Enamel

A PRESENTATION COVERING THE COMPOSITION,STRUCTURE AND FORMTION OF ENAMEL.

1. ENAMEL COMPOSITION, STRUCTURE & FORMATION DR.VIGNESH R, BDS

2. CONTENTS PHYSICAL PROPERTIES OF ENAMEL CHEMICAL COMPOSITION MICROSCOPIC STUDY OF ENAMEL STRUCTURAL UNITS OF ENAMEL OTHER MICROSCOPIC FEATURES DENTINO-ENAMEL JUNCTION AGE CHANGES ENAMEL FORMATION - AMELOGENESIS

3. INTRODUCTION What makes Enamel unique? FORMS THE OUTER COVERING OF TOOTH CROWN THE ONLY EPITHELIAL COMPONENT OF THE TOOTH – DERIVED FROM ??? MOST MINERALIZED TISSUE IN HUMAN BODY – 96% minerals HARDEST SUBSTANCE IN HUMAN BODY.

4. PHYSICAL PROPERTIES HARDNESS BRITTLENESS THICKNESS COLOR WEAR & TEAR PERMEABILITY BIREFRINGENCE.

5. PHYSICAL PROPERTIES HARDNESS ENAMEL  HIGH MINERAL CONTENT (96%) EXTEREMELY HARD COMPARAED TO THAT OF MILD STEEL HELPS WITHSTAND MASTICATORY FORCES

6. PHYSICAL PROPERTIES BRITTLENESS HIGH CONTENT OF MINERALS (96%) ALONG WITH HARDNESS, MAKES ENAMEL VERY BRITTLE. VERY SUSCEPTIBLE TO FRACTURES UNDER PRESSURE / TRAUMA SUPPORT FROM UNDERLYING DENTIN HELPS PREVENT ENAMEL FRACTURE TO SOME EXTENT

7. PHYSICAL PROPERTIES THICKNESS IN NOT UNIFORM IN THICKNESS IN THE SAME PERSON & ON THE SAME TOOTH CUSP TIPS – MAXIMUM THICKNESS OF ABOUT 2.5 mm CERVICAL AREA – THINNEST – KNIFE EDGE LIKE CUSPS – GET THEIR FINAL SHAPING BY ENAMEL FORMATION.

8. PHYSICAL PROPERTIES COLOUR ENAMEL IS TRANSLUCENT . NO COLOUR OF ITS OWN REFLECTS THE YELLOWISH COLOR OF UNDERLYING DENTIN MORE TRANSLUCENT ENAMEL  TEETH APPEAR YELLOWISH IF ENAMEL OPAQUE  TEETH APPEAR MORE GRAY / BLUE.

9. PHYSICAL PROPERTIES WEAR & TEAR ENAMEL IS SUSCEPTIBLE TO FRACTURES SUPPORTED BY UNDERLYING DENTIN AVASCULAR DOES NOT REFORM AFTER IT IS LOST BY ATTRITION / FRACTURE .

10. PHYSICAL PROPERTIES PERMEABILITY ACTS LIKE A SEMI-PERMEABLE MEMBRANE ALLOWS THE PASSAGE OF ONLY SELECTED MOLECULES THROUGH IT. THIS PROPERTY IS MADE USE OF IN FLUORIDE TREATMENT OF TEETH AGAISNT DENTAL CARIES .

11. PHYSICAL PROPERTIES BIREFRINGENCE OPTICAL PROPERTY OF MINERAL CRYSTALS OF ENAMEL ?????

12. CHEMICAL COMPOSITION 96% INORGANIC MATTER 4% ORGANIC MATTER & WATER

13. CHEMICAL COMPOSITION INORGANIC MATTER: HYDROXYAPATITE CRYSTALS WITH CALCIUM & PHOSPHORUS IN THEM, smaller quantities of other minerals – Na, K, Cl, F, Mg, etc. ORGANIC MATTER AMELOGENINS – Low Molecular weight proteins, form 90% of enamel proteins NON AMELOGENINS – Complex group of proteins, form 10% of enamel proteins

14. MICROSCOPY OF ENAMEL How to Study??? Microscopic study of HARD tissues  By routine DECALCIFICATION, processing & staining techniques HEMATOXYLIN & EOSIN STAINS ENAMEL  96% MINERALIZED ALL MINERAL CONTENT WILL BE WASHED OFF DURING DECALCIFICATION. NO STRUCTURE WILL BE AVAILABLE FOR STUDY.

