Development of enamel, Histological structure of enamel, age changes in enamel, systemic disorders affecting enamel

2.  The anatomic crown of a tooth is covered by an
avascular, highly mineralized material known as
ENAMEL.
 Origin- Enamel has an ectodermal origin

3.  Forms a protective covering of variable thickness- on the cusps- 2-
2.5 mm maximum thickness, knife edge thickness at the neck of the
tooth.
 Comparatively thicker at the lingual surface of maxillary molars and
buccal surface of mandibular molars.
 Hardest calcified tissue in human body-forms a resistant covering-
suitable for mastication.
 Brittle in nature but the underlying dentin provide some resilience.
 Less elastic than dentin.
 Specific gravity is 2.8.
 Acts as a semi permeable membrane.
 Colour- yellowish white to greyish white.

5.  Organic substances and water: 4% by weight
 Inorganic material- (apatite crystals)- 96% by weight
 In volume the organic matter and water are nearly equal to the inorganic contents.
 Organic substances:
 2 main proteins:
1 Amelogenins : low molecular weight protein, 90% of enamel matrix protein,
hydrophobic, rich in Proline, Histidine, Glutamine, and Leucine.
2 non amelogenins: high molecular weight proteins, 10% of enamel matrix proteins, rich
in glycine, aspartic acid, and serine,. Examples are- Enamelin, Ameloblastin, tuftlin.
o Inorganic material:
o Hydroxyapatite – Ca10(PO4)6(OH4)2
o Crystals are hexagonal in cross section.
o The shape of a single crystal was observed to be a rod with an equilateral
hexagonal base.
o The crystals are arranged to form enamel rods or enamel prisms.
o Water is present as apart of crystal, between crystals and surrounding the rods.

7.  At the stage preceding the formation of hard
structure( dentin and enamel) the enamel organ
, originating from the stratified epithelium of the
primitive oral cavity, , consists of 4 distinct
layers; OEE, stellate reticulam, Stellate
intermedium and IEE.
 The borderline between the IEE and the
connective tissue of dental papilla is the
subseqent DEJ.
 Thus its outline determines the pattern of the
occlusal or incisal part of the crown.

9.  In the early stage, the OEE consists of single layer of
cuboidal cells, separated form surrounding connective
tissue of the dental sac by a delicate basement
membrane.
 Prior to the formation of hard structures, this regular
arrangement of the OEE is maintained only in the cervical
part of the enamel organ. At the highest convexity of the
organ, the cells of OEE is irregular in shape.
 The capillaries of the connective tissue surrounding the
epithelial enamel organ proliferate and protrude toward it.
 During enamel formation , cells of the OEE develop villi
and cytoplasmic vesicles and large number of
mitochondria, all indicating cell specialization for the active
transport of material.

10.  In the stellate reticulum , the cells are star shaped,
with long processes reaching in all direction from a
central body..
 The structure of the stellate reticulum render it
resistance and elastic. Therefore it seems probable
that it acts as a buffer against physical forces that
might distort the conformation of the developing
DEJ, giving rise to gross morphological changes.
 It seems to permit only a limited flow of nutritional
elements from the outlying blood vessels to the
formative cells.
 The SR is reduced in thickness when the first layer
of dentin are laid down, and the inner enamel
epithelium is thereby cut off from the dental papilla.

11.  The cells of stratum intermedium is situated
between the SR and the IEE.
 They are flat to cuboidal in shape and are
arranged in 1-3 layers.
 The functions of SI in not understood but it is
believed to play a role in production of the
enamel itself , either through control of fluid
diffusion into and out of the ameloblasts or
by the actual contribution of necessary
formative elements or enzymes.

12.  The cells of IEE is derived from the basal
layer of the oral epithelium.
 Before enamel formation begins, these cells
assumes a columnar form and differentiate
into ameloblasts that produce the enamel
matrix.

13.  At the free border of the enamel organ the
outer and inner enamel epithelial layers are
continuous and reflected into one another as
cervical loop.
 When the crown has been formed , the cells
of this portion gives rise to Hertwig’s root
sheath.

