Oral Biology S1 PDF

Formation of Three Germ Layers Dr Sandeep Gupta Assistant Professor Learning Objectives To understand formation of germ layers To understand development of the human face and oral cavity Overview Early facial development of all vertebrate embryos is similar Many events occur-c...

Formation of Three Germ Layers Dr Sandeep Gupta Assistant Professor Learning Objectives To understand formation of germ layers To understand development of the human face and oral cavity Overview Early facial development of all vertebrate embryos is similar Many events occur-cell migrations, interactions, differential growth, and differentiation Lead to formation of maturing structures progressively Sometimes abnormal developmental alterations may give rise to some common human malformations. Formation of germ layers After fertilization of the ovum, a series of cell divisions gives rise to an egg cell mass known as the morula in mammals major portion of the egg cell mass forms the extraembryonic membranes and other supportive structures, such as the placenta  The inner cell mass embryoblast separates into two layers, the epiblast and hypoblast  Only the epiblast forms the embryo The hypoblast and other cells forming supporting tissues, such as the placenta. Process of formation of 3 germ layer is called as GASTRULATION. Formation of Primitive Streak. Primitive Node.  Epiblast cells divide and move through the primitive streak and replace the hypoblast cells forming endoderm. The cells remaining between epiblast and endoderm forms the middle germ layer, the mesoderm. Cells remaining in the epiblast form the ectoderm, completing formation of the three germ layers. Notocord formation Depression appears in the center of Primitive Knot called as Blastopore. Prenotocordal cells pass cranially in the midline between the ectoderm and endoderm till it reaches the Prochordal plate These cell form a solid cord called as Notochordal process  Importance of Notochord – Position later occupied by the Vertebral column. Part of it persist in the region of each vertebral disc as NUCLEUS PULPOSIS. Provides scaffold for formation of Neural tube.  The Neural Tube formation The Ectoderm overlying Notochord in the midline undergoes Slipper shaped thickening forming Neural Plate in front of Primitive Pit. Formation of Neural Folds. Neural tube formation Neural Crest Cells The neural crest cells are multipotent cells. They give rise to variety of cells like Odontoblasts Melanocytes Ganglia Suprarenal Medulla Parafollicular Cells Of Thyroid Gland Connective tissue, and blood vessels of head and neck region  The enamel organ develops from the ectoderm. The ectomesenchyme consists of neural crest cells and mesodermal cells. The migration of sufficient number of neural crest cells is essential for the normal growth of head region. Development of Pharyngeal Arches The gradual appearance of pharyngeal (branchial) arches contributes to the development of the face and neck. In each arch a skeletal element, artery, muscles supplied by the nerve of that arch is formed. Ectodermal clefts and endodermal pouches thus formed between the arches give rise to various structures. Derivatives of first Pharyngeal arch Also called as mandibular arch Muscles Muscles of mastication Mylohyoid Anterior belly of digastric, Tensor veli Palatini & tensor tympani Cartilages Meckel’s cartilage- Symphysis region of mandible Malleus, Incus , anterior ligament of malleus Sphenomandibular ligament  Nerve Mandibular nerve supplies muscles of mastication Chorda tympani nerve Maxillary artery Derivatives of second Pharyngeal arch Also called as hyoid arch Muscles Muscles of facial expression Posterior belly of digastric Stylohyoid Stapedius  Cartilages Reichert’s cartilage: stapes, stylohyoid ligament, Lesser cornu and upper half of body of hyoid bone Styloid process Facial nerve Stapedial artery Derivatives of Third Pharyngeal arch Muscle: Stylopharyngeus Muscle Cartilage: Greater horn and lower part of body of hyoid bone Blood supply: Common carotid artery and its terminal branches Nerve supply: Glossopharyngeal nerve Derivatives of 4th and 6th Pharyngeal arch Muscle: Crico-thyroid Levator palatine Constrictor of Pharynx Intrinsic muscle of larynx: Cartilage: Laryngeal cartilages Blood supply: Common carotid artery and its terminal branches Nerve supply: (branches of Vagus nerve) Superior Laryngeal: 4th arch Recurrent laryngeal: 6th arch Pharyngeal Pouches and Clefts Thank You development of teeth Dr Sandeep Gupta Oral Pathologist Learning objectives At the end of the lecture student should be able to inform about Role of dental lamina in tooth formation Various stages of tooth development Various changes in the process of calcification and tooth form Overview The tooth is formed from the ectoderm and ectomesenchyme. At 37 days of development, a continuous band of thickened epithelium forms around the mouth in the presumptive upper and lower jaws. are roughly horseshoe-shaped Correspond in position to the future dental arches of the upper and lower jaws  Each band of epithelium, called the primary epithelial band, quickly gives rise to two subdivisions They in-grow into the underlying mesenchyme colonized by neural crest cells. These are the dental lamina The second subdivision forms the vestibular lamina Initiation of tooth development starts with formation of localized thickenings or placodes within the primary epithelial bands  Teeth are formed in relation to the alveolar process. Ten Epithelial thickenings in Dental lamina Enamel organs: Series of 10 local thickenings on dental lamina in each alveolar process. Each placode forms one deciduous tooth. Ectomesenchymal cells accumulate around these outgrowths.  From this point, tooth development proceeds in three stages: the bud, cap, and bell. These terms are descriptive of the morphology of the developing tooth. Stages in formation of tooth Bud stage : Characterized by formation of a tooth bud. The epithelial cells begin to proliferate into the ectomesenchyme of the jaw.  The bud stage is represented by the first epithelial incursion into the ectomesenchyme of the jaw The supporting ectomesenchymal cells are packed closely beneath and around the epithelial bud The epithelial bud continues to proliferate into the ectomesenchyme This increases cellular density increases immediately adjacent to the epithelial outgrowth This process is classically referred to as a condensation of the ectomesenchyme. Bud stage (Initiation) CONDENSATION Bud stage Cap stage : Formation of dental papilla. The enamel organ & dental papilla forms the tooth germ. Formation of ameloblasts. Formation of odontoblasts.  Enamel organ in cap stage shows an unequal rate of proliferation in different parts instead of uniform expansion. This leads to a stage where the enamel organ looks like a cap. The cells of the enamel organ in the convex portion of the cap are cuboidal in shape and form the outer enamel epithelium The cells in the concavity of the cap are columnar in shape and form the inner enamel epithelium.  The cells in the center of the enamel organ (between the outer and the inner enamel epithelium) synthesize glycosaminoglycans That absorb water as it is hydrophilic causing stretching of intercellular bridges This gives them appearance like stars So it is termed as stellate reticulum (star-shaped branch like network) The fluid in stellate reticulum acts as shock absorber and protects enamel forming cells  The cells in the centre of the concavity of the ‘cap’ form a knob-like enlargement projecting towards the underlying dental papilla. This structure is called the primary enamel knot. Enamel knot extends vertically running across the center of the enamel organ - called the enamel cord  Dental Papilla in cap stage Cells of the dental papilla appear more crowded in this stage. The dental papilla also shows signs of becoming more vascular. Dental Sac in cap stage The dental sac appears more condensed and fibrous.  Enamel Organ in bell stage As the enamel organ further invaginate with growth in the margins, it takes the shape of a bell. In this stage, the crown of the tooth gets its final shape (morpho-differentiation) Cells that form the hard tissues of the crown (the ameloblasts that form the enamel and the odontoblasts that form dentin) acquire histo- differentiation. Bell stage:  enamel organ can be identified in this stage as four layers: Inner enamel epithelium Stratum intermedium Stellate reticulum Outer enamel epithelium Some layers of squamous cells seen between the inner enamel epithelium and stellate reticulum are called stratum intermedium.  Stratum intermedium exhibit a high enzyme alkaline phosphatase activity. This layer plays an important role in regulating the formation of enamel. Inner enamel epithelium: A single layer of columnar cells differentiates into tall columnar cells called ameloblasts before the formation of enamel (amelogenesis).  