physical and chemical properties, structure, age changes, clinical consideration of enamel. hypocalcified and surf

1. Enamel
Dr.madhusudhanreddy

3. Contents
• Introduction
• Physical characteristics
• Chemical characteristics
• Structure
• Development
• Life cycle of ameloblast
• Amelogenesis
• Clinical considerations

5. Introduction
• Enamel is an epithelially derived protective covering of
variable thickness over the entire surface of the crown
• It is the hardest biologic tissue in the body
• It attains the maximum thickness of about 2-2.5mm on the
cusps of molars and premolars.
• It thins down to almost knife edge at the neck of the tooth

6. Physical characteristics
PHYSICAL PROPERTIES
2-COLOR
5-PERMEABILITY
1-THICKNESS
4-BRITTLNESS
3-HARDNESS

7. Physical characteristics
1. Thickness
– 2.5 mm (thickest) over cusp of molar
– 2.0 mm over incisal edge
– Knife edge thickness at the cervical region
– Thick at maxillary lingual surfaces of molars and
mandibular buccal surface

8. 2. Color
– Depends on thickness and translucency of enamel
– Grayish white to yellowish white
– Yellowish – at thin areas underlying dentin
– Grayish – thick opaque enamel
– Bluish – incisal area

9. 3. Hardness
– Enamel is the hardest calcified tissue in the body due to
• 1) High content of mineral salts.
• 2) Its crystalline arrangement.
– Enamel of the permanent teeth is harder than that of the
deciduous ones.
– Enamel microhardness is
• 1) greater at the surface and decrease towards the
DEJ
• 2) greater at the cusp and incisal ridges and decreases
towards the cervical line.

10. 4. Brittleness
– Its structure and hardness render it brittle, specially
when it looses its elastic foundation of healthy dentin
5. Solubility: dissolves in acidic media
6. Permeability:
– It acts has a semi permeable membrane for certain ions
and dye stuffs of small molecular size through pores
between the crystals.
– Permeability is mainly from saliva to outer layers of
enamel. But less from the pulp to the inner enamel
layers across the dentin.
7. Specific gravity: 2.8
8. Translucency: semi translucent

11. Chemical properties
• Inorganic content – 96%
• Organic content – 4%
• Inorganic content
– Minerals
• Hydroxyapatite (calcium phosphate)
• Ions – strontium, megnesium, lead, fluoride.

12. • Organic content : mainly proteins (Amelogenenins, Non
Amelogenins)
• Amelogenins
• 90%
• Low molecular weight
protein
• Rich in proline, histidin,
glutamin, leucine.
• Non amelogenins
• 10%
• High molecular weight
• Proteins – ameloblastin,
tuftelin, enamelin.
• Rich in glycine, aspartic
acid and serine.

13. Structure of enamel
• Rods
• Rod sheath
• Inter-prismatic substance
• Striations
• Directions of rods
• Hunter-schreger bands
• Incremental lines of ritzius
• Surface structures
• Enamel cuticle
• Enamel lamellae
• Enamel tufts
• Dentinoenamel junction
• Odontoblast processes and enamel spindles

14. • Hypocalcified areas of enamel
– Rod sheath
– Incremental lines of ritzius
– Enamel lamellae
– Enamel tuft
– Enamel cracks
– Enamel spindles
– Neonatal lines

15. Enamel rods
• Basic structural unit
• Head of enamel rod is formed by one ameloblast and tail is
formed by three ameloblasts
• Thus each rod is formed by four ameloblasts
• Shape: hexagonal, oval , fish scale, key hole
• Starts from DEJ to outer enamel surface

16. • Number:
• Lower lateral incisor - 5 millions
• Upper 1st molar - 12 millions
• Course: Tortous from DEJ
• Length: greater than thickness of enamel
• Diameter: 4 µm in light microscopy.
• Increases from DEJ to outer enamel surface by a ratio of
1:2 since outer surface of enamel is greater than inner
surface
• Appearance : clear crystalline.

17. • Light microscopy:
• Rods appear hexagonal
• In cross section: fish scale appearance
• Recently – arcade outline near DEJ and keyhole outline at
enamel surface.

