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  1. 1. ENAMEL Introduction Enamel forms a protective covering of variable thickness over the entire surface of the crown. On the cusp of molars and premolars the enamel attains a maximum thickness of about 2 to 2.5 mm, thinning down to almost a knife edge at the cervical region. The shape and contour to the cusps receive their final modeling in the enamel. It is the hardest calcified tissue in the human body because of its high content of mineral salts and their crystalline arrangement. Physical characteristics Because of high mineral content, enamel is extremely hard, a properly that enambles it to withstand the mechanical forces applied during its functioning, this hardness also makes it brittle, therefore an underlying layer of more resilient dentine is necessary to maintain its intergrity. The specific gravity of enamel is 2.8 another physical property of enamel is its permiability. It has been found with radisactive tracers and dyes 1
  2. 2. that the enamel acts like semipermeable membrane, permitting complete or partial passage of certain molecules like c-labeled urea etc. Enamel is translucent are varies in color from light yellow to grayish white, because the various in thickness that 2 to 2.5 mm the colour also changes i.e. the underlying dentine is seen through the enamel. - Incisal areas may have a bluish finge where the thin edge consists only of a double layer of enamel. Chemical properties Enamel consists of 96% of inorganic materials and 4% organic materials and water. The inorganic content of enamel consists of a crystalline calcium phosphate known as hydroxyapatite which is also found in bone, calcified cartilage, dentine and cementum. Various ions – Introtium, magnesium, lead and fluoride, the ions are incorporated into or absorbed by the hydroxyapatite crystals if there ions are present during enamel formations. A fine lacy network of organic material appears between the densely packed hydroxyapatite crystals. 2
  3. 3. The bulk of the organic material consists of the TRAP (Tyrosine rich amelogenin protein) peptide highly bound to the hydroxyapatite crystal as well as nonnuelogenin proteins. Structure of Enamel Enamel in prepared ground sections can be studied under the light microscope by means transmitted light, such sections show it to be composed primarily of elongated structure termed rods. Structures Rods the enamel is impact of enamel rods or prisms rod sheets and in some regims a cementing interprismatic sultanae. The number of enamel rods has been estimated as ranging from 5 mm in lower laterals in users to 12 millem in to upper first molars. From to dentinoenamel for the rods run tortuous cause ofward to the surface of the fork. The length of most rods is grater than the thickness of the enamel because of the oblique direction and tortuous course of the rods. The rods located in cusps the thicker part of the enamel are longer than those at the cervical areas of the teeth. The diameter of the rods averages 4mm, the diameter of the rods increases from DE in towards the surface of the tooth at ratio of 1:2. 3
  4. 4. Enamel rods have a crystalline appearance permitting light to pass through them, under light microscope they appear henogonal round or oral. In cross section they appear – as “Fish Scales”. Submicroscopic structure The rods are cylindrical in shape in made of apatite crystals whose long axis rods parallel to the layitudanal axis of rod, this is applicable to crystals in the cervical axis of the rod, the crystals flare laterally to an involved degree as they approach the rod periphery. The inter rod regions is an area Surrounding such rod is which crystals are oriented in a different directions from the those making up the rods. Rod sheath: the boundary where crystals of the rod must those of the interod regions at sharp analysis. A more common pattern in a keyhole pattern or paddle shaped prism in human enamel, when cut longitudinally, section through the head or bodies of one ow of rods and to “tails” of an adjacent row. This interrod substance. These rods measure about 5mm in breath and 9mm in length. The bodies of the rods are nearer occlusal or incisaly whereas the tails point cervically. Striations: Each enamel rod is built up of segments separated by chak lines that give it straighten appearance. These striations demarcate the rods, the 4