Stellate reticulum- star-shaped They serve to protect the underlying inner enamel epithelial cells. After a layer of dentin is formed, the inner enamel epithelium does not get their nutritional from the dental papilla. The stellate reticulum collapses before the formation of enamel to provide nutrition from the dental follicle  Outer enamel epithelium: The cuboidal cells are connected to the adjacent cells by junctional complexes. It is smooth in the initial stages. As the stellate reticulum collapses before enamel formation, it gets into folds This brings the capillaries present in the dental follicle closer to the just formed ameloblasts.  Dental papilla in bell stage There is formation of acellular zone between enamel organ and dental papilla The peripherally placed undifferentiated ectomesenchymal cells of the dental papilla increase in size before the enamel formation begins. They are initially cuboidal and later become columnar, occupy the acellular zone and differentiate into odontoblasts.  The basement membrane which separates the enamel organ and dental papilla just before dentin formation is called membrana preformativa.  Dental Follicle in bell stage Collagen fibrils occupy the extracellular spaces between the fibroblasts of the dental follicle These collagen fibrils orient themselves circularly around the enamel organ and the dental papillae. These fibers of the dental follicle that later differentiate into periodontal fibers Crown Pattern Determination The other events that occur during the bell stage are: The breaking up of dental lamina Determination of the crown pattern of the tooth (morphodifferentiation) In bell stage, the dental lamina (which joins the enamel organ to the oral ectoderm) is invaded by the surrounding cells of the dental follicle.  Causes separation of the enamel organ from the oral ectoderm. Then clusters of epithelial cells usually degenerate, If the cells persist in this region form the epithelial islands (cell rests of Serres). Sometimes, cysts are formed over the developing tooth by these cell rests, delaying the eruption of the tooth.  Advanced Bell Stage Advanced bell stage is characterized by the beginning of mineralization and root formation.  Mineralization The peripheral ectomesenchymal cells of the dental papilla are differentiated into odontoblasts This occurs under the influence of the inner enamel epithelial cells. The line separating the newly differentiated odontoblasts and the inner enamel epithelium outlines the dentinoenamel junction. (membrana preformativa)  Odontoblasts begin to differentiate and form organic matrix of dentin along the dentinoenamel junction It generally begins in the region of future cusp. This matrix proceeds in pulpal and apical direction and mineralizes later. After the first layer of dentin is formed, the inner enamel epithelial cells elongate and exhibit the reversal of polarity  Turn into functional ameloblasts. These ameloblasts produce an organic matrix of enamel against the newly formed dentin. This organic matrix mineralizes to become the initial layer of enamel. As the enamel formation proceeds from the dentinoenamel junction towards the outer surface, the ameloblasts move away from dentin in coronal and cervical region. Reciprocal Induction An important step in the development of tooth is the terminal differentiation of ameloblasts and odontoblasts They form two principal hard tissues of the tooth: enamel and dentin.(histodifferentiation) Differentiation of odontoblasts - from the ectomesenchymal cells of the dental papilla This is influenced by the cell of inner enamel epithelium  Once the odontoblasts are differentiated - a single layer of dentin matrix is laid down This process stimulate inner enamel epithelial cells to differentiate into functional ameloblasts The differentiation of ameloblasts and odontoblasts is interdependent (reciprocal induction) ROOT FORMATION When dentinoenamel line reaches the future cementoenamel junction, root development begins. From the cervical portion of the enamel organ Hertwig’s epithelial root sheath formation occurs plays an important role in the determination of the shape, length, size and number of roots Also, it initiates radicular dentin formation.  Sheath is a double layer of cells composed only of the inner and outer enamel epithelia. inner enamel epithelial layer of the sheath influence the formation of a layer of odontoblasts from the outermost portion of radicular dental papilla. This layer of odontoblasts lays down the first layer of radicular dentin.  After the first layer of radicular dentin is formed, the cells of the dental follicle/sac proliferate They invade the double layer of sheath, dividing it into epithelial strands. Connective tissue cells of the dental follicle meet the surface of the newly formed radicular dentin. They differentiate into cementoblasts from the cells of the dental follicle, To deposit cementum on the surface of the radicular dentin.  Along with, Cells of the Dental follicle like Fibroblasts differentiate to form the periodontal ligament Osteoblasts differentiate to form the alveolar bone Most of the cells of sheath are removed by invasion by the cells of the dental follicle, some remnants are left behind. These remnants are called cell rests of Malassez They may be found as strands of epithelial cells in the periodontal ligament of erupted teeth May contribute to odontogenic tumors an cysts  Formation of a Single-Rooted Tooth During root development, the plane of the epithelial diaphragm remains fixed, and the lengthening of the root is accompanied by the movement of the crown in an axial direction. With the increase in the length of the root sheath, more root is formed with the formation of the cementum, periodontal ligament and alveolar bone  Formation of a Multi-Rooted Tooth In case of multirooted teeth, tongue-like extensions develop on the horizontal diaphragm due to differential growth of the diaphragm. lower molars show two such extensions The upper molars show three such extensions, The free ends of which grow towards each other and fuse. Thank You Development of tooth Part II Basic and Preventive Sciences Department thu. Oct. 21. 2021 BMC Development of tooth/Oral Biology Learning objectives At the end of the lecture student should be able to Understand and be well versed with various stages tooth formation Know the significance of histophysiology of tooth formation Applied aspects of tooth development Anodontia and Oligodontia Decreased activity of dental lamina Anodontia is the congenital absence of tooth germ of the entire dentition. Absence of single tooth germ or multiple tooth germs is termed oligodontia. Teeth commonly found missing are upper lateral incisors, third molars and lower second premolars. Applied aspects of tooth development Supernumerary Teeth Teeth which are present in addition to the normal number are called supernumerary teeth. This occurs due to hyperactivity of the dental lamina, leading to the initiation of additional tooth buds. The most common supernumerary teeth are the mesiodens (present between two upper central incisors) and paramolars (present by the side of the molars). Applied aspects of tooth development Macrodontia and Microdontia Macrodontia is an abnormally larger tooth and microdontia is an abnormally smaller tooth. This can occur because of abnormal proliferation of the tooth germ at the bud stage and can affect a single tooth or the complete dentition. Applied aspects of tooth development Gemination and Fusion Gemination is division of tooth germ Fusion is the union of the adjacent tooth germs Occur during the cap stage of tooth development. Dens Invaginatus Abnormal invagination of the enamel organ into the dental papilla Can cause an appearance of tooth within the tooth Called dens invaginatus or dens in dente. Applied aspects of tooth development Dens Evaginatus Occurs in bell stage It is cusp-like elevation seen in the occlusal surface of premolars or molars This aberrancy occurs due to the abnormal proliferation of inner enamel epithelium into the stellate reticulum Results in a core of dentin with intervening pulpal tissue covered by enamel. With occlusal wear or fracture of this cusp-like structure, pulp exposure and can occur Applied aspects of tooth development Tetracycline Staining Tetracycline is an antibiotic which has high affinity for calcified tissue. Ingestion of this antibiotic during the mineralization of enamel and dentin can lead to discoloration. This consequent discoloration of enamel and dentin occurring at the time of tooth development is called tetracycline staining. DEVELOPMENT OF A TOOTH: HISTOPHYSIOLOGICAL PROCESS On the basis of the histo-physiological