15. MICROSCOPY OF ENAMEL How to Study??? THE INORGANIC MINERAL CONTENT OF ENAMEL HAS TO BE PRESERVED GROUND SECTIONS ARE PREPARED & STUDIED. TOOTH IS SECTIONED, AND GROUND ON AN ARKANZA’S STONE TILL IT BECOMES VERY THIN (LES THAN PAPER THICKNESS) VIEWED UNDER MICROSCOPE WITHOUT STAINING  MINERAL CONTENT SEEN

16. TISSUE PROCESSOR MICROTOME

17. Arkanza’s Stone Ground Section of Tooth

18. MICROSCOPIC STRUCTURE OF ENAMEL SMALLEST STRUCTURAL UNIT OF ENAMEL  ENAMEL RODS IN CROSS SECTION – RODS - HEXAGONAL / PRISM LIKE STRUCTURE. HENCE THE NAME ENAMEL PRISMS USED BY SOME TEXT BOOKS.

19. ENAMEL RODS NUMBER OF RODS  5 MILLION (in lower laterals) to 12 MILLION (upper first molars) RODS ARE SEEN BOTH IN CROSS SECTIONS & LONGITUDINAL SECTIONS. THEIR APPEARANCE VARIES

20. ENAMEL RODS EACH ROD  CYLINDRICAL SHAPE EACH ROD  PACKED WITH MINERAL CRYSTALS CRYSTALS ARE ORIENTED ON THE RODS DIFFERENTLY IN DIFFERENT REGIONS OF THE SAME ROD. 3 STRUCTURES MAKE UP THE SMALLEST STRUCTURAL UNIT OF ENAMEL:

21. ENAMEL RODS ENAMEL RODS / PRISMS: Contains mineral crystals on them. ROD SHEATH: A narrow structure covering the rod structure, Organic. INTER-ROD SUBSTANCE: The highly organic portion present surrounding & in-between the rods.

22. ENAMEL RODS THE LENGTH OF RODS > THICKNESS OF ENAMEL RODS ARE NOT STRAIGHT RUN A WAVY COURSE IN ENAMEL . RODS IN CUSPS LONGER THAN RODS IN CERVICAL AREAS. DIAMETER OF RODS INCREASES FROM DEJ TO OUTER SURFACE.

23. ENAMEL RODS IN LONGITUDINAL SECTIONS EACH ROD IS SEEN TO HAVE: HEAD (ROUND) TAIL (NARROW) NECK (SMALL CONSTRICTION BETWEEN HEAD & TAIL) WHEN SECTIONS ARE CUT, THEY PASS THROUGH HEADS OF ONE GROUP OF RODS AND TAILS OF ANOTHER ROD GROUP BECAUSE THE RODS ARE PACKED TOGETHER IN ENAMEL IN DIFFERENT DIRECTIONS .

24. ENAMEL RODS IN CROSS SECTIONS

25. ENAMEL RODS IN CROSS SECTIONS MAY HAVE ONE OF THE FOLLOWING SHAPES: PATTERN I : THE ENAMEL RODS ARE CIRCULAR IN SHAPE. MORE INTER-ROD SUBSTANCE MAY BE SEEN HERE. PATTERN II : ENAMEL RODS ARE IN PARALLEL ROWS & ELONGATED.

26. ENAMEL RODS IN CROSS SECTIONS PATTERN III : ENAMEL RODS ARE IN STAGGERED ROWS. TAIL OF ONE ROD NESTS BETWEEN THE HEADS OF 2 RODS BELOW IT. MOST COMMON PATTERN IN HUMAN ENAMEL – TYPE III – KEY HOLE PATTERN . OTHER 2 PATTERNS-ALSO SEEN, BUT LESS EACH ROD CONTACTS 4 NEIGHBOURING RODS: ONE ABOVE, ONE BELOW, 2 ON EITHER SIDE .

27. ENAMEL RODS IN CROSS SECTIONS THE APPEARANCE OF ENAMEL RODS IN CROSS-SECTIONS IN HUMAS ALSO TERMED AS “FISH SCALE APPEARANCE”.

28. ENAMEL RODS MINERAL CRYSTALS ARE ARRANGED IN A ROD DIFFERENTLY IN HEAD OF THE ROD  CRYSTALS ORIENTED PARALLEL TO LONG AXIS OF THE ROD. IN THE TAIL REGION  CRYSTALS ORIENTED AT AN ANGLE OF 60-70 DEGREES TO THE LONG AXIS OF THE ROD.