15.  According to their function, can be divided
into 6 stages:
1. Morphogenic stage.
2. Organizing stage.
3. Formative stage.
4. Maturative stage.
5. Protective stage.
6. Desmolytic stage.

17.  Before the ameloblasts are fully differentiated and produce
enamel, they interact with the adjacent mesenchymal
sells, determining the shape of DEJ and the crown.
 During this stage the cells are short and columnar, with
large oval nuclei that almost fill the cell body.
 The golgi apparatus and the centrioles are located in the
proximal end of the cell , whereas the mitochondria are
evenly dispersed throughout the cytoplasm.
 The IEE is separated from the CT of dental papilla by a
delicate basal lamina.
 The adjacent pulpal layer is a cell-free, narrow, light zone.

19.  In this stage of development the IEE interacts with the adjacent CT
cells, which differentiate into odontoblasts.
 IEE become longer, and the nucleus free zone at the distal of the cells
become almost as long as the proximal parts containing the nuclei.
 A reversal of functional polarity of the cells take place by the migration
of the centrioles and golgi region from the proximal ends of the cells to
the distal ends.
 At the same time the cell free zone between the IEE and the and the
dental papilla disappears, probably because o elongation of epithelial
cells towards the papilla.
 Thus the epithelial cells comes in the close contact with the CT of the
cells of the pulp, which differentiate into odontoblasts.
 During the terminal phase of this stage, the formation of the dentin by
odontoblasts begins.
 When dentin forms , it cuts off the ameloblasts from their original
source of nourishment, and from then on they are supplied by he
capillaries that surround and may even penetrate the OEE.

21.  The ameloblasts enter the formative stage after the
first layer of the dentin has been formed.
 During formation of enamel matrix the ameloblasts
retain approximately the same length and
arrangement.
 Changes in the organization and number of
cytoplasmic organelles and inclusions are related to
the to the initiation of secretion of enamel matrix.
 The earliest apparent change is the development of
blunt processes on the ameloblasts surfaces which
penetrate the basal lamina and enter the pre
dentin.

23.  Enamel maturation occurs after most of the thickness of
the enamel matrix has been formed in the occlusal or
incisal area.
 In the cervical parts of the crown, enamel matrix formation
is still progressing at this time .
 During maturation the ameloblasts are slightly reduced in
in length and are closely attached to enamel matrix.
 The cells of SI lose their cuboidal shape and regular
arrangement and assume a spindle shape.
 During maturation ameloblasts display microvilli at their
distal extremities, and cytoplasmic vacuoles containing
material resembling enamel matrix is present.
 These structures indicate an absorptive function of these
cells.

25.  After enamel has fully developed and fully
calcified, the ameloblasts cease to be arranged
in a well defined layers and can no longer be
differentiated from the cells of SI and OEE.
 These cell layers then form a stratified epithelial
covering of the enamel, the so called Reduced
enamel epithelium.
 The main function of REE is that of protecting
the mature enamel by separating it from CT
until the tooth erupts.

27.  The REE proliferates and seems to induce
atrophy of CT separating it from the oral
epithelium, so that the fusion of two epithelia
can occur.
 It is probable that the epithelial cells
elaborate enzymes that are able to destroy
CT fibres by desmolysis.
 Pre mature degeneration of the REE may
prevent the eruption of teeth.

31.  Rods or Prisms
 interrods
 Rod sheath
 Striations
 Hunter schreger bands
 Incremental lines of retzius
 Surface structures
 Enamel cuticle
 Enamel lamellae
 Enamel tufts
 Dentino-enamel junction
 Odontoblast processes or enamel spindles.

32.  Rod sheath
 Incremental lines of retzius
 Enamel lamellae
 Enamel tufts
 Enamel cracks
 Enamel spindles
 Neonatal lines.

33.  RODS OR PRISMS :
 Basic structural unit of enamel.
 Shape: like a cylinder
 INTERROD:
 Thin peripheral layer.
 Surrounds each rod.
 The direction are orientated in a direction
different from those making the rods.
 ROD SHEATH:
 The narrow space containing organic material
demarcating the rod and interrod.

