presentation includes characteristics, properties ,functions, and anomalies related to enamel.

2.  PRESENTED BY
 DR MEENAL ATHARKAR
 MDS
 DEPT OF ENDODONTICS
AND CONSERVATIVE
DENTISTRY

3.  INTRODUCTION
 ENAMEL
 DENTIN
CEMENTUM
DENTIN
 CEMENTUM
 CONCLUSION
 REFERENCES

4.  Physical characteristics
 Chemical characteristics
 Functions
 Structure
Age changes Age changes
 Development
 Clinical considerations
 Anomalies

5.  Histologically, dental hard tissues include enamel,
dentin and cementum.
 Enamel- rigid, inert and acellular tissue that covers
the crown.
 Dentin- forms bulk of the tooth. Has a tougher
foundation that provides enough support forfoundation that provides enough support for
enamel.
 Cementum- in the root area, the dentin is covered
by cementum which anchors periodontal ligament
fibers.

6.  These tissues form a highly organised and complex
structure with ideal functional and structural
capabilities which assist in sustaining mastication
induced mechanical loading.

7.  Definition- Enamel forms a protective covering of
variable thickness over the entire surface of crown.

8.  Hardness- enamel is hardest calcified tissue in
the human body
- high content of mineral salts and their
crystalline arrangement.
- hardness and density decrease from- hardness and density decrease from
cuspal/incisal tips towards the cervical margin and
from surface towards dentinoenamel junction.

9.  Brittleness- the structure and hardness of enamel
render it brittle.
- compensated by cushioning effect of
underlying resilient dentin.
- more brittle than dentin.- more brittle than dentin.
 Permeability- act as a semipermeable membrane.

10.  Thickness- it varies with shape of tooth and its
location.
- on cusps of molars, premolars-
maximum thickness- 2-2.5 mm, thinning down to
almost a knife edge at the neck of tooth.almost a knife edge at the neck of tooth.
- enamel is thicker in palatal surfaces of
maxillary molars and in buccal surfaces of
mandibular molars.

11.  Color- yellowish white to grayish white.
- naturally transparent.
- translucency increases with age.

12.  Modulus of elasticity- more on surface- 84Gpa.
 Specific gravity- 2.8, decreases from surface to deeper
regions and from cuspal to incisal region.
 Enamel is nonelectrical conductive material and an
insulator at room temp.
 Compressive strength- 384 Mpa Compressive strength- 384 Mpa
 Tensile strength- 10 Mpa.
 Knoop hardness number- 350-430 KHN
 Solubility- it dissolves in acid media. Surface enamel is
less soluble than deeper enamel.
 Abrasion resistance- is high, allowing it to wear down
slowly.

13.  Composition:
Inorganic organic water
(96%) (1-2%) (4%)(96%) (1-2%) (4%)

14.  Inorganic composition:
 Main component is
hydroxyapatite.
 [Ca10(PO4)6(OH)2].
The crystals of The crystals of
hydroxyapatite are
hexagonal in cross section.
 The crystals are arranged
to form enamel rods and
enamel prisms.

15.  Organic composition:
 Proteins found in enamel- amelogenin and non
amelogenin.

16.  Water
 Is present as a part of crystal between crystals and
between rods and surrounding the rods.
 Pores are present between the crystals, especially at
the boundaries of the rods and these are filled withthe boundaries of the rods and these are filled with
water.

17.  It protects the less mineralised underlying dentin of
the tooth.
 It serves as a surface for chewing, grinding and
crushing of food.

18.  Rods-
 Enamel prisms are cylindrical, in
longitudinal section.
 No. of enamel rods ranges from 5
millions in the lower lateral incisors to 12millions in the lower lateral incisors to 12
millions in upper first molars.
 Diameter- 4 um.
 Have clear crystalline appearance,
permitting light to pass through them.
 Diameter of enamel rods increases from
DEJ to outer surface at a ratio about 1:2.

19.  The length of most rods is greater than the
thickness of enamel because of oblique direction
and wavy course of the rods.
 The rods located at the cusps are longer than the
cervical region of the teeth.cervical region of the teeth.
 In cross- sections of human enamel, rods resemble
fish scales.
 Newer studies show that rods have arcade outlines
near DEJ and keyhole shaped outlines at enamel
surface.

