ORAL-HISTO-P2-Reviewer.pdf

ORAL HISTOLOGY P2 Reviewer/Sas 8-13 - Development and Growth of Teeth : Crown Development Root Development - Tooth Eruption and Shedding Dental Enamel - - Dentin Dental Pulp - ...

ORAL HISTOLOGY P2 Reviewer/Sas 8-13 - Development and Growth of Teeth : Crown Development Root Development - Tooth Eruption and Shedding Dental Enamel - - Dentin Dental Pulp -  II. BUD STAGE (8th week) TOOTH CROWN DEVELOPMENT Extensive proliferation of the dental lamina form into buds or oral masses penetrating into the mesenchyme. At the end of the proliferation, each arch will Phases of Tooth Development: have 10 buds corresponding to the future deciduous teeth. (See the next figure.) (occurring in both deciduous and permanent teeth) Enamel organ resembles a small bud. 1. Pre-eruptive phase – initiation of tooth development until completion of crown 2. Pre-functional phase – root development Peripheral - low columnar cells 3. Functional phase – tooth eruption and maintenance of occlusion Central - polygonal cells VERICAL DIMENSIONS OF REST & OCCLUSION : (will be gone if the patient becomes edentulous) · VERTICAL DIMENSION OF REST : · resting position of the jaws (2-4mm) · lips would contact but jaws and teeth would not. · VERTICAL DIMENSION OF OCCLUSION : · when we clench our teeth. How do know that to occlusion ? we our body is trying maintain · By maintaining the vertical dimension of rest & occlusion is that there is wearing , away Permanent tooth would erupt lingual to the temporary teeth. of the tooth structure due to chewing. CEMENTUM will be deposited at the APICAL AREA. EPITHELIAL INCURSION: The process begins with the dental lamina a band of epithelial tissue, PUSH up/down I ] Deposition of the cementum > - the tooth in order to maintain contact with the opposing teeth. growing down into the underlying ectomesenchyme (a type of mesenchymal tissie found in the jaw). Stages of Crown Development: Formation of the Epithelial Bud: This downward growth forms a small rounded structure known as the Initiation / Dental lamina stage (induction) EPITHELIAL BUD. Bud stage (proliferation) Cap stage (proliferation) Condensation of Ectomesenchyme: Bell stage (differentiation) as the epithelial bud continues to proliferate into the ectomesenchyme, there Apposition stage (induction) is a noticeable increase in cellular density immediately adjusted to the bud. This Maturation stage (maturation) phenomenon is known as the condensation of ectomesenchyme, which is essential for further tooth development. I. DENTAL LAMINA / Initiation Stage (6th - 8th week) How would permanent teeth more during eruption ? 1 action of the tongue Dental lamina appears as a thickening of the oral epithelium adjacent to condensation of ectomesenchyme.. 2 counter action of the lips. 20 areas of enlargement or knobs appear, which will form tooth buds for the 20 primary teeth. Not all will appear at the same time. CAP STAGE (9th- 10th week) The first to develop are those of the anterior mandible region At this early stage the tooth buds have already determined their crown morphology. Enamel organ forms into cap surrounding mass of dental papilla from the Successional lamina: lamina from which permanent teeth develop. (Except for mesynchyme and is surrounded by a mass of dental sac also from the permanent molars). mesenchyme. The dental lamina begins to function at 6th prenatal week and continues to 15th Formation of the tooth germ (see figure 5-12) year of birth (3rd molar). At the leading edge of the lamina, 20 areas of enlargement appears, which form tooth buds for the 20 primary teeth. Initiation Process: Tooth initiation begins at the 6th week in utero, when ectomesenchymal cells build up immediately under the oral epithelium. These cells are thought be derived from the neural crest cell population. - Another structure seen during the cap stage is the presence of the The oral epithelium then proliferates down into the ectomesenchyme to form a successional dental lamina. It appears to be an extension of the dental primary epithelial band (see Figure 5-3). lamina into the mesenchyme lingual to the developing primary tooth germs. At the 7th week in utero, the primary epithelial band differentiates into the These structures would later on give rise to the succedaneous permanent teeth. vestibular and dental laminae (see Figure 5- 4): o Vestibular lamina (buccal/ facial) – forms the oral vestibule (the external opening to the oral cavity). o Dental lamina (lingual) – forms the teeth Within the dental lamina, epithelial swellings form – these are known as the dental buds, of which there are 10 in each jaw. They give rise to the enamel organs (precursor to tooth enamel), signalling the first stages of individual tooth type development.  