This document discusses the structure and properties of enamel. It begins with an overview of the layers of the tooth and describes enamel in more detail. Enamel is composed primarily of hydroxyapatite crystals arranged in prisms/rods. It covers the anatomical crown and is the hardest substance in the body. The document outlines various properties of enamel like thickness, hardness, permeability, and discusses its microscopic structure including rods, interrod substance and enamel lamellae. It also compares primary and permanent enamel and summarizes the processes of amelogenesis and age-related changes in enamel.

3.  Introduction
 Physical properties
 Chemical properties
 Structure[Histology]
a. Enamel prism
b. Direction of rods
c. Inter rod substance
d. Striation
e. Direction of rod
f. Hunter scherger bands

4. g. Surface structures
h. Enamel lamelle
i. Enamel tuft
j. DEJ
k. Enamel spindle
 Diff. bw primary & permanent tooth
 Amelogenesis
 Age changes.
 Clinical considerations
 Conclusion.
 Reference

5.  Tooth Layers
› Enamel
› Dentine
› Pulp
› Cementum
 ENAMEL
› The anatomic crown of a tooth is covered by an acellular,
avascular, highly mineralised material known as ENAMEL.

6.  Thickness
 Hardness
 Tensile strength
 Permeability
 Color
 Translucency
 Solubility

7.  Thicker at incisal & occlusal areas
 Thinner at CEJ
 CLINICAL SIGNIFICANCE ???
Incisors – 2mm
Premolars – 2.3 to 2.5mm
Molars – 2.5 to 3mm

8. HARDNESS
 Hardest calcified tissue in the human body
 It forms a resistant covering of the teeth –helps in mastication
 Hardness may vary over the external tooth surface according to
location; it decreases inward with hardness lowest at DEJ

9.  Although it is hard , enamel is extremely brittle thus it has low
tensile strength and depends on the strength of the underlying
dentin.
 CLINICAL SIGNIFICANCE ???
TENSILE STRENGTH

10.  Enamel is selectively permeable, permitting partial
or complete passage of ions due to the presence of
microscopic pores.
PERMEABILITY

11. COLOR
 Light yellow to grayish (bluish white)
 CLINICAL SIGNIFICANCE ???

12.  Translucency depends on degree of calcification &
homogeneity of enamel
 Translucency increased with increasing wavelengths
 Transmission co-efficient at 525nm was 0.481 mm-1
 Dehydration decreased the translucency but it was
reversed on rehydration
TRANSLUCENCY

13. Enamel dissolves in acid media.
Its surface is less soluble than deep enamel.
 Clinical significance???
SOLUBILITY

14.  Inorganic material – 96%
 Organic substance & Water – 4%

15.  Crystals are Hexagonal in cross section
› Shape of a single crystal was observed in SEM to be
a rod with equilateral hexagon base
› Crystals are arranged to form enamel rods or prisms
› The core of crystal the crystals are richer in Mg &
carbonate & this accounts for their greater solubility
in acids than peripheral portions

16. HYDROXYAPATITE CRYSTALS ETCHED ENAMEL

17. › Proteins
 Amelogenins
 Nonamelogenins
 Amelogenins (90%)
› Hydrogenous group of low molecular weight protein
› Hydrophobic – rich in proline, histidine, & leucine
 Nonamelogenins (10%) [enamelin, ameloblastin, tuftelin]
› High molecular weight protein rich in glycine, aspartic acid
& serine

18. › Present as a part of the crystal, b/w crystal & b/w rods &
surrounding the rods
› Also present in pores present b/w the crystal

19.  Prisms or rods.
 Rod sheath.
 Inter-prismatic substance.
 Striations.
 Direction of rods.
 Hunter-Schreger bands.
 Incremental lines.
 Surface structures.
 Enamel lamellae.
 Enamel tufts.
 Dentino-enamel junction.
 Odontoblastic processes and enamel spindles.

21.  Basic unit of enamel
 Number: 5 – 12 millions.
 Direction: Run in oblique direction and wavy course.
 Length: greater than the thickness.
 Diameter average: 4 µm.
 Appearance: Have a clear crystalline appearance.

23. › Usually at right angles to the Dentinal surface.
› Follow a wavy course in clockwise and anticlockwise
deviation.
› At the cusps or incisal edges: gnarled enamel.

24. › A thin peripheral layer.
› Darker than the rod.
› Relatively acid-resistant.
› Less calcified and contains more organic matter than
the rod itself.

25. › Cementing Enamel rods together.
› More calcified than the rod sheath.
› Less calcified than the rod itself.
› Appears to be minimum in human teeth.