35.  Number of rods: it varies in different tooth; lower central incisor – 5
million, upper first molar- 12 million.
 Dimension of rods: breadth – 5 microns, length- 9 microns, diameter-
4 microns , approximately.
 It is claimed that the diameter of rods increases from DEJ towards the
surface of enamel at a ratio of 1:2.
 Length of the rod:
 From DEJ the rods runs in a wavy and tortuous course outward the
surface of the tooth.
 Length of the rod> thickness of the enamel
 Length of the rod in the cusp area> length of the rod at the cervical
area
 Appearance: has a clear crystalline structure.
 Cross section: occasionally appear hexagonal, sometimes round or
oval. In human enamel , they resemble fish scales.
 If we see the ultra structure, the most common pattern is a key hole or
paddle shaped prism in human enamel.
 Key hole pattern has a ‘body’ and a ‘tail’.

38.  Generally, rods are oriented at right angles to the dentin surface.
 In cervical areas- the rods deviate from a horizontal to an apical
orientation.
 Near the incisal edge or cusp tips they change gradually to an
increase oblique direction until they are almost vertical in the
region of edge or cusp tip.
 In deciduous teeth they are approximately horizontal in cervical
and central part.
 GNARLED ENAMEL:
 An optical illusion when cut in an oblique plane- seen near
cusps or incisal edge- due to bundles of rods are intertwined
more irregularly.
 At pits and fissure- rods converge in their outward course.

41.  Each enamel rods is built up of segments
separated by dark lines the give it a striated
appearance.
 These cross striations demarcate rod segments
and become more visible by the action of mild
acids.
 The rods are segmented because the enamel
matrix is formed in rhythmic manner. In human
these segments can be seen in to be a uniform
length of about 4 microns.
 There is a diurnal rhythm in the enamel formation.
 Striated areas also show variation in composition.

43.  It confers strength to the enamel.
 Because of interwoven network of rods, teeth can
resist masticatory forces upto 20-30 lbs per tooth.
 Their direction is important consideration in the
cavity preparation for restoration.
 Fracturing of unsupported rods in poorly designed
restorative preparation cause loss of enamel
around the margin of the restorative material
resulting in marginal leakage and makes the tooth
more susceptible to caries.
 The different inclination of rods in permanent and
deciduous teeth must be accounted for during
cavity preparation.

44.  This is an optical phenomenon seen in reflected light.
 Alternate light and dark bands are seen in ground
longitudinal section.
 Dark bands- parazones
 Light bands- diazones
 Due to-
1) Abrupt change in the direction of enamel rods. (most
accepted theory)
2) Variation in calcification of enamel.
3) Alternate zones having different permeability and organic
material.
 They originate from the DEJ and pass outward ending at
some distance from the outer enamel surface.

47.  Increment lines of growth
 Eccentric growth rings.
 Brownish bands in ground section
 Reflect variation in structures and mineralization.
 Broadening of these lines in case of metabolic
disturbances.
 In longitudinal section they surrounds the tip of the dentin.
In the cervical part they run obliquely from DEJ to surface
then deviate occlusally.
 Etiology:
 Periodic bending of enamel rods.
 Variations in organic structure.
 Physiologic calcification rhythm.

49.  PRISMLESS ENAMEL
 PERIKYMATA
 ENAMEL PITS
 ENAMEL CAPS
 ENAMEL BROCHS

50.  A relatively structureless layer of enamel,
approximately 30 microns thick, called
prismless enamel, it has been described in in
70% of the permanent teeth and all
deciduous teeth.
 The structureless enamel is found least often
over the cusp tip and most commonly
towards the cervical areas of the enamel
surface.
 It is also somewhat more heavily mineralized
than the bulk of enamel beneath it.

52.  Perikymata are transverse wave like
grooves, believed to be the external
menifestations of the striae of retzius.
 They are continuous around a tooth and
usually lie parallel to each other and to the
CEJ.
 ordinarily, there are 30 perikymata per mm in
the region of CEJ and their concentration
generally decrease to about 10 per mm near
the occlusal/incisal edge.

