Oral Histology And Embryology Tooth Development And Their Stages PDF

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Notes on development of teeth. ...

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ORAL HISTOLOGY AND EMBRYOLOGY TOOTH DEVELOPMENT (CHAPTER THREE) 11/3/16 Three main features of this topic: 1. Initiation  Which sites in the oral mucosa you will find teeth 2. Patterning  Includes Bud, Cap and Bell stages  Different types of teeth 3. Morphogenisis  Differentiation  Different shapes  Morpho, Cyto, Histo

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Primary and Permanent Dentitions o Considered Diphyodont o Sharks have teeth replacing teeth replacing teeth (Polyhyodont)

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Epithelium produces the enamel o 96% mineralization o Hardest structure in the body ECTOMESENCHYME = dentin, cementum and alveolar bone Muscles in the head still come from Mesoderm

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PRIMARY DENTITION - 20 teeth - Develops during the prenatal period - Development of a placode over the maxilla and mandible TOOTH DEVELOPMENT - Odontogenisis: tooth development o Continuous process - Stepwise fashion - Primary dentition = 6th 7th week o Embryonic Period - Maturation = mineralization of teeth o Doesn’t occur all at once o Takes time to fully mineralize -

Oral epithelium is the determinant of initiation stage o NOT NCC Bud stage is the first stage where the NCC are the signaling entity o Said to determine the shape of the tooth

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Cap Stage is the invagination of the epithelium Bell Stage starts to pinch off at the bottom o Discrete internal cavity which eventually becomes the pulp cavity PREDENTIN IS FIRST NOT ENAMEL**

INITIATION STAGE - First stage - Requires some sort of cellular signaling among the layers - Involves the physiological process of induction o Interaction between embryological tissue types - Beginning of the 6th week - Stomodeum (4th week) is lined by ectoderm & tooth development begins - Considered an EMT (epi-mensenchymal transition) - Start to get a thickening = initiation o Induced because of low cal overlying the alveolar bone o Thickening = PRIMARY EPITHELIAL BAND - Have a basement membrane between overlying epi and the underlying connective tissue - Signaling beginning between the two layers - First indication = primary epithelial band o Also known as dental arch - As it starts to invaginate  BUD STAGE - With thickened epithelium there is a second invagination - DENTAL LAMINA = first structure following the thickened epithelium (Primary Epithelium Band) - Clinical Issues During this Stage: o Can have missing teeth o Smaller teeth o Commonly genetic issues o Environment plays a role o Mechanisms are unknown o Teratogens o Can have too many teeth - Tooth comes from the Dental Lamina o Too many dental lamina = too many teeth BUD STAGE - 8th Week - Two weeks after initiation - Extensive proliferation of the dental lamina into buds penetrating into the ectomesenchyme - See much larger dental lamina with an end cap on connecting stalk - These cells are still largely undifferentiated - Each arch will have 10 buds! - Missing a number of teeth due to the primary dentition lacking premolars

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Still has a basement membrane Each bud comes from the dental lamina, together with the surrounding ectomesenchyme will eventually develop into a tooth ger - NO CLEAR STRUCTURAL CHANGES YET - Ectomesenchyme produces dentin, cementum and periodontium - Not too much of a morphological change - Clinical Problems in the Bud Stage: o Abnormal Proliferation Issue:  Hypo = small teeth (MICRODONTIA)  Hyper = large teeth (MACRODONTIA) CAP STAGE - 9th and 10th week - Differentiation of cell types appears o Proliferation and differentiation - Start to get a tooth here - Now have a tooth germ - Basement membrane still exists between the enamel organ and the dental papilla and will be the site of the DEJ o Involves:  Enamel Organ (epithelium—produces enamel—future crown))  Dental Papilla (ectomesenchyme—pulp cavity)  Dental Sac (ectomesenchyme—dentin, cementum, alveolar bone) - Enamel Knot = organizer, responsible for tooth shape o Inhibits proliferation and differentiation o Creates cusps o Important for generating tooth morphologies o Transient & Develops o Epithelium folds - Secondary Dental Lamina develops in a palatal or lingual direction - Ectomesenchyme becomes very thick

Enamel organ

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Indention is the Dental Papilla o The shit around it is the dental sac or follicle Stellate reticulum works with trigger pressure

o Collects water - Dental Papilla creates dentin and the pulp cavity o Pulp = connective tissue, nerve from apical foramen, vessels o Eventually produces cells that line up on the Enamel Organ and become Odontoblasts which create DENTIN  Appositional Growth  The Basement Membrane between the Enamel Organ and Dental Papilla with become the DENTINOENAMEL JUNCTION (DEJ) o Trigeminal Nerve is going up into the Pulp - Dental Sac o All around the Enamel Organ o Creates the Cementum, PDL, Alveolar Bone  Osteoblasts, Cementoblasts o This is the primordium of the tooth  Tooth Germ SUMMARY OF CAP STAGE