  5. 5. striations are more pronounced in enamel that is insufficient calcified. The rods are segmented became the enamel matrix is formed in a rythemic manner. In humans there segments seem to be uniform length of about 4mm. Directions of rods Generally the rods are oriented at right angles to dentine surface. The cervical and central part of it crown of Deciduous tooth they are approximately horizontal. Near the incisal edge cusp tip they change gradually to an increasingly oblique direction until they are they are almost vertical. The permanent teeth is similar in the overall two thirds of the crown. In the cervical region however, the rods deviate from the horizontal in an apical direction (way course mention). Deviation: Example it the middle part of the crown in divided into thin horizontal disc, the rods in the adjacent discs bend in opposite directions, i.e. if an discs start from the dentine in a oblique directions and bend more or less sharply to the left side, whereas it adjacent disc the rods bend towards the right. This alternating clock wire deviation from radial direction can be observed at all levels of the crown if the discs are cut in the places of like general rod direction. 5
  6. 6. If discs in cut in oblique plane especially near the dentine in the regions of cusp tips or incisal edges, the rod aggregate appears more complicated, to bundles of rods seen to interwine more irregularly. This appearance of enamel is called Gnarled enamel. The enamel rods forming the developmental fissure and patients concern in their outward course. Hunter schileger bands Change in directions of rods in responsible for the appearance of the hunter schreger bands. There are alternative dark and light strips of varying widths (seen in longitudinal sections and oblique reflected light). They originate at DE/n and pass outward ending at some distance from out enamel surface. Some investigators claims that variations is calcification of the enamel that coinside with the distribution of the bands of hunter schreger. Hunter Schreger bands are composed of alternative zones having a slightly different permeability and a different content of organic material. 6
  7. 7. Incremental lines of Retzices Appear as brownish bands in ground sections of the enamel, incremental pattern of the ename. That is successive apposition of layers of enamel during formation of the crown. The incremental line have been attributed to periodic bending of the enamel rods, to variations in basic organic structure, or to a physiologic calcification rhythem. Incremental lines if prevent in moderate intensity are considered normal due to metabolic disturbance during formation of enamel broading of the incremental line take place and reading them more prominent. Surface structure A relatively structures layer of enamel approximately 30 mm thick is seen 70% permit teeth and all deciduous teeth, seen monthly over cusp tips and cervical area, in this layer prism outline are visible and all apatite crystals are parallel to one pillar and perpendicular. To strike of Retzines, it hevily mineralized area. Other microscopic details seen are like newly erupted teeth as 1. Prikymata 2. Rod ends. 3. Cracks (lamellae) 7
  8. 8.  Perikymata are transverse, wave like grooves, believed to be to external manifestation of the strike of Retzines.  They are continues mound the tooth and usually lie prallel to each other and to the cemetoenamel.  Enamel rod ends are concave and vary in depths and shape, they are shallowest in the cervical regions and depth near the incisal or occlusal edges.  Cracks are the outer edges of lamellae and a right angles to DE for. Enamel lamellae are their leaf like structures the extended from the enamel surface towards a dentin enamel for and also may penetrate dentin. The consist of organic material but with little mineral intent. Lamellae may develop in planes of tensins, where rods cross such plane, a short segment of rods may not calcify, if it distribution in more seven a crack may develop. 3 types of lamellae are seen. Type A – Lamellae composed of poorly calcified rod segments. Type B – Lamellae caristing of degradation colds. Type C – Lamellae arising in erupted teeth where be cracks are filled with organic matter. 8