29. DIRECTION OF ENAMEL RODS GENERALLY, RODS ARE AT RIGHT ANGLES TO THE DENTIN SURFACE IN CERVICAL AREA OF A TOOTH, RODS ARE HORIZONTAL NEAR CUSP TIPS / INCISAL EDGES , THEY ARE ALMOST VERTICAL BUT THEY ARE ALWAYS AT RIGHTANGLES TO DENTIN SURFACE.

30. DIRECTION OF ENAMEL RODS

31. ENAMEL RODS GROUPS OF ADJACENT RODS - RUN AROUND THE CIRCUMFERENCE OF THE TOOTH IN DIFFERENT DIRECTIONS ONE GROUP RUNS TO THE RIGHT THE ADJACENT GROUP RUNS TO THE LEFT.

32. ENAMEL RODS THIS SUDDEN CHANGE IN DIRECTION OF ADJACENT GROUPS OF RODS IS RESPONSIBLE FOR MANY OPTICAL EFFECTS IN ENAMEL STRUCTURE.

33. ENAMEL RODS WHEN LONGITUDINAL GROUND SECTIONS SEEN UNDER REFLECTED LIGHT ALTERNATE DARK & LIGHT BANDS SEEN IN THE ENAMEL STRUCTURE CALLED HUNTER-SCHREGER BANDS. CORRESPOND TO SUDDEN CHANGE IN DIRECTION OF ADJACENT ROD GROUPS, AND THE LIGHT WHICH PASSES THROUGH THEM.

34. ENAMEL RODS THOSE ROD GROUPS WHICH ALLOW MORE LIGHT THROUGH THEM – DARK BAND – DIAZONES THOSE WHICH TRANSMIT LESS LIGHT – LIGHT BANDS – PARAZONES . NOT TRUE STRUCTURE – OPTICAL PHENOMENA DUE TO SUDDEN CHANGE IN ROD DIRECTION

35. NOTE CHANGE IN DIRECTION OF ADJACENT ROD GROUPS

36. HUNTER-SCHREGER BANDS

37. GNARLED ENAMEL SUDDEN CHANGE IN DIRECTION OF ADJACENT ENAMEL ROD GROUPS ALSO PRODUCES ANOTHER OPTICAL PHENOMENON. IN SOME AREAS – CUSP TIPS, ROD BUNDLES SEEM TO INTERMINGLE WITH EACH OTHER. THIS HIGHLY IRREGULAR APPEARANCE OF ENAMEL RODS  GNARLED ENAMEL NOT TRUE STRUCTURE.

38. NASMYTH’S MEMBRANE PRIMARY ENAMEL CUTICLE A DELICATE MEMBRANE COVERING THE CROWN (ENAMEL) OF A NEWLY ERUPTED TOOTH REMOVED ONCE MASTICATION BEGINS. SECRETED BY AMELOBLASTS WHEN ALL ENAMEL FORMATION IS COMPLETED. TO PROTECT THE NEW CROWN DURING ERUPTION STAGE.

39. PELLICLE A COVERING SEEN ON FULLY ERUPTED CROWNS FORMED AFTER PRIMARY ENAMEL CUTICLE IS LOST. A PRECIPITATE OF SALIVARY GLYCOPROTEINS AFTER SCALING, THE PELLICLE RE-FORMS WITHIN 6-24 HOURS ON THE TOOTH SURFACE.

40. ENAMEL LAMELLAE THIN LEAF LIKE STRUCTURES EXTEND FROM OUTER ENAMEL SURFACE TO DEJ SOMETIMES EXTEND ACROSS DEJ INTO DENTIN MORE OF ORGANIC MATERIAL – ENAMEL PROTEINS (HYPOMINERALIZED AREA)

41. ENAMEL LAMELLAE SEEN BEST IN TRANSVERSE GROUND SECTIONS OF ENAMEL EARLIER, ANOTHER STRUCTURE CALLED “CRACKS” WERE DESCRIBED THOUGHT TO BE FAULTS DURING PREPARATION OF GROUND SECTIONS ON DEMINERALIZATION OF GROUND SECTIONS, CRACKS DISAPPEARED, WHILE LAMELLAE REMAINED ???

42. ENAMEL LAMELLAE NOW, BOTH LAMELLAE AND CRACKS ARE THOUGHT TO BE THE SAME MAY NOT BE ACTUAL STRUCTURES, BUT FAULTS DURING SECTION PREPARATION. TYPES OF LAMELLAE  H.W.