process taking place, the development of a tooth can be studied under the following stages: Initiation Proliferation Histodifferentiation Morphodifferentiation Apposition Initiation Initiation of tooth development depends on the epithelial– ectomesenchymal interaction. The dental lamina formed due to such interaction has the ability to form enamel organs of both the dentitions Lack of initiation results in the absence of a tooth, a condition called anodontia. The tooth commonly absent are the upper lateral incisors, third molars and lower second premolars (missing teeth). Initiation An abnormal initiation can result in the formation of single or multiple supernumerary teeth (Extra teeth). The most common supernumerary teeth are The mesiodens (between two upper central incisors) The Para-molars (by the side of the molars) Similarly, aberration in initiation can result in the tooth developing at abnormal locations (ovary). Proliferation The enamel organ formed due to initiation undergoes proliferation to give the crown of the tooth its final size and shape. Any disturbance in proliferation will have effects on the developed tooth depending on the stage at which the disturbance occurs. Histodifferentiation As the cells continue to proliferate, they undergo Structural, biochemical changes Prepare themselves to carry out their function e.g. deposition of organic matrix (apposition) In this process, the cells may give up some of the properties they possessed earlier, like their ability to proliferate. Seen in the bell stage just before the formation and apposition of the enamel and dentin. Histodifferentiation In the bell stage, Inner enamel epithelium influences the adjacent cells of the dental papilla They differentiate into odontoblasts which form the dentin matrix. This constitutes the histodifferentiation of odontoblasts. Then, the inner enamel epithelial cells are differentiated into the ameloblasts That form the enamel matrix. This process is called as Reciprocal induction. Histodifferentiation When there is vitamin A deficiency, the ameloblasts fail to differentiate properly Their organizing influence on the adjacent cells of dental papilla is disturbed. As a result, odontoblasts fail to differentiate properly The dentin formed by these odontoblasts is known as osteodentin. Morphodifferentiation The morphological form and shape of the tooth are determined The dentinoenamel junction and the dentinocemental junction are characteristic for different teeth and determine the shape of the crown and root They are established before the formation of the hard tissue In accordance with their shape, the formative cells deposit enamel, dentin and cementum, to give the tooth its characteristic form and size. Morphodifferentiation Disturbances occurring during the morphodifferentiation can affect the morphology of the crown or root depending on the stage at which the disturbance occurs. E.g. In the crown - the formation of supernumerary cusp, loss of cusp and peg- shaped teeth. Formation of supernumerary root Dilaceration (abnormal curvature in the root caused due to trauma) Apposition Apposition is the deposition of the matrix of dental hard tissues, characterized by alternate periods of activity and rest. It is this regular and rhythmic appositional growth that gives the tooth its final shape. Apposition involves formation of the organic matrix and its subsequent calcification or mineralization. Hypoplasia is the term used to indicate disturbances involving the matrix formation Apposition Hypocalcification or hypomineralization indicates disturbances involving the calcification or mineralization of the matrix. Various genetic and environmental factors can cause disturbances in the formation of enamel matrix leading to enamel hypoplasia. Thank You  development of face and palate Dr Sandeep Gupta Assistant Professor  Learning objectives At the end of the lecture student should – Know about the germ layers and formation of various components of orofacial structures – Know about the process of development of palate – Know about process of development of tongue Embryo at 4-5 weeks (Lateral view)  Introduction Face is derived from the following structures that lie around the stomodaeum (4th week): 1. Fronto-nasal process 2. 1st Pharyngeal (mandibular) arch of each side: (a) Maxillary process (b) Mandibular process  Formation of mandibular & maxillary processes (4th week) The single fronto-nasal prominence ventral to the forebrain. The paired maxillary prominences develop from the cranial part of first branchial arch. The paired mandibular prominences develop from the caudal part of first branchial arch.  Five facial primordia appear as prominences around the stomodeum: FNP The single frontonasal prominence The paired maxillary prominences The paired mandibular prominences  1 Frontonasal prominence 2 Maxillary prominences 2 Mandibular prominences Stomatodeum  Further development of face Formation of nasal placodes and lens placodes (4th week). Nasal placodes sinks below to form nasal pits (5th week). Elevations of the nasal pits form the medial and lateral nasal processes. Nasal placodes are primordia of the nose and nasal cavities.  Derivatives of Facial Components  Fronto-nasal prominence forms the: Forehead and the bridge of the nose Frontal and nasal bones  Maxillary prominences form the: Upper cheek regions and most of the upper lip Maxilla, zygomatic bone & secondary palate Mandibular prominences fuse and form the: Chin, lower lip, and lower cheek regions Mandible The lateral nasal prominences form the alae of the nose The medial nasal prominences fuse and form the intermaxillary segment Development of Palate The medial nasal swellings enlarge, grow medially and merge with each other in the midline to form the intermaxillary segment. Human embryo: 7 weeks  Intermaxillary Segment Gives rise to the: Philtrum of lip Premaxillary part of the maxilla, that bears the upper 4 incisors and the associated gums. Primary palate (region of hard palate just posterior to the upper incisors).  Palatogenesis Begins at the end of the 5th week. Gets completed by the end of the 12th week. The most critical period for the development of palate is from the end of 6th week to the beginning of 9th week. The palate develops from two primordia: The Primary palate The Secondary palate  The Primary Palate Begins to develop:  Early in the 6th week.  From the deep part of the intermaxillary segment, as median palatine process. Lies behind the premaxillary part of the maxilla. Fuses with the developing secondary palate.  The primary palate represents only a small part lying anterior to the incisive fossa, of the adult hard palate Primary palate Hard palate Secondary palate Soft palate  The Secondary Palate Is the primordia of hard and soft palate posterior to the incisive fossa. Begins to develop:  Early in the 6th week.  From the internal aspect of the maxillary processes, as lateral palatine process.  In the beginning, the lateral palatine processes project inferomedially on each side of the tongue. With the development of the jaws, the tongue moves inferiorly. During 7th & 8th weeks, the lateral palatine processes elongate and ascend to a horizontal position above the tongue. Tongue  Gradually the lateral palatine processes:  Grow medially and fuse in the median plane.  Also fuse with the: Posterior part of the primary palate & The nasal septum  Fusion with the nasal septum begins anteriorly during 9th week, extends posteriorly and is completed by 12th week. Bone develops in the anterior part to form the hard palate. The posterior part develops as muscular soft palate Embryological subdivisions of the palate Development of Tongue  Formation of tongue 1st,2nd, 3rd, 4th pharyngeal arches Median swelling-tuberculum impar Two lateral swellings –lingual Caudal medial swelling-hypobrachial eminence  Anterior 2/3 of the tongue Formation: median and lateral tongue buds that arise from the floor of the 1st pharyngeal arch and then grow rostrally. thus it is formed by fusion of -- tuberculum impar, two lingual swellings The tongue buds are then invaded by occipital myoblasts that form the intrinsic muscles of the tongue.  Thus anterior 2/3rd of tongue is supplied by lingual branch of mandibular nerve and chorda tympani nerve Posterior 1/3rd of tongue is supplied by glossopharyngeal nerve (nerve of 3rd arch) Most posterior 1/3rd of tongue is supplied by superior laryngeal nerve (nerve of 4th arch)  Musculature of tongue is derived from occipital myotomes--explains nerve supply by hypoglossal nerve, nerve of these myotomes.  