  9. 9. If has suggested that enamel lamellae may be a site of crack in a tooth and may form a road of entry for bacteria that initate caries. Neonatal lini or Neoratal ring The enamel of the deciduous teeth develops partly before and partly after birth, the boundary between the two portions of enamel in deciduous teeth in marked by an accentuated incremental line of Rotizices, it is as a result of abrupt change in the environment and nutritions of the newborn infront. Enamel criticle A delicate membrane called Nasmyth’s membrane, or primary enamel cuticle careers covers the entire crown of the newly erupted tooth but a probably soon removed by masticators. This membrane in a typical buccal lamina found beneath most epithelia. (Re basal lamellae is secrated by the endoblast when enamel formation is completed) Enamel tufts Enamel tufts are at dentinoenamel for to the enamel to about one fifths to one 3rd of its thickness, they are narrow, ribbon like structure and resemble tufts of grass, so they are named enamel tufts. 9
  10. 10. Tufts consists of hypocalcified enamel rods and inter prismatic stubstance. Dentinoenamel function The surface of dentine is pitted at dentioenamel function, shallow depression of the dentine facing to dentine fit round enamel projections, in assure to form hold of enamel cap into the dentine. In microradiograph of ground sections a hypominerlized zone about 30mm thick can sometimes be demonstrated at DE/n. Odontoblast process and Enamel spindles Occlusally odontoblast process pass across to dentino enamel functions into enamel there are formed as enamel spindles. The direction of the odontoblast process and spindles in the enamel corresponds to the original directions of ameloblast – i.e. at right angles to the surface of the dentine. Age Changes 1. Most apparent age change is wear of occlusal surface and proximal contact point as a result of mastications. 10
  11. 11. 2. Surface of unerrupted and recently erupted teeth are covered completely with proximal rod ends and perikymata and later gingival loss of the rod ends and perikymata disappear completely. 3. Localized the certain elements such as nitrogen and fluorine have been found into superficial enamel layers of older teeth. 4. As the results of age changes in to organic portions of enamel, their resistance to decay may be increased. 5. Enamel become harder with age (eg. Of reduced permeability of old teeth). Clinical Considerations 1. Cavity cutting Unsupported enamel rods are not lift at the margins, they would break and produce leakage. 2. Brittleness of Enamel Enamel is brittle and does not withstand forces in thin layers or in areas where there is no underlying dentine. 3. Deep enamel fissures Although these are not considered pathological, food lodgenet and difficult clear it area may lead to dental caries, caries penetrate the floor of fissures 11
  12. 12. rapidly become to enamel in there areas is very this. As the destructure process reaches the dentin, it spread along to DE/n under rising to enamel. 4. Dental lamellae – may also be predisposing locations for caries because they contain much organic materials. Fluoride There has been a reduction by 40% or more in the incidence of caries in children after topical application of Sodium fluoride Stannous fluoride • Incorporate of fluoride containing dentifrice’s. • Fluoride containing mixtures such as stannous fluoride parts, sodium fluoride rinse are used to alter the surface of enamel for more substance to caries. • Adjustment of fluoride level in commercial water supply to 1 parts per millimeters. 5. Cervical region Should be kept smooth and well polished, if it rough, food debris bacterial plaque accurately and gingiva coming with this cause may lead to gingival inflammation and progress to even severe periodontal disease. 6. Glue of pit and fissure sealents. 12
  13. 13. Histological clinical considerations Hypoplasia Manifested by pitting, following or even total absence of enamel and hypo-calcifications in form of opaque or chalky areas. This may due to 1. Systems 2. Local 3. Genetic Systemic inflame • Nutritional deff. • Endocarinopathies • Febrile eliseases • Chemical intoxication’s  Dentist should exert has inflame as his patient to ensure sound nutritional practices. Recommended immunization procedure during periods of gestations and postnatal endogessor.  Hypoplasia and hypocalcification If matrix formation is affected, enamel hypoplasia will ensure. If maturation is lacking or incomplete hypocalcifications results. 13
  14. 14. 1. Systemic origin hypoplasia is termed as chronologic hypoplasia. 2. Hypoplasia due to congenital synthesis. • Hutchisons teeth in anterior • Mulberry molars 3. Enamel hypoplasia due to hypocalcemia Developed level of calcium in blood (mainly U / D) it caries molar pitting variety of hypoplasia. 4. Hypoplasia due to berter injuries Caries  traumatic birth  prematurity born children  children who suffer from treatment hemolytic disease at birth. 5. Hypoplasia due to fluoride  Mottled enamel (ingestion of fluoride coating deficiency molar during to time of tooth formation may result melted enamel. Canal – distribution of the anelo blasts during formation stage of tooth development. There can be white spotting on enamel, white opaque areas, pitting and brownish staining corroded appearance. 14
