Amelogenesis and Dentinogenesis PDF

AMELOGENESIS TOMES PROCESS LIFE CYCLE OF AMELOBLASTS The Tomes' process has 3 parts: PRE-SECRETORY STAGE cells prepare 1. Non-secretory side...

AMELOGENESIS TOMES PROCESS LIFE CYCLE OF AMELOBLASTS The Tomes' process has 3 parts: PRE-SECRETORY STAGE cells prepare 1. Non-secretory side for enamel secretion Secretory sides: 1. Morphogenic stage 2. Differentiating stage (Organizing stage) 2. Proximal portion (TPP): Responsible for the formation of interrod enamel SECRETORY STAGE where enamel (IR) secretion happens 3. Distal portion (TPD): Responsible for the formation of rod enamel (R) 3. Secretory stage (Formative stage) D. MATURATIVE STAGE (CALCIFYING STAGE). POST-SECRETORY STAGE maturation and protection of enamel is done 1. Ameloblast reduced in length. 4. Maturative stage (Calcifying stage) 2. Decrease of number of cell organelles. (50% of 5. Protective stage ameloblasts undergo apoptosis) 6. Desmolytic stage 3. Disappearance of tomes processes. 4. Distal end of the cells alternatively become ruffled (Active Take note of colors: STAGES accdg. to ENAMEL SECRETION state) and flat (less active). a. Process of modulation ruffled- every 6-8 hours A. MORPHOGENIC STAGE E. PROTECTIVE STAGE INNER ENAMEL EPITHELIUM (IEE) – Determine the shape of the PRIMARY ENAMEL CUTICLE crown After complete maturation of enamel , ameloblast lose their 1. Columnar cells separated from ruffled border and secrete thin organic layer on the crown termed primary dental papilla by basement enamel membrane. 2. Large centrally located nucleus. REDUCED ENAMEL EPITHELIUM 3. Active cells contain RER,GC, ribosomes and mitochondria. Ameloblast become flat and lose their regular 4. Proximal end: The end of IEE facing stellate reticulum. arrangement and cannot be differentiated from 5. Distal end: The end of the Inner dental epithelium facing dental the other cells of dental organ. papilla. All cells of dental organ form a layer cover the crown termed reduced dental epithelium which protect the crown from the B. DIFFERENTIATING STAGE (ORGANIZING STAGE) surrounding connective tissue. 1. The cell become tall columnar If the reduced dental epithelium is destroyed from above the crown, leading to disappearance of cell the enamel may be resorbed by the action of connective tissue cells. free zone. F. DESMOLYTIC STAGE 2. Nucleus move toward proximal end. (REVERSAL OF During process of tooth eruption to the oral cavity, POLARITY) the reduced dental epithelium proliferate by cell 3. Mitochondria move toward division and secrete enzyme for destruction of proximal end. connective tissue separating it from oral epithelium. 4. GC & RER move toward the distal end. This enzyme is termed desmolytic enzyme. Then, the 5. Cells of the dental papilla starts becoming odontoblasts, signalling reduced enamel epithelium fused with the oral the ameloblast to secrete enamel. epithelium and become part of gingiva during tooth 6. Ameloblast begin to secrete the organic matrix of enamel. erupt. 7. Ameloblast cells are attached together by desmosome termed web which are two types: AMELOGENESIS -the process of enamel formation on teeth a. Proximal terminal web at the proximal end. b. Distal terminal web at the distal end. MINERALIZED TISSUES C. SECRETORY STAGE (FORMATIVE STAGE) Mineralized tissues are biological tissues that incorporate minerals into soft matrices. 1. Ribosomes out from the nucleus to Example: RER in the cytoplasm. 1. Bone 2. Protein is formed inside RER 2. Tooth enamel according to the amino code of 3. Dentin ribosomes. 4. Cartilage 3. RER form small granule contain 5. Tendon protein. 4. This small granule go to Golgi Composition: Organic Matter & Inorganic Matter Apparatus to add CHO and form secretory granules contain enamel MINERALIZATION- multifactorial and complex process that results in matrix and out to the cytoplasm. the deposition of mineral crystals in the extracellular matrix of various 5. This granule go toward the distal tissues. end of the ameloblast and get out from the cell in the front of newly formed dentin.  