Enamel Physical and Chemical Properties - Life Cycle of Ameloblasts PDF

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 t...

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