21.  Ultrastructure-
 keyhole or paddle shaped prism in human enamel.
 When cut longitudinally, sections pass through the heads or
bodies of one row of rods and the tails of an adjacent row.
 These rods measure about 5 micrometers in breadth and 9
micrometers in length.
 The bodies of rods are nearer occlusal and incisal surfaces
whereas tails point cervically.whereas tails point cervically.
 Polarized light and Roentgen ray study indicated that apatite
cystals are arranged approximately parallel to long axis of
prisms.
 Cystals take pyramidal shape with their bases towards DE J.
 Clinical significance- confer strength to enamel, their
direction is an important consideration in cavity preparation.

22.  Fracturing of unsupported rods in poorly designed
restorative preparations causes loss of enamel
around the margins of the filling material resulting
in marginal leakage and makes the tooth more
susceptible to carious attack.susceptible to carious attack.
 Additionally, it is also important to note that the
inclination of rods differs in permanent and primary
teeth and must be accounted for during cavity
preparation.

23.  Striations-
 each enamel rod is built up of segments
separated by dark lines that give it a striated
appearance.
 These cross striations demarcate rod
segments and become more visible by thesegments and become more visible by the
action of mild acids.
 The cross striations seen in light microscope
is suggested to be due to a diurnal rhythm
in the enamel formation and those in rods
show varicosities and variation in
composition.

25.  Direction of rods-
 generally, they are oriented at right angles to
dentin.
 in cervical and central parts of crown of a
deciduous tooth, they are approximately horizontal.

26.  Enamel rods are not always
straight.
If the disks are cut in an
oblique plane, especially near
the dentin in the region ofthe dentin in the region of
the cusps or incisal edges,
the rod arrangement appears
to be further complicated-
the bundles of rods seem to
intertwine more irregularly.
This optical appearance of
enamel is gnarled enamel.

27.  At the incisal edge or
cusp tip the enamel
rod has a twisted
course and is called
gnarled enamel
Gnarled
enamel
Twisted course of
enamel
rod
s
gnarled enamel

28. More or less changes in the direction of rods may be
regarded as functional adaptation minimizing the risk of
cleavage due to occlusal loading forces.
This changes in direction of rods is responsible for
appearance of the Hunter- Schreger bands.
Alternate Light And Dark Bands Of Varying Widths.Alternate Light And Dark Bands Of Varying Widths.
• Originate At Dentinoenamel Border & Pass Outward,
Ending At Some Distance From Enamel Surface.
• Can Be Best Seen In Longitudinal
Ground Section Under Oblique Reflected Light.

29.  Prisms That Are Cut Longitudinally –
Produce Dark Bands - Called Parazones.
 Those That Are Cut Transversely –
Produce Light Bands - Called Diazones
 Angle between them is 40 degree.

30.  Appear As Brownish Bands In Ground
Section.
They Illustrate Successive Apposition Of
Layers Of Enamel During Crown
Formation.Formation.
In Transverse Section - Concentric
Circles.
If Present In Moderate Intensity – Normal.
But Due To Metabolic Disturbances , Rest
Periods Become Unduly Prolonged – Lines
Become More Prominent

31.  In longitudinal sections, they surround the tip of
the dentin.
 In cervical parts, they run obliquely.
 Incremental lines reflect variations in structure and
mineralization that occur during growth of enamel.

32.  The enamel of deciduous
teeth develops partly
before and partly after
birth.
 The boundary between
the two portions of
enamel in deciduous
teeth is marked by an
enamel in deciduous
teeth is marked by an
accentuated incremental
line of Retzius, the
neonatal line or ring.
 It is the result of abrupt
change in environment
and nutrition of newborn
infant.
 The prenatal enamel is
better developed than
postnatal enamel.

33.  Prismless enamel-
 relatively structureless layer of enamel,
 approx 30 micrometers thick
 in 70% permanent teeth and all deciduous teeth.
In this surface layer no prism outlines are visible In this surface layer no prism outlines are visible

34.  Perikymata
 Outer surface of newly
erupted teeth
 Perikymata are transverse,
wavelike groove, believed
to be the external
manifestation of striae of
Retzius,Retzius,
 Ordinarily there are about
30 perikymata per
millimeter in the region of
CEJ and it decreases to 10
per millimeter near
occlusal/ incisal edge.

35.  Pits of 1-1.5 um in diameter and small elevations of
about 10-15 um called enamel caps.
 Larger enamel elevations- enamel brochs.

