ORAL HSTOLOJ

ORAL HISTOLOGY ASSC.PROF.DR.MELTEM KURUS

The alimentary mucosa is the surface across which most substances enter the bodyThe alimentary mucosa performs numerous functions in its role as an interface between the body and environment.

These functions include the followingSecrectionAbsorptionBarrierImmunologic protection

Secretion: The lining of the alimentary canal secretes, at specific sites, digestive enzymes, hydrochloric acid, mucin, and antibodies

Absorption: The epithelium of the mucosa absorbs metabolic substrates (e.g, the breakdown products of digestion) as well as vitamins,wate, electrolytes, recylable materials such as bile components and cholesterol, and other substances essential to the functions of the body

Barrier: The mucosa serves as a barrier to prevent the entry of noxious substances, antigens, and pathogenic organisms

Immunologic protection: Lymphatic tissue within the mucosa serves as the body`s first line of immune defenseOral CavityThe oral cavity consists of the mouth and its structures, which include the tongue, teeth and their supporting, structures (periodontium) major and minor salivary glands and tonsils

The oral cavity is divided into Vestibulum orisOral cavity proper

The vestibule is the space between the lips, cheeks, and teethThe oral cavity proper lies behind the teeth and is bounded by hard and soft palates superiorly, the tongue and floor of the mouth inferiorly and the entrance to the oropharynx posteriorly

The oral cavity is lined by the oral mucosa that consist of;

1-Masticatory Mucosa2-Lining Mucosa3-Specialized Mucosa

Masticator MucosaThe masticator mucosa is found on the gingiva (gums) and hard plateIt has a keratinized and, in some areas, a parakeratinized stratified squamous epithelium

parakeratined stratified squamous epithelium is smiliar to keratinized epithelium except that the superficial cells do not lose their nuclei and their cytoplasm does not stain intensely with eosin

The nuclei of the parakeratinized cells are pyknotic (highly condensed) and remain until cell is exfoliated.The keratinized epithelium of the masticatory mucosa resembles that of the skin but lacks a stratum lucidum.

The underlying lamina propria consist of a thick papillary layer of loose connective tissue that contains blood vessels and nerves, some of which send bare axon endings into the epithelium as sensory reseptors, and some of which in Meissner`s corpusculeDeep to lamina propria is reticular layer of more-dense connective tissueAs in the skin, the deep and number of connective tissue papillae contribute to the relative immobility of the masticatory mucosa, thus protecting it from frictional and shearing stress.

At the midline of the hard palate, in the palatine raphe, the mucosa adheres firmly to the underlying bone.The reticular layer of the lamina propria blends with the periosteum and thus there is no submucosa.The same is true of the gingivaLining MucosaThe lining mucosa is found on the lips, cheeks, alveolar mucosal surface, floor of the mouth, inferior surfaces of the tongue and soft palate.

Where there is submucosa underlying the lamina propria on the hard palate, it contains adiposa tissue anteriorly (fatty zone) and mucous glands posteriorly (glandular zone) that are continuous with those of the soft palate.In the submucosal regions, thick collagenous bands extend from the mucosa to the bone.

At these sites it covers striated muscle (lips, cheeks, and tongue), bone(alveolar mucosa) and glands (soft palate, cheeks, inferior surface of the tongue)The lining mucosa has fewer and shorter papillae so that is can adjust to the movement of its underlying muscles.

Generally, the epithelium of the lining mucosa is nonkeratinized, although in some places it may be parakeratinized.The epithelium of the vermilion border of the lip (the reddish portion of between the moist inner surface and facial skin) is keratinized

The nonkeratinized lining epithelium is thicker than keratinized epithelium.It consists of only 3 layersStratum basaleStratum spinosumStratum superficiale

Stratum basale; a single layer of the basal laminaStratum spinosum; which is several cells thickStratum superficiale; the most superficial layer of cells, also referred as the surface layer of the mucosa

The cells of mucosal epithelium are similar to those of the epidermis of the skin and include keratinocytes, Langerhans`s cells, melaoncytes and Mercel`s cells.The lamina propria contains blood vessels, nerves that send bare axon endings into basal layers of the epithelium, and encapsulated sensory endings in some papillae

The sharp contrast between numerous deep papillae of the alveolar mucosa and the shallow papillae in the rest of lining mucosa allows easy identification of the 2 different regions in a histologic section.

A distinct submucosa underlies the lining mucosa except on the inferior surface of the tongueThis layer contains large bands of collagen and elactic fibers that bind the mucosa to the underlying muscle;it also contains the many minor salivary glands of the lips, tongue, and cheeks.