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The enamel organ may abnormally invaginate into the dental papilla—DENS IN DENTE o Permanent Maxillary Incisors are affected by this o “Tooth within a tooth” o Duplication o Upside down o Thought to be genetic o Dr. P thinks certain teratogens can cause this as well o 0.4-10% GEMINATION - In the cap stage - Tooth starts to divide - Genetic

FUSION - In the cap stage - Two teeth fuse into one BELL STAGE - Really important - See cytodifferentiation - Differentiation on all levels to its furthest extent - Just beyond the cap stage - Internal cells with a lot of space - Cells lining up on the inside and outside of the enamel organ o Inner and Outer Enamel Epithelium  Eventually touch each other and signal the generation of roots

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Dental Papilla = within the enamel structure Dental Sac = all around it o Also called a follicle Stellate Reticulum o Give the tooth structure o Pull water

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Stratum Intermedium o Aid in enamel mineralization Outer cells become odontoblasts and create dentin EMT’s occur o Telling each other to differentiate to become different cells

OUTER ENAMEL EPITHELIUM - Protecting the supporting cells

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The ________ germ layer creates IEE? o Ectoderm STELLATE RETICULUM o Star shaped cells in many layers forming a network o Synthesize GAGs o Water is drawn in between the cells which stretches them apart

o As they move further apart, the stellate reticula maintain contact with each other through cell junctions (DESMOSOMES)  Creates unique start shape appearance STRATUM INTERMEDIUM o Made up of a compressed layer of flat to cuboidal cells o Layer of two or three cells between the enamel epithelium and the newly forming cells of the stellate reticulum  Layered cake o First appears during the early bell stage o ~14th week of prenatal development o Notably high alkaline phosphate activity o This layer along with IEE plays a role in enamel formation -

Both of these two intermediately placed layers of the enamel organ help support the production of enamel

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The dental papilla is undergoing extensive differentiation so that it now consists of two types of tissue in layers: 1. Outer cells of the dental papilla 2. Central cells of the dental papilla

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The outer cells of the dental papilla will differentiate into ODONTOBLASTS in the future The inner cells are the primordium for the PULP

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The outer dental sac/follicle increases the amount of collagen fibers o Undergoes differentiation into its dental tissue during a later time period than the enamel organ and dental papilla o WILL DIFFERENTIATE INTO CEMENTUM, PDL, AND ALVEOLAR BONE

CROWN STAGE (Apposition and Maturation) - Final stages of odontogenesis - Enamel, dentin and cementum are secreted in successive layers o These are initially secreted as a matrix - The final stage, MATURATION, is reached when the dental tissue types subsequently fully mineralize - The time period of Apposition and Maturation varies according to the tooth involved - Mineralize at the top of the crown first o First snow on the mountains - 3-4 months o 12-16 weeks - Involves induction and proliferation - Meloblast and Odontoblast

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Formation of Preameloblasts first o After the formation of the IEE of the bell shaped enamel organ, these innermost cells grow even more columnar or elongate as they differentiate into preameloblasts  During this differentiation, IEE cells undergo REPOLARIZATION

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After that differentiation into preameloblasts, the outer cells of the dental papilla are induced by the perameloblasts to differentiate into ODONTOBLASTS o These line up as well and go through repolarization o Odontoblasts now begin dentinogenesis  Apposition of the dentin matrix or PREDENTIN

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The odontoblasts start their secretory active some time before the enamel matrix production begins The dentin layer is slightly thicker than the corresponding layer of enamel matrix o Due to the earlier beginning

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Has to switch the secretory side with the side that is attached to the basement membrane Basement membrane between the preameloblasts and the odontoblasts disintegrates o Plays a role in the preameloblasts to differentiate into ameloblasts  After they become ameloblasts, they no are no longer mitotic Ameloblasts now begin amelogenesis (apposition of enamel matrix) o Laying it down on their side of the now disintegrating basement membrane o The enamel matrix is secreted from TOMES’ PROCESS  Angled part of each ameloblast as the ameloblasts move away from the dentin interface  THE DEJ IS TECHNICALLY FORMED ONCE ENAMEL SECRETION HAS COMMENCED FROM DR. P’S NOTES:

**SEQUENCE: formation of preameloblasts, then odontoblasts and pre-dentin matrix, which causes the BM to disintegrate, this signals pre-ameloblasts to become ameloblasts and the enamal matrix is secreted and mineralizes, now have DEJ, then dentin mineralizes.

