Enamel presentation. prepared by mohammed yahia
Download as PPTX, PDF44 likes7,124 views
This document discusses the structure and formation of enamel. It begins by defining enamel and outlining its formation through the stages of odontogenesis and amelogenesis. Key details are provided on the histological layers involved in enamel formation, as well as the life cycle of ameloblasts. The physical and chemical properties of enamel are then examined, including its hardness, permeability and solubility. The document concludes by describing various histological features of enamel such as enamel rods, striations of Retzius, and the dentino-enamel junction.
Enamel presentation. prepared by mohammed yahia
- 1. Enamel
- 2. objectives 1- Introduction 2- Formation of enamel 3- Physical characteristics 4- Chemical composition 5- Structure of enamel 6- Histological features of enamel 7- Defects of enamel 8- Treatment
- 3. Introduction Definition: * Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. . It is the normally visible dental tissue of a tooth because it covers the anatomical crown and must be supported by underlying dentin. * Also define as “Acellular hard mineralized tissue that forms the protective covering of variable thickness over the entire surface of the crown”
- 4. Formation of enamel Odontogenesis “ tooth development” 1- initiation stage - 6th to 7th week 2- Bud stage – 8th week 3- Cap stage- 9th to 10th week 4- Bell stage – 11th to12th week 5- apposition stage – varies per tooth 6- maturation stage – varies per tooth Amelogenesis “Enamel formation” 1- secretory phase. 2 – maturation phase.
- 5. Cap stage The proliferation and growth are unequal in the different parts of the tooth bud, leading to formation of cap shaped structure with deep central depression attached to dental lamina termed enamel organ. Dental sac Bell stage This stage characterize by continuation of the proliferation and further morphodifferentiation and histodifferentiation. That’s lead to formation of four well differentiated cells types within the enamel organ.
- 6. The enamel organ consist of four layer : • Outer enamel epithelium • Stellate reticulum • Stratum intermedium • Inner enamel epithelium
- 8. amelogenesis • Secretory Phase • Partially mineralized enamel (30%) • Full thickness of enamel is formed • Maturation Phase • Influx of minerals • Efflux of organic material and water
- 9. amelogenesis To understand the amelogenesis (formation of enamel) we must understand the life cycle of ameloblast (cells that forming the enamel). Life cycle of amelobalst • Morphogenic Stage • Differentiation Stage • Secretory Stage • Maturation Stage • Protective Stage • Desmolytic Stage
- 10. Morphogenetic Stage • Occurs during early Bell Stage of tooth development • Inner Enamel Epithelium – Low columnar to cuboidal cells – Centrally placed nucleus – Golgi bodies placed proximally. – Mitochondria and other cytoplasmic bodies are scattered.
- 11. Differentiation Stage • Occurs during late Bell stage • IEE Ameloblasts • Ameloblasts (Histological changes) • Elongates • Nucleus shifts proximally. • Golgi complex increases in volume & migrate to central core of cell. • Increase in ER • Mitochondria shift proximally. Basal lamina
- 12. Secretory Stage • Synthesis of enamel proteins Endoplasmic Golgi apparatus Reticulum Condensed and packaged membrane bound secretory granules Contents released over newly formed dentin from distal end of ameloblast • Immediate mineralization of enamel matrix
- 13. Maturative Stage Water and organic material is selectively removed from enamel with addition of inorganic material. • Ruffle-ended ameloblast – Release of inorganic material – Proximal junctions are leaky and distal junctions are tight. • Smooth ended ameloblast – Removal of proteins and water – Distal junctions are leaky while proximal junctions are tight.
- 14. Protective Stage • Ameloblasts + SI + SR + OEE together form stratified epithelium – Reduced Enamel Epithelium. • Function – Protect mature enamel till eruption by separation from the connective tissue.
- 15. Protective Stage • Anomalies may develop in case connective tissue comes in contact with enamel surface. • At CEJ, ameloblasts may retract resulting in deposition of afibrillar cementum on the enamel surface.