Occasionally, sebaceous glands not associated with a hair follicle are found in the submucosa just lateral to the corner of the mouth and in the cheeks opposite the molar teethThey are visible to the eye and are called Fordyce spots

The submucosa contains the larger blood vessels, nerves and lymphatic vessels that supply the subepeithelial neurovascular networks in the lamina propria throughout the oral cavity

Specilazed MucosaSpecilazed mucosa is associated with the sensation of taste and is restricted to the dorsal surface of the tongue.It contains papillae and taste buds responsible for generating the chemical sensation of taste

Oral mucosa forms an important protective barrier between the external environment of the oral cavity and internal environments of the surrounding tissueIt is resistant to the pathologic organisms that enter the oral cavity and to indigenous microorganisms residing there as microbial floraHowever, in individuals with immunodeficiency or undergoing antibiotic therapy in which the balance between microorganisms and protective mechanisms is disrupted, oral infections are rather common TonsilsThe tonsils consist of aggregations of lymphatic nodules that are clustered around the posterior opening of the oral and nasal cavities

Lymphatic tissue is organized into a tonsillar (Waldeyer`s) ring of immunologic protection located at the shared entrance to the digestive and respiratory tracts

This lymphatic tissue surrounds the posterior orifice of the oral and nasal cavities and contains aggregates of lymphatic nodules that include the following :

Palatine tonsils, or simply the tonsils, which are located at either side of the entrance to the oropharynx between the palatopharyngeal and palatoglossal arches

Tubal tonsils, which are located in the lateral walls of the nasopharynx posterior to the opening of the auditory tubePharyngeal tonsil, or adenoid, which is located in the roof of the nasopharynxLingual tonsil, which is located at the base of the tongue on its superior surface LIPSThe upper and lower lips are usually in contact with one another and thus resemble a drawstring in that they guard the entrance into the oral cavityThe core of the lips is composed of skeletal muscle fibers that are responsible for the lips mobility

Each lip may be subdivided into three regions; the external aspect, vermilion zone, and mucous (internal,wet) aspectThe external aspect of the lip is covered with thin skin and is associated with sweat glands, hair follicles, and sebaceous glands

The region is continous with the vermilion zone, the pink region of the lip, which is also covered by thin skin.However, the vermilion zone is devoid of sweat glands and hair follicles, although occasional, nonfunctional sebaceous glands are present here

LIPSThe interdigitation between the epithelium and connective tissue components of the oral mucosa (rete apparatus) is highly developed, so that capillary loops of the dermal papillae are close to the surface of the skin, imparting a pink color to the vermillion zone.

The absence of functional glands in this region necessitates the occasional moistening of the vermilion zone by the tongue

The mucous (internal) aspect of the lip is always wet, and is lined by stratified squamous nonkeratinized epithelium.

LIPSThe subepithelial connective tissue is of the dense, irregular collagenous type and houses numerous, mostly mucous, minor salivary glands

PALATEThe oral and nasal cavities are seperated from each other by the hard and soft palates.The hard palate positioned anteriorly, is immovable and receives its name from bony shelf contained within it.

In contrast, the soft palate is movable, and its core is occupied by skeletal muscle responsible for its movements

The mucosa on the oral aspect of the hard palate is composed of stratified squamous keratinized (or parakeratinized) epithelium underlain by dense, irregular collagenous connective tissue.

The connetive tissue of the anterior region of the hard palate displays clusters of adipose cells, whereas posteriorly it exhibits acini of mucous minor salivary glands.The nasal aspect of the hard palate is covered by respiratory epithelium with occasional patches of stratified squamous nonkeratinized epithelium

The soft palate is covered by a stratified squamous nonkeratinized epithelium on its oral surfaceThe subjacent dense, irregular collagenous connective tissue has mucous minor salivary glands that are continous with those of the hard palate

The epithelium of its nasal aspect, as that of the hard palate, is pseudostratified ciliated columnarThe posterior-most extension of the soft palate is the uvula, whose histological appearance is similar to that of the soft palate, except that its epithelium is composed solely of stratified squamous nonkeratinized epithelium

TEETH AND SUPPORTING TISSUETeeth are a major component of the oral cavity and are essential for the beginning of the digestive processTeeth are embedded in and attached to the alveolar process of the maxilla and mandible

Children have 10 deciduous (primary, milk) teeth in each jaw, on each side;A medial (central) incisor, the first tooth erupt (usually in the mandible) at approximately 6 months of age (in some infants, first teeth may not erupt until 12-13 months

A lateral incisor, which erupts at approximately 8 monthsA canine tooth, which erupts at approximately 15 monthsTwo molar teeth, the first of which erupts at 10 to 19 months and the second of which erupts 20 to 31 months

During a period of years, usually beginning at about age 6 and ending at about age 12-13, deciduous teeth are gradually replaced by 16 permanent (secondary) teeth in each jaw