Posterior 1/3rd of tongue Formed from cranial part of hypobranchial eminence ( copula) The second arch mesoderm gets buried below the surface. The third arch mesoderm grows over it to fuse with mesoderm of first arch. posterior one third of tongue thus formed by third arch mesoderm. posterior most part of tongue is derived from fourth arch  Thus swellings from the floor of the 3rd and 4th pharyngeal arches overgrow the 2nd arch and fuse with the anterior 2/3 of the tongue. Posterior 1/3 of the tongue is derived from the 3rd and 4th arches Intrinsic musculature is also derived from occipital myoblasts. The line of fusion of the anterior 2/3 and posterior 1/3 of the tongue is indicated by the terminal sulcus. Thank You ENAMEL Dr Sandeep Gupta  CONTENTS INTRODUCTION PHYSICAL PROPERTIES CHEMICAL PROPERTIES AMELOGENESIS ENAMEL Enamel is the hard, vitreous like substance that covers the outer regions on the tooth crown. It is the cap that covers and protects the underlying tissues.  INTRODUCTION Protective covering - variable thickness over crown. Enamel starts to form when embryo is 18 weeks.  Enamel-ectodermal origin  PHYSICAL PROPERTIES STRUCTURE OF THICKNESS COLOR HARDNESS MATRIX MODULUS OF STRENGTH RESISTANCE SPECIFIC GRAVITY ELASTICTY REFRACTIVE PERMEABILITY INDEX  PHYSICAL PROPERTIES  Hardest calcified tissue in human body -high content of mineral salts & crystalline arrangement.  Extremely hard-- enables to withstand the mechanical forces applied during tooth functioning.  PHYSICAL PROPERTIES 4% 96%  PHYSICAL PROPERTIES- Thickness  Maximum thickness of over cusps/ incisal edge, thinning to knife edge at neck of tooth/ pit / groove area.  0 to 2 mm (incisors)/ 2.6 mm (molars)  PHYSICAL PROPERTIES- colour n translucency enamel is usually translucent, Underlying Dentin is yellow Color-ranges from yellowish white to greyish white Greyish teeth more opaque enamel. Yellowish teeth- thin, translucent enamel- yellow color of dentin visible  PHYSICAL PROPERTIES- colour n translucency  Cervical areas- thin enamel-reflects yellow color of dentin.  Incisal areas -bluish tinge thin edge of double layer of enamel  Hardness-350-500 Tooth enamel ranks 5 on mohs hardness scale and a KHN young’s modulus of 83 Gpa Compressive strength 50x103 psi/ 350 MPa Strength Shear strength 13x103 psi/ 90 MPa Tensile strength 1.5x103 psi/ 10 Mpa(low) Abrasion resistance high. Modulus of Elasticty -high, 19x106 psi/ 130 GPa Abrasion resistance high. Enamel of Deciduous teeth 2.95 Specific gravity Enamel of Permanent teeth 2.97 Permeability complete or partial 1.655 (in comparison Porcelain is 1.5 and Quartz is Refractive index 1.54) CHEMICAL PROPERTIES CHEMICAL CONTENT INORGANIC ORGANIC 96% 4% (INCLUDES WATER,related to porosity & transport of fluoride ions) INORGANIC CONSTITUENTS ORGANIC CONSTITUENTS Major– Calcium Enamel & Non enamel Hydroxyapatite Proteins- proteins Minor– fluoride & zinc are carbohydrates(80-95% other trace- silver, sugars & 5-20% amino aluminum, barium, acids). copper, nickel, selenium, titanium, Lipid content (approx vanadium& lead. 1%)   Hydroxyapatite crystals-hexagonal in cross section. Molecular arrangement within each unit cell of crystallite-hydroxyl group surrounded by 3 uniformly spaced calcium ions which in turn are surrounded by 3 similarly spaced phosphate ions. 6 calcium ions in a uniform hexagon enclose phosphate ions.  Fluoride in hydroxyl position of hydroxyapatite Calcium hydroxyapatite  AMELOGENESIS ‘Amelogenesis is the formation of enamel on teeth and begins when the crown is forming during the advanced bell stage of tooth development after dentinogenesis, forms a first layer of dentine’  ENAMEL PROTEINS The organic matrix of enamel is made up of noncollagenous proteins only and contains several enamel proteins and enzymes. AMELOGENINS NONAMELOGENINS 90% ARE HETEROGENEOUS GROUP OF LOW MOLECULAR 10% ARE– ENAMELIN , AMELIN WEIGHT PROTEINS OR SHEATHLIN, TUFTELIN  AMELOGENINS Enamel proteins Physical Properties characteristics Amelogenins Major secretory Accumulates during forms– 25kDa, 23kDa, secretory stage N-terminal domain is Undergo major short tyrosine rich. term and long term Central part is leucine degradation rich. Regulate growth & thickness NONAMELOGENINS Ameloblastin (amelin or sheathlin) Enamelin Sulfated glycoprotein Tuftelin BUD STAGE H & E– 10 X CAP STAGE H & E– 10 X EARLY BELL STAGE H & E– 10 X  ADVANCED BELL STAGE DECALCIFIED SECTION, H & E– 10 X  Development Of Enamel EPITHELIAL ENAMEL ORGAN-Originates from the stratified squamous epithelium of the primitive oral cavity.  AMELOGENESIS ‘Amelogenesis is the formation of enamel on teeth and begins when the crown is forming during the advanced bell stage of tooth development after dentinogenesis, forms a first layer of dentine’  AMELOGENESIS Enamel formation occurs in 2 phases SECRETORY PHASE MATURATIVE PHASE ENAMEL PROTEINS SECRETION AND FORM MATRIX VESICLES PROVIDE CLOSED ORGANIC MATRIX ENVIRONMENT TO INITIATE CRYSTAL FORMATION IN PREFORMED ORGANIC MATRIX.  MATRIX PROTIENS CONTINUES TO BE SECRETED BY AMELOBLASTS-UNTIL ENTIRE THICKNESS OF ENAMEL LAID. Enamel crystallite formed-grow rapidly in length within organic matrix  PROTEASES SECRETED BY DEGRADE & HARDEST ENAMEL AMELOBLASTS REMOVE FIRST-SOFT/ MODERATELY ENAMEL HARD ENAMEL PROTEINS/ AMELOGENIN SECRETORY PHASE MATURATIVE PHASE 30%, MINERALISED INFLUX OF ADDITIONAL ENAMEL MINERAL TO ATTAIN 96% PROTEIN-66% PROTEIN-4% WATER-5% WATER-1% LIFE CYCLE OF AMELOBLASTS According to function ,life span of cells of inner enamel epithelium – divided into 6 stages 1. Morphogenic 2. 6. Desmolytic Organizing/ Differential AMELOBLAST LIFE CYCLE 3. 5. Protective Formative/ Secretory 4. Maturative 1. MORPHOGENIC STAGE P Early bell stage. IEE Low cuboidal cells Resting on basement membrane; separating it from dental papilla. D PROXIMAL-ADJACENT TO STRATUM INTERMEDIUM DISTAL-ADJACENT TO ENAMEL MORPHOGENIC STAGE P Cells are short & columnar,with large oval nuclei (almost fill cell). Golgi apparatus & centrioles located in proximal end of cell. D Mitochondria evenly distributed throughout cytoplasm.  2. Organizing/ inductive stage Late bell stage Ameloblasts Elongated up to 40 microns. Resting on basement membrane; separating it from newly formed odontoblasts.  Shift proximally towards NUCLEI stratum intermedium Cluster in proximal region,few MITOCHONDRIA scattered. Increased in number. rER Increases its volume & migrate Golgi complex towards central core of cytoplasm. Ameloblasts become reversely polarised with majority organelles in cell body distal to nucleus.  SECRETORY STAGE Basal lamina supporting ameloblasts disintegrates after deposition of predentin.  SECRETORY STAGE Development of junctional complexes Proximal Terminal Web Distal Terminal Web  SECRETORY STAGE Synthesis of enamel proteins & secretion STARTING OF AMELOGENESIS Structureless layer of enamel deposited  Ameloblasts migrate away from dentin surface permitting formation of Tomes’ Process Tomes’ Process Contains secretory granules and small vesicles Secretion of enamel confined to 2 sites FIRST SITE Adjacent to proximal part of process Around the periphery of cell SECOND SITE One surface of Tomes’ process. Later fills pit with matrix. SECRETORY STAGE Wall being formed Pits enclosing the by first site Tomes’s process Maturative Stage MATURATIVE STAGE Enamel maturation -occurs after most of thickness of enamel matrix formed in occlusal /incisal region (cervical –enamel matrix formation still progressing). Two third of amelogenesis time is occupied by maturation stage Maturative Stage Cyclic Process There is modulation of cells, the cyclic creation, loss and recreation of ‘ruffle ended’ and ‘smooth ended ameloblasts’. Maturative Stage- Cyclic Process Ruffle ended Smooth ended Proximal Proximal junctions junctions (Leaky ) (Tight) Distal Distal junctions junctions (Tight) (Leaky) Induction of inorganic material Removal of proteins & water PROTECTIVE STAGE When enamel completely developed & fully calcified-ameloblasts cease to be arranged in a well defined layer PROTECTIVE STAGE These cell layers –form stratified epithelial covering of enamel –called REDUCED ENAMEL EPITHELIUM. Function of REE –protecting mature enamel by separating it from C.T until tooth erupts. DESMOLYTIC STAGE REE proliferates & seems to induce atrophy of CT separating it from oral epithelium – fusion of two epithelia can occur. DESMOLYTIC STAGE Epithelial cells elaborate enzymes  destroy CT fibres by desmolysis. DESMOLYTIC STAGE Premature degeneration of REE may prevent eruption of tooth. THANK YOU enamel- structure age changes clinical considerations Dr Sandeep Gupta Assistant Professor  CONTENTS STRUCTURE AGE CHANGES CLINICAL CONSIDERATIONS STRUCTURES SEEN IN ENAMEL Enamel Rods Hunter Schreger Bands Incremental Lines of Retzius Perikymata Enamel cuticle SURFACE STRUCTURES Enamel cracks Enamel Lamellae Neonatal Lines Enamel Spindles Gnarled Enamel Enamel Tufts Dentinoenamel Junction Odontoblastic Processes  ENAMEL Enamel rods RODS Enamel rods are the fundamental structural unit of enamel; each rod is extending from its site of origin at the dentino-enamel junction (DEJ) to the outer surface of enamel  The inter rod region surrounds each rod and its crystals are ENAMEL oriented in a direction different from those making up the RODS rod. Rods (prisms, R) and interrod enamel. (interprismatic substance, IR)  ENAMEL RODS The boundary between rod and inter rod enamel is delineated by a narrow space containing organic material known as ‘rod sheath’.  