26.  Optical appearance of enamel cut in oblique plane
 Bundles of rods appear interwine more irregularly

27. › Each enamel rod is built up of segments separated by
dark lines give it a striated appearance
› These striations are more pronounced in enamel that is
insufficiently calcified
› The rods are segmented because enamel matrix is formed
in rhythmic manner - uniform length of 4nm

28. › Alternating dark and light strips.
› Have varying width.
› Seen in longitudinal ground section (oblique reflected light).
› Originate from the DEJ.
 The dark bands (Diazones) absorb the light where the light bands
(Parazones) reflect the light….

29. › Incremental Lines of Retzius
› Neonatal Line

30. Incremental Lines of Retzius
› Brownish bands in ground sections.
› Reflect variation in structure and mineralization.
› Broadening of these lines occur in metabolic disturbances
› Etiology
 Periodic bending of E. rods.
 Variation in organic structure.
 Physiologic calcification rhythm.

31. Neonatal Line
› The Enamel 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.

32. Etiology
•Due to sudden change in the environment and nutrition.
•The antenatal Enamel is better calcified than the
postnatal Enamel
•The quality of enamel formed before birth is better than
that formed after birth, because of the more protected
conditions and constant nutrition of the fetus

33.  Structureless layer (E. skin)
 Perikymata
 Rod ends
 Cracks
 Enamel cuticle

34. › About 30 µm thick.
› In 70% permanent teeth and all deciduous teeth.
› Found least often over the cusp tips.
› No Enamel 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.

35. › Transverse wave like grooves.
› Thought to be the external manifestation of
the striae of Retzius.
› Lie parallel to each other and to CEJ

36. › 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.
› 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

37. › Are concave and vary in depth and shape.
› Are shallow in the cervical regions.
› Deep near the incisal or occlusal edges.

38. › 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.

39. 1. Primary E. cuticle (Nasmyth’s membrane).
2. Secondary E. cutile (afibrilar cementum).
3. Pellicle (a precipitate of salivary proteins).

40. Primary E. cuticle (Nasmyth’s membrane)
 Covers the entire crown of newly erupted tooth.
 Thickness: 0.2 µm.
 Removed by mastication (remains intact in
protective areas).
 Secreted by postamloblasts.

41. Secondary E. cutile (afibrilar cementum).
 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 Enamel organ retracted from the cervical region
during tooth development

42. Pellicle (a precipitate of salivary proteins).
 Re-form within hours after mechanical cleaning .
 May be colonized by microorganisms to form a bacterial
plaque.
 Plaque may be calcified forming calculus.

43.  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.

44.  Represent site of weakness in the tooth and
three types; A, B, and C.
 They are faults that develop as a result of
failure of maturation processes. They are
filled with organic material and water

45. TYPE A TYPE B TYPE C
CONSISTENCY Poorly calcified
rod segments
Degenerated
cells
Organic matter
from saliva
TOOTH unerupted unerupted erupted
LOCATION Restricted to E Restricted to D Restricted to D
OCCURENCE Less common Less common More common

46.  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 hypo calcified E. rods and
interprismatic substance.

47.  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.

48.  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.
A, Enamel spindle; B, Odontoblastprocess; C, Enamel rod

49.  Scalloped junction – the convexities towards Dentine
 The outline of the junction is preformed by the arrangement of
the ameloblasts and the Basement membrane.
 This helps in better interlocking between enamel and dentin.

50. PRIMARY TOOTH PERMANENT TOOTH
Thickness Thinner (1mm) Thicker (2-3mm)
Rods In cervical area directed occlusally In cervical area directed
gingivally
Bands of retzius Less common More common
Contacts Broad & flat Point contacts
Color Usually lighter Darker
Mammelons Incisors have no developmental grooves
or mammelons
Newly erupted incisors-
present
Caries rate More prone to acid attack – increased
caries rate
Less prone to caries attack
Neonatal line seen Not seen in permanent tooth
except in permanent first
molar

52.  The process of amelogenesis involves
› MATRIX FORMATION
› MINERALIZATION
› MATURATION

55.  MORPHOGENIC STAGE
 ORGANIZING STAGE
 FORMATIVE STAGE
 MATURATIVE STAGE
 PROTECTIVE STAGE
 DESMOLYTIC STAGE

61.  Cells of REE release enzymes that cause dissolution of C.T
cells, over it.

62.  Attrition
 Modification of surface layer
 Increase in inorganic content
 Decrease permeability
 Decrease in water content.
 Change in color of tooth.

64.  BACTERIAL
› Caries
 NON BACTERIAL
› Attrition
› Abrasion
› Erosion
› Abfraction

65.  DENTAL CARIES
It is an infectious, microbiologic disease of teeth that results
in localized dissolution and destruction of the calcified
tissues.
 ENAMEL CARIES
› Smooth surface caries
› Pit & fissure caries

66.  Initial lesion - white spot
 Eventual loss of continuity of the enamel
surface which feels rough to the point of an
explorer
 It typically forms a triangular or a cone shaped
lesion with the apex towards the DEJ and the
base towards the surface
 The carious process has extended into dentin
but there is still no cavitation

67.  Caries beginning in a fissure with
decalcification extending from its
sides and bottom.
 It forms a cone shaped lesion with
the base at the DEJ and apex at
towards the surface
 It reaches the dentin and spreads
laterally.
 There is separation of enamel and
dentin and fracture of the enamel roof.