ENAMEL a higly mineralised structure covering the anatomic crown of tooth. only tissue that is totally acellular 4% Organic m. PHYSICAL PROPERTIES 96% Mineralization Colour: appears: bluish white or greyish at the thick opaque areas & yellow-white at the thin areas reflecting underlying dentin. Hardness: hardest structure of the body Permeability: selectively Organic matter permeable. The organic matrix of enamel contains Enamel Proteins composed of Density: decreases from the surface of enamel to the dentino- Amelogenins 90% and Non-Amelogenins (10%) divided into enamel junction. Ameloblastin and Enamelin. Thickness: thickness over the cusps of the molars where it measures 2.5 mm & incisal edges of incisors where it is 2.0 mm. FORMATION OF ORGANIC MATTER ENAMEL HISTOLOGICAL STRUCTURES The deposition of organic materials moves from the Ameloblast downwards, resulting for the enamel organ to rise up. Enamel lamellae- are a type of hypomineralized structure By the end of the Formative Stage, the deposition of Organic in teeth that extend either from the (DEJ) to the surface of Matrix is done. the enamel, or vice versa.These structures contain proteins, proteoglycans, and lipids. REMEMBER: ameloblast produces enamel proteins (organic) tome’s process secretes inorganic minerals (inorganic) Enamel Spindles- are also linear defects, but they too can be found only at the DEJ, because they are formed by entrapment of odontoblast processes between ameloblasts prior to and during amelogenesis. Enamel tufts- hypomineralized ribbon-like structures that run longitudinally to the tooth axis and extend from the junction (DEJ) MINERALIZATION (DEPOSITION OF INORGANIC MATTER) PHASE 1 Dentino-enamel Junction- The DEJ is a complex scalloped structure associating at least two calcified tissues and preventing the propagation The secretory sides secretes the HYDROXYAPATITE CRYSTAL of cracks from enamel to dentin. FROM DIFFERENT DIRECTIONS. RODS (aka) ENAMEL PRISMS and INTERRODS are formed ENAMEL HISTOLOGICAL STRUCTURES from this process. The Non-Secretory side causes the enamel sheath to be formed (an area where only organic material is present) Hunter-schreger bands- alternating light and dark bands that appear in tooth enamel when viewed under reflected light. They PHASE 2 are caused by the intersection of enamel rods or prisms. PHASE 2 STARTS: with the disappearance of Tome’s Process and INCREMENTAL LINES start of Modulation Process: NEONATAL LINE is a dark Striae of Retzius, but it represents the first PURPOSE OF MODULATION: enamel formed after birth and it separates prenatal enamel from postnatal - the continuous supply of the minerals causes the enamel. -it is caused by the sudden change of oral environment after hydroxyapatite crystals to enlarge and take up most of the birth. psace of the enamel matrix - this causes the organic materials (enamel proteins) to be STRIAE OF RETZIUS -indicates the weekly development of enamel - squeezed out and be dissolved by the digestive enzymes contains 7-10 cross-striations present in the ameloblast. PERIKYMATA- clinical manifestation of Straie of Retzius -the continuous supply of the minerals causes the hydroxyapatite crystals to enlarge and take up CROSSSTRIATIONS -indicates the daily (every 24 hours) most of the space of the enamel matrix development of enamel -this causes the organic materials (enamel GNARLED ENAMEL -enamel structure seen histologically under a proteins) to be disintegrated, squeezed out, and be cusp dissolved by the digestive enzymes present in the ameloblast. ANOMALIES IN ENAMEL STRUCTURE AMELOGENESIS IMPERFECTA- rare, genetic disorder that affects the development of tooth ename  DENTINOGENESIS formation of Dentin Odontoblast Cells -forms Dentin PARTS OF THE DENTIN: 1. Coronal dentin 2. Root dentin STAGES OF DENTINOGENESIS: Type I Hypoplastic Pitted, Local, Smooth, Rough, 1. Odontoblast differentiation: The dental papilla differentiates into Enamel Genesis odontoblasts, which are the cells responsible for dentin formation. 1 Type II Hypomature Pigmented, Generalised, 2. Organic matrix deposition: Odontoblasts secrete an organic Snow-capped teeth matrix. Type III Hypocalcified Generelised 3. Mineralization: The organic matrix mineralizes to form dentin. Type IV Hybrid (hypomature Associated w taurodontism 4. Modification of the organic matrix: The organic matrix is & hypocalcified modified. 