55.  The surface of enamel appears very uneven
. Pits of about 1-1.5 microns in diameter and
small elevations of about 10-15 microns
called enamel caps are seen.
 The surface pits are said to represent the
ends of ameloblast and the caps are due to
enamel deposition on non- mineralizable
debris.
 Larger enamel elevations are termed enamel
brochs.

57.  It is present in all deciduous teeth and 1st
permanent molar.
 It is the most prominent incremental line in
primary teeth.
 This line separates the enamel formed before
birth and enamel formed after birth.
 This line is due to sudden change of nutrition
and environment after birth.
 Prenatal enamel is less pigmented and more
free of defects than postnatal enamel.
 More frequently absent in permanent 1st molar
of boys than girls.

60.  It is a delicate membrane called Nasmyth’s
membrane or primary enamel cuticle.
 This is typical lamina that is secreted by
ameloblasts after completion of enamel
formation.
 This thin membrane covers the newly
erupted teeth but soon after eruption it is
removed by masticatory forces.

62.  A layer directly on the top of enamel 1-3
microns thick ( could reach upto 10 microns)
 Mainly the precipitate of salivary proteins.
 The pellicle reforms within hours after an
enamel surface is mechanically cleaned.
 Within a day or two after the pellicle has formed
, it becomes colonized by microorganisms to
form bacterial plaque.

64.  These are thin leaf like structure extends from enamel
surface to DEJ, sometimes may penetrate dentin.
 Lamellae are rich in protein with little mineral content.
 Lamellae may also develop in planes of tension. The rods
crosses such planes and short segments of rod remains
uncalcified those later on are filled with organic contents.
 3 types of lamella can be differentiated:
1) Type A: lamellae containing poorly calcified rod
segments. These are restricted to enamel.
2) Type B : consisting of degenerated cells. May cross the
DEJ and reach the dentin
3) Type C: lamellae in erupted teeth where cracks are filled
with salivary proteins.
 CRACKS: fissures like structures seen on the surface,
they are outer edges of lamellae. They are less than 1
mm in length.

66.  It arises at the DEJ and reach into the
enamel to about 1/5th to 1/3rd of its thickness.
 They were so termed because they
resemble tufts of grass when viewed in
ground sections.
 Tufts consists of hypocalcified enamel rods
and interprismatic substances.

68.  The surface of the dentin at the DEJ is pitted.
 Into the shallow depression of the dentin fit the
rounded projections of the enamel.
 DEJ therefore appears as a scalloped line – the
convexity of the scallops are towards the
dentine.
 The pitted DEJ is pre formed even before the
development of hard tissues and is evident in
the arrangement of the ameloblasts and the
basement membrane of the dental papilla.

70.  Occasionally odontoblast processes pass
across the DEJ into the enamel.
 Since many are thickened at their end, they
have been termed enamel spindles.
 They seem to originate from processes of
odontoblast that extended into the enamel
epithelium before hard substances are
formed.
 These are hypomineralized or partially
mineralized structures.

72.  The most apparent age change in enamel is attrition or wear of the
occlusal surface and proximal contact points as a result of mastication.
 The surface of unerupted and recently erupted teeth are covered
completely with pronounced rod ends and perikymata. At the points of
highest contour of the surface these structures soon begin to
disappear.
 Facial and lingual surfaces lose their structure much more rapidly than
do proximal surfaces, and anterior teeth lose their structure more
rapidly than do the posterior teeth.
 Localized increase in certain elements such as nitrogen and fluorine,
however, have been found in the superficial enamel layers of the older
teeth.
 As a result of age changes in the organic portion of the enamel,
presumably near the surface, the teeth may become darker, and their
resistance to decay may increased.
 Age changing is greatly related to reduced permeability of older teeth
to fluids.