ENAMEL RODS Enamel rods-clear crystalline structure- permitting light. Cross section under light microscope- appear hexagonal/round/oval resemble fish scales. Keyhole Or Paddle Shaped Prism In Enamel.  ENAMEL RODS In transverse section, the enamel rods have a keyhole shape A HEAD formed by the rod -commonly directed towards the incisal or occlusal aspect A TAIL formed by interrod- directed towards the cervical region of the teeth  Key hole pattern of enamel rods ENAMEL RODS formed by four each rod ameloblasts 1 contributes 3 2 to four each different rods ameloblast 4  ENAMEL RODS Enamel is built from closely packed and long ribbon like crystals- Apatite crystals Length-0.05 – 1 micrometer Avg. thickness-30 nanometer Width-90 micrometer  ENAMEL RODS Calcium phosphate unit cell has a hexagonal symmetry and gives hexagonal outline to crystal.  ENAMEL RODS Enamel rods- from DEJ to enamel run tortuous course. Oblique direction & wavy course of rods-length of rods greater than thickness of enamel. Rods in cusp region are longer than in cervical region.  STRIATIONS STRIATIONS Each enamel rod built of segments separated by dark lines- gives it striated appearance Segments- 4 micrometer G.S CROSS STRIATIONS OF RODS  DIRECTION OF RODS Right angles to dentin surface. Deciduous-cervical & central part approx. horizontal,cusp & incisal region increasingly oblique-almost vertical in cusp. Permanent-similar in occlusal third,in cervical-deviate from horizontal in apical direction.  GNARLED GNARLED ENAMEL ENAMEL If the disks are cut in an oblique plane, especially near the dentin ; in the region of the cusps or incisal edges, the rod arrangement appears to be complicated—the bundles of rods seem to intertwine more irregularly. This optical appearance of enamel is called gnarled enamel G.S 40 X  GNARLED ENAMEL CLINICAL SIGNIFICANCE- The irregular twist intertwining may be associated with increased strength of enamel enabling it to withstand strong masticatory forces.  HUNTER SCHREGER BANDS Originate at DE border & pass outward ending at some distance from outer enamel surface. Alternate zones of slightly different permeability & different content of organic material.  HUNTER SCHREGER BANDS  INCREMENTAL LINES / STRIAE INCREMENTAL LINES / STRIAE OF RETZIUS OF RETZIUS These are the incremental growth lines in enamel representing the rhythmic deposition of enamel. STRIAE OF RETZIUS In a longitudinal sections of the tooth they are seen as a series of dark lines extending from dentinoenamel junction toward the tooth surface.  INCREMENTAL The evenly spaced striae of Retzius LINES / STRIAE OF RETZIUS represent a 6–11 day rhythm in enamel formation while other Retzius lines are suggested to be due to stress. It is estimated that about 25–30 striae do not reach the surface. A. Stria of Retzius B. Dentino-enamel junction  INCREMENTAL NEONATAL LINE LINES / STRIAE OF RETZIUS Enamel of deciduous teeth develop partly before and partly after birth boundary between two portions marked by accentuated incremental line of retzius-NEONATAL LINE/RING. Result of abrupt change in environment and nutrition of newborn. prenatal enamel postnatal enamel DENTINOENAMEL JUNCTION Structurally unique interphase uniting two mineralized tissues with very different matrix composition and physical properties. Into shallow depressions of dentin fit rounded projections of enamel In sections DEJ appears as scalloped line- convexities of the scallops directed towards dentin. STRUCTURES SEEN IN ENAMEL Enamel Rods Hunter Schreger Bands Incremental Lines of Retzius Neonatal Lines Perikymata Enamel cuticle SURFACE STRUCTURES Enamel cracks Enamel Lamellae Enamel Spindles Enamel Tufts Gnarled Enamel Dentinoenamel Junction SURFACE STRUCTURES Relatively structureless layer of enamel approx 30 micrometer thick. No prism outlines visible Apatite crystals parallel to one another & perpendicular to striae of retzius. Heavily mineralised than bulk of enamel beneath it. PERIKYMATA Also called IMBRICATION LINES. Transverse wave like grooves, external manifestations of striae of retzius. ENAMEL CUTICLE Delicate NASMYTH’S MEMBRANE – covers newly erupted crown removed by mastication.  ENAMEL CUTICLE Erupted enamel – covered by pellicle-precipitate of salivary proteins. Reforms within hours after enamel surface is mechanically cleaned. ENAMEL LAMELLAE Enamel lamellae are thin, leaf like structures that extend from enamel surface toward the dentinoenamel junction. They may extend to and sometimes penetrate into dentin. Hypomineralised G.S 40 X  ENAMEL LAMELLAE Type A- Type B- Type C poorly calcified lamellae cracks filled with rod segments. consisting of organic restricted to degenerated matter(from enamel cells. saliva). may reach UPto reach into dentin dentin CRACKS Narrow, fissure like structures In ground sections caused by grinding of the specimen. cracks (contain saliva & oral debris). Extend to varying distances along surface at right angles to DEJ(from which they originate). ENAMEL TUFTS Is a narrow,ribbonlike structure, Arise at DEJ & reach into enamel to about 1/3 or 1/5 of its thickness. Appear as tufts of grass in G.S Extend in direction of long axis of crown. ENAMEL TUFTS  ENAMEL SPINDLES ENAMEL SPINDLES The slender projections OF underlying odontoblasts that traverse the dentinoenamel junction are called enamel spindles.  ENAMEL SPINDLES These hair like processes, thickened at end In G.S of dried teeth – organic content of spindles disintegrates – replaced by air-spaces appear dark in transmitted light.  AGE CHANGES ATTRITION/WEAR OF OCCL/PROXIMAL CONTACT POINTS PERIKYMATA DISAPPEAR COMPLETELY COLOR- DARKER RESISTANCE TO DECAY REDUCED PERMEABILITY  AGE Attrition/wear of occl/proximal contact points –result CHANGES of mastication. Wear facets are increasingly pronounced in older people.  AGE CHANGES Generalised loss of rod ends & slow flattening of perikymata- Finally –perikymata disappear completely  AGE CHANGES CHANGE IN PERMEABILITY OF OLDER TEETH TO FLUIDS increase in the size of the crystal. Decreases the pores between them causing a reduction in permeability CLINICAL CONSIDERATIONS CLINICAL CONSIDERATIONS POSTDEVELOPMENT CAVITY PREPARATION & CARIES OF THE ENAMEL STRUCTURE LOSS CARIES ENAMEL STRUCTURES ACID ETCHING OF PREDISPOSE TEETH TO ENAMEL CARIES POSTDEVELOPMENTAL LOSS OF TOOTH STRUCTURE TOOTH WEAR- ATTRITION is the loss of tooth structure caused by tooth to-tooth contact during occlusion and mastication. Some degree of attrition is physiologic.  ABRASION - loss of tooth structure caused by a mechanical process.  variety of patterns- depending on the cause. EROSION - loss of tooth structure caused by a chemical process. The acidic source - foods or drinks, vitamin C, swimming pools with poorly monitored pH. voluntary regurgitation (e.g.. psychologic problems, bulimia, occupations CARIES OF THE ENAMEL Smooth Surface Caries Pit & fissure caries Deep enamel fissures predispose teeth to carie CLINICAL CONSIDERATIONS IN CAVITY PREPARATION Course of enamel rods –importance in cavity preparation. Cavity prep-no unsupported enamel rods –to be left-at cavity margins- break & produce leakage-bacteria lodge-secondary caries. ENAMEL STRUCTURES PREDISPOSE TEETH TO CARIES Deep enamel fissures Dental lamellae  ENAMEL- pit fissure sealants coating the susceptible areas of the enamel with the so-called pit fissure sealants  more recently developed techniques in operative dentistry consists of the use of composite resins. These materials can be mechanically “bonded” directly to the enamel surface. THANK YOU Growth and development of Maxilla and Mandible Dr. Sandeep Gupta Learning objectives At the end o the lecture one should be able to know: Embryological development of both the jaws Process of growth of maxilla and mandible Age changes in mandible Growth and Development of Jaw Both the jaws develop from the tissues of first branchial arch Mandible forming within mandibular process Maxilla forming within maxillary process  Development of the maxilla It includes development of: 1. Maxilla proper 2. Premaxilla 3. Accessory cartilages 1. Maxilla proper It develops in the mesenchyme of the maxillary process of the mandibular arch as intramembranous ossification. It has one center of ossification which appears in a band of fibrous tissue immediately lateral to and slightly below the eye bulges  The ossified tissue appears as a thin strip of bone. It spread in different directions as: Backward: Below the orbit toward the developing zygomatic bone. Forward: Toward the future incisor region Upward: To form the frontal process of the maxilla. downward: To form the outer alveolar plate for the maxillary tooth germs  Toward the midline: Ossification spreads with the development of the palatal process towards midline. This pattern of bone deposition forms a bony trough that carries infraorbital nerve From this trough a downward extension forms the lateral alveolar process 2. Premaxilla Two centers of ossification for the premaxilla Palato-facial center The prevomerine center ( paraseptal center )  The palato-facial center: Appear at the end of 6 week intrauterine It starts close to the external surface of the nasal capsule above the germ of the lateral deciduous incisor. From this center bone formation spreads: Above the teeth germ of the incisors. Then downward behind them. To form the inner wall of their alveoli & palatal part of the premaxilla.  