buds, thirst; reflexes such as swallowing, etching, gagging and salivating

3. Secretion: Salivary secretion

4. Thermal regulation: Important in dogs not in humans

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Organization of the Oral MucosaOrganization of the Oral Mucosa

3 types according to FUNCTION:

1. Masticatory Mucosa: 25% of total mucosa. Gingiva (free, attachedand interdental) and hard palate. Primary mucosa to be in contact with foodduring mastication. MASTiCATORY MUCOSA IS USUALLY KERATINIZED.

2. Lining Mucosa: 60% of total mucosa. Covers the floor of mouth, ventral(underside) tongue, alveolar mucosa, cheeks, lips and soft palate.Does not function in mastication and therefore has minimal attrition.Non-keratinized; soft and pliable.

3. Specialized Mucosa: 15% of total mucosa. Covers dorsal tongue andcomposed of cornified epithelial papillae.

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Masticatory MucosaMasticatory Mucosa

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Lining MucosaLining Mucosa

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Specialized MucosaSpecialized Mucosa

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General Features of Oral MucosaGeneral Features of Oral Mucosa

1. Separated from the skin by vermillion zone of the lips which is more deeplycolored than rest of the oral mucosa

2. Factors affecting color of the oral mucosa:a. Concentration and state of dilation of the blood vessels in underlying connective tissueb. Thickness of the epitheliumc. Degree of keratinizationd. Amount of melanin pigmentation

Clinically, color of oral mucosa is very important. For example, inflamed oraltissues appear red rather than the normal pale pink

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How is the oral mucosa different from skin?How is the oral mucosa different from skin?

1. Color

2. Moist surface

3. Absence of adnexal skin structures such as hair follicles, sweat glandsand sebaceous glands (exception in Fordyce’s disease)

4. Fordyce’s disease: Sebaceous glands in oral cavity predominantly in upperlip, buccal mucosa and alveolar mucosa

5. Presence of minor salivary glands in oral mucosa

6. Texture of surface: Oral mucosa is smoother than the skin (few exceptionslike dorsal tongue – due to papillae; hard palate – rugae; gingiva – stippling)

7. Firmness: Oral mucosa varies in its firmness. For example buccal mucosaand lips are loose and pliable whereas the gingiva and hard palate are firmso critical clinically while giving injections

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Skin Oral Mucosa-Cheek

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Fordyce’s SpotsFordyce’s Spots

• Pale yellow spots

• Normal variation

• Lips, buccal mucosa, alveolar mucosa and tonsillar pillar

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Structure of Oral MucosaStructure of Oral Mucosa1. Overlying oral epithelium2. Underlying connective tissue (lamina propria and submucosa)

In skin called epidermis and dermis

Rete ridges/pegs

Connective tissue papilla

http://www.usc.edu/hsc/dental/ohisto/Cards/muc/01_bb.html


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The oral epithelium is keratinized or non-keratinized stratified squamous epithelium

The interface between epithelium and connective tissue is comprised of astructureless layer called basement membrane

This interface is irregular and is composed of downward projections of epitheliumcalled rete ridges or rete pegs, and upward projection of connective tissue termedas connective tissue papillae

A: EpitheliumB: Connective tissueC: Salivary gland

A: Startum basaleB: Startum spinosumC: Startum superficiale

http://dentistry.ouhsc.edu/intranet-WEB/Courses/CELL8002/Home.html

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Junction between oral epithelium and lamina propria is more obvious than that betweenlamina propria and submucosa

No muscularis mucosae layer seen in oral mucosa

Loose fat and glandular tissue with blood vessels and nerves seen underneath oral mucosafrom underneath bone or muscle layer - this layer is termed SUBMUCOSA – provides flexibility

In gingiva and hard palate, no submucosa is seen and the lamina propria is directlyattached to the periosteum of the underlying bone which provides firm, inelastic attachment –this is called ORAL MUCOPERIOSTEUM

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Connective tissue in oral cavity is comprised of salivary glands, sebaceous glands(Fordyce’s disease) and lymphoid tissue (tonsillar tissue)

Salivary glandsSalivary glands Sebaceous glandsSebaceous glands Lymphoid tissue (tonsil)Lymphoid tissue (tonsil)

www.usc.edu/hsc/dental/opfs/QL/09tn.html

http://www.usc.edu/hsc/dental/ohisto/index.html

High Power view of sebaceous glands


http://www.usc.edu/hsc/dental/opfs/QL/09tn.html


http://www.usc.edu/hsc/dental/opfs/QL/14bb.html

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Oral EpitheliumOral Epithelium

Progenitor population: Divide and provide new cells (Proliferation)Maturing population: Undergo differentiation (maturation)