- 16. Desmolytic Stage • Epithelium induces atrophy of connective tissue, thus facilitating fusion of oral epithelium and REE. • Epithelial cells release enzymes to destroy connective tissue by desmolysis. • Premature degeneration may prevent the eruption of tooth. (impaction of teeth)
- 17. Physical characteristics • Thickness • Color • Hardness • Tensile strength • Permeability • Solubility
- 18. Thickness The thickness of enamel varies in different areas of the same tooth and from one type of tooth to another type. Tooth type thickness Anterior tooth (incisal edge) 2 mm Premolar tooth (cusp) 2.3 to 2.5 mm Molar tooth (cusp) 2.5 to 3 mm Thickness of enamel decrease gradually from cusps or incisal edges to CEJ. Color The color of enamel is usually gray and translucent in nature. But the color of tooth mainly depends upon three factors: 1- color of underlying dentin. 2- thickness of enamel. 3 – amount of stains in enamel. Hardness Enamel is the hardest calcified tissue in the body Because of its high content of minerals.( 96% ) Enamel can withstand load of mastication and resist wear process
- 19. Tensile strength Although it is hard , enamel is extremely brittle thus it has low tensile strength and depends on the strength of the underlying dentin. Significance Because of high compressive strength of dentin than enamel, the dentin acts as a cushion for enamel when masticatory forces are applied on it. For this reason, during tooth preparation, for maximal strength of underlying remaining tooth structure all enamel rods should be supported by healthy dentin base. Permeability Enamel is selectively permeable, permitting partial or complete passage of ions due to the presence of microscopic pores Solubility Enamel dissolves in acid media. Its surface is less soluble than deep enamel. Significance Acid etching of enamel which is very important technique for conditioning enamel for many clinical procedures such as fissure sealants, restoration, cementing or orthodontic bands..etc.
- 20. Chemical composition Mature enamel consists of: • Mainly(96%) inorganic substances, Mainly calcium phosphate crystals (calcium hydroxyapatite crystals). • Small (3%) amount of organic substances, Mainly non collagenous proteins: A- amelogenins. B- non-amelogenins - ameloblastin - enamelin - tuftelin • (1%) water
- 21. Main structures are: 1- rods 2- inter rod 3- rod sheath Structure of enamel
- 22. Enamel rod The basic unit of enamel Number: 5 – 12 millions. Direction: Run in oblique direction and wavy course. Length: greater than the thickness of E. Diameter average: 4 μm. Appearance: Have a clear crystalline appearance. Cross-section: hexagonal, round
- 23. Keyhole shaped E. rods Hexagonal ameloblasts
- 24. Inter rod substance •Cementing E. rods together. •More calcified than the rod sheath. •Less calcified than the rod itself. •Appears to be minimum in human teeth. Rod sheath The boundary between rod and interrod enamel is marked by a narrow space filled with organic materials known as rod sheath
- 25. Immunocytochemical preparation showing rodsheath
- 26. Histological features of enamel GNARLED ENAMEL Gnarled enamel is found at the cusps of teeth. Its twisted appearance results from the orientation of enamel rods and the rows in which they lie…Significance: This part of enamel is resistant to cutting while tooth preparation. D Twisted course of enamel rods Gnarled enamel
- 27. Stria of Retzius • During development of enamel, variations in the metabolism of the organism cause variations in the amount of organic material deposited in the enamel. This causes changes in the coloration of the enamel that is layedown at that time so that alternating dark (higher organic material) and light (less organic material) banding occurs. These bands are called Stria of Retzius. The stria of retzius usually intercept the dentino-enamel junction.
- 29. Perikymata Striae of Retzuis often extend from the DEJ to the outer surface of the enamel, where they end in shallow furrows know as perikymata (or imbrication line )
- 30. Neonatal line: * It is an enlarged stria of Retzius which present in all deciduous teeth and 1st permanent molar. * This line separates between enamel formed before birth and enamel formed after birth. * This line is due to the sudden change of nutrition and environment due to birth. * The quality of enamel formed before birth is better than that formed after birth, because of the more protected conditions and constant nutrition of the fetus.