The prevomerine center ( paraseptal center ): It begins at about 8-9 weeks of intrauterine life along the outer alveolar wall. It is situated beneath the anterior part of the vomer bone it forms that part of the bone which lies mesial to the nasal paraseptal cartilage. At 8 week of Intrauterine life union occurs between the maxilla and premaxilla  ACCESSORY CARTILAGES Accessory cartilaginous center appears in the region of the future zygomatic process and this undergoes rapid ossification Also small areas of secondary cartilaginous center appears along the growing margin of the alveolar plate. In the midline of the developing hard palate between the two palatine processes. GROWTH OF THE MAXILLA Sutural growth Alveolar process development Subperiosteal bone formation Enlargement of maxillary sinus Bone resorption and bone deposition  Sutural Growth It continues till 10 years of age then becomes less significant. The maxilla articulates with the other bones of the skull by 4 main sutures: a) Fronto-maxillary suture. b) Zygomatico-maxillary suture. c) Zygomaticotemporal suture. d) Pterygopalatine suture  All these sutures are parallel to each other They are directed from upward anteriorly to downward posteriorly. So growth at these sutures will shift the maxilla forward and downward.  Alveolar process development It will add to the height of the maxilla. Eruption of teeth specially the permanent set that serves much in this direction Eruption of the upper permanent molars adds to the length of the arch.  Subperiosteal bone formation Occurs throughout life serves as a main factor for the growth of the maxilla  Enlargement of the maxillary sinus It plays an important role in the growth of the body of the maxilla. The sinus, which occupies most of the body of the maxilla, expands by bone resorption on the sinus side and bone deposition on the facial surface of the maxillary process. A process known as pneumatization.  Bone resorption and bone deposition Occurs also in other sites than the sinus. Bone resorbtion at the floor of the nasal cavity Bone deposition on the oral surface of the palate Aids in the enlargement of the nasal cavity and increase the height of the maxilla  DEVELOPMENT OF THE MANDIBLE The Mandible Is the largest and strongest bone of the face, serves for the reception of the lower teeth. It consists of a curved, horizontal portion, the body, and two perpendicular portions, the rami, Unite with the ends of the body nearly at right angles.  Development of the mandible will be divided into: Body of the mandible. The rami The alveolar process  THE BODY OF THE MANDIBLE The mandible is ossified in the fibrous membrane covering the outer surfaces of Meckel's cartilages. These cartilages form the cartilaginous bar of the mandibular arch and are two in number, a right and a left.  Meckel’s cartilage has a close relationship to the mandibular nerve at the junction between proximal and middle third Here the mandibular nerve divides into the lingual and inferior alveolar nerve. The lingual nerve passes forward, on the medial side of the cartilage, The inferior dental nerve lies lateral to its upper margins Then runs forward parallel to it and terminates by dividing into the mental and incisive branches.  From the proximal end of each cartilage the Malleus and Incus, two of the bones of the middle ear, are developed The Ossification takes place in the membrane covering the outer surface of Meckel's cartilage at 6th week Each half of the bone is formed from a single center that appears in the region of the bifurcation of the mental and incisive branches From this initial ossification, the ramifying bones developed forward, backward and upward, to form the symphysis and the mandibular body respectively  At the same stage the notch containing the incisive nerve extends ventrally around the mental nerve to form the mental foramen. A similar spread of ossification in the backward direction produces a trough of bone in which lies the inferior dental nerve and much later the mandibular canal is formed.  THE RAMUS OF THE MANDIBLE The ramus of the mandible develops by a rapid spread of ossification backwards into the mesenchyme of the first branchial arch diverging away from Meckel’s cartilage. This point of divergence is marked by the mandibular foramen.  Somewhat later, accessory nuclei of cartilage make their appearance as A wedge-shaped nucleus in the condyloid process and extending downward through the ramus. A small strip along the anterior border of the coronoid process. Condylar cartilage (appears in the 12th ): Carrot shaped cartilage appears in the region of the condyle and occupies most of the developing rami. Forms condyle head and neck of the mandible. Forms posterior half of the ramus to the level of inferior dental foramen  The coronoid cartilage: It is relatively transient growth cartilage center ( 4th. - 6th. MIU). it gives rise to: Coronoid process. The anterior half of the ramus to the level of inferior dental foramen  The alveolar process It starts when the deciduous tooth germs reach the early bell stage. The bone of the mandible begins to grow on each side of the tooth germ. By this growth the tooth germs come to be in a trough or groove of bone, which also includes the alveolar nerves and blood vessels.  Later on, septa of bone between the adjacent tooth germs develop to keep each tooth separate in its bony crept. The mandibular canal is separated from the bony crypts by a horizontal plate of bone. The alveolar processes grow at a rapid rate during the periods of tooth eruption. GROWTH OF THE MANDIBLE This process occurs with: Growth by secondary Cartilage. Growth with the alveolar process Subperiosteal bone apposition and bone resorption  Growth by secondary Cartilage It occurs mainly by secondary cartilages (mainly condylar cartilage), this helps in: Increase in height of the mandibular ramus Increase in the overall length of the mandible Increase of the inter condylar distance dentin Dr Sandeep Gupta Oral Pathologist  INTRODUCTION Dentin is hard tissue portion Bulk of tooth Protects pulp Supports enamel 2  DENTIN PULP COMPLEX? RELATED Embryologically Histologically Functionally  Types of dentin Coronal dentin Radicular dentin Primary dentin Secondary dentin Tertiary dentin  Primary dentin Mantle dentin Circumpulpal dentin Tertiary dentin Reactionary dentin Reparative dentin Osteodentin  Sclerotic dentin Intratubular dentin Intertubular dentin Interglobular dentin Predentin  Dentinogenesis Primary dentin can be of two types Mantle dentin – occupies the peripheral area where the basement membrane was earlier present Circumpulpal dentin – remaining larger segment of dentin  Odontoblast differentiation Important in understanding formation of normal dentin and reparative dentin too  Mantle dentin formation Odontoblasts differentiate from ectomesenchymal cells ↓ Secrete organic matrix collagen (type III) into preexisting ground substance of dental papilla ↓ The collagen fibrils are of large diameter (0.1-0.2μm called von Korff’s fibres) ↓ These intermingle with the aperiodic fibrils (type VII collagen ) dangling from the basal lamina and are aligned at right angles to the basal lamina  Organic matrix of mantle dentin thus contains these large diameter collagen fibrils along with the ground substance ↓ Also the odontoblast gives out short stubby processes, one of which may penetrate the basal lamina – enamel spindles ↓ The odontoblast also bud off a number of small membrane bound vesicles called matrix vesicles  Odontoblast retreat backwards towards the pulp ↓ short stubby processes of the odontoblast becomes accentuated and forms the principal extension of the cell called odontoblastic process ↓ Matrix vesicles lie between the collagen fibrils ↓ Matrix vesicles contain calcium and phosphate