  15. 15. • If is different o retain restoration in such teeth. • They wear and even fracture easily. Treatment: For cosmetic rains – bleady  In race heredity disturbances of the enamel orgats caled odontodysplasia, apposition and maturation of the enamel are disturbed such teeth have both eater appearance (poorly calcified teeth).  Tetracycline stains Deposition it mainly on the dentin, a small ansent of drug may be deposited on enamel. (composite can be used).  Amelogenesis Imperfeeta (Hereditary brown enamel, Heriditary Enamel Dysplasia) it is a endodermal disturbance. 3 bacillus types 1) Hypolactice type  defective formation of matrix. 2) Hypominaralization type  defective mineralization of the formed matrix. 3) Hypomaturation type  when enamel crystallation remains inmature. C/F if may be present as 1. Discoloration 15
  16. 16. 2. Total absence of enamel. 3. Numerous parallel wrinkles or grooves. 4. Chipped a show depression. 5. Open contact points between teeth. 6. Overall surface or incisal edge abraded. Treatment  no 4 except of cosmetic improvement. Tooth Development At certain points along the dental lamina, each representing the location of one of the 10 mandibular and 10 maxillary deriduous teeth, the ectodermal cells multiply still more rapidly and from knobs that grow into the underlying mesenchyme. Each of there little downgrowths from the dental lamina represents the beginning of the enamel organ. As cells proliferation continues, each enamel organ increases in size and changes in shape. Stages  Bud stage  Cap stage  Bell stage  Advanced bell stage 16
  17. 17. Enamel development starts from the cap stage. Cap stage – As the tooth bud starts to proliferates if it does not expand uniformly, instead unequal growth in different parts of the tooth bud leads to the cap stage. The peripheral cells of the cap stage are cuboidal cover to convexity of the “cap” and are called the outer enamel epithelium, the cells into concavity of the cap become face, columnar cells and represents the inner enamel epithelium. Bud stage – The inner enamel epithelium consists of a single layer of cells that differentiate prior to amelogenesis into fall columnar cells called anelsblasts. There cells are 4 to 5 mm in diameter and 40 mm high, there cells are attached to one another by junctional complexes literary and to cells in to stratum intermedium by dismosorces. Stratum intermedium – A few layers of squamous cells form the statum intermedium between the inner enamel epithelium and stellate reticulum there cells are closely attached by desmosorces and gap functions. Stellate reticulum – Before enamel formation begins the stellate reticulum collapics, reducing the distance between the centrally situated ameloblasts and 17
  18. 18. the nutrient capillaries near the outer enamel epithelium, this changes begins at the heights of the cusp or incisal edge and forgives cervically. Outer enamel epithelium – The cells of the outer enamel epithelium flatter to low aiboidal form, at end of the bell stage and during the enamel formation the surface of outer enamel epithelium is laid into folds, between to folds form papillae that contains capillary loops which provides a rich nutritional supply for the intense metabolic activity of vascular enamel organ. Dental lamina – In all teeth except permanent molars in proliferates at its deep and give rise to enamel organs of the permanent teeth. Advanced bell stage: During the advanced bell stage the boundary between, inner enamel epithelium and odentoblasts outline form future DE/n and in addition the cervical portion of the enamel organ gives rise to epithelial root sheath of hertwig. Life cycle of ameloblasts Ameloblasts life cycle starts in the inner enamel epithelus or omeloblastic layer, and the near through ameloblasts in six stages 1. Morphologic stage 2. Organizing stage 3. Formation stage 4. Maturation stage 18
