The enamel is the outermost covering of the tooth crown. It is the hardest tissue in the body, composed mainly of inorganic hydroxyapatite crystals and water. Histologically, enamel is made up of enamel rods that extend from the dentin into the enamel in a pattern that provides strength. The rods are arranged into Hunter-Schreger bands that further reinforce the enamel. Properties of enamel allow it to function in mastication but also make it susceptible to conditions like dental caries if not properly cared for and maintained. Clinical applications include fluoride to strengthen enamel, acid etching to promote bonding in restorations, and bleaching to change the appearance of enamel.

1. ENAMEL
Guided by:
Dr.(Prof.) Debaprasad Das
Dr.(Prof.) Anirban Bhattacharya
Dr. Asim Bikash Maity (Sr. Reader)
Dr. Mahboob Rahman (Sr. Lecturer)
The function of the enamel is to form a resistant covering of the
teeth,
rendering them
suitable for
mastication.

2. The outermost
Covering of the crown
Of the tooth.

3. CONTENTS
Introduction
Characteristic properties (Physical/ Chemical)
Histology
Clinical consideration
Clinical implications

4. INTRODUCTION
• It is a hard, highly mineralized, dead, ectodermal
in origin covering the anatomical crown of the
tooth.

5. PHYSICAL CHARECTERISTICS
• Hardest calcified tissue in the human body.
• It is a semi permeable membrane.
• Color of the enamel covered crown ranges from
yellowish white to grayish white.
Colour is determined by translucency of the
enamel. Yellow colour is because of thin enamel,
through which yellow colour of dentin is visible.
Grayish white color is because of opaque enamel.
Translucency is attributed to variation in the degree
of calcification and homogeneity of enamel.

6. • Specific gravity- 2.8
• Density decreases from surface to deeper
regions.
• It has been observed as an non electrical
conductive material; in fact is an insulator in
room temperature.
• Knoop hardness Number is 343.

7. CHEMICAL CHARECTERISTICS
• Consists mainly of inorganic(96%) and organic
materials and water (4%).
• Organic materials- consist of unique proteins in the
enamel as Amelogenins(90%) and
Nonamelogenins(10%).
Amelogenins are heterogenous group of low molecular
weight, rich in proline, histidine, glutamine and leucine.
Nonamelogenins are high molecular weight proteins rich
in glycine, aspartic acid and serine.

8. • Inorganic material- they are hydroxyapetite, and
the crystals are hexagonal in cross-section. The
crystals are arranged to form enamel
rods/prisms.

9. • Average concentration of enamel constituents:
Major: oxygen- 43.4%
calcium-36.6%
phosphorus-17.7%
Minor: sodium-0.67%
carbon-0.64%
magnesium-0.35%
• Water is present as a part of the crystals
(hydroxyapetite), between crystals and between
rods and surrounding the rods.

10. HISTOLOGY

11. STRUCTURE OF ENAMEL
•ENAMELRODS
•HUNTER-SCHREGERBANDS
•INCREMENTALLINEOF RETZIUS
•ENAMELCUTICLE
•ENAMELLAMELLAE
•ENAMELTUFTS
•DENTINOENAMELJUNCTION
•ENAMELSPINDLES

12. ENAMEL RODS/PRISM
• Enamel rods, under light microscopy, appear
hexagonal, round or oval.
• In cross section of human enamel rods resemble
fish scales.

13. • Rods vary in various teeth. Its 5millions in the lower
incisors and upto 12millions in upper first molar.
• Enamel rods extend the full thickness of enamel.
• The average diameter of the
prism is 4µm near the
dentinal surface and
increases to about
8µm at the surface
to compensate for the
greater outer surface.

14. DIRECTION OF RODS
• Generally rods are oriented at right angles to the
dentin and horizontal in cervical and central parts
of the crown of a deciduous tooth.
• Near incisal edge or cusp tip they gradually
change in oblique
direction and are
vertical in the
region of edge or
cusp tips.

15. • The arrangement of rods in permanent teeth is
similar in the occlusal two thirds of the crown.
However in cervical region deviate from horizontal
to apical direction.
• Follow a wavy course from dentin to enamel
surface.

16. • Course of enamel rods is important in cavity
preparations. Rods run perpendicularly to the
underlying dentin or tooth
surface and horizontal close
to cement-enamel junction.
While cavity preparations,
unsupported enamel rods
should not be left at cavity
margins as they would soon
break and cause leakage,
resulting in bacterial lodgment
in these spaces, inducing
secondary dental caries.

17. • GNARLED ENAMEL:
Near the dentin in the region of the cusps or the incisal
edges, the rod arrangements appear to Intertwine
irregularly. This optical
appearance of enamel is
called
GNARLED ENAMEL.
It is not subjected to fracture as much as a regular
enamel.

18. HUNTER-SCHREGER BANDS
• The change in direction of rods is responsible for the
appearance of the Hunter-Schreger Bands.
• These are alternative dark and light strips of varying
widths seen in a longitudinal ground section under
oblique reflected light.