ions, alkaline phosphatase enzyme and calcium binding lipids ↓ This permits formation of hydroxyapatite crystals within the matrix vesicles  Once crystals are formed in the matrix vesicle, membrane around the vesicle disappears ↓ The crystals grow and more crystals form around them ↓ Islands of calcifications are formed that fuse ↓ Collagen fibrils are obscured ↓ Deposition of mineral lags behind the organic matrix formation ↓ There is always a layer of unmineralised matrix called predentin between the odontoblast and the mineralising front Circumpulpal dentin formation Intercellular space between the odontoblast is obliterated - the organic matrix has no contribution from the subodontoblastic layer Collagen fibrils are smaller, type I & closely packed and interwoven with each other and aligned at right angles to the odontoblastic process No matrix vesicles. Mineralisation involves heterogenous nucleation  Control of mineralisation Mineral deposition In matrix vesicles At the mineralization front Calcium channels Alkaline phosphatase activity Calcium ATPase activity  Pattern of mineralization 2 types – depending on rate of dentin formation Globular – best seen in mantle dentin Linear – when rate of formation is slow Both types – circumpulpal dentin  Formation of root dentin Differentiation of odontoblasts is initiated by epithelial cells of HERS Radicular dentin is structurally and compositionally different from coronal dentin  Initial collagen fibres are deposited parallel to the CDJ in contrast to mantle dentin formation (Initial collagen fibres are deposited perpendicular to the DEJ) Radicular odontoblasts differ from those of the crown in that they develop fine branches which loop. This forms the Tomes granular layer  Large number of interglobular areas and incorporation of some epithelial remnants into peripheral dentin – due to difference in the origin of IEE cells and also breakdown of HERS Radicular dentin forms at a slower rate Initial calcospherites are smaller  Physical properties Color: Light yellowish Becomes darker with age  Hardness: Harder than bone and cementum Softer than enamel – more radiolucent than enamel Harder in the central part than near the pulp or on its periphery Dentin of primary teeth slightly harder than that of permanent teeth Viscoelastic and subject to slight deformation  Strength: Organic matrix and tubular architecture – greater compressive strength, tensile and flexural strength than enamel Permeability: Depends on size and patency of tubules which will decline with age  Chemical composition Inorganic content: 70% Hydroxyapatite crystals – plate shaped and smaller than enamel Phosphates, Carbonates, sulfates, Fluoride Organic content: 20% Collagen type I, III, V – not arranged in bundles Lipids Non collagenous proteins Water: 10% NON COLLAGENOUS PROTEINS- Includes-  Amelogenins  Dentin Phosphoprotein/Phosphoryn(DPP)  Dentin Sialoprotein(DSP)  Dentin Glycoprotein(DGP)  Mantle dentin First formed mineralised 16 dentin Outermost part of primary dentin Seen in the crown between DEJ and interglobular dentin  Seen in the root underlying the Tomes granular layer 16 About 20 μm thick Fibrils are perpendicular to DEJ and are larger in size than those in circumpulpal dentin Has fewer defects than circumpulpal dentin  Circumpulpal dentin Forms the bulk of the tooth and the dentin that is formed before the root formation is complete Collagen fibrils are smaller, closely packed More mineralised than mantle dentin (4%)  Secondary dentin Represents dentin formed after the root formation is complete 19_bb A narrow band of dentin bordering the pulp Has fewer tubules than primary dentin There is a bend between primary dentin and secondary dentin  Tertiary dentin Reactive, reparative, or 21_bb irregular secondary dentin Localised formation of dentin on the pulp dentin border - Produced only by cells directly affected  Produced in reaction to various stimuli – attrition, caries, 22_bb restorative procedures Tubules may be Regular Irregular and sparse in number No tubules at all Osteodentin – odontoblasts entrapped in dentin; mimicking osteocytes in bone  Dentinal tubules COURSE: S shaped curve - called PRIMARY CURVATURE Doubly curved course starting at right angles to the pulpal surface and ending perpendicular to the DEJ and CDJ  First convexity is directed towards the apex of the tooth Course taken by odontoblasts during dentinogenesis. They crowd as they move from DEJ towards the pulp SECONDARY CURVATURES Smaller oscillations within the primary curvatures 26_bb  EXTENT: Crown – DEJ to pulp Root – CDJ to pulp Tubules are longer than the thickness of dentin DIAMETER: 25_bb 2.5μm near pulp 1.2μm in mid portion 900nm near the DEJ  DENSITY Tubules are farther apart in the periphery and closer near the pulp Number of tubules per unit area on the pulpal and outer surface of dentin is about 4:1 Near the pulpal surface – 50,000 – 90,000 tubules per square mm More tubules per unit area in the crown than in the root  BRANCHING Major: 500-1000μm in diameter Represent terminal branching of tubules More frequent in root dentin than in coronal dentin  Intratubular dentin Also known as peritubular dentin A hypermineralised ring of dentin found within the dentinal tubule (9% or 40% more than that of intertubular dentin) Lost in decalcified sections as they are highly mineralised and appear as empty space surrounding the odontoblastic process  Intertubular dentin Constitutes the main body of the dentin Located between the dentinal tubules or between zones of peritubular dentin Mineralised but retained after decalcification  Interglobular dentin Areas of hypomineralised / unmineralised dentin Found in crown of teeth in the circumpulpal dentin just below mantle dentin where pattern of mineralisation is largely globular  Normal architecture of dentinal tubules remains unchanged as they run uninterruptedly through the interglobular area No intratubular dentin where the tubules pass through the globules  Incremental growth lines Dentinogenesis occurs 39_bb rhythmically Alternating phases of activity and quiescence Daily rhythmic recurrent deposition of matrix as well as hesitation in daily formative process is represented as incremental lines of von Ebner  Seen best in longitudinal sections Run at right angles to the dentinal tubules Distance between the lines varies from 4-8 μm in crown and much less in root Daily increment decreases after a tooth reaches functional occlusion  Contour lines of Owen Accentuated incremental lines Disturbance in matrix and mineralisation process They represent hypocalcified areas Earlier referred to a line resulting from coincidence of secondary curvatures of neighbouring dentinal tubules  Neonatal line Accentuated contour line Seen in deciduous teeth and permanent first molars Reflects abrupt change in environment that occurs at birth  Separates prenatal dentin and post natal dentin Dentin matrix formed before birth is of better quality May be a zone of hypocalcification  Tomes granular layer In dry ground sections – granular zone adjacent to cementum in 42_bb transmitted light Increases in amount from CEJ to root apex Caused by coalescing and looping of terminal portions of dentinal tubules  Earlier thought to be minute hypomineralised 43_bb areas of interglobular dentin These are spaces seen only in ground sections and not in H&E stained sections OR electron micrographs Looping is said to be related to lower rate of dentin formation in the root  Predentin 31_bb Located adjacent to pulp tissue 2-6 μm wide unmineralised dentin  As collagen fibres undergo mineralisation at the predentin-dentin junction, predentin becomes dentin and a new layer of predentin forms circumpulpally In mineralised dentin, collagen fibrils are of larger diameter (100nm) and more closely packed than in predentin Odontoblastic process / Tomes fibres These are cytoplasmic extensions of the odontoblasts Odontoblasts are seen at the pulp- predentin border and the processes extend into the dentinal tubules  Largest in diameter near the pulp (3-4 μm) In dentin it tapers to 1 μm Diameter of cell body of odontoblast is 7 μm and length is 40 μm  Extent of odontoblastic processes into dentin – Enamel spindles 10  Dentinal junctions Dentinoenamel junction (DEJ) Cementodentinal junction (CDJ)  Age changes Vitality of dentin Reparative dentin Dead tracts Sclerotic dentin  Vitality Has odontoblast and its process as an integral part Has the capacity to react to physiologic and pathologic stimuli Dentin is laid down throughout life  Reparative dentin Abrasion, erosion, caries, operative procedures – odontoblast processes are 68big exposed or cut, odontoblasts die or form reparative dentin Odontoblasts killed are replaced by migration of undifferentiated cells (cell rich zone / undifferentiated perivascular cells)  