36.  Enamel cuticle-
 A delicate membrane called Nasmyth’s membrane, after
its first investigator or the primary enamel cuticle
covers the entire crown of newly erupted teeth.
 This cuticle is apparently secreted after the epithelial
enamel organ retracts from the cervical region duringenamel organ retracts from the cervical region during
tooth development
 It is visible in light microscope because of its wavy
course.
 Function- to protect surface of enamel from resorptive
activity of adjacent vascular tissue prior to eruption of
teeth.

37.  Erupted enamel is normally
covered by a pellicle, which
is apparently a precipitate
of salivary proteins.
 This pellicle reforms within
hours after an enamelhours after an enamel
surface is mechanically
cleaned with in a day or
two after the pellicle has
formed it is become
colonized by
microorganism to form
bacterial plaque

38.  Enamel lamellae-
 are thin leaf like structure extend the enamel
surface toward the dentinoenamel junction
 In ground section these structure may be confused
with cracks caused by grinding
 decalcification of ground substance of enamel
makes possible the distinction between cracks and
enamel lamellae
 Three types of lamellae can be differentiated
 Type A -lamellae composed of poorly calcified rod
segment
 Type B- lamellae consist of degenerated cell
 Type C-lamellae arising in erupted teeth
 Lamellae of type A are restricted to the enamel
surface those of type B and type C reach to dentin

39.  Enamel lamellae may
be the site of
weakness in a tooth
and may form a road
of entry for bacteria
that initiate caries.

41.  Enamel tuft-
 An enamel tuft is a narrow,
ribbonlike structure.
 Tufts consist of hypocalcified
enamel rod and
interprismatic substance.
 Like lamellae ,they extend in Like lamellae ,they extend in
the direction of long axis of
the crown
 SEM studies show that
enamel tufts are tubular
structures with cross
striations.

42.  Dentinoenamel junction-
 Dentinoenamel junction is not
a straight but as a scalloped
line
 The convexities of the
scallops are directed toward
the dentinthe dentin
 DEJ is preformed even before
the development of hard
tissue and is evident in the
arrangement of the
ameloblast basement
membrane of dental papilla

44.  Odontoblastic processes and
enamel spindles-
 when odontoblast process pass
across dentinoenamel junction,
thickened processes at the end
in the enamel are – enamel
spindles.
 a. enamel spindle-right angled a. enamel spindle-right angled
to the dentin
found mainly in cusp tips.

45.  Enamel is a nonvital tissue that is incapable of
regeneration.
 Most apparent age change is attrition or wear of
occlusal and proximal surfaces.occlusal and proximal surfaces.
 with age it becomes progressively worn away.
 enamel include discoloration, reduced permeability and
modification in the surface layer. these changes lead to
apparent reduction in the incidence of caries.
 Teeth darken with age.
 Enamel become less permeable with age
 Water content of enamel also decrease with age

46.  Epithelial enamel organ: 4 distinct layers-
 Outer enamel epithelium
 Stellate reticulum
 Stratum intermedium
 Inner enamel epithelium(ameloblastic layer)

47.  Outer enamel epithelium
 Single layer of cuboid cells separated by basement
membrane.
 Prior to the formation of hard structures, this
regular arrangement of outer enamel epithelium is
maintained only in cervical parts of enamel organ.
regular arrangement of outer enamel epithelium is
maintained only in cervical parts of enamel organ.
 During enamel formation, cells of the outer enamel
epithelium develop villi and cytoplasmic vesicles
and large number of mitochondria, all indicating
cell specialization for the active transport of
materials.

48.  Stellate reticulum
 Middle part
 Cells are star shaped with long processes reaching
in all directions from a central body.
 They are connected with each other and with the They are connected with each other and with the
other cells of outer enamel epithelium and stratum
intermedium by desmosomes.
 The structure of stellate reticulum renders it
resistant and elastic.

49.  Stratum intermedium
 The cells are situated between stellate reticulum
and inner enamel epithelium.
 Flat to cuboidal in shape.
 Arranged in one to three layers. Arranged in one to three layers.
 Tonofibrils found in cytoplasm.

50.  Inner enamel epithelium
 The cells are derived from basal cell layer of oral
epithelium.
 Before enamel formation begins, these cells assume
a columnar form and differentiate into ameloblastsa columnar form and differentiate into ameloblasts
that produce the enamel matrix.