43. INCREMENTAL LINES IN ENAMEL ARE STRUCTURAL LINES IN ENAMEL DENOTE THE INCREMENTAL PATTERN OF ENAMEL DEPOSITION ENAMEL IS DEPOSITED IN INCREMENTS (LAYER BY LAYER) DISTANCE BETWEEN TWO ADJACENT LINES  RATE OF ENAMEL DEPOSITION .

44. INCREMENTAL LINES IN ENAMEL TWO TYPES OF INCREMENTAL LINES IN ENAMEL: SHORT PERIOD LINES = CROSS STRIATIONS LONG PERIOD LINES= LINES OF RETZIUS (STRIAE OF RETZIUS)

45. CROSS STRIATIONS SHORT PERIOD INCREMENTAL LINES AT AN INTERVAL OF 4µm. SHOWS THAT HUMAN ENAMEL IS FORMED AT THE RATE OF 4µm/ DAY. DENOTE DAILY INCREMENT OF ENAMEL FORMATION. ARE AT RIGHT ANGLES TO THE ENAMEL RODS.

46. STRIAE OF RETZIUS LONG PERIOD INCREMENTAL LINES DENOTE THE WEKLY PATERN OF ENAMEL DEPOSITION. SEEN BEST IN LONGITUDINAL GROUND SECTIONS IN LS, SEEN AS LONG DARK LINES, FROM DEJ TO TOOTH SURFACE, OBLIQUELY . IN CS , SEEN AS CONCENTRIC RINGS LIKE GROWTH RINGS OF TREE.

47. STRIAE OF RETZIUS THE STRIAE OF RETZIUS ARE SEEN CLINICALLY ON THE CROWN SURFACE AS TRANSVERSE WAVY GROOVES ON THE SURFACE OF ENAMEL THESE EXTRENAL MANIFESTATIONS OF STRIAE OF RETZIUS ARE CALLED “PERIKYMATA”

48. NEONATAL LINES ENAMEL OF DECIDUOUS TEETH & PERM. I MOLARS  PARTLY BEFORE & PARTLY AFTER BIRTH A CLEAR DEMARCATION BETWEEN THE PRE-NATAL & POST NATAL ENAMEL IN THE FORM OF A DARK LINE NEONATAL LINE

49. NEONATAL LINES PRE-NATAL ENAMEL  SMOOTH STRUCTURE (NO DISTURBANCE IN MOTHER’S UTERUS) POST-NATAL ENAMEL  MORE ROUGH STRUCTURE (DUE TO ENVIRONMENTAL EFFECTS) NEONATAL LINE  THOUGHT TO BE A PROMINENT STRIA OF RETZIUS .

50. DENTINO-ENAMEL JUNCTION JUNCTION BETWEEN ENAMEL & UNDERLYING DENTIN NOT A STRAIGHT LINE IS SCALLOPED ???? THE CONVEXITY OF ENAMEL INSERTS INTO THE CONCAVITIES OF DENTIN ALL CONVEXITIES FACE DENTIN .

51. DENTINO-ENAMEL JUNCTION MANY STRUCTURES ARE SEEN AT DEJ ENAMEL TUFTS ENAMEL SPINDLES ENAMEL LAMELLAE (which extend across DEJ)

52. ENAMEL TUFTS ARE STRUCTURES WHICH RESEMBLE A TUFT OF GRASS APPEAR TO ARISE FROM DEJ PROJECT FOR A SMALL DISTANCE INTO ENAMEL APPEAR TO ARISE FROM A SINGLE POINT AND THEN BRANCH NOT TRUE STRUCTURES

53. ENAMEL TUFTS THOUGHT TO OCCUR BECAUSE OF OPTICAL PHENOMENON WHEN GROUPS OF RODS CHANGE DIRECTION ABRUPTLY AT DEJ CONTAIN MORE OF ENAMEL PROTEINS (HYPOMINERALIZED AREA)

54. ENAMEL SPINDLES DURING FORMATION OF DEJ, SOME ODONTOBLAST PROCESSES (FROM UNDERLYING DENTINAL TUBULES) EXTEND INTO ENAMEL AS SMALL CLUB SHAPED STRUCTURES EXTEND TO SOME LENGTH OF ENAMEL ACROSS DEJ CALLED ENAMEL SPINDLES EXTENSIONS OF ODONTOBLAST PROCESSES – NOT A PART OF ENAMEL TRUE STRUCTURES.