Compendum OF ORAL Histology AND Embryology_part1 PDF

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COMPENDUM OF ORAL HISTOLOGY AND EMBRYOLOGY INTRODUCTION TO THE TEETH ORAL CAVITY -

Found on the head bounded anteriorly by lips; posteriorly by pharynx, laterally by cheeks, superiorly by palate.

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It has two dental arches: maxillary arch and mandibular teeth  Oral vestibule – bounded by the lips anteriorly, the cheeks internally and the labial or buccal surfaces of the lower and upper teeth at the posterior.  Oral cavity proper – bounded by lingual surfaces of upper and lower teeth anteriorly and laterally hard and soft palate superiorly and sublingual sulcus and the tongue inferiorly

Para – Oral Tissues -

Are structures functionally, associated with the oral cavity. The different para oral structures are: a. Lips b. Cheeks c. Hard and soft palate d. Sublingual sulcus e. Tongue f. Tonsils g. Salivary glands h. Teeth and the supporting structures

** these tissues maybe considered as an organ system because all >contributes to the function of mastication, to speech, articulation and to digestion.

Tongue -

The largest organ in the mouth located in the floor of the cavity.

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There are three parts  Tip (apex)  Body (Corpus)  Base (root)

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The dorsal mucosa covering the anterior part is irregular (unlike the ventral surface which is covered by smooth and thin mucosa) because of the presence of evagination and invaginationsas the lingual papillae which are 4 types:  Filiform papilla – are numerous fine, pointed, cone-shaped or cubshaped structure about 2.5mm long consisting of core of connective tissue  Fungiform papillae are mushroom-shaped or round reddish prominences about 1.5mm long with dome-shaped top and narrow base processing one or more taste buds.  Foliate papillae are narrow mucosal folds bilaterally located along the posterior border of the body about 4 to 8 in number and bear taste buds. These are well-developed at birth and becomes atrophied in matured individual.

 The vallate (circumvallate) papillae are the largest papilla at about 1mm or more the height is 2.5mm or more in width and 8-10 in numbers arranged in v-shape manner Taste Buds -

Are ovoid or barrel –shaped intraepithelial organs for taste perception about 80 microris in height and 40 microns in width. The broad bases are found to touch the basement membrane and the tip is covered by few flat cells of the epithelium surrounding a small opening known as taste pore taste buds contains of two types of cells:  Taste cells – (gustatory cells , neuro-epithelial cells) are slender columnar dark staining cells (hyperchromatic) and elongated nuclei, 4 to 20 in number per bud and possess stiff hair like processes (taste hair) projecting from free surface into the taste pore.  Sustentacular cells – (supporting cells). These are the outer cells arranged like staves of barrel with ovoid or round hypochromatic nuclei.

Muscles of the tongue: movements of the tongue are produced by striated muscles which constitute the main bulk of the tongue. The lingual muscles are: a. Intrinisc (within the tongue and has different directional path) -

Vertical (peripheral edge or lateral margin)

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Transverse (from lingual septum)

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Longitudinal (located above and below the transverse muscles*

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Superior longitudinal (dorsal)

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Inferior Longitudinal (ventral)

b. Extrinsic muscles -

Styloglossus

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Hyoglossus

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Genioglossus

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Palatoglossus

Vascular Supply: the blood supply of the tongue comes from the lingual artery which has the following branches: a. Dorsal Lingual (base of the tongue) b. Sublingual artery (lingual sulcus) c. Deep lingual artery (ventral surface body and tip)

Lymphatic Supply: -

Tongue has plenty of lymphatic supply. The drainage of the apex is received by submental nodes to the submandibular or deep cervical nodes. The lymph from the body of the tongue drains into the submandibular nodes and from the base, lymph flows to the deep cervical nodes

Nerve Supply -

Two nerve supply of the tongue are the lingual nerve which innervates the apex and the body of the tongue and the glossopharyngeal nerve which innervates the base or posterior third of the tongue. The tongue epithelium has three types of nerve endings.

TONSILS

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Are masses of lymphoid tissue with the primary function of producing lymphocytes and has a role in immunization. These are four in number and forms a protective ring of Waldeyer along the buccopharyngeal junction. 1. Two palatine or faucial tonsils – ovoid bilateral structures situated in the pharyngeal folds about 1 by ½ inch. 2. Lingual tonsils – are found at the base of the tongue posterior to the vallate papillae. There are about 35-90 lymphoid units that make up the lingual tonsils. 3. Pharyngeal tonsils (adenoids) located on the median surface of the dorsal wall of the nasopharynx as longitudinal folds about 3 cms. long

Salivary Glands -

There are two groups of salivary glands on the basis of size: A. Major Salivary glands (Extrinsic gland) – Gland which has noncontinuous secretions.  Parotid Gland  Submandibular Gland  Sublingual Gland B. Minor Salivary glands (Intrinsic gland) – glands which discharge their secretions continuously.  Labial gland  Small buccal gland  Palaitne gland