18. • Ultrastructure/ electron microscopy
• RODS surrounded by rod sheaths separated by interrod
substance.
• KEYHOLE or PADDLE- SHAPED pattern is observed.
• When cut longitudinally sections passes through heads or bodies
of one row and tails of adjacent row.
• Measures 5 µm in breadth and 9 µm in length.
• Bodies of rods are towards occlusal/incisal surface and tails
point cervically

19. • Hydroxyapatite crystals
• Arranged approximately parallel to the long axis of the
rods
• Length 0.05 to 1µm
• Width 90 µm
• Pyramid shape

20. The rod sheath
• A thin peripheral layer
• Darker than rod
• Relatively acid resistant
• Less calcified and contains more organic matter than the
rod itself

21. Inter-prismatic substance
• Cementing enamel rods together
• More calcified than the rod sheath
• Less calcified than the rod itself
• Appears to be minimum in human teeth

22. STRIATIONS
• Enamel rods is built up of segments of uniform length of
about 4µm, seperated by dark lines that gives it a straited
appearance
• More visible by action of mild acids
• Appearance is because of formation of enamel matrix in
rhythmic manner.
• More pronounced in hypocalcified areas
Cross-striation within a ground, longitudinal section of enamel

23. Direction of Rods
– ORIENTED at right angles to the dentin surface
– The bundles of rods seem to intertwine irregularly in
the region of cusp or incisal edges. This optical
appearance of enamel is called Gnarled enamel.
Direction of rods in deciduous
teeth Direction of rods in permanent
teeth

24. • In deciduous teeth, direction of rods is horizontal in
cervical and central parts of the crown. Near incisal edge
or tip of cusp they gradually increase in oblique direction
and almost vertical in the cusp tip region
• In permanent teeth, in occlusal two third of the crown
direction of rods is oblique.
• In cervical direction rods deviate from the horizontal in
apical direction

26. • GNARLED ENAMEL
• Near the dentin in the region of cusps or incisal edge,
bundles of rods seem to interwine more irregular,
especially in section cut obliquely. This optical appearance
of enamel is called gnarled enamel.

27. HUNTER- SCHREGER BANDS.
• Optical phenomenon seen in reflected light
• Seen in longitudinal ground section
• Due to abrupt change in direction of enamel rod
• Alternating light (diazones) and dark (parazones) strips of
varying widths best seen in longitudinal ground section
under oblique reflected light.
• Originate at the DEJ and pass outward, ending at some
distance from the outer enamel surface.

28. • Hunter schreger bands are due to
– Change in the direction of enamel rods
– Variation in calcification of the enamel
– Alternate zones having different permeability and
organic material

30. INCREMENTAL LINE OF RETZIUS
• Incremental lines of ritzius, Strae of ritzius
• Appear as Brownish bands in ground sections of enamel.
• Incremental pattern of enamel formation.
• In longitudinal sections - surround the tip of the dentin. In
cervical parts of the crown they run obliquely.

33. • In transverse section - appears as concentric circles.
• DEJ to outer surface of enamel
• Reflects variations in structure and mineralization that
occur during growth of enamel.
• Broadening of incremental lines may reflect metabolic
disturbance at the time of matrix formation
• NEONATAL LINE or NEONATAL RING: Accentuated
incremental line of Retzius.
• Where they end as shallow furrows known as perikymata

35. Neonatal line
• The enamel of the deciduous teeth and 1st permanent
molar (it is incremental line that is boundary between the
enamel formed before and after the birth)
• The neonatal line is usually the darkest and thickest striae
of ritzius
• Etiology
– Due to sudden change in the environment and nutrition
– The antenatal enamel is better calcified than the
postnatal enamel

37. • SURFACE STRUCTURES:
– Prismless enamel
– Perikymata
– Rod ends
• Enamel caps
• Enamel brochs
– Enamel cracks
– Enamel cuticle
– Enamel lamellae

38. • PRISMLESS ENAMEL
• About 30µm thick
• Present in 70% permanent teeth and all deciduous teeth
• Found least often over the cusp tips
• Found commonly in the cervical areas
• No enamel prisms visible.
• All the apatite crystals are parallel to one another and
perpendicular to the striae of ritzius
• More mineralized than the bulk of enamel beneath it,

39. • PERIKYMATA
• These are transverse wave like grooves, believed to be the
external manifestations of striae of ritzius
• 30 perikymata in number per mm in the region of CEJ
• Their concentration gradually decreases near occlusal or
incisal surface to about 10 per mm

41. • ENAMEL ROD ENDS
• These are concave and vary in depth
• They are shallow cervically and deep occlusally/incisally
• Pits - 1-1.5µm in diameter
• Enamel caps - 10-15µm elevations
• Enamel brochs - Larger enamel elevations