IV. APPOSITION STAGE AND MATURATION STAGE III. BELL STAGE (11th - 12th week) (varies per tooth) During the bell stage, the outer cells of the dental papilla will induce the inner enamel epithelium to differentiate into pre-ameloblasts. Then the membrana The Inner Enamel Epithelium (IEE) will differentiate into preameloblasts. performativa will dissolve. The outer cells of the dental papilla are induced by the preameloblasts to Upon the dissolution of the membrana performativa, the preamaloblast will induce differentiate into odontoblasts. back the outer cells of the dental papilla, so that these outer cells of the dental The odontoblasts now begin dentinogenesis with the apposition of predentin papilla will differentiate into odontoblasts and start secreting dentin. (uncalcified dentin). The odontoblasts therefore start their secretory activity some Thus, its not enamel that forms first, but the dentin. time before the enamel matrix begins. This explain why the dentin layer in any location in a developing tooth crown is slightly thicker than the corresponding Cells further differentiate, especially within the inner enamel epithelium, enamel matrix. where preameloblasts will later give rise to ameloblasts, the cells responsible for With the start of odontoblastic activity, the membrana preformativa enamel formation. Cusp Formation: In teeth with multiple cusps, this is when the cusp tips start to disintegrates. As this happens, the preameloblasts come in contact with develop as the shape of the crown becomes more defined. the spooked dentin inducing them to differentiate into ameloblasts and start amelogenesis. The enamel matrix is secreted from the Tome’s process. With the contact between the predentin and the enamel matrix formed, the disintegrating membrana performativa will be mineralized forming the dentinoenamel junction (DEJ). Mineralization follows by layer and or in totality of the thickness of the hard dental tissues formed. Maturation of the hard dental tissues follows next. Membrana Performativa (Basement Membrane) - will later become the DENTINOENAMEL JUNCTION (DEJ) - a membrane in between inner enamel epithelium and outer cells of the dental papilla. - prevents premature cell interaction. Calcium Hydroxyapatite - predentin (protein structure) The first layer of dentin will induce the Pre-Ameloblast that will recognize the ameloblast to form the enamel. " Thus. the DENTIN forms first than ENAMEL. Enamel is 96% mineralized. Dentin is 55-65% mineralized. When the total thickness of the enamel has been reached: The outer enamel epithelium and the ameloblast would fuse together to form the Reduced Enamel Epithelium. Reduced Enamel Epithelium - a thin protective layer, that covers the enamel surface of a tooth before it erupts to the oral cavity, - It guides the eruption process of the teeth.  Additional Info : Stem cell niche - areas in the teeth that would determine how many epithelial diaphragm would develop from HERS. · Primate space - > space between the canine and temporary molars. > - ensures proper placement of the teeth / NO MALOCCLUSION. Epithelial rest of Malassaez ULTIMATE FUNCTION: · primary teeth should be in place during the eruption of the succedaneous teeth It proliferates or enclosed all the necrotic products that comes out from the ↓ apical foramen so that there will be no spread of infection. because this will GUIDE THE TOOTH IN PLACE - · Importance of the disintegration of HERS : · How do we know that our body is trying to maintain occlusion ? - when the wearing away of the tooth structure world take place due to - Root dentin will be exposed to the stem cells of the dental sac CHEWING , there would come a time wherein our VERTICAL DIMENSIONS OF or dental follicle , some of the cells in contact with the root dentin REST and OCCLUSION. will differentiate into I · Why is it that we do not feel any deformity of our teeth ? · cemento blasts (forms the cementum) because of the maintenance of occlusion osteoblasts (forms the alveolar bone) - · · fibroblast (secretes collagen tibers & form the PDL) Undifferentiated mesenchymal cells ROOT DEVELOPMENT · ↳ (Pre-functional Phase) sac/follicle stem cells of dental ↳ they will stimulate to form ROOT FORMATION: into a specific cell. Begins at the cervical loop (where the IEE and OEE join) after the tooth · Placenta - the structure that would provide a lot of stem cells. crown is already formed. As the cervical loop elongates and proliferates