 Anterior and posterior lingual gland  Von Ebner’s gland  Glossopalatine glands

GENERAL CHARACTERISTIC OF DENTAL TISSUES: ENAMEL - the hardest calcified tissue covering the anatomical crowns of teeth (hard yet brittle) DENTIN - the main bulk of the tooth underneath the enamel and cementum PULP – the soft connective tissue found at the center of the tooth. CEMENTUM - the calcified tissue that covers the anatatomical root (softest part of tissue) ALVEOLAR BONE – the part of the maxilla or mandible that forms the alveolar socket where the roots of the teeth are embedded GINGIVA – is a firm oral mucosa around the neck of the teeth PERIODONTAL LIGAMENT – is the fibrous connective tissue found in between the roots of the alveolar bone

FUNCTIONS OF PARA-ORAL TISSUES 1. Ingestion – the engulfing or taking in of foods with the help of the lips and teeth in particular. 2. Mastication – is the process of biting, cutting, crushing and grinding of foods by the teeth with the aid of the lips, cheeks, tongue and palate.

3. Deglutition – the act of swallowing foods that has been processed in the oral cavity.  Biting in centric occlusion  Pressing the tip of the tongue to the lingual of the lower of the anterior teeth and force the mid-dorsum of the tongue to the hard palate  With forceful contraction of mylohyoid muscle, the dorsum of the anterior part of the pushing the bolus of the foods into the esophagus. 4. Taste – dorsum of the tongue possess lingual papillae of various forms. The fungi form and the vallate papillae has taste buds, that react to different basic taste like sweet, sour, bitter, and salty. Soft palate also contains few taste buds. 5. Digestion – physical digestion of foods involve mastication and lubrication. The chemical digestion involves the preliminary digestion of the carbohydrates thru the action of ptyalin the cheeks, tongue, palate, salivary glands are engaged in this function. 6. Speech – the lips, teeth, cheeks, tongue hard and soft palate play a role in speech especially in the pronounciation of consonants.

DEVELOPMENT AND GROWTH OF THE TEETH (ODONTOGENESIS) Stages in the life Cycle of a tooth I.

Growth

 Physiologic Processes -

Initiation

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Proliferation

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Histodifferentiation

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Morphodifferentiation

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Apposition  Morphologic Stage

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Dental lamina

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Bud stage

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Early cap stage

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Advanced cap stage

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Early bell stage

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Advanced bell stage

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Calcification

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Eruption

IV.

Attrition

The life cycle of a tooth is a complex process because it has to undergo 3 developmental processes before it could be in function, instead of the usual on or two processes.

Initiation Stage

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The beginning of the first sign of human tooth development occurs at about the 6th week of embryonic life in an 11 mm embryo. The stomodeum or primitive oral cavity at this time is lined by mucous membrane consisting of epithelium and connective tissue. Dental lamina is the first sign of tooth development.

Bud Stage -

The first bud to form are those of mandibular anterior teeth at about 6th -7th week (17mm embryo) the buds for maxillary anterior teeth form at about 7th and one half week and for deciduous molars at abput 8th week (25mm) long.

Cap Stage -

The epithelial buds will continue to proliferate and expand laterally Histologically, 3 layers of cell will be seen in an early cap –shaped dental organ.  Outer dental epithelium – is the layer of cells (low columnar) that lines the convex portion of the dental organ.  inner dental epithelium – layer of cells (columnar) that lines the concave part of the dental organ  stellate reticulum (enamel pulp) – network of star-shaped cells occupying the central core of dental organ (between the outer and inner dental epithelium) *during advanced cap-stage, another layer of flat cells occurs between the stellate reticulum and the inner dental epithelium known as stratum intermedium.

Enamel Knot (ahern’s knot) – is a condensation of cells at the middle of the enamel which may project towards the underlying dental papilla, so the center of the invagination shows slight bud-like enlargement. Enamel cord – is the vertical extension of the enamel knot, believed to maintain the invaginated part of the cap –shaped dental organ. Enamel navel is an identation of the outer dental epithelium next to enamel cord to indicate the attachement of enamel cord.

Bell Stage -

The dental organ increases in size (by proliferation of the margins) and changes in shape. The cells of the outer dental epithelium become flatten to low cuboidal. The stellate reticulum expands further by increase of intercellular fluid.

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The stratum intermedium become several layers. Some of the cells of inner dental epithelium differentiate into tall columnar cells (ameloblasts) especially those at the growth center, prior to enamel formation.

Dental Papilla -

The invaginated part of the dental organ is occupied by condensation of mesenchymal tissue known as dental papilla. The central part of denta papilla will become the pulp tissue.

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The dental papilla contains numerous cells, some are stellate in shape or fusiform in shape with numerous processes. Those are the primitive fibroblasts and mesenchyme cells.

