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Dental Anatomy: Enamel

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This Slide, gives a Brief introduction to the Anatomy of the tooth specifically the outer shell, the enamel, including the structures, development and abnormalities.
Created by Dr. Mohsen S. Mohamed
For Ozident.com

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Dental Anatomy: Enamel

  1. 1. ENAMEL Dr. Mohsen S. Mohamed BDS, Misr International Universtiy, Cairo, Egypt. Certification, Universitätsklinikum Carl Gustav Carus. Owner and Author of OziDent.com Dental Anatomy Created For www.Ozident.com
  2. 2. Physical Characteristics 1. Forms a protective covering (2 mm – knife edge). 2. Forms a resistant covering (suitable for mastication). 3. The hardest calcified tissue in human body. 4. Brittle. 5. The specific gravity is 2.8. 6. Acts as semipermeable membrane. 7. Color: yellowish white to grayish white.
  3. 3. Tooth Layers longitudinal cross section of the Tooth showing : Enamel, Dentine, Pulp and Cementum
  4. 4. Chemical Properties • Inorganic materials (apatite crystals) 96% By weight • Organic substances and water 4% • In volume the organic matter and water are nearly equal to the inorganic contents.
  5. 5. Structure I. Prisms or rods. II. Rod sheath. III. Inter-prismatic substance. IV. Striations. V. Direction of rods. VI. Hunter-Schreger bands. VII. Incremental lines. VIII. Surface structures. IX. Enamel lamellae. X. Enamel tufts. XI. Dentino-enamel junction. XII. Odontoblastic processes and enamel spindles.
  6. 6. Enamel Rods or Prisms
  7. 7. Characteristics  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, oval, or fish scales.
  8. 8. Enamel Rods
  9. 9. Submicroscopic Structure Of Enamel Rods  Keyhole or paddle-shaped.  Separated by interrod substance.  About 5 µm in breadth and 9 µm in length.  The bodies are near the occlusal or incisal surface.  The tails point cervically.  The crystals; parallel to the long axis of the prism heads.  Deviate about 65° from the tails.
  10. 10. Keyhole shaped E. rods Hexagonal ameloblasts Note crystal orientation Enamel Rod’s Shape
  11. 11. Crystals in rod and inter-rod enamel are similar in structure but diverge in orientation
  12. 12. Enamel Crystal  Crystals length: 0.05 – 1 µm.  Thickness: about 300 A°.  Average width: about 900 A°.  Cross sections: somewhat irregular.
  13. 13. Enamel Crystal Longitudinal Section Transverse Section
  14. 14. A thin peripheral layer. Darker than the rod. Relatively acid-resistant. Less calcified and contains more organic matter than the rod itself. Electron Microscope : often incomplete. The Rod Sheath
  15. 15. •Cementing E. rods together. •More calcified than the rod sheath. •Less calcified than the rod itself. •Appears to be minimum in human teeth. Inter-prismatic Substance
  16. 16. •E. rod is built-up of segments (dark lines). •Best seen in insufficient calcified E. •Represent rhythmic manner of E. matrix formation. •Segment length: about 4 µm. Striations
  17. 17. Cross-striations
  18. 18. •Usually at right angles to the D. surface. •Follow a wavy course in clockwise and anticlockwise deviation. •At the cusps or incisal edges: gnarled enamel. •At pits and fissures: rods converge in their outward course. Direction of Rods
  19. 19. Direction of Enamel Rods
  20. 20. •Alternating dark and light strips. •Have varying width. •Seen in large ground section (oblique reflected light). •Originate from the DEJ. Hunter-Schreger Bands
  21. 21. Hunter-Schreger Bands
  22. 22. Hunter-Schreger Bands
  23. 23. Hunter-Schreger Bands This is Due to: 1. Change in the direction of E. rods. 2. Variation in calcification of the E. 3. Alternate zones having different permeability and organic material. 4. Optical phenomenon.
  24. 24. A. Incremental Lines of Retzius B. Neonatal Line Incremental Lines
  25. 25. Incremental Lines of Retzius:  Brownish bands in ground sections.  Reflect variation in structure and mineralization.  Broadening of these lines occur in metabolic disturbances.  Etiology 1. Periodic bending of E. rods. 2. Variation in organic structure. 3. Physiologic calcification rhythm.
  26. 26. Incremental Lines of Retzius:
  27. 27. Neonatal Line  The E. of the deciduous teeth and the 1st permanent molar develop partly before birth and partly after birth, the boundary between both is marked by neonatal line or ring.  Etioloyg  Due to sudden change in the environment and nutrition.  The antenatal E. is better calcified than the postnatal E.
  28. 28. Neonatal Line
  29. 29. SURFACE STRUCTURES Created For www.Ozident.com
  30. 30. Surface Structures a. Structureless layer (E. skin) b. Perikymata c. Rod ends d. Cracks e. Enamel cuticle
  31. 31. a. Structureless layer  About 30 µm thick.  In 70% permanent teeth and all deciduous teeth.  Found least often over the cusp tips.  Found commonly in the cervical areas.  No E. prisms.  All the apatite crystals area parallel to one another and perpendicular to the striae of Retzius.  More mineralized than the bulk of E. beneath it.