Estimated time necessary to replace all the cells in the epithelium: turnover time

Skin: 52 to 75 daysGut: 4 to 14 daysGingiva: 41 to 57 daysCheek: 25 days

Nonkeratinized epithelium turns over faster than keratininzed epithelium

Clinical correlation: Oral ulcers during cancer chemotherapeutic treatment

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Types of Oral EpitheliumTypes of Oral Epithelium

Orthokeratinized stratifiedOrthokeratinized stratifiedsquamous epitheliumsquamous epithelium

Parakeratinized stratifiedParakeratinized stratifiedsquamous epitheliumsquamous epithelium

Nonkeratinized stratifiedNonkeratinized stratifiedsquamous epitheliumsquamous epithelium

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Components of Oral Epithelium Components of Oral Epithelium

Lining Mucosa:

Stratum Basale: Basal cell layer comprised of cuboidal cells. Progenitorcells that divide and provide new cells by mitotic division that migrate to thesurface to replace cells that are shed.

Stratum Spinosum (or intermedium): Cells are oval and represent bulkof the epithelium. Stratum Superficiale: Cells are flat and contain small oval nuclei that arecontinuously shed.

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Histology of LipHistology of Lip

A: SkinB: Vermillion zoneC: Oral (labial) mucosaD: Minor salivary glands

Skin: keratinized stratified squamousepithelium with adnexal skin structures

Oral Mucosa: Moist-surface, covered bynonkeratinized stratified squamous epitheliumassociated with small round seromucousglands of the lamina propria. In thesubmucosa fibers of orbicularis oris muscle isnoted.

Vermillion zone: Very thin keratinizedepithelium that contains no adnexal skinstructures (can contain sebaceous glands)

What gives the vermillion zone the red color?1. Epithelium is thin2. Epithelium contains eleidin, which is

transparent3. Blood vessels are present near the surfaceEleidin is a semi-fluid clear substance presentin the stratum lucidum of the skin epithelium


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Skin of the LipSkin of the Lip Vermillion Zone and Labial MucosaVermillion Zone and Labial Mucosa

A: Sweat glandsB: Sebaceous glandsC: Hair follicles

A: Vermillion zoneB: Labial mucosaC: Orbicularis oris muscle


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Soft palateSoft palate

A: Hard PalateB; Soft palateC: Nasal cavity

1. Nonkeratinized2. Highly vascularized so more pink

than hard palate2. Lamina propria and submucosa

present (unlike hard palate whenonly lamina propria is noted – mucoperiosteum)

3. Submucosa contains salivaryglands and muscle soft palatehttp://dentistry.ouhsc.edu/intranet-WEB/Courses/CELL8002/Home.html

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Cheeks (Buccal Mucosa)Cheeks (Buccal Mucosa)

Similar to lips and soft palate

Nonkeratinized stratified squamous epithelium, lamina propria and submucosa

Submucosa of cheeks contain fat cells along with lobules of minor salivaryglands and muscle fibers

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Ventral surface of tongueVentral surface of tongue

Nonkeratinized stratified squamousepithelium, lamina propria andsubmucosa

Extremely dense muscle fibersinterlacing connective tissue fibersin submucosa

Floor of mouthFloor of mouth

Nonkeratinized stratified squamousepithelium, lamina propria and submucosa

Epithelium is loosely attached tolamina propria

No muscle

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Epithelium that covers gingiva and hard palate

Mucosa is thicker than nonkeratinized because of the keratin layer

Stratum basaleStartum spinosum

Stratum granulosum: Cells contain keratohyaline granules

Stratum corneum: Contains thin, flat and nonnucleated cells which are filled withkeratin. In contrast to the hard keratin seen in nails and hair, keratin overlyingnormal masticatory oral mucosa is soft. Keratin is tough, nonliving material thatis resistant to friction and impervious to bacterial invasion

Same as nonkeratinized epithelium

Miller SE. Histology for Pathologists. 3rd edition. LWW. 2007

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Types of Keratinized EpitheliumTypes of Keratinized Epithelium

The superficial cells are dead but retain the nucleus in parakeratinized epitheliumbut the nuclei are lost in orthokeratinized epithelium

The rete pegs are long and slender in keratinized epithelium

Mucoperiosteumhttp://dentistry.ouhsc.edu/intranet-WEB/Courses/CELL8002/Home.html

Miller SE. Histology for Pathologists. 3rd edition. LWW. 2007

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Gingiva and Epithelial AttachmentGingiva and Epithelial Attachment

Free or marginal gingiva

Attached gingiva attaces with the neckof the tooth by means of junctional epithelium