Membrana Performativa -

The former basement membrane separating the dental papilla from the inner dermal epithelium is the membrane performativa (future dentino-enamal junction)

Histodifferntiation Stage -

This is a stage in tooth growth where the cells of inner dental epithelium differentiates into ameloblats and through the influence of the ameloblats, the formative cells of dentin known as odontoblats are formed from the cells of the periphery of dental papilla.

Morphodifferentiation Stage -

A stage in tooth growth where the form and shape of the crown to be developed is determined by the membrane performativa.

Apposition Stage -

This is a stage in tooth growth where there is deposition of enamel, dentin and cementum.

FUNCTIONS OF DIFFERENT LAYERS OF CELLS IN DENAL ORGAN 1. INNER DENTAL EPITHELIUM - will become tall columnar cells to a height of 40 microns known as ameloblasts. 2. STRATUM INTERMEDIUM - it provides a stimulus for the ameloblasts and helped in the formation of the enamel. 3. STELLA RETICULUM structures are believed to give protective and supportive functions to the inner cells and reserve the space for the developing enamel.

4. OUTER DENTAL EPITHELIUM - serves to transmit nutritional substances from the capillaries of dental sac to the inner cells and structures FUNCTIONS OF DENTAL LAMINA 1. It initiate the development of the whole deciduous dentition 2. It initiates the development of succeeding permanent, by proliferation of bud from enamel organ 3. It initiates the development of permanent molars from the distal extension of dental lamina. Development of the root -

Hertwig’s epithelial root sheath is an epithelial structure that arise from the junction of the outer and inner dental epithelium along the margins of dental organ. It consists only of inner and outer dental epithelium without stratum intermedium and stellate reticulum.

ENAMEL Enamel – is the hard translucent tissue covering the anatomical crowns of the teeth of man and most mammals. It acts as protective covering of the crown dentin and resist the forces of mastication. Physical properties 1. Enamel is the hardest calcified tissue in the human body due to high mineral contents and crystalline arrangement of calcium phosphate 2. Enamel is brittle and inelastic

3. Enamel is translucent. Translucency increases with the increase in the degree of calcification 4. Enamel is permeable in young individuals 5. Color of enamek (comes from color of dentin) ranges from yellowish white to grayish white. 6. Specific gravity is 2.8 Chemical Characteristics a. chemical composition – enamel consists of 96% (may even be up to 98%) inorganic substance and 4% organic substance and water. 90% of the inorganic components (CA3) (PO4)2 b. Reaction to Acid and incinerations – enamel is soluble in acid and only traces will remain, the inorganic substance will be dissolved and only the organic substance will be left.

Structural Characteristics 1. Band of Retzius – brownish lines that mark the growth periods of enamel (the beginning and ending of layers of enamel. It reperesents every primary calcification in enamel. 2. Enamel lamellae – are leaf like structural defects extending from the surface of the enamel towards the interior. 3. Enamel tufts – are narrow ribbon – like structure composed of bundles of poorly calcified rods and interred cementing substance originating from dentino-enamel junction occupying about 1/5 or 1/3 of entire thickness of enamel.

4. Enamel spindles – are club-shaped extensions or projections of the dentinal tubules into the enamel. This is one of the factors that causes the hypersensitivity of the DEJ. 5. Hunter- schreger’s bands – are alternating loght and dark bands originating from dentino-enamel junction towards the surface. 6. Transverse striations – are lines crossing the rods with 4 microns interval, which become more visible when in contact with acid. Clinical Consideration  Age changes in enamel -

There is a continuous wearing away of enamel and later dentin on the incisal occlusal and even proximal areas (flattening of proximal surface) physiologically known as attrition. There is loss of perikymata on the surface of the enamel.

The organic substance of DEJ which favors the spread of decay are: 1. Greater volume of interprismatic substance of DEJ 2. Enamel spindle and dentinal tubules crossing the DEJ 3. Dentinal part of lamella 4. Greater branching of dentinal tubules 5. Persistence of organic substance at DEJ

Amelogenesis -

Is the process of development of enamel consisting of 2 phase:

a. Formative phase – where there is formation of enamel matrix b. Mineralization and maturation phase – where there is primary and secondary calcification of the enamel matrix and transformation of calcium phosphate into crystal forms known as crystallization. Life cycle of ameloblasts 1. Morphologic or morphogenetic stage - before ameloblasts are fully differentiated and produce enamel, they interact with the adjacent mesenchymal cells determining the shape of DEJ and the crown 2. Organizing Stage – the ameloblasts interact with the cells of dental papilla at the periphery which later differentiates into odontoblasts 3. Formative stage – ameloblasts from the enamel matrix 4. Maturative stage - ameloblasts play a role in maturation of formed matrix 5. Protective stage - forms the primary enamel cuticle as the first protective covering of the enamel. 6. Desmolytic stage – there is destruction of the connective tissue along the pathway of eruption....