19. • Originate at dentinoenamel border and pass
outward ending at some distance from outer
enamel surface.
DEJ
H-S
BANDS
OUTER
ENAMEL
SURFACE

20. • Prisms that are cut longitudinally to produce dark
bands are called PARAZONES. Prisms cut
transversely to produce light bands are called
DIAZONES.
• Angle between parazones and diazones is about
40degree.

21. • Optimize resistance to attrition, abrasion and
tooth fracture.
• It appears that certain aspects of HSB packing
densities and distributions have beneficial roles
in enamel bonding.
• Hunter-Schreger Band patterns seem to
passively facilitate conditions such as abfraction
and cracked tooth syndrome.

22. INCREMENTAL LINE OF RETZIUS
• In longitudinally cut-ground section, they are seen
as series of dark brownish bands surrounding the
tip of dentin.
• In transverse ground section, they appear as
concentric rings.

23. • Perikymata or imbricational lines: Perikymata are
furrows or grooves that are created where the
Retzius lines reach the enamel surface. In human
deciduous teeth, perikymata are much more
scarce due to the scarcity of Retzius lines,
especially in the prenatal enamel.
• The first 30–40 striae are obscured under the
incisal edge. The average human incisor contains
about 150 brown striae.

24. ENAMEL CUTICLE
• The delicate membrane that covers the entire
crown of a newly erupted teeth but is soon
removed my mastication.
• Also known as NASMYTH’S MEMBRANE.

25. • This membrane is replaced by an organic
deposit called the PELLICLE.

26. • The spacing between the striae represents
about 7 days' growth; they have therefore been
used for determining the age of death in
contemporary humans and fossil hominids.
• Visible with light microscope due to its wavy
course.
• It is a typical basal lamina found beneath most
epithelia. This basal lamina is secreted by
ameloblasts when enamel formation is
completed.

27. • It is to protect the surface of enamel from
resorptive activity of the adjacent vascular
tissue prior to eruption of tooth.
• Micoorganisms may attach to pellicle, to form
bacterial plaque, and being acidogenic, can be a
potential precursor to dental disease.

28. ENAMEL LAMELLAE
• Thin leaf like structures that extends from enamel
surface to DEJ. Consists of organic material but with
low mineral content.
• In ground sections these
structures are sometime
confused with cracks.
• Reaches dentin
• Lamella extends in
longitudinal and radial
direction of the tooth,
the cervical region.

29. • 3types:
• Type A- lamella composed of poorly calcified rod
segments
• Restricted to enamel
from tip of the crown to
• Type B- lamella consisting of degenerated cells
• Reaches dentin
• Type C- lamella arising in erupted teeth where
the cracks are filled with organic matter.

30. ENAMEL TUFTS
• Arise at the DEJ and reach into the enamel
about one fifth to one third of its thickness.
ENAMEL TUFT

31. • It is a narrow ribbon like structure, inner end of
which arises at the dentin
• They are so named because they resembles
tuft of grass when viewed in ground sections.
• Consists of hypocalcified
enamel rods and
interprismatic substance.
• Extends in the direction
of long axis of the crown.

32. • Plays a role in spread of dental caries.

33. PRISMLESS ENAMEL
• A structureless outer layer of enamel of about
30µm thick found toward cervical area and less
in cusp tips, having no visible prism outline and
apetite crystals parallel to one another and
perpendicular to striae of Retzius are reffered
as prismless enamel.
• Heavily mineralized

34. • Microscopically, the surface is rough,
contributing to adherence of plaque material,
resulting caries attack.

35. DENTINOENAMEL JUNCTION
• The interface of enamel and dentin is known as
dentino-enamel junction.
• It is scalloped or wavy in outline, with
convexities towards the dentin.

37. • The rounded projections of enamel fits into the
shallow depression of dentin, assuring firm
attachment.
• More pronounced in occlusal area, where
masticatory stresses are greater.

38. • The scalloped nature of the DEJ confers a
biomechanical advantage to the integrity of the
tooth during mastication.

39. ENAMEL SPINDLES
• Originate from odontoblastic process and
extends upto enamel epithelium.
• They are hypomineralized or partially
mineralized structures.
• Found in cusp tip regions.

40. • Direction of spindles corresponds to the original
direction of the ameloblasts at right angles to
the surface of the dentin.
• Direction of spindles and rods is divergent.
• 2µm in diameter containing small needle like
crystals of about 70nm in length and 5nm in
width.

41. • Enamel spindles serve as pain receptors, thus
explaining pain sensitivity, during tooth
preparation.

42. CLINICAL CONSIDERATIONS

43. 1. Hypoplasia- manifested by pitting, furrowing or
even total absence of enamel.
• Occurs when matrix formation is affected.
• Hypoplasia of systemic origin is called “chronologic
hypoplasia”.
• Crowns are yellow-brown, smooth, glossy and hard
and their shape resembles teeth prepared for
jacket crown.