downwards, Hertwig’s epithelial root sheath (HERS) is formed, which shapes the root(s) and ultimately surrounds the majority of the dental papilla. Its most apical ROOT DENTIN FORMATION : (Module 9) segment, the epithelial diaphragm, turns medially, ensuring that the · ROOT DENTINOGENESIS begins with the induction of the OUTER CELLS of the root tapers as odontogenesis proceeds. dental papilla. The cells undergo differentiation and become odontoblasts and start As root formation continues, the tooth erupts, leaving the epithelial diaphragm always at the same location. This eventually forms the apical DENTINO GENESIS. foramen. As radicular dentin is formed, HERS begins to disintegrate, leaving · After the root dentin is formed , the BASEMENT MEMBRANE that separates the HERS behind patches of epithelial cells called epithelial rests of Malassez. and odontoblasts disintegrate and become the Epithelial RESTS of Mallassez The collapse of HERS enables ectomesenchymal cells (stem cells or. undifferentiated cells) of the dental follicle to contact dentin and differentiate into the formative cells of the periodontium: cementoblasts (forming cementum), osteoblasts (forming alveolar bone proper), and ROOT DEVELOPMENT IN MULTIROOTED TEETH : fibroblasts (forming the PDL). To picture multiple root formation, one must · Root development in multirooted teeth originates as a single root imagine the root sheath as a skirt hanging from the enamel organ. Visualizing two tongues of epithelium growing toward each other from on the base of the crown or ROOT TRUNK ! this collar allows an appreciation of how a primary apical foramen is. converted into two secondary apical foramina and how, if three tongues are formed, three secondary apical foramina arise (Figure 5-28). · Epithelial Diaphragm > - long. tongue-like horizontal epithelial flaps , develops within the NOTE: usually single cervical opening of the coronal enamel organ. There is NO Stellate reticulum and stratum intermedium because they only then divides into two or three openings. provide nutrition for the production of enamel, and there is no production of enamel needed in the root development. · Pulpal surfaces of these holes. DENTINOGENESIS starts after induction of odontoblasts and disintegration of HERS. · Only at the PERIPHERY of each opening are CEMENTOBLASTS induced to form cementum on itself proliferates downwards and orient HORIZONTALLY newly formed dentin. and enclose most of the DENTAL PAPILLA size and shape of the roofs · Root development then proceeds in the same manner that of the single rooted teeth. ↑ ↑ as Cervical Loop > - Hertwig's Epithelial Root Sheath (HERS) · Composition of HERS : ① Outer Enamel Epithelium ↓ of HERS outgrows disintegrates and form will form ② Outer cells of the Dental Papilla Epithelial Rests of Malassaez L Epithelial Diaphragm ↳ number of roots ↳ point of fusion will become the multirooted tooth. the furcation area of 1.4. Formation of Accessory Canals TOOTH ERUPTION AND SHEDDING If the continuity of the HERS is broken before the dentin is formed it will result to missing or abnormal epithelial cells. (Functional Phase) When the epithelial cells are missing the odontoblasts do not differentiate and dentin does not form opposite the defect that occurred in the HERS. · Reduced Enamel Epithelium (RDE) The result is a small lateral canal sometimes also called as a supplementary canal. It will connect the main root canal to the periodontal ligaments. Two parts : 2. Formation of the Pulp ⑦ Outer Enamel Epithelium ② Ameloblast After the primary dentin has been developed along the periphery of the dental papilla, the central portion of the dental papilla differentiate into the pulp. · Intermittent eruption of teeth (during at rest , bone will develop 3. Cementum Formation (Cementogenesis) (see Figure 2) cells · Odontoblast - are temporary that are responsible for the resorption of Cementogenesis in the root area occurs when HERS disintegrates. This allows temporary teeth. the undifferentiated mesenchymal cells of the dental sac to come in contact with root dentin and is thus induced to differentiate into cementoblasts. > - comes from MACROPHAGES (scavenger cells) The cementoblasts move to cover dentin and undergo cementogenesis. A one layer of acellular cementum is deposited and succeeding layers of a cellular · Resorption only takes place for DECIDUOUS TEETH/ temporary teeth. cementum will be deposited after. Mineralization then takes place after the full Eruption should be -INTERMITTENT thickness of the cementoid is reached and the cementodentinal junction (CDJ) is · - formed. · Eruptive force > - MULTIFACTORIAL 4. Formation of the Periodontal Ligament and Bone As the crown and root develop, the surrounding tissues of the tooth are also developing. 