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  1. 1. Done By : Dr.Mohamad Ghazi Kassem
  2. 2. • Enamel is an Epithelially derived hard, protective covering of teeth • Fully formed enamel is the most highly mineralized extracellular matrix known • It is highly brittle yet exhibits certain degree of resistance to withstand fracture
  3. 3. • Enamel is the hardest substance of the body, its hardness is comparable to mild steel. • Average knoop hardness number for enamel is approximately 343 • Surface of enamel is more mineralized and hard than deeper enamel. • Unlike other calcified structures in the body enamel is unique as it is totally acellular.
  4. 4. Composition of enamel Enamel consists of approximately 96% of inorganic material and 4% of organic material and water by weight. The organic component forms the matrix and the inorganic component comprises of various minerals. Percentage of dental tissue components by weight
  5. 5. The organic matrix of enamel is made from non-collagenous proteins and enzymes. Of the enamel proteins 90% are amelogenins and 10% are nonamelogenins. The different types of nonamelogenins associated with formation of enamel are ameloblastin, enamelin and tuftelin. The primary function of the organic material is to direct the growth of enamel crystals.
  6. 6. The inorganic component hydroxyapetite crystals. of enamel is comprised almost entirely of Enamel hydroxyapetite crystals are the largest hydroxyapetite crystals of all the calcified tissues in the body. In addition to hydroxyapetite crystals enamel also contains carbonates and trace elements. These crystals are susceptible to dissolution by acids and hence provides the basis for dental caries. SEM
  7. 7. Enamel is translucent and varies in colour from light yellow to whitish It varies in thickness, with maximum over cusps (2.5 mm) to a feather edge at the cervical line Thickness of enamel in primary teeth is nearly half than that in permanent teeth
  8. 8. Although enamel is an extremely hard tissue it is partially permeable to some fluids, bacteria and other products of the oral cavity The permeability of enamel is due to the presence of cracks and microscopic spaces on the surface of enamel which allows penetration of fluids The permeability of enamel decreases and hardness increases with age
  9. 9. Structure of enamel Rod and interrod enamel The fundamental units of enamel are rods and interrod enamel. The rod and interrod enamel is built from closely packed and long ribbon like hydroxyapetite crystals. The rod is shaped like a cylinder with a wide head portion, a neck and a thinner tail portion . Each rod is formed by four ameloblasts. SEM
  10. 10. ameloblasts SEM
  11. 11. Rods are formed nearly perpendicular to DEJ and curve slightly towards the cusp tip The follow a wavy course as the traverse from the DEJ to the surface of the crown The length of most rods is much longer than the thickness of enamel SEM
  12. 12. The diameter of the rod at the outer surface is double the diameter at DEJ Crystals that surround each rod are called interrod enamel Rod and interrod enamel is formed from the Tomes process of Ameloblasts SEM
  13. 13. The Tomes process of Ameloblasts
  14. 14. Enamel rod and Interrod enamel SEM
  15. 15. The boundary between rod and interrod enamel is marked by a narrow space filled with organic materials known as rod sheath Immunocytochemical preparation showing rodsheath
  16. 16. Dentino-enamel junction (DEJ) DEJ represents the interface between dentine and enamel It appears scalloped which increases the surface area and enable the two dissimilar matrices to interlock
  17. 17. SEM Scalloped nature of DEJ as seen with SEM
  18. 18. Features of enamel Enamel spindles Enamel spindles 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.
  19. 19. Enamel tufts Enamel tufts also originate from the DEJ, run a short distance in the enamel or sometimes to one half of the thickness. They represent protein (enamelin) rich areas in the enamel matrix that fail to mature. They are formed during the formative stages of enamel. Enamel Tufts
  20. 20. 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 process. • They are filled with organic material and water.
  21. 21. Cross striations Cross striations are periodic bands that appear along the full length of enamel rod (appears like a ladder). They appear at regular intervals that is in agreement with the rate of enamel deposition (which is approximately 4μm per day).
  22. 22. Striae of Retzuis Striae of Retzuis also represent incremental growth. In ground cross sections they appear like concentric growth rings similar to those found in trees. In ground longitudinal sections they appear to be dark line extending from the DEJ to the tooth surface.
  23. 23. where they end in shallow furrows know as perikymata (or imbrication lines)
  24. 24. Ageing and changes in enamel • Worn out because of masticatory attrition. • Decrease in the permeability of enamel. • Discoloration and a change in the surface layer. Enamel attrition and discoloration
  25. 25. Defects of enamel formation Generally three conditions effect enamel during its formative stages • Defects caused by febrile disease. • Defects caused by tetracycline. • Finally defects caused by excess fluoride. Dental Fluorosis (mottled enamel)
  26. 26. Fluoridation If fluoride ion is incorporated into the hydroxyapetite crystals then it becomes more resistant to acid dissolution. The amount of fluoride must be controlled because high fluoride can cause mottled enamel (in excess of 5ppm). Treated with sodium fluoride solution
  27. 27. TEM Treated with sodium fluoride solution
  28. 28. Acid etching Acid etching of enamel is a very important technique for conditioning enamel for many clinical procedures. Acid etching is used when doing fissure sealants, restoration, orthodontic bracket etc. It is carried out by using a mild acid like orthophosphoric acid on the enamel surface for a controlled period of time.
  29. 29. Enamel before acid etching Enamel after acid etching
  30. 30. SEM images of specimen conditioned with 37% phosphoric acid
  31. 31. Acidic Soft Drinks Effects The demineralization areas of enamel surface in the in vitro Coca-Cola group (1000X magnification).
  32. 32. The demineralization areas in enamel surface in the in vitro Sprite group (500X magnification).
  33. 33. Evaluation of the bleached human enamel by Scanning Electron Microscopy
  34. 34. Evaluation of the bleached human enamel by Scanning Electron Microscopy
  35. 35. References: • Scanning electron microscopic observation of morphological modifications produced by Fluorostom on enamel surface CRISTINA NICOLAE, MIHAELA HÎNCU, C. AMARIEI Faculty of Dental Medicine, “Ovidius” University, ConstantaRom J Morphol Embryol 2011, 52(4):1255–1259 • http://www.scielo.br/scielo.php?script=sci_arttext&pid=S167877572005000200021&lng=en&nrm=iso • http://www.sciencephoto.com/media/74508/view • http://www.sciencedirect.com/science/article/pii/S0300571209002127 • http://www.jbc.org/content/278/21.cover-expansion • http://i-need-more.com/amelogenesis-2/