51.  The hydroxyapatite crystal has a central core of
hydroxyl ion around which calcium and phosphorus
ions are arranged.
 During formation, magnesium can replace calcium
and carbonate can replace hydroxyl ion.and carbonate can replace hydroxyl ion.
 They destabilize the lattice due to poorer fit of
these ions in the lattice structure.
 The core of crystals are richer in Mg and carbonate
and this accounts for their greater solubility in acids
than peripheral portion.

52. Six stage
1) Morphogenic
2) Organizing
3) Formative3) Formative
4) Maturative
5) Protective
6) Desmolytic

53. 1.Morphogenic stage
 The cell are short and columnar with large oval
nucleus that almost fill the cell body
 The golgi apparatus and the centrioles are located
in the proximal end ,where as the mitrochondria are
evenly dispersed through out cytoplasm.
 Inner enamel epithelium is separated from the
connective tissue of the dental papilla by a delicate
basal lamina.

54. 2.Organizing stage
 In organizing stage of development the inner enamel
epithelium interacts with the adjacent connective tissue
cell,which differentiate into odontoblast
 This stage is characterised by the change in the
appearance of the inner enamel epithelium
3.Formative stage
The ameloblast enter their formative stage after the first The ameloblast enter their formative stage after the first
layer of dentin has been formed.
 The presence of dentin seems to be necessary for the
beginning of enamel matrix formation.
 Mutual interaction between one group of cells and
another is one of the fundamental laws of
oraganogenesis and histo differentiation.

55. 4.Maturative stage
 Enamel maturation( fully mineralization)occur after
most of the thickness of enamel matrix has been
formed in the occlusal or incisial area
During enamel maturation the ameloblast are During enamel maturation the ameloblast are
slightly reduced in length and are closely attached
to enamel matrix
 The cell of stratum intermedium lose their cuboidal
shape and regular arrangement and assume a
spindle shape

56. 5.Protective stage
 when the enamel has completely develop and has
fully calcified ameloblasts cease to be arranged in a
well defined layer
 no longer differentiate from the stratum
intermedium and outer enamel epithelium
no longer differentiate from the stratum
intermedium and outer enamel epithelium
 stratified epithelial covering of the enamel is so
called reduced enamel epithelium
 function- that of protecting the mature enamel
epithelium by separating it from the connective
tissue until the tooth erupts

57.  6.Desmolytic stage
 the reduced enamel epithelium proliferate and
seems to induce atrophy of the connective tissue
separating it form the oral epithelium so that fusion
of two epithelial can occur.of two epithelial can occur.
 it is probable that epithelial cells elaborate
enzymes that are able to destroy connective tissue
fiber by desmolysis

59.  On the basis of ultrastructure and composition two
process are involved in the development of enamel
 1 Organic matrix formation
 2 Mineralization
1) Formation as the enamel matrix:
 The ameloblast begins their secretory activity when a
small amount of dentin has been laid down.
 The ameloblast loose the projections that had penetrate
the basal lamina separating them from the predentin
lands of enamel matrix are deposit along the predentin
as enamel deposition proceeds, a thin layer ,continuous
layer of enamel is formed along the dentin

60.  Amelogenin is the major protein in matrix
formation.
 Ameloblastin and enamelin are other important
proteins of the enamel matrix. They undergo
extracellular processing like amelogenin but at a
rapid rate
 Time interaction between nonamelogenin and
amelogenin is limited. it helps in nucleation and
growth of crystalgrowth of crystal
 Tuftelin is involved in cell signaling.
 Recently amelotin, a new protein was reported to be
secreted by maturative ameloblast.

61. Development of Tomes’ process
 The surface of ameloblast facing the developing enamel
are not smooth.
 There is an interdigitation is partly a result of the fact
that the long axes of the ameloblasts are not parallel to
the long axes of rods.
 the projection of the ameloblast into the enamel the projection of the ameloblast into the enamel
matrix have been named Tomes’ process.

62.  Distal terminal bars:
 The junctional complexes which encircle ameloblast
at their distal and proximal ends have fine actin
filaments extending into cytoplasm forming webs.
 They serve to control the substance which pass They serve to control the substance which pass
between ameloblast and enamel.
 The junctional complexes which form at distal end
are known as distal terminal bars.
 They separate Tome’s processes from cell proper

63.  Secretion from area close to junctional complex and
adjacent ameloblasts form the interrod enamel.
 At least two ameloblast are involved in the
synthesis of enamel rod.
 The bulk of the head of each rod is formed by one
ameloblast the tail of each rod is formed by four
ameloblast.
 So each rod is formed by 4 ameloblasts and each So each rod is formed by 4 ameloblasts and each
ameloblast contributes to 4 different rods.