1.1. Tooth Eruption Undifferentiated mesenchymal cells of the dental sac differentiate into fibroblasts Process whereby a tooth moves axially from its development position and osteoblasts. within the alveolar crypt of the jaw into its functional position within the Fibroblasts synthesize collagen fibers at the same time cementum is formed by oral cavity. cementoblasts and bone is formed by osteoblasts. The ends of the fiber The main direction of the eruptive force is AXIAL in direction however bundles insert into the outer portion of cementum and surrounding alveolar bone movements also occur in other planes accounting to tilting and drifting. to support the tooth. These fibers undergo mineralization and are often Eruption rates are greatest at the time of crown emergence. The rate of referred to as Sharpey’s fibers. eruption represents a balance between eruptive force and resistive force. Resistive force is being offered by the overlying soft tissue and alveolar Further bone development then surrounds the tooth and periodontal ligaments bone, viscosity of the surrounding periodontal ligaments (dental follicle) which at this time has formed into a lattice or plexus in time for tooth eruption. and occlusal forces. The lattice or plexus of fibers will later on reorganize into fiber groups. 1.2. Theories on Tooth Eruption Root growth Existence of a temporary ligament Vascular pressure Contractile collagen Hormonal signals to genetic targets Growth of dentin Pressure from muscular action Effect of nutrition Inherent tendencies to erupt Apposition and resorption of bone Periodontal ligament traction 1.3. The Eruptive Mechanism The eruptive mechanism is a property of the periodontal ligament or the dental follicle. It does not require a tractional force pulling the tooth towards the mouth. It is multifactorial in that more than one agent makes important contribution to the overall eruptive force. It could involve a combination of fibroblast activity and vascular or tissue hydrostatic pressures. 1.4. Tooth Eruption Phases Pre-eruptive Tooth Movement: the movement that brings the developing tooth from the site of its development to the site from which it will erupt into the oral cavity. Eruptive Tooth Movement: the movement of the tooth from the site from which it erupts up to the time it reaches its antagonist Post-eruptive Movement: the movement that compensates for occlusal and proximal wear. 1.5 Deciduous Tooth Eruption After enamel apposition, ameloblasts secrete an acellular dental cuticle known as the Primary Enamel Cuticle or the Nasmyth’s Membrane to cover the newly formed enamel. The enamel organ cells (outer enamel and ameloblasts) undergo compression to become the Reduced Enamel Epithelium (REE). The REE fuses with the oral epithelium. Enzymes from the REE disintegrate the central portion of the fused tissue leaving an epithelial tunnel for the tooth to erupt through into the surrounding oral epithelium. As the tooth erupt, the coronal portion of the fused epithelial tissues peel back off the crown leaving the cervical portion still attached to the neck of the tooth. This serves as the temporary junctional epithelium and will later be replaced by a definitive one as the root is formed. Once the primary enamel cuticle will be removed in during tooth function, it will be replaced by a Secondary Enamel Cuticle derived from saliva. 1.6. Deciduous Tooth Shedding Shedding begins as the succedaneous permanent tooth develops lingual to it. Initiation of resorption of the deciduous teeth prior to shedding is brought about by pressure from the developing permanent successor and the increase pressure exerted by the developing muscles of mastication. Undifferentiated cells from the periodontal ligament space differentiate into osteoclasts (for the resorption of alveolar bone) and odontoclasts (for the resorption of cementum, dentin and parts of the enamel). The process is intermittent and the wobbling tooth may become tightened due to the action of osteoblasts, odontoblasts and cementoblasts. 1.7. Permanent Tooth Eruption The process of eruption of permanent teeth follows the same pattern as that of the deciduous teeth. Tooth Eruption Process : 1.8. Post-eruption Changes Shedding of deciduous teeth under the influence from the Tooth within BONE of the permanent teeth with no shedding of permanent teeth that will. 1 development occurs - developing jaw in take place Diastemas or spacings bony crypts separate from from the Continuous eruption of teeth to compensate for loss of tooth oral epithelium. substance Epithelial attachment grows apically as age advances. 