68.  SURFACE ZONE
 BODY OF THE LESION
 DARK ZONE
 TRANSLUCENT ZONE

69. › Attrition
› Abrasion
› Erosion
› Abfraction

70.  Defined as physiological continous, process
resulting in loss of tooth structure from direct
frictional forces between contacting teeth.
• It occur both on occlusal and approximal
surfaces.
• Attrition is accelerated by parafunctional
mandibular movements, especially bruxism.

71.  Pathologic wearing away of tooth substance through
some abnormal mechanical process.
(mechanical wear other than mastication)
 Generally occurs on exposed surfaces of roots.

72.  Irreversible loss of dental hard tissue by a chemical
process that does not involve bacteria.

73.  Pathologic loss of both enamel and dentin caused
by biomechanical loading forces.

74.  Amelogenesis
Imperfecta
 Enamel Hypoplasia
 Mottled Enamel
 Enamel Pearls
 Tetracycline Stains

75.  A structural defect of tooth enamel.
 There is disturbance in the differentiation or viability
of ameloblast.
 Both deciduous as well as permanent dentitions
usually are involved.
 Three types:
hypoplastic(60-73%),
hypocalcified(7%), and
hypomature(20-40%).
 No specific treatment, except for improvement of
cosmetic appearance

76. Hypoplastic AI
Hypocalcified AI
Hypomature AI

77.  Incomplete or defective formation of organic
enamel matrix.
 Rickets during formation of enamel is most
common cause of Enamel hypoplasia.
 vitamin A & C have been named as
cause.
 Considerable controversy are there about any
relation between caries & enamel hypoplasia.
It is most reasonable to assume that the two
are not related, although hypoplastic teeth
appear to decay at somewhat more rapid rate
once caries has been initiated.

78.  Term mottled enamel is described by GV Black and Frederick S McKay in
1916.
 Ingestion of fluoride containing water during time tooth formation is most
important.
 More than 1 ppm of fluoride causes significant mottling.

79.  Arises from a small group of misplaced
ameloblast.
 Common in bifurcations or trifurcations of
maxillary molars.

80.  Discoloration occurs due to prophylactic administration of
tetracycline to pregnant female or postpartum in the infants.
 Yellowish or brownish-gray discoloration.
 Crucial period is 4 months in utero to about 7 years of age.

81.  It is important technique in clinical practice.
 It involves use of etchant to produce change in surface
texture of enamel.
 There are three types of Enamel etching seen
Type A- Dissolve enamel prism core
Type B- Dissolve prism peripheries
Type C- no prism structure is evident.

82.  It achieves desired effects in two stages:-
1) Removes plaque and other debris
2) Increases the porosity of exposed surfaces
 Increases the free surface energy of enamel.
 Micromechanical bonding.

83.  Bleaching may be defined as the lightening of color of
tooth through application of chemical agent to oxidize
organic pigmentation of tooth.
 H₂O₂ has low molecular weight that enables it to fuse
through enamel.

84. Microabrasion techniques improve appearance of fluorotic teeth.
› McCloskey reported that Kane successfully removed fluorosis stains by
applying acid and heat in 1916.
› In 1960s, McInnes used five parts of 36% HCL, five parts of 30% H₂O₂
and one part of Ether.
Ether – Removes surface debris
HCL – Etches Enamel
H₂O₂- Bleaches Enamel
Fluoride-stained teeth are difficult to bleach and require longer and repeated
sessions to decolorize them.

85. An alternative method to removal of superficial white spots.
Uses a 12-fluted composite finishing bur or a fine grit
finishing diamond at high speed.
Next, a 30-fluted composite finishing bur is used.
Final polishing is achieved with an abrasive rubber point.

86.  Increases resistance to caries.
 When laser technique is used with fluoride -cavities
were completely stopped.

87.  Life long preservation of the patient’s own enamel is one of the
defining goals of the dentist
 Although enamel is capable of life long service, its crystallized
mineral make up and rigidity as well as stress from occlusion,
make it vulnerable to acid demineralization (caries), attrition
(wear) and fracture
 Compared to other tissues mature enamel is unique in that
except for alterations in the dynamics of mineralization repair or
replacement is only possible through dental therapy

88.  Orban’s oral histology and embryology [ 12th edition]
 Text book of operative dentistry – sturdevant
 Grossman’s endodontics practice.[12th edition]
 Ten Cate’s oral histology [ 7th edition]
 Clinical operative dentistry –Remyaraghu and raghu
sreenivasan [2nd edition]