Each side of both upper and lower jaws consists of the following;A medial (central) incisor, which erupts at age 7 to 8 A lateral incisor, which erupts at age 8 to 9A canine tooth which erupts at age 10-12

Two premolar teeth which erupt between ages 10 and 12Three molar teeth which erupt at different times; the first molar usually at age 6, the second molar in the early teens and the third molar (wisdom teeth) during the late teens early twenties

Incisors, canines, and premolars have one root each except for the first premolar of the maxilla, which has two roots. Molars have either two roots (lower jaw) or three (upper jaw), and on rare occasion four roots.All teeth have the same basic structure, however

Teeth consist of several layers of specialized tissuesEnamelDentinCementum

Enamel; a hard thin, translucent layer of acellular mineralized tissue that covers the crown of the tooth

Dentin; the most abundant dental tissue; it lies deep to the enamel in the crown an cementum in the root.Its unique tubular structure and biochemical composition support the more rigid enamel and cementum overlying the surface of the tooth

Cementum, a thin, pale-yellowish layer of bone like calsified tissue covering the dentin of the root of the teeth. Cementum is softer and more permeable than dentin and is easily removed by abrasion when the root surface is exposed to the oral environment

ENAMEL

Enamel is the hardest substance in the body; it is consists of 96 to 98% calcium hydroxyapatite.Enamel is an acellular mineralized tissue that covers the crown of the tooth.Once formed it cannot be replaced.

Enamel is unique tissue because, unlike bone which is formed from connective tissue, it is a mineralized material derived from epithelium.Enamel is more highly mineralized and harder than any other mineralized tissue in the body; it is consist of 96 to 98% calsium hydroxyapatite

Enamel is composed of enamel rods that span the entire thickness of the enamel layer.

Although the enamel of an erupted tooth lacks cells and cell processes, it is not static tissueIt is influenced by the secretion of the salivary glands, which are essential to its maintenance.The substance in saliva that affect teeth include digestive enzymes secreted antibodies and a variety of inorganic (mineral) components

Mature enamel contains very little organic material.Despite its hardness, enamel can be decalcified by acid-producing bacteria acting on food products trapped on the enamel surface

This is the basis of the initiation of dental cariesFluoride added to the hydroxyapatite complex makes the enamel more resistant to acid deminerilization.The widespread use of fluoride in drinking water, toothpaste, pediatric vitamin supplements, and mouthwashes significantly reduces the incidence of dental caries

Enamel is produced by ameloblasts of the enamel organ, and dentin is produced by neural crest derived odontoblasts of the adjancent mesenchyme.The enamel organ is an epithelial formation that derived from ectodermal epithelial cells of the oral cavity

CEMENTUMCementum covers the root of the toothThe root is the part of the tooth that fits into its alveolus, or socket in the maxillla or mandible.Cementum is a thin layer of bonelike material that is secreted by cementocytes, cells that closely resemble osteocytes.

Like bone, cementum is 65 % mineral.The lacunae and canaliculi in the cementum contain the cementocytes and their processes, respectively.They resemble those structures in bone that contain osteocytes and osteocyte processes

Unlike bone, cementum is avascular. Also, the canaliculi in cementum do not form an interconnecting network.A layer of cementoblasts (cells that resemble the osteoblasts of the surface of growing bone) is seen on the outer surface of the cementum, adjancent to the periodontal ligament

DentinDentin is a calcified material that forms most of the tooth substanceDentin lies deep to the enamel and cementum

Dentin is secreted by odontoblasts that form an epithelial layer over the inner surface of the dentin, i.e the surface that is in contact with the pulp

Like ameloblasts, odontoblasts are columnar cells that contain a well-devolep r ER, a large Golgi apparatus and other organelles associated with the synthesis and secretion of other large amounts of protein

Predentin is newly resecreted organic matrix, closest to the cell body of the odontoblast, which has yet to be mineralized

Dentin is produced by odontoblast.Dentin is the first mineralized component of the tooth to be deposited

Dental Pulp and Central Pulp Cavity The dental pulp cavity is a connective tissue compartment bounded by the tooth dentinThe central pulp cavity is the space within a tooth that is occupied by dental pulp, a loose connective tissue that is richly vascularized and supplied by abundant nerves.

Supporting Tissues of the TeethSupporting tissues of the teeth include the alveolar bone of the alveolar processes of the maxilla and mandible, periodontal ligaments and gingiva

The alveolar processes of the maxilla and mandible contain the sockets or alveoli for the roots of the teeth

The gingiva is the part of the mucous membrane commonly called the gums.The gingiva is a specialized part of the oral mucosa located around the neck of the tooth.It is firmly attached to the teeth and to underlying alveolar bony tissue