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Histology of GingivaHistology of Gingiva

Thick (250 µm), either orthokeratinized or parakeratinized stratifiedsquamous epithelium with a stippled surface

A: Rete pegsB: Conective tissue papillaC: ParakeratinD: Spinous layer

In healthy attached gingiva “stippling” is seen which appears as small pits in the epithelium andare due to deep rete pegs. The lamina propria is composed of long narrow papillae which are nothighly vascular. No distinct submucosa is noted as the overlying mucosa is directly attachedto the underlying periosteum and cementum by collagen fibers


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Free Gingiva: Keratinized; NOT STIPPLED; bound on inner margin by thegingival sulcus, which separates it from the tooth; bound on its outer margin bythe oral cavity; and apically by the free gingival groove.

Attached Gingiva: Keratinized; STIPPLED; separated from the alveolar mucosaby the mucogingival junction (groove). Attached to the tooth by junctional epithelium.

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In A note the difference inkeratinization, thickness ofepithelium and ridge pattern.

In B stained with an elasticstain, note the presence ofelastic fibers in lamina propriain alveolar mucosa. Notmuch difference in theepithelium is seen betweenthe two types of mucosa.

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Dentogingival Junction and Junctional EpitheliumDentogingival Junction and Junctional Epithelium

Dentogingival junction is theregion where the oral mucosameets the surface of the tooth

Very important because it is aweak area in the oral mucosawhich is otherwise continuous

Bacteria on the surface of thetooth produce toxins that canincite inflammation and damageif it enters into the mucosal tissues

Gingival sulcus in healthy individuals is ~ 0.5 to 3 mm (mild inflammation is present-1.8 mm average)

Depth greater that 3mm is considered pathologic; and the sulcus representsperiodontal pocket

Floor of the sulcus and the epithelium cervical to it is called junctional epitheliumwhich is in contact with the tooth surface (enamel and sometimes cementum)

Wall of the gingival sulcus is lined by nonkeratinizing stratified squamous epithelium that isderived from and continuous with the rest of the oral mucosa – oral sulcular epithelium

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Junctional EpitheliumJunctional Epithelium

The epithelium that is attached to the tooth (enamel or sometimes cementum) surfacecontinuous with sulcular epithelium

Derived from reduced enamel epithelium of the tooth germ

Junctional epithelium consists of flat cells aligned parallel to the tooth surfaceincreasing in thickness from the apex to the crown

Attached to enamel by internal basal lamina and to the connective tissue by externalbasal lamina. Hemidesmosomes are present in both basal laminas.

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Epithelial cell turnover in gingivaEpithelial cell turnover in gingiva

Similar to all other epithelia, the deepercells adjacent to the connective tissueundergo cell division to replenish thoselost at the surface

High rate of cell division

Migrate about 2 to 3 cell layers from thetooth surface and then join a main migratoryroute in a coronal direction, parallel to toothsurface, to be desquamated into thegingival sulcus.

Key point: Junctional epithelium readilyregenerates from the sulcular epitheliumor oral epithelium if it is damaged or surgicallyexcised

Connective tissue normally contains plenty of neutrophils which is differentthan the normal oral mucosa

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Col (or depression): This is how the gingiva looks in the interdental area. Similarto an outline of a depression or col with buccal and lingual peaks. Col epitheliumis identical to junctional epithelium and has the same origin (from dental epithelium)and is also replaced continually by cell division.

Not sure if there is any significance that the col is more vulnerable to inflammation,but the incidence of gingivitis is greater interdentally.

ColCol

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How does Gingiva develop?How does Gingiva develop?

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A quick note on…..

Blood supply to the gingiva: Derived from periosteal vessels in the periosteumof the alveolar process

Blood supply to the dentogingival junction: Continuation of interalveolar arteries

Nerve supply to the gingiva: terminal branches of periodontal nerve fibers and bybranches of the infraorbital and palatine, or lingual, mental, and buccal nerves

PLEASE REVIEW TABLE 12-4 AND 12-5 IN THE TEXT BOOK

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Histology of Hard PalateHistology of Hard Palate

Thick orthokeratinized (or parakeratinized in areas) epithelium showing ridges (rugae)

Lamina propria shows long papillae with thick dense connective tissue

Submucosa is mucoperiosteum with dense collagenous connective tissue attachingdirectly to periosteum. Contains fat and salivary glands

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Specialized Mucosa – Dorsal TongueSpecialized Mucosa – Dorsal Tongue

Types of papilla: 4 typesTypes of papilla: 4 types

A: Foliate C: CircumvallateD: Filiform

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1.1. Filiform papilla:Filiform papilla: Makes up majority of the papillae and covers the anterior partof the tongue. They appear as slender, threadlike keratinized projections(~ 2 to 3 mm) of the surface epithelial cells. These papillae facilitate mastication(by compressing and breaking food when tongue is apposed to the hard palate) and movement of the food on the surface of the tongue. The papillae is directedtowards the throat and assist in movement of food towards that direction. NO TASTE BUDS.