  19. 19. 5. protractive stage 6. dismolytic stage Morphologic stage The cells are short columnar with large oral nuclei that almost fill to cell body. High apparatus and controls are located in the proximal end of the cell, into enclria are evenly disappeared throughout cytoplasm. Organizing stage Cells become longer and majorities of the contribute and golgi regimes from proximal ends to into dental ends of to cell. Formation stage Cells retain same size and arranged as previous stage, blunt cell process or to endoblast cell surface which penetrate the basal lamina enter the predentine, in the stage intiation of secreature of enamel matrix tube place. Maturative stage Enamel maturation occurs after most of the thickness of the enamel matrix has been formed in the occlusal or incisal area, in the cervical parts of the crown, enamel matrix formation is still progressing at this fine. 19
  20. 20. Cells are slightly reduced in size in length and are closely attached to enamel matrix. Ameloblasts display microvilli at their distal extremities cytoplasmic vacuoles containing material resembling enamel matrix are present. Protective stage When the enamel has completely developed and has fully calcified, the endoblasts leave to the arranged in a well defined layer and can no longer be differentiated from to cells of stratrum intermedium and outer enamel epithelium. There are layer form a satisfied epithelial covering of the enamel called reduced enamel epithelium. Function is to protect the mature enamel by separating it from the connective tissue unit tooth erupts, if connective tissue come in contact with the enamel anomalies may develop. Desmolytic stage In this stage the reduced enamel epithelium proliferates and seems to induce atrophy of connective tissue, epithelial cells elaborate enzymes that destroy connective tissue fibers by clesmolysis. 20
  21. 21. Amelogenis On the basis of ultrastructure and composition two process are involved in the development of enamel. 1. Organic matrix formation 2. Mineralization Formation of the enamel matrix Ameloblasts begin their secretary activity when a small amount of dentine has been laid down. Ameloblast lose the profection which had penetrated the basal lamina separating from the predentine. A thin layer of enamel forms along the dentin. This has been termed the dentinenamel membrane, the presence of membrane shows that the distal ends of enamel rods are not in direct contact with dentin. Development of tomes process The surfaces of the ameloblasts facing the developing enamel are not smooth, this is became the long axis ameloblasts are not parallel to the long axis of rod. The profections of the ameloblasts into the enamel matrix in called tomes processes. 21
  22. 22. They also contain typical secretion granules as well as rough endoplasmic reticules and mitochondria. Distal terminal bars When the tomes process begin to form, terminal bars appear at the distal ends of ameloblasts, separating T.P. from the cell proper. Structurally the terminal bars are localized condensations of lytoplasmic substance closely associated with thickness code membrane. The function is unknown. Ameloblasts covering maturing enamel Ameloblasts over maturing enamel are considerably shorter than the ameloblast over in completely formed enamel, these short ameloblasts have a villous surface near the enamel, and the ends of the tell are packed with mitochondria.  Their morphology is typical of absorption cells, organic components and water are lost in minerlization due to the obsorptive property of ameloblasts. 22
  23. 23. Mineralization and Maturation of enamel matrix Mineralization takes place in two stages 1. Immediate partial mineralization. 2. Maturation  Immediate partial mineralization occur in those matrix segment and inter prismatic substance as they are laid down. ( this amount to 25% to 30% of total mineral content).  First mineral actually is in the form of crystalline apatite.  Maturation – is the gradual completion of mineraliztion, maturation process starts from the height of the crown and progress cervicaly.  The incisal and occlusal regims reach maturity ahead of the cervical regims. Maturation is characterized by growth of the crystal seen an primary phase, crystal increase in thickness more rapidly than width, same time organic matrix gradually become thinned and widely spaced to make room for the growing crystals. This loss of volume of organic matrix is caused by with drawn of substantial amount of protein as well as water. 23
  24. 24. Cervical loop At the free border of the enamel organ the outer the outer and inner enamel epithelial layer are continuous and reflected into on outer as the cervical loop. When the crown has been formed the cells of this portion given rise to Hertwig’s epithelial root sheath. 24