- 31. Enamel Lamellae * Enamel lamellae extend from the surface to varying depths of the enamel * They are faults that develop as a result of failure of maturation processes. They are filled with organic material and water * Some studies say the lamellae is the pathway of bacteria
- 32. Enamel spindles ENAMEL * It originate from the DEJ * Before enamel forms, some developing odontoblasts process extend into the ameloblast layer, and when enamel formation begins become trapped to form enamel spindles. Significance: Spindles serve as pain receptors, that is why, when we cut in the enamel patient complains of pain.
- 33. ENAMEL TUFTS * It originate from the DEJ, run a short distance in the enamel or sometimes to one half of the thickness. * They are considered to be ‘faults’ by some researchers while others consider them to be necessary to anchor dentine to enamel... Significance: Enamel tufts are hypomineralized structure in the enamel, thus play role in spread of dental infection.
- 34. Hunter-Schreger bands * Hunter Schreger bands are seen here with special illumination in longitudinal ground sections of enamel as light and dark bands * The dark bands (Diazones) absorb the light where the light bands (Parazones) reflect the light.. Significance: They are considered to resist and disperse the strong forces.
- 35. Dentino-enamel junction * It is a border between the Enamel and Dentin (composed from both). * DEJ is pitted/scalloped in which crests are toward enamel and shallow depressions are in dentin. * This helps in better interlocking between enamel and dentin.
- 36. Defects of enamel Genetic Non Genetic 1- Amelogenesis imperfcta A - Hypoplastic (type 1) B- Hypomaturation (type 2) C- Hypocalcified (type3). 1- caries 2 – attrition 3 – abrasion 4- erosion 5- localized nonhereditary enamel hypoplasia 6- localized nonhereditary enamel hypocalcification 7-fluorosis
- 37. Amelogenesis imperfecta is a group of conditions caused by defects in the genes encoding enamel matrix proteins. Type 1: hypoplastic amelogenesis imperfecta • The main defect is in formation of the matrix (protein). • Enamel is not formed to full thickness because ameloblasts fail to lay down sufficient matrix. • Enamel is randomly pitted, grooved or very thin, but hard and translucent. • Affected teeth appear small with open contacts due to very thin or nonexistent enamel causing thermal sensitivity. • Teeth are not susceptible to caries unless the enamel is scanty and easily damaged. • Commonly in men.
- 38. Type 2: hypomaturation amelogenesis imperfecta • Occurs during matrix apposition. • Enamel is softer and chips from the underlying dentin. • Enamel has a mottled brown-yellow-white color. • Contact points present as enamel is of normal thickness. • Radiographically enamel approaches the radiodensity of dentin.
- 39. Type 3: hypocalcified amelogenesis imperfecta • Occurs during the calcification stage. • Most common type. • Enamel is of normal thickness but soft, friable, and easily lost by attrition. • Enamel appears dull, lustrous, honey colored and stains easily.
- 40. Non Genetic attrition: defined as physiological continous, process resulting in loss of tooth structure from direct frictional forces between contacting teeth. • It occur both on occlusal and approximal surfaces. • Attrition is accelerated by parafunctional mandibular movements, especially bruxism.
- 41. Abrasion: It refers to the loss of tooth substance induced by mechanical wear other than of mastication.
- 42. Localized nonhereditary enamel hypoplasia: Refers to the localized defects in the crown of the portion tooth caused by to injury to ameloblasts during the enamel matrix formation stage. Localized nonhereditary enamel hypocalcification: Refers to localized defects in the crown of a tooth due to injury to the ameloblasts during the mineralization stage. • In these defects, the enamel is normal in structure but its mineralization is defective. • The color of lesion varies from chalky to yellow, brown, dark brown or grayish.