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Hairy Tongue

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2.2. Fungiform papillaFungiform papilla: (Fungus-like) These are interspersed between the filiform papilla.More numerous near the tip of the tongue. Smooth, round structures that appearred because of their highly vascular connective tissue core, seen through a thin,nonkeratinized stratified squamous epithelium. Taste buds are usually seen withinthe epithelium.

Filiform papilla

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3.3. Foliate PapillaFoliate Papilla: (Leaf-like). Present on the lateral margins of the posterior tongue.Consist of 4 to 11 parallel ridges that alternate with deep grooves in the mucosa,and a few taste buds are present in the epithelium. They contain serous glandsunderlying the taste buds which cleanse the grooves.

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4.4. Circumvallate papillaCircumvallate papilla: (Walled papilla). 10 to 14 in number these are seen alongthe V-shaped sulcus between the base and the body of the tongue. Large, ~ 3 mmin diameter with a deep surrounding groove. Ducts of von Ebner glands (seroussalivary glands) open into the grooves. Taste buds are seen lining the walls ofthe papillae.

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Taste BudsTaste Buds: Unique sense organs that contain the chemical sense for taste.Microscopically visible barrel-shaped bodies found in the oral epithelium.Usually associated with papillae of the tongue (circumvallate, foliate andfungiform). Also seen in soft palate, epiglottis, larynx, and pharynx.Referred to as NEUROEPITHELIAL STRUCTURES. But most correctly referredas epithelial cells closely associated with clib-shaped sensory nerve endings. Thesenerves arise from the chorda tympani in anterior tongue and glossopharyngeal inposterior tongue and come to lie among the taste cells. Each taste bud has ~ 10 to14 cells. Majority are taste cells with elongated microvilli that project into thetaste pore. (Epiglottis and larynx – Vagus nerve)

Type 1 dark cell (60% of cells)Type 2, light cells (30%)Type 3 (7%) and Type 4 (basal cells ~ 3%)

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Taste Buds in the Human AdultTaste Buds in the Human Adult

Location NumberTongue 10,000Soft palate 2,500Epiglottis 900Larynx/pharynx 600Oropharynx 250

4 taste sensations: Sweet, salty, sour and bitter

Sweet and salt: ant tongueSour: lateral tongueBitter: region of circumvallate papilla

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Epithelial maturationEpithelial maturation

KeratinizationKeratinization NonkeratinizationNonkeratinization

GingivaHard palateSome areas of dorsal tongue

No granular cell layer

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Basal cells interface with a membrane separating the epithelium and lamina propria.The membrane is called basal lamina. Basal cells attached to basal lamina byhemidesmosomes.

Epithelial cell-cell contact is made through desmosomes (in oral cavity appearsdiscoid and called macula adherens). These are anchored intracellularly bytonofibrils.

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Nonkeratinocytes in oral epitheliumNonkeratinocytes in oral epithelium

Constitute about 10% of epithelial cell population. Three major cells which are allclear cells with a halo around their nuclei.

1. Langerhan’s cells: found on stratum spinosum (suprabasal) and function inantigen trapping and processing. Dendritic cells. No desmosomes or tonofilaments.

2. Merkel cell: Located in basal cell layer (mostly in gingiva). Function as touchreceptors. Nondendritic. Sparse desmosomes and tonofilaments.

3. Melanocytes: Found in basal cells. Melanin-producing cells (mostly in gingiva).Dendritic. Presence of melanin granules (melanosome).

4. Lymphocytes and leukocytes: Inflammatory cells that are not clear cells.Associated with inflammatory response in oral mucosa

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Lamina PropriaLamina Propria

Superficial papillary layer (associated with rete ridges) and deeper reticular layer(between papillary layer and deeper structures)

Reticular refers to the netlike arrangement of collagen fibers (nothing to do withreticulin fibers)

Papillary layer has thin and loose collagen fibers with many capillary loopsReticular layer has collagen fibers arranged in thick bundles that are parellel to surface

Lamina propria also contains various cells, blood vessels, nerves and fibers(collagen and elastic) embedded in an amorphous ground substance

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Cell Types in the Lamina Propria of Oral MucosaCell Types in the Lamina Propria of Oral Mucosa

Oral Histology, Embryology and Genetics Spring 2008

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