2 Soon after the formation of the root is initiated the , tooth begins to erupt 1.9. Factors Relevant to Eruption in Relation to Occlusion and more in AXIAL DIRECTION Normal period of eruption which is the actual time the teeth. emerge into the oral cavity As. 3 eruptive movement begins the crown is still covered with Reduced Enamel Epithelium Normal sequence of eruption which is the usual order the teeth ,. emerge into the oral cavity. 4 The bone overlying the tooth is resorbed , and crown passes through the connective 1.10. True Teething Symptoms tissues of the mucosa. Low grade fever Slight pain or itchiness or a feeling of discomfort in the overlying. 5 The Reduced Enamel Epithelium and Oral Epithelium fuse and form a solid mass of mucosa. epithelial cells the of tooth over crown the Swelling of the overlying mucosa. Irritability of the baby. 6 The central cells in this mass degenerates forming an EPITHELIAL CANAL Cyanosis of the overlying mucosa (BLUISH color where the tooth would erupt · Hypersalivation ↓ which the crown of the tooth ERUPTS. 1.11. Standard Calendric Age at which the Deciduous Teeth Start to and leaving cellular debris the Resorb (Rule: it takes around 3 years to fully resorb the teeth) on crown. 4 years old – all central incisors 5 years old – all lateral incisors. 7 As the tooth pierces in the oral epithelium I. 6 years old – NO RESORPTION TAKES PLACE 7 years old – all first molars DENTOGINGIVAL JUNCTION forms from : 8 years old – all second molars 9 years old – all canines > - the epithelial cells of the oral epithelium 1.12. Nolla’s Ten Stages of Tooth Development > Reduced Enamel Epithelium - 0 – absence of crypt 1 – presence of crypt 2 – initial calcification 3 – 1/3 of crown completed 4 – 2/3 of crown completed 5 – crowm almost completed 6 – crown completed 7 – 1/3 of root completed 8 – 2/3 of root completed 9 – root almost completed with open apex 10 – apical end of root completed  ENAMEL (Substancia Adamantina or Amelo) Enamel Lamella Physical Properties ribbon like cracks in enamel extending from the surface going towards the Hard and brittle due to high inorganic content DEJ. Soluble in acids It can be a place for the ENTRY of bacteria. Permeable to certain ions specially in young individuals Less calcified areas of the enamel (defects). Variable thickness (thickest at the cusps and thinnest at the cervical area of the tooth crown) Enamel Tufts Translucent color hypocalcification areas extending from the DEJ towards the enamel surface. Yellowish white or grayish white in color These are narrow, ribbon-like structures composed of purely calcified rods Specific gravity of 2.8 and interrod cementing substances that originate from the DEJ until about 1/5 or 1/3 of the entire enamel thickness. Chemical Composition 96% inorganic substances (Calcium Hydroxyapatite crystals) It can promote LATERAL SPREAD OF CARRIES. 4% organic substances and water Enamel Spindles (part of the odontoblasts) extensions of odontoblastic processes into the enamel. It is the cause of MICROSCOPIC FEATURES: DEJ hypersensitivity during cavity preparation. Enamel Rods and Prisms Tome’s Processes basic unit of enamel secretory parts of the ameloblasts. in cross section appears in a key hole or fish scale pattern They are also the projections of ameloblasts into the enamel matrix. extends the width of the enamel thickness from the DEJ to the outer Most ameloblast are held together by gap junctions. surface less than 90 – 60 degrees in curvature Primary Enamel Cuticle / Nasmyth’s Membrane / Developmental Cuticle varies in length, shows varying degrees of curvature and reflects the LAST SECRETORY product of the AMELOBLAST that cover the crown of a movement of the ameloblasts newly erupted tooth, before it fuses with the odontoblasts. requires four ameloblasts to produce one enamel rod (1 head : 3 tail) It will be replaced by a secondary enamel cuticle derived from the saliva. Hunter-Schreger Bands alternating light and dark bands due to periodic changes in the direction Cross or Transverse Striations of rods and can only be visualized thru the use of special light. lines crossing the rods at 4 microns interval marking the daily appositional growth of the enamel rods. Gnarled Enamel highly convoluted arrangements of rods at the cusp tips and incisal Amelogenesis edges. It represents irregular intertwining of bundles of rods from the Requirements for ameloblasts to undergo amelogenesis: good blood supply, DEJ. alkaline phosphatase, contact from stratum intermedium and poor nutritive supply. Incremental Lines of Retzius / Lines of Retzius / Bands of Retzius / Enamel matrix formed consists of two protein types: Striae of Retzius - amelogenin (90%, 22-30 kDa) brownish bands or lines that mark the growth periods of enamel. It - enamelin (10%, 48-70 kDa). reflects the layer upon layer of enamel apposition and primary calcification. Four waves of mineralization occur: Note: everyday 1 line is produced. 