Enamel Dentin

F = terminal bar apparatus (junctional epi)

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Terminal bar apparatuses connect the Tomes' processes. Tonofilaments separate the developing enamel from the enamel organ.

An enamel rod is the basic unit of tooth enamel o Tightly packed, highly organized mass of hydroxyapatite crystals o Found in rows along the tooth o Has cross striations or incremental lines  Thought to be formed by the daily rhythm of the ameloblasts laying down more and less mineralized enamel STRIA OF RETZIUS - Variations in the metabolism of the organism cause variations in the amount of organic materal deposited in the enamel - Causes changes in the coloration of the enamel - Dark = higher organic material - Light = less organic material - These bands are called Stria of Retzius (Perikymata)

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Neonatal line isn’t a line—it is a layer o It would conform with the surface of the mineralized enamel of the tooth o Due to stress at birth Wavy patterned enamel = gnarled enamel 1. Repolarization of the IEE

2. Now have a surface facing out to secret, change the OEE to odontoblasts 3. Then create dentin FIRST SIGN = PREDENTIN MINERAL ENAMEL IS FIRST - Tomes’ process is associated with the enamel matrix o What secretes the enamel matrix - Terminal bars keep the ameloblasts in line with each other o Junctional complexes do this - Enamel structure looks like rods

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DENTIN Primary Dentin o Laid down before the completion of the apical foramen o Two types: mantle and circumpupal o Mantle:  Laid down first  Tends to be visible  Hypomineralized (less mineralized)  Loosely packed collagen fibrils o Circumpulpal:  Most of dentin is this  Surrounds the pulp early in development  Hypermineralized (more mineralized)  Formed before root completion Regular/Secondary Dentin o Formed after the tooth root is formed o A little narrower o Seems like the direction changes o Responsible for the reduction of the pulp chamber over time Tertiary Dentin o Can be regular (reactionary) or irregular (reparative) o First is due to a slow process of repair or stress o Second results from a rapid change o Two types: reactionary and reparative o Reactionary: using existing odontoblasts that have to react to a “breech”  Irregularly arranged and few dentinal tubules o With age and severe damage, this can totally obliterate the pulp cavity o Reparative: fix the whoopses o These two types deal with the insults to teeth Also have incremental lines!

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Lines of von Ebner are similar to the ones in enamel (5um) o Day to day fluctuations o CROSS STRIATIONS OF DENTIN = von Ebner Lines

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Lines of Owen o Contour lines o Intercept the DEJ o Meet up with the accompanying Stria of Retzius that was formed at the same time o Meet because they’re produced at the same time

A = contour lines of Owen B = Stria of Retzius

GLOBULAR DENTIN - Layer of dentin between mantle and circumpulpal - Calcified globules that don’t fuse evenly INTERGLOBULAR DENTIN - Less calcified areas of dentin - Irregular shaped crescents*** Peritubular and Intertubular dentin - Around the tube = peritubular - In the dentin = intertubular dentin

Mantle dentin = first to be laid down Mantle & Circumpulpal make up primary dentin

A =enamel B = DEJ C = Mantle dentin D = Circumpulpal dentin (striations in this layer are from the dentinal tubules that cross through it) E = Predentin

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Enamel tends to be darker—more mineralized

DEVELOPMENTAL DISTURBANCES DURING STAGES OF APPOSITION AND MATURATION - Enamel dysplasia = hyper or hypo mineralized - Certain factors may interfere with the metabolic processes of the ameloblasts & results in enamel dysplasia - Local enamel dysplasia = trauma or infection occurring in a small group of ameloblasts - Systemic enamel dysplasia: involves larger numbers of ameloblasts and may result from traumatic birth, systemic infections, nutritional deficiencies or dental fluorosis ENAMEL HYPOPLASIA - Hutchinson’s incisors & mulberry molars are caused by teratogen syphilis (prenatal) - Results from a reduction in the quantity of enamel matrix - Hutchinson’s teeth has screwdriver shaped incisors - Mulberry molars have enamel tubercles on the occlusal surface - Enamel hypocalcification results in reduction in the enamel quality - Teeth appear more opaque, yellow, or brown o Due to intrinsic staining of enamel o Can have a single affected area or white “sparkle spot” DENTAL FLUOROSIS - Enamel hypoplasia and hypocalcification may occur together and effect entire dentitions - Fluoride substitution - Enamel looks stained - Mostly a cosmetic concern until it becomes brittle - 0.7-1 ppm is the appropriate amount AMELOGENESIS IMPERFECTA - Hereditary etiology - Can affect all teeth of both dentitions - Very thin enamel DENTIN DYSPLASIA - Faulty development of dentin - Interference with the metabolic processes of the odontoblasts during dentinogenesis - More rare than enamel dysplasia - Can be due to local or systemic affects o Can involve either dentin hypoplasia or hypocalcification or both - Tends to be more rare than problems with enamel - Partial lack of coronal pulp chambers and small root canals are common - Problem with the structure of dentin o More liquid or viscous o Matrix is being disrupted, but the mineralization is still occurring