64. Ameloblast covering maturing enamel
 in light microscopic level, one can see that the
ameloblast over maturing enamel are considerably
shorter than the ameloblast over incompletely
formed enamel.
 the changes occuring in the ameloblasts after
secretory stage and prior to onset of maturation
process are called transition stageprocess are called transition stage
 During this stage ameloblasts reduced in height,
enamel secretion stop completely.
 50% ameloblast undergo apoptosis

65.  Ameloblast alternate cyclically in developing
smooth and ruffled border in the apical cytoplasm
during the maturative stage in the cervicoincisial
direction.
 These changes are referred to as modulation.
 It occur many times in a day. (every 5-7 hours)
 the period of maturation is much longer than
secretory phase.secretory phase.

66. Mineralization and maturation of the enamel matrix
 Two stages
 First stage: an immediate partial mineralization
occur in the matrix segment and the interprismatic
substance as they are laid down
 second stage or maturation is characterized by
gradual completion of mineralizationgradual completion of mineralization

67.  First stage:
 No matrix vesicles are observed in enamel
formation.
 Nucleation is initiated by apatite crystallites of
dentin on which enamel is laid.dentin on which enamel is laid.
 Studies show that initial mineral formed is
octacalcium phosphate which may act as a template
for hydroxyapatite.

68.  Second stage:
 Maturation process starts from the height of the
crown and progresses cervically.
 Maturation begins before the matrix has reached its
full thickness.full thickness.
 Rate of enamel formation is 4 um/day.
 The rate of enamel formation is more in permanent
teeth than in deciduous teeth.

69.  perikymata are surface manifestation of the
incremental lines usually found at the cervical end
of the crown. Some perikymata are more prominent
and will present difficulties to the clinician, who
may confuse them with calculus
enamel rods interlock to prevent fracture and enamel rods interlock to prevent fracture and
splitting of the tooth. enamel rod groups also
intertwine, there by preventing separation
 the rod direction in the crown is normally
perpendicular to the incisal surface which provide
additional support in preventing fracture

70.  in preparing cavities, it is important that
unsupported enamel rod are not left at the cavity
margins because they would produce leakege.
Bacteria would lodge in these spaces, including
secondary cariessecondary caries
 Enamel is brittle and does not withstand forces in
thin layer or in the areas where it is not supported
by the underlining dentin

71.  Amelogenesis Imperfecta
 Enamel Hypoplasia
 Mottled Enamel
 Enamel Pearls
Tetracycline Stains Tetracycline Stains

72.  Amelogenesis imperfecta:
 A structural defect of tooth enamel.
 There is disturbance in the differentiation or viability of
ameloblast.
 Both deciduous as well as permanent dentitions usually Both deciduous as well as permanent dentitions usually
are involved.
 Three main groups: hypoplastic(60-73%),
hypocalcified(7%), and hypomature(20-40%).
 Classification of amelogenesis imperfecta according to
Witcop :
 Type Ι Hypoplastic
 Type ΙΙ Hypomaturation
 Type ΙΙΙ Hypocalcified Type
 Type ΙV Hypomaturation-hypoplastic with taurodontism

74.  Enamel hypoplasia:
 Manifestated by pitting, forrowing or even total absence
of enamel in which enamel matrix formation is affected.
 Incomplete or defective formation of organic enamel
matrix.
Cause-systemic, local or genetic Cause-systemic, local or genetic
 Rickets during formation of enamel is most common
cause of Enamel hypoplasia.
 Hypoplasia of systemic origin- chronological
hypoplasia.
 Mostly occur during first year of life.

76.  Mottled enamel (hypocalcification):
 Opaque or chalky areas on normally contoured enamel
surfaces.
 Occurs due to lacking or incomplete maturation.
 There is deficiency in mineral content.
 Ingestion of fluoride containing water during time of tooth
formation is most important cause.formation is most important cause.
 More than 1 ppm of fluoride causes significant mottling.
 There is wide range of severity in the appearance of mottled
teeth, varying from
 I. Mild changes (white opaque areas)
 II. Moderate and severe (pitting and brownish staining)
 III. A corroded appearance of the teeth.

77.  Tetracycline stains:
 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.