5. Peritubular and secondary dentin formation: Peritubular and secondary dentin form. DENTAL FLUOROSIS 6. Tertiary dentin formation: Tertiary dentin forms in response to a cosmetic condition that occurs when a child consumes too much injury. fluoride while their teeth are developing 1. ODONTOBLAST DIFFERENTIATION: ENAMEL PEARLS Enamel pearls are developmental variations of teeth that present as beads or nodules of enamel in places where they are not normally observed, usually in the furcation areas of molars AMELOBLASTOMA a rare, benign, or cancerous tumor that originates in the cells that form tooth enamel 2.ORGANIC MATRIX DEPOSITION: Odontoblasts secrete an organic matrix.. -Organic Matrix serves as the Dentin scaffolding TOME’S FIBERS - cellular structures or microscopic channels that extend from odontoblasts into dental canals: - facilitating the exchange of nutrients and waste products between the pulp tissue and surrounding dentin. FORMATION of TOME’S FIBERS - during dentinogenesis when part of an odontoblast remains in its location while the main body of the odontoblast moves toward the center of the tooth's pulp. FORMATION OF PREDENTIN - Organic Matrix serves as the Dentin scaffolding - may act as inhibitor or promoter of mineralization DENTINAL TUBULES These channels radiate from the pulp to the enamel or cementum border, and contain fluid and Tomes' fibers. They transmit sensations of hot and cold, and can be affected by acidic or sticky stimuli  5. PERITUBULAR AND SECONDARY DENTIN FORMATION: Peritubular and secondary dentin form. - Secondary dentin is formed by the same odontoblasts that formed primary dentin, but at a slower pace. It's a gradual process that continues throughout life. - It is formed after root completion. - found in the roof and floor of pulp chamber 3. MINERALIZATION: The organic matrix mineralizes to form dentin. 6. TERTIARY DENTIN FORMATION: Tertiary dentin forms in response to injury. a reparative dentin which is produced in response to adverse external stimuli, e.g., advancing caries or tooth breakage. due to the fast response of tertiary dentin, it is less organized than the primary dentin. Once the organic matrix is deposited, a portion of the matrix will be 2 Types of Tertiary Dentin: mineralized. The Predentin will remain unmineralized, and is present in all 1.REACTIVE DENTIN formed by odontoblasts if there’s only mild Odontogenesis. stimulus, or shallow injury 2. REPARATIVE DENTIN formed by newly differentiated odontoblasts, if the injury is severe. The mineralized portion is the MANTLE DENTIN Just below the mantle Dentin, there is an area called the, - if the injury is too severe that it caused the odontoblast to die, MINERALIZATION FRONT nearby mesenchymal cells will differentiate into odontoblasts - these newly differentaited odontoblast will release the reactive dentin. As mineralisation is happening, Tome’s Fibers elongates to form HISTOLOGICAL FEATURES: the middle, and major layer of the dentin, which is the CIRCUMPULPAL DENTIN. DENTINAL TUBULES - These channels radiate from the pulp to it has a Mineralized compartment (MINERALIZATION FRONT), the enamel or cementum border, and contain fluid and Tomes' and an umineralized compartment (Just above the predentin). fibers. They transmit sensations of hot and cold, and can be affected by acidic or sticky stimuli. PERITUBULAR DENTIN -Dentin that surrounds the Dentinal Tubules INTERTUBULAR DENTIN- Dentin that surrounds the Peritubular dentin. DEAD TRACTS - empty dentinal tubules that appear as dark areas. BLIND TRACT - contains sclerotic dentin (dentin with tubules that are completely obliterated. DENTINAL ANOMALIES DENTINOGENESIS IMPERFECTA 5. PERITUBULAR AND SECONDARY DENTIN FORMATION: Peritubular and secondary dentin form. Teeth are discolored, translucent, and weaker than normal, making them more likely to break, wear down, or be lost. Other -Secondary dentin is formed by the same odontoblasts that formed characteristics include small teeth and an altered enamel-dentin primary dentin, but at a slower pace. It's a gradual process that continues junction. throughout life. Usually associated with Osteogenesis imperfecta. 6. Tertiary dentin formation: Tertiary dentin forms in response to DENTIN DYSPLASIA injury. a rare genetic disorder that affects the production of dentin in teeth, -a reparative dentin which is produced in response to adverse external resulting in abnormal tooth development. It's characterized by stimuli, e.g., advancing caries or tooth breakage. malformed roots and abnormal dentin structure. DENS INVAGINATUS Dens invaginatus is a developmental malformation, in which there is an infolding of enamel into dentine.