DENTINOGENESIS IMPERFECTA - Hereditary basis - Blue-gray of brown teeth with an opalescent sheen - Lose tubule structure - Lack of support from the abnormal underlying dentin - Lots of Interglobular Dentin

Little Arrow = odontoblasts Medium Arrow = predentin Large Arrow = Dentin

ROOT DEVELOPMENT Primary: laid down during development and eruption o First outermost layer Secondary: dentin follows root formation, often associated with a change in direction, slower and less regular o Around the pulp Tertiary: reaction to a stimulus (cavity or damage), can be: o Reactive = fast kind, reacting to an insult o Reparative = more long term, new cells

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Root development takes place after the crown is completely shaped and the tooth is strating to erupt Cervical Loop: where the IEE and OEE touch o RESPONSIBLE FOR ROOT DEVELOPMENT Cervical loop grows deeper apically into the dental sac (ectomesenchyme) o It elongates and moves away from the newly formed crown area to enclose more of the dental papilla tissue to form HERS (fusion of IEE and OEE—double layer of ectoderm) (IS MAKING THE HERS) HERS: cuboidal cells in a layer touching each other (IEE and OEE) o Signaling the pulp cells to become odontoblasts o Hertwig’s epithelial root sheath ***The sheath or membrane is to shape the root(s) and induce dentin formation in the root area so it is continuous with coronal dentin***

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Cervical loop starts to extend out Stratum intermedium and Stellate Reticulum are taken out of play

- The odontoblasts are going to be signaled to proliferate and become odontoblasts ROOT DENTIN FORMATION - After the differentiation of odontoblasts, these cells undergo dentinogenesis and begin to secrete predentin -

Due to them lacking the intermediate layers (stratum and stellate), HERS induces odontoblastic differentiation but this is not preceeded by enamel-forming ameloblast differentiation (Accounts for the absence of enamel in roots)

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When the root dentin formation is completed… o The basement membrane and HERS disintegrates After this disintegration, the cells become epithelial rests of Malassez (ERM)

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Cell signaling and differential growth of HERS causes the root trunk of the multirooted teeth to divide into two or three roots. KNOW EPITHELIAL DIAPHRAGM CREATED BY HERS (SLIDE 9, TOOTH DEVELOPMENT III) KNOW THE FORKING OF THE DIAPHRAGM = FURCATION

DEVELOPMENT OF CEMENTUM - Cementoblasts are coming from ectomesenchyme o From the sac/follicle o Undergo cementogenesis  Laying down cementum matrix or cementoid  Including collagen - There are different kinds of cementum o Acellular or Primary Cementum  Cervical margin to 2/3 of root  Thin  No cells  More calcified  Forms before the tooth reaches occlusal plane o Cellular Cementum or Secondary  Apical 3rd and inter-radicular region  Forms after the tooth reaches the occlusal plane  Cellular (contains cementocytes)  Thick and irregular  Less calcified -

Cementoblasts can become trapped by the cementum they produce and become mature cementocytes (not everywhere) o Acellular or primary cementum vs. cellular or secondary cementum

Main Types of cementum: location cellularity, fibers or not, origin of fibers

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Dentinocemental Junction (DCJ) is the result of apposition of cementum over the dentin o Interface between dentin and cementum CEJ (cementoenamel junction) is the overlap of enamel and cementum Fibroblasts make the PDL

SUMMARY OF TYPES 1. Acellular, afibrillar cementum = found as coronal cementum; no attachments 2. Acellular, extrinsic cementum = type I collagen. Sharpey’s fibers of PDL (not usually visible); cervical 2/3rds or root; major role in anchorage 3. Cellular, intrinsic fiber cementum = contains cementocytes, not much intrinsic fibers cementum; repair sites no anchorage and may be covered by extrinsic cementum 4. Cellular, mixed fiber cementum = apical third and furcations; Sharpey’s fibers readily identifiable -

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Dentin looks like tubes in cellular images Tome’s Granular layer looks like tubes sticking right out at you o Believed to be caused by coalescing and looping of terminal portion of dentinal tubules Cementum is right on top

DEVELOPMENTAL DISTRUBANCES WITH CEMENTAL FORMATION - Concrescense - Over production (hyperpoliferation of cementoblasts) -...