  32. 32. b. Perikymata  Transverse wave like grooves.  Thought to be the external manifestation of the striae of Retzius.  Lie parallel to each other and to CEJ.  Number:  About 30 perik./mm at the CEJ.  About 10 perik./mm near the incisal edge.  Their course is regular, but in the cervical region, it may be quite irregular.  Powdered graphite demonstrates them.  It is absent in the occlusal part of deciduous teeth but present in postnatal cervical part (due to undisturbed and even development of E. before birth)
  33. 33. The relationship between the striae of Retziuz and surface perikymata Striae of Retziuz Perikymata
  34. 34. c. Rod ends  Are concave and vary in depth and shape.  Are shallow in the cervical regions.  Deep near the incisal or occlusal edges.
  35. 35. Rod ends
  36. 36. d. Cracks  Narrow fissure like structure.  Seen on almost all surfaces.  They are the outer edges of lamellae.  Extend for varying distance along the surface.  At right angles to CEJ.  Long cracks are thicker than the short one.  May reach the occlusal or incisal edge.
  37. 37. Cracks
  38. 38. e. Enamel cuticle 1. Primary E. cuticle (Nasmyth’s membrane). 2. Secondary E. cutile (afibrilar cementum). 3. Pellicle (a precipitate of salivary proteins.
  39. 39. Primary enamel cuticle  Covers the entire crown of newly erupted tooth.  Thickness: 0.2 µm.  Removed by mastication (remains intact in protective areas).  Secreted by postamloblasts.  EM: similar to basal lamina.
  40. 40. Secondary enamel cuticle  Covered the cervical area of the enamel.  Thickness: up to 10 µm.  Continuous with the cementum.  Probably of mesodermal origin or may be elaborated by the attachment epithelium.  Secreted after E.O. retracted from the cervical region during tooth development.
  41. 41. Pellicle  Re-form within hours after mechanical cleaning .  May be colonized by microorganisms to form a bacterial plaque.  Plaque may be calcified forming calculus.
  42. 42. ENAMEL LAMELLAE Created For www.Ozident.com
  43. 43. Enamel Lamellae  Are thin, leaf like structures,  Develop in planes of tension.  Extends from E. surface towards the DEJ.  Confused with cracks caused by grinding (decalcification).  Extend in longitudinal and radial direction.  Represent site of weakness in the tooth and three types; A, B, and C.
  44. 44. Enamel Lamellae Type A Type B Type C Consistency Poorly calcified rod seg. Degenerated cells Organic matter from saliva Tooth Unerupted Unerupted Erupted Location Restricted to the E. Reach into the D. Reach into the D. Occurrence Less common Less common More common
  45. 45. Enamel Lamellae
  46. 46. Enamel Lamellae
  47. 47. ENAMEL TUFTS Created For www.Ozident.com
  48. 48. Enamel Tufts  Arise from DEJ.  Reach to 1/5 – 1/3 the thickness of E.  In ground section: resemble tufts of grass.  Do not spring from a single small area.  The inner end arises at the dentin.  Consist of hypocalcified E. rods and interprismatic substance.  The extend in the direction of the long axis of the crown (best seen in horizontal sections).
  49. 49. Enamel Tufts
  50. 50. Enamel Tufts
  51. 51. DENTINO-ENAMEL JUNCTION Created For www.Ozident.com
  52. 52. Dentino-Enamel Junction  Scalloped junction – the convexities towards D.  At this junction, the pitted D. surface fit rounded projections of the enamel.  The outline of the junction is performed by the arrangement of the ameloblasts and the B. M.
  53. 53. Dentino-Enamel Junction
  55. 55. Odontoblastic Processes and Enamel Spindles  The odontoblasts processes may cross DEJ (before the hard substance is formed) to the E. and ends as E. spindles.  They are filled with organic matter.  The processes and spindles are at right angle to the surface of the dentin.  The direction of spindles and rods is divergent.  Spindles appear dark in ground sections under transmitted light.
  56. 56. Odontoblastic Processes and Enamel Spindles
  57. 57. LIFE CYCLES OF THE AMELOBLASTS Created For www.Ozident.com
  58. 58. Life Cycles of the Ameloblasts  According to their function, can be divided into six stages: 1. Morphogenic stage. 2. Organizing stage. 3. Formative stage. 4. Maturative stage. 5. Protective stage. 6. Desmolytic stage.
  59. 59. Amelogenesis 1. Organic matrix formation (follows incremental pattern – brown striae of Retzius). 2. Mineralization.
  60. 60. Organic Matrix Formation a. Amelodentinal membrane. b. Development of Tome’s processes. c. Distal terminal bars. d. Ameloblasts covering maturing enamel.
  61. 61. dpTP=distal portion of Tome’s process ppTP=proximal portion of Tome’s process Sg=secretory granules(E. protein) Organic Matrix Formation
  62. 62. Ameloblasts are perpendicular to the rods (arrow=cell membrane, p=Tome’s process, s=incomplete septum)
  63. 63. Depression in enamel surface which were occupied by Tome’s processes
  64. 64. Mineralization a. Partial mineralization (25-30%). b. Maturation (gradual completion of mineralization).
  65. 65. Crystal Mineralization Recently formed crystals Mature crystals
  66. 66. Abnormalities  Interference during E. matrix formation may cause Enamel hypoplasia.  Interference during Enamel maturation may cause Enamel hypocalcification.  Each condition may be caused by systemic, local, or hereditary factors.
  67. 67. Abnormalities Enamel Hypocalcification Enamel Hypoplasia
  68. 68. THANK YOU ALL RIGHTS RESERVED 2013 OZIDENT Created For www.Ozident.com