1. First/Primary (30% of the matrix is mineralized) 2. Second/Secondary (surface to innermost) 3. Third/Tertiary (innermost to surface) 4. Fourth/Quaternary (surface). · RATIO of AMELOBLAST that world form the enamel rod : During the mineralization process the following processes occur: crystal growth organization, removal of water and proteins, introduction of protein bound calcium ions, packing, and retreat of ameloblasts. 7 : 4 Ameloblasts : ↓ ↓ (7 head : 3 tail) · PRE-NATAL ENAMEL > - enamel that is deposited before the birth of the baby. enamel ameloblasts rod > - near the DES. POST-NATAL ENAMEL is enamel that deposited after the birth of the baby · > -. > - far from the DES · Direction of Enamel rods (in the proximal areas) : > - ON TOP of the neonatal line in mandibular teeth. > - Decidrous teeth - OCCLUSAL in direction > BELOW the neonatal line of maxillary teeth -. > - Permanent teeth - APICAL or GINGIVAL in direction · Neonatal Line ↳ a sign of a disturbance strong enough to cause the disturbance of · Waves of Enamel Mineralization : amelogenesis or enamel formation. ↳Can determine whether died 1st Wave : Enamel is 30 % mineralized. the baby inside or outside the womb : if the died baby · INSIDE the womb : NO NEONATAL LINE 2nd Wave : Surface to innermost. if the baby died after birth /OUTSIDE · : HAS NEONATAL LINE 3rd Wave : Innermost to surface. 4th Wave : Surface PROVIDES STRENGTH TO THE ENAMEL :. · & & Enamel Rods ② Gnarled Enamel Imbrication Lines of Pickerill raised areas representing the external manifestations of the Striae ③ Interprismatic Substance or Retzius Perikymata transverse wave-like grooves representing the external - will act as a primary shock absorber for the stresses found in enamel. manifestations of the Striae of Retzius ① Hunter-Schreger Bands Neonatal Line or Ring ⑤ Cross Strictions accentuated Striae of Retzius differentiating the prenatally deposited enamel to postnatal one. It results to the abrupt change in the environment and nutrition of · Development of the ENAMEL would first take place at thei the infant. > - Incisal areas or cuspal areas  CLINICAL CONSIDERATIONS: Primary Dentin dentin formed up to the time of tooth eruption before the completion of the Enamel Hypoplasia apical foramen. deficient quantity of enamel as a result of a disturbance in First layer of pre dentin. matrix formation. Secondary Dentin Enamel Hypocalcification deficient quality of enamel as a result of a disturbance in the dentin formed from the time the tooth becomes functional up to the time the mineralization of the enamel matrix. tooth becomes nonvital. Amelogeneis Imperfecta Tertiary Dentin or Reparative Dentin a pathologic condition due to a disturbance in the formation dentin formed under an area of injury. and maturation of the enamel matrix. Age Changes Interglobular Dentin Attrition (physiologic wearing away of enamel resulting from hypocalcified dentin areas the masticatory process) found next to the DEJ. Loss of Perikymata Decrease in permeability to ions from the saliva Tome’s Granular Layer hypocalcified dentin areas found next to the cemento-enamel junction (CEJ) or in the roots. Sclerotic Dentin or Transparent Dentin dentin wherein the tubules are filled with inorganic salts and thus appear DENTIN (Substancia Eburnea) transparent in transmitted light and dark in reflected light. Physical Properties Dead Tracts Hard dental tissue that makes up the bulk of the tooth structure dentin wherein the tubules are filled with air due to the degeneration of the Yellow in color odontoblastic processes. Resilient so as to support brittle enamel Dead tracts can be caused by: caries, erosion, crowding of Tome’s fibers, Is a wet tissue due to the presence of dentinal fluid attrition and toothbrush abrasion. Is a perforated tissue due to the presence of the odontoblastic processes Below it is another type of dentin called the REPARATIVE DENTIN (which plug the area to avoid entry of bacteria). Chemical Composition SCLEROTIC DENTIN /Reparative Dentin/ Tertiary Dentin 65% inorganic substances (Calcium Hydroxyapatite crystals) - is the opposite of