Dead tracts Odontoblastic process may be lost – caries, attrition, abrasion, cavity preparation, erosion especially in area of narrow pulp horns due to crowding of odontoblasts Odontoblastic processes disintegrate and the empty tubules are filled with air  Sclerotic dentin Also called transparent dentin – similar refractive indices Stimuli - caries, attrition, abrasion, cavity preparation, erosion Reparative dentin formation Collagen fibres and apatite crystals appear in the dentinal tubules Seen in older individuals especially in the roots  Blocking of tubules – a defensive mechanism of dentin Sclerosis Reduces the permeability of dentin Prolongs pulp vitality Appear white in transmitted light & black in reflected light  Dentin sensitivity 3 theories for pain transmission through dentin Direct neural stimulation Fluid/hydrodynamic theory Transduction theory  Direct neural stimulation Stimuli in some unknown manner reach the nerve endings in the inner dentin  Hydrodynamic theory Most popular and accepted theory Stimuli affect fluid movement in the dentinal tubules Stimuli could be – heat, cold, air blast dessication, mechanical or osmotic pressure Fluid movement – inward/outward causes mechanical disturbance of the nerves closely associated with odontoblast and its process. They act as mechanoreceptors  Transduction theory Odontoblastic process is excited by the stimulus and impulse is transmitted to nerve endings in the inner dentin  CONTENTS OF DENTINAL TUBULES Odontoblastic process Dentinal fluid – dental lymph? Lamina limitans Peritubular dentin Nerve endings – predentin and inner dentin no farther than 100-150 μm from the pulp  Clinical considerations 1mm2 of exposed dentin – 30,000 cells damaged Not be insulted by bacterial toxins, drugs, undue operative trauma, unnecessary thermal changes, irritating restorative materials Sealed with non irritating insulating substance  Spread of caries – Tubular system undermining of enamel at the DEJ Invasion of micrcoorganisms Dentin sensitivity – not a symptom of caries unless pulp is affected  Trauma from operative instruments Aspiration of odontoblast within the tubule Reperative dentin formation – sub odontoblastic layer Thank You O cementum Dr Sandeep Gupta Oral Pathologist  INTRODUCTION 2  Is mineralized dental tissue covering the anatomic roots of human teeth.  Beginsat cervical portion of the tooth at the cementoenamel junction & continues to the apex.  Furnishes a medium for the attachment of collagen fibers that bind the tooth to surrounding structures.  Makes functional adaptation of the teeth possible. 3 THICK CEMENTUM ON ROOT APICES IN AN ELDERLY PERSON 4  PHYSICAL CHARACTERSTICS 5  Hardness is less than that of dentin.  Light yellow in color.  Can be distinguished from enamel by its lack of luster & its darker hue.  Semi-permeable to a variety of materials.  CHEMICAL COMPOSITION 6  Contains 45% to 50% inorganic substances & 50% to 55% organic material & water.  Cementum has the highest fluoride content of all the mineralized tissues.  Organic portion consists primarily of type I collagen & protein polysaccharides (proteoglycans).  Inner dental epithelium Outer dental epithelium Hertwig’s epithelial root sheath Stratum intermedium  Prior to the beginning of root formation, the root sheath forms the epithelial diaphragm The outer & the inner enamel epithelium bend at the future cementoenamel junction into a horizontal plane, narrowing the wide cervical opening  The proliferation of the cells of the epithelial diaphragm is accompanied by the proliferation of the cells of the connective tissues of the pulp, adjacent to the diaphragm The free end of diaphragm does not grow into the connective tissue but the epithelium proliferates coronal to the epithelial diaphragm  Connective tissue of the dental sac surrounding the root sheath proliferates & invades the continuous double epithelial layer dividing it into network of epithelial strands  Epithelial Cell Rests of Malassez The epithelial rests appear as small clusters of epithelial cells which are located in the periodontal ligament adjacent to the surface of cementum. They are cellular residues of the embryonic structure known as Hertwig's epithelial root sheath.  13 Cellular components of cementum  CEMENTOBLASTS 14  Soon after Hertwig’s sheath breaks up, undifferentiated mesenchymal cells from adjacent connective tissue differentiate into cementoblasts.  Synthesizecollagen & protein polysaccharides which make up the organic matrix of cementum.  Have numerous mitochondria, a well-formed golgi apparatus, & large amounts of granular endoplasmic reticulum. 15 16 ULTRASTRUCTURE OF CEMENTOCYTE NEAR CEMENTUM SURFACE. 17 Cementocytes  CEMENTOID TISSUE 19  The uncalcified matrix is called cementoid.  Mineralization of cementoid is a highly ordered event & not the random precipitation of ions into an organic matrix.  Fibers are embedded in the cementum & serve to attach the tooth to surrounding bone. Their embedded portions are known as Sharpey’s fibers. 20  TYPES OF CEMENTUM 21  Cementum can be differentiated into: acellular & cellular cementum.  Acellular cementum does not have spiderlike cementocytes incorporated into it.  Acellular cementum is found at the coronal half whereas the cellular cementum is found at the apical half.  Cementum is thinnest at the cementoenamel junction & thickest toward the apex.  Cementocytes are either degenerating or are marginally active cells. Acellular cementum 23 CELLULAR CEMENTUM 24  Schroeder’s classification 25  Acellular afibrillar cementum Contains neither cells nor extrinsic or intrinsic collagen fibers, except for mineralized ground substance. Coronal cementum.(1-15um)  Acellular extrinsic fiber cementum Composed almost entirely of densely packed bundles of Sharpey’s fibers. Cervical third of roots. (30- 230um)  Cellular mixed stratified cementum - Composed of extrinsic & intrinsic fibers & may contain cells. Co-product of cementoblasts & fibroblasts. Apical third of roots, apices & furcation areas. (100-1000um)  27  Cellular intrinsic fiber cementum Contains cells but no extrinsic collagen fibers. Formed by cementoblasts. It fills resorption lacunae.  Intermediate cementum Poorly defined zone near the cementodentinal junction. Contains cellular remnants of Hertwig’s sheath embedded in calcified ground substance.  INCREMENTAL LINES 28  Incremental lines of Salter  29  Are highly mineralized areas with less collagen and more ground substance than other portions of the cementum.  The thickness of cementum does not enhance functional efficiency by increasing the strength of attachment of the individual fibers.  CEMENTODENTINAL JUNCTION 30  Smooth in permanent teeth.  Scalloped in deciduous teeth.  Dentin is separated from cementum by a zone known as the intermediate cementum layer.  This layer is predominantly seen in apical two-thirds of roots of molars & premolars. 31  CEMENTOENAMEL JUNCTION 32  In 60% of the teeth, cementum overlaps the cervical end of enamel for a short distance.  In 30% of all teeth, cementum meets the cervical end of enamel in a relatively sharp line. edge to edge  In 10% of the teeth, enamel & cementum do not meet. RELATION OF CEMENTUM TO ENAMEL AT THE CEMENTOENAMEL JUNCTION 33  CLINICAL CONSIDERATIONS 34  Cementum is more resistant to resorption than is bone, & it is for this reason that orthodontic tooth movement is made possible.  It is because bone is richly vascularized, whereas cementum is avascular.  Cementum resorption can occur after trauma or excessive occlusal forces.  In most cases of repair, there is a tendency to re- establish the former outline of the root surface by cementum. This is called anatomic 35 repair.  However, if only a thin layer of cementum is deposited on the surface of a deep resorption, the root outline is not reconstructed, & a bay like recess remains.  In such areas the periodontal space is restored to its normal width by formation of a bony projection, so that a proper functional relationship will result. the outline of the alveolar bone in these cases follows that of the root surface. This is called functional repair.  HYPERCEMENTOSIS 36  Is an abnormal thickening of cementum.  May affect all teeth of the dentition, be confined to a single tooth, or even affect only parts of one tooth.  If the overgrowth improves the functional qualities of the cementum, it is termed cementum hypertrophy.  If the overgrowth occurs in non-functional teeth or if it is not correlated with increased function, its termed hyperplasia.  37  Extensive hyperplasia of cementum is occasionally associated with chronic periapical inflammation.  Hyperplasia of cementum in non-functioning teeth is characterized by a reduction in the number of Sharpey’s fibers embedded in the root.  Knob like projections are designated as excementoses. Thank You