42. • ENAMEL CRACKS
• They are actually outer edges of lamellae
• Extent:
• They originate from incisal edge and extend to varying
distances in enamel in perpendicular direction towards
DEJ
• Length:1mm mostly

43. • ENAMEL CUTICLE
• The delicate membrane covers the crown of newely
erupted tooth called Nasmyths membrane or primary
enamel cuticle.
• This is soon removed by mastication
• This is secreted after epithelial enamel organ retracts from
cervical regions during tooth development
• It protects the surface of enamel from resorptive activity of
adjacent vascular tissue

44. • PELLICLE
• Erupted enamel is covered by a precipitate of salivary
proteins called pellicle
• This pellicle reforms within hours after mechanical
cleaning.
• It becomes colonized by microorganisms within a day or
two after formation which forms bacterial plaque

45. • ENAMEL LAMELLAE
• Thin leaf like structures that extend from enamel surface
towards DEJ
• Composition mainly organic, little mineral
• May be confused with cracks.
• Origin:
• Develops in planes of tension. When rods cross such a
plane, they may not fully calcify.
• If the disturbance is more severe, a crack may develop
• Crack is filled either by surrounding cells if it has occurred
in unerupted tooth, or by organic material if it has
occurred after eruption

46. • Types
• Type A : consists of poorly calcified rod segments
• Resticted to enamel
• Type B:
• Consists of degenerating cells. May reach into dentin
• Type C: containing organic material, presumably from
saliva.
• If connective tissue invades the cracks in enamel,
cementum may be formed

47. • Significance:
• It has been suggested that lamellae may be a site of
weakness in a tooth and may form a road of entry for
bacteria that initiate caries

49. `
• ENAMEL TUFTS
• Arises from DEJ
• Thin ribbon like structure, resembling tufts of grass which
is created by examining such area under low magnification
in thick ground section
• Tufts consists of hypo calcified enamel rods and
interprismatic substance.

50. • They arise at DEJ and reach to enamel to about 1/5 to 1/3rd
of its thickness
• Their presence and their development are consequence of
an adaptation to spatial condition of enamel
• Significance
• Enamel tuft prevents enamel fractures

52. • DENTINOENAMEL JUNCTION
• Scalloped structure: the surface of the dentin at DEJ is
pitted, in shallow depression of dentin, fir rounded
projection of enamel.
• It appears scalloped due to the mixing of crystals of dentin
and enamel with each other

53. • Significance of scalloping:
• It ensures firm hold of the enamel cap to dentin

54. • ENAMEL SPINDLES
• Occasionally odontoblastic process passes across DEJ into
enamel, since many are thickened at their end, they have
been termed enamel spindles.
• Directions of spindles and rods are divergent as rods are
formed at right angle to ameloblast and spindles are
parallel to ameloblasts.

57. • Hypocalcified areas of
enamel
– Rod sheath
– Incremental lines of
ritzius
– Enamel lamellae
– Enamel tuft
– Enamel cracks
– Enamel spindles
– Neonatal lines
• SURFACE
STRUCTURES:
– Prismless enamel
– Perikymata
– Rod ends
• Enamel caps
• Enamel brochs
– Enamel cracks
– Enamel cuticle
– Enamel lamellae

58. Age changes
• Most common change s are – attrition or wear of occlusal
and proximal surfaces
• Loss of verticle dimension of crown and by flattening of
proximal contour.

59. • Perikymata and rod ends
• At eruption these are prominent
• With age they reduce
• Generalized loss of rod ends
• Flattening of perikymata.
• The rate at which structures are lost depends upon
– Location of surface of tooth location of tooth in mouth

60. • WITH AGE
• Teeth darken
– Increase in organic content
– Deepening of dentin colour
• Decrease in permeability
• Fluoride ions increase with age
• Nitrogen increases with age
• Their resistant to decay may be increased
• Reduced permeability of older teeth to fluid
• Enamel may become harder with age

61. Clinical considerations
• Grooves and fissures on the occlusal surfaces of molars
and premolars – weak spots for the action of caries as the
maintenance is difficult – use of pit fissure sealants
• Lamellae, tufs and spindles may facilitate spread of caries.
• Striae of ritzius are the areas of hypomineralization thus
fecilitate the lateral spread of caries.
• Fluoridation decreases caries.

62. Clinical application
• Acid etching
• Removes plaque
• Increases porosity through selected dissolution