44. • Since systemic influences causing enamel
hypoplasia are during first year of life, so
incisors, canines and 1st molars are mainly
affected. Upper lateral incisors are sometimes
not affected as their development starts after
the mentioned teeth.
• Hereditary type enamel hypoplasia is a
generalized disturbance of the ameloblasts,
therefore entire enamel of all the teeth,
deciduous as well as permanent , is affected.
Enamels of such teeth are so thin that cannot
be noticed clinically or radiographically

45. 2. Hypocalcification - manifested by opaque or chalky
areas on normally contoured enamel surfaces.
• Occurs when maturation is lacking or incomplete.
• Deficiency in mineral content of enamel is found.
Example- Mottled enamel.
• (more than 1 part of fluoride per 1million parts of
water)

46. 3. Deep enamel fissures predispose teeth to
caries. Caries penetrate the floors of fissures
rapidly as enamel in these areas are very thin.
This destruction reaches the dentin and rapidly
spreads through dentino-enamel junction,
undermining their enamel without any warning
since the pathway is very minute.

47. 4. Dental lamellae is also a predisposing location
for dental caries because they contain much
organic material.

48. 5. The cervical region if not kept cleaned, and
becomes decalcified or rough, food debris,
bacterial plaques accumulates. The gingiva in
contact roughens, debris covered enamel
undergoes inflammatory changes leading to
periodontal diseases.

49. PIT & FISSURE
• Failure of the enamel of the developmental
lobes to coalesce results in a deep invagination
of the enamel surface, referred as FISSURE.
• Noncoalesced enamel at the deepest point of
fossa is termed as PIT.
• Pit and fissure act as food and bacterial traps,
predisposing the tooth to dentinal caries.

50. CLINICAL IMPLICATIONS

51. • FLUORIDATION:
Fluorides containing mixtures such as
stannous fluoride pastes, sodium fluoride
rinses and acidulated phosphate fluoride
are used to alter the outer surfaces of
enamel to make it more resistant to
decay.

52. • EFFECTS OF FLUORIDE ON ENAMEL:
Increases enamel reduction in enamel
solubility.
Increases rate of post eruptive maturation.
Remineralisation of incipient lesion.
Inhibition od demineralization
Interference with microorganism
Modification of tooth morphology.

53. • ACID ETCHING: Acid etching of the enamel
surface or enamel conditioning achieves the
desired effect in two stages- first, it removes
plaque and other debris, along with thin layer of
enamel; second, increases porosity of exposed
surfaces, providing better bonding surface for
restoration and adhesive materials.
Acid etching approximately removes 10µm of
enamel and creates a morphologically porous
layer of 5-50µm deep.

54. GIC: It is an attractive dental material, with
anticariogenic property due to release of
fluorides.
• The chemical adhesion of GIC to enamel and
dentin is achieved by reaction of phosphate ions
in the dental tissue with carboxylate groups from
polyacrylic acid.
• Surface conditioner: polycarboxylic, citric,
phosphoric acids acting as an etchant removes
smear layer and improves bond strength.
(open access materials, 2010, Ulrich Lohbauer)

55. • REMINERALIZATION & REPAIR OF ENAMEL SURFACE
BY BIOMIMETIC ZN- CARBONATE HYDROXYAPETITE:
• The deposition of a synthetic nanostructured
carbonate hydroxyapetite microcrystals rich coating
could lead o remineralizing/repairing effect of the
enamel surface, in the teeth treated using Zn-CHA
toothpaste.
• Only the use of a toothpaste containing Zn-
substituted CHA nanocrystals can produce a
biomimetic coating on the enamel surface, thus
mimicking the composition, structure, morphology
and surface reactivity of the biological enamel
hydroxyapetite.
• (frontiers in philosophy, 5 september 2014)

56. CLASS II COMPOSITE RESTORATION: IMPORTANCE
OF CERVICAL ENAMEL
The fracture strength of the marginal ridge in
composite classll restoration that extend below is
significantly lower than when the restoration margin
is located coronally to the CEJ. The area of available
cervical enamel in the preparation has a positive
influence on the fracture strength. Classll restoration
that extend below the CEJ have a predominance of
adhesive fracture, while those with available cervical
enamel have a predominance of cohesive fractures.
(Operative Dentistry, 2011, 36-2, 187-195, T Laegreid, NR Gjerdet, PV von Steyern,A-K
Johansson)

57. • OZONE TREATMENT:
• It’s a powerful biocide. It rapidly penetrates the
bacteria and kill them and their niche.
• Alters metabolic production of bacteria that
inhibits mineralization.

58. • BLEACHING:
• High concentration of carbamide peroxide(35-
37%) is indicated as pre-treatment and in
association with at-home vital bleaching.
• Minor superficial alterations were noted for 37%
carbamide peroxide.
• According to clinical experiences and researches ,
daily exposure to 10% carbamide peroxide is
apparently safe and effective procedure for
whitening tooth hard tissues.

60. • As a result of bleaching regimens, reduction in
Knoop microhardness due to mineral loss can be
naturally controlled by saliva, and with
remineralization solution such as artificial saliva
and fluorides.
• No remineralizing effect can recover the enamel
initial surface roughness promoted by polishing
with diamond pastes during specimen
preparation. To recover surface smoothness and
lustrous, high concentrated hydrogen peroxide gel,
are applied. Enamel polishing after bleaching
session is required.

61. THANK YOU!!