tpwhat happened to dead tracts because with dead tracts, air is filled but in this case, it will be minerals that will be 35% organic substances (collagen and other proteins) filled with air. MICROSCOPIC FEATURES: Dentinal Tubules INCREMENTAL LINES: are regularly arranged canals that radiate from the pulp to the DEJ it takes on a gentle S direction as it traverses the entire thickness of dentin Incremental Lines / Imbrication Lines of von Ebner the opening of the dentinal tubules is wider at the area near the fine lines running at right angles to the dentinal tubules. It reflects the daily odontoblastic layer of the pulp and becomes narrower as it would traverse rhythmic and recurrent deposition of dentin. the entire thickness of dentin tubules contain dichotomous branches that communicate with other tubules Contour Lines of Owen accentuated incremental lines of von Ebner due to disturbances in the matrix Tome’s Fibers / Odontoblastic Processes / Dentinal Fibers and mineralization process are cytoplasmic extensions of odontoblasts found inside the dentinal tubules. Other contents of the dentinal tubule are the intratubular nerve and Neonatal Line tubular fluid implicated in dentin hypersensitivity.. Accentuated incremental lines in dentin differentiating the prenatally deposited dentin to postnatal one. Peritubular Dentin It results to the abrupt change in the environment and nutrition of the infant. dentin forming the walls of the dentinal tubules in cross sections. Theories on Dentin Sensitivity Direct Neural Stimulation Theory Intertubular Dentin Odontoblast Receptor Theory or Transduction Theory dentin found in between the dentinal tubules in cross sections. Hydrodynamic Theory Pre-dentin a layer of uncalcified dentin deposited next to the odontoblasts. It is made up mostly of proteins. · PRENATAL DENTIN -1 found near the DES. Mantle Dentin · POSTNATAL DENTIN--found near the pulp. the outermost layer of dentin found in very close proximity to the dentino- enamel junction. It is the first dentin layer formed. Dentinogenesis Preparatory Phase: differentiation of the outer cells of the dental papilla and Circumpulpal Dentin changes in the membrana preformativa or other membrane. layer around the outer pulpal wall that represents dentin formed after mantle Apposition Phase: secretion of predentin (formation of Korff’s fibers, ß fibers dentin. and influx of ground substance) and mineralization every after apposition (primary and secondary). · Two forms of Calcium Mineralization is mainly the introduction of globules or linear calcospherules Hydroxyapatite Crystals : of calcium hydroxyapatite crystals. 1 Globular Crystals 2. Linear Crystals PULP (Endodontium) Parts of the Pulp: Coronal Pulp (part of the pulp in the pulp chamber) Radicular Pulp (part of the pulp in the radicular canal) Histologic Features Zones of the Pulp (Outer to inner) Odontogenic Zone: Odontoblastic Zone (contain the odontoblasts) Cell Free Zone or Zone of Weil (layer containing fine nerves and collagen fibers) Cell Rich Zone (contains fibroblasts and undifferentiated mesenchymal cells, RBCs and WBCs) Other Microscopic Features: Other cells found in the pulp (Macrophages for phagocytic functions and Mast Cells which are present during inflammatory conditions) Ground Substance - a microscopic feature of the pulp that functions to suspend the cells and structures in it. (on which cells, fibers, blood vessels, lymph vessels and nerves are suspended) Age Changes Increase in the number of fibers with a decrease in the number of cells. Decrease capacity to heal when infected. Increase in the number of pulp stones present. Pulp Stones / Denticles According to Structure True Denticles False Denticles Diffuse Calcifications Pulp Stones According to Location in Relation to the Dentinal Wall Free Denticle Attached Denticle Embedded Denticle Decrease in size. Functions of the Pulp: Inductive – induce cells to differentiate into specific cell types Nutritive – provide nutrients to the odontoblasts and other cells Formative – continuous formation of dentin and is the main function of the pulp Protective – formation of secondary or tertiary dentin Defensive – a. Morphotic Response (formation of reparative dentin) b. Inflammatory Response Nerve Supply to the Pulp: Branches from the maxillary and mandibular nerves of the trigeminal nerve enter into the pulp via the apical foramen. Raschkow plexus (myelinated) – pulp core Remak’s fibers (unmyelinated) – zone of Weil and innervate cell free zone. Subodontoblastic plexuses of nerves – beneath and between odontoblasts Intratubular nerves – dentinal tubules