This document provides information on the composition, structure, and formation of enamel. It discusses the physical properties of enamel including its hardness, brittleness, thickness, color, wear resistance, permeability, and birefringence. It describes the microscopic structural units of enamel including enamel rods, rod sheaths, interrod substance, and how the rods are oriented. It covers other microscopic features such as Hunter-Schreger bands, gnarled enamel, Nasmyth's membrane, and the pellicle. It also discusses the dentino-enamel junction, age changes to enamel, and the process of amelogenesis.

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.

23. 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.

24. •

25. 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.

26. •

27. •

28. ENAMEL RODS
IN CROSS SECTIONS

29. 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.

30. 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.

31. •

32. •

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

34. 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.

35. 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.

36. DIRECTION OF
ENAMEL RODS

37. 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.

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

39. 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.

40. 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

41. NOTE CHANGE IN DIRECTION
OF ADJACENT ROD GROUPS
•

42. HUNTER-SCHREGER BANDS
•

43. 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.

44. •

45. 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.

46. 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.

47. •

48. •

49. 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)

50. 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 ???

51. 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.

52. 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.

53. 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)

54. 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.

55. •

56. •

57. 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.

58. •

59. •

60. 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”

61. 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

62. 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.

63. •

64. 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.

65. •

66. •

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

68. 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

69. 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)

70. •

71. •

72. 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.

73. •