74.  The course of the enamel rods is of importance in cavity
preparations. The choice of instruments depends on the
location of the cavity in the tooth.
 Generally the rods run at a right angle to the underlying
dentin or the tooth surface. close to the CEJ the rods run
in a more horizontal direction. In preparing cavities, it is
important that unsupported enamel rods are not left at the
cavity margins, because they would soon break and
produce leakage.
 Enamel is brittle in nature and does not withstand forces in
thin layers or in areas where it is not supported by the
underlying dentin.
 Caries penetrate the floor of fissures rapidly because the
enamel in these areas are very thin. As the destructive
process reaches the dentin, it spreads along the DEJ
undermining the enamel.

75.  Dental lamella may also be predisposing locations
for caries because they contain much organic
material.
 Fluoride-containing mixtures such as stannous
fluoride pastes, sodium fluoride rinses, and
acidulated phosphate fluoride are also used to alter
the outer surface of enamel so that it becomes
more resistance to caries.
 The most effective means for mass control of dental
caries to date has been adjustment of fluoride level
in communal water supplies to 1 parts per million.
 The surface of the enamel in the cervical region
should be kept smooth and well polished by proper
home care and by regular cleansing by dentist.

76.  Composite resins are mechanically bonded
directly to the enamel surface. In this process
the enamel surface is first etched with an acid.
This produces an uneven dissolution of enamel
rods and their sheath so that a relatively smooth
enamel surface becomes pitted and irregular.
 It helps in mechanical bonding of composite to
the enamel surface.
 Prismless enamel found on the surface does
not provide enough mechanical retention so
etching should go beyond the prismless enamel
to the prismatic enamel below it.

77. GENETIC NON GENETIC
1)Amelogenesis 1) caries
imperfecta: 2) Attrition
A) Hypoplastic (type1) 3) abrasion
B) Hypomaturation(type2) 4)Erosion
C) Hypocalcified (type3) 5) localized non hereditary
enamel hypoplasia
6)localized non hereditory
enamel hypocalcification.
7) fluorosis.

78.  It is a group of conditions caused by defects
in the genes encoding enamel matrix
proteins.

79.  The main defect is in formation of the matrix (protein).
 Enamel is not formed to full thickness because
ameloblasts fail to lay down sufficient matrix.
 Enamel is randomly pitted , grooved or very thin, but hard
and translucent.
 Affected teeth appear small with open contacts.
 due to very thin or non existent of enamel causes thermal
sensitivity.
 Teeth are not susceptible to caries .
 The enamel is scanty and easily damaged.
 Commonly in men.

81.  Occurs during matrix maturation stage.
 Enamel is softer and chips from the
underlying dentin.
 Enamel has a mottled brown yellow white
colour.
 Contact points present as enamel is of
normal thickness.
 Radiographically enamel approaches the
radiodensity of dentin.

83.  Occurs during the calcification stage.
 Most common type.
 Enamel is of normal thickness but soft,
friable, and easily lost by attrition.
 Enamel appears dull, lustrous, honey
coloured and stains easily.

86.  It is an irreversible microbial disease of the
calcified tissue of the teeth , characterized by
demineralization of the inorganic portion and
destruction of the organic substance of the
tooth, which often leads to cavitation.

88.  Defined as physiological continuous, process
resulting in loss of tooth structure from direct
frictional forces between contacting teeth.
 It occurs both on occlusal and proximal
surfaces.
 Attrition is accelerated by parafunctional
mandibular movements especially bruxism.

90.  It refers to the loss of tooth substance
induced by mechanical wear other than of
mastication.

92.  Abfraction is a theoretical concept explaining a
loss of tooth structure not caused by tooth
decay (non-carious cervical lesions).
 It is suggested that these lesions are caused by
forces placed on the teeth during biting, eating,
chewing and grinding, the enamel especially at
CEJ, undergoes large amount of stress ,
causing micro fracture and tooth tissue fracture.

94.  It is defined as irreversible loss of dental
hard tissue by a chemical process that does
not involve bacteria.
 Dissolution of mineralized tooth structure
occurs upon contact with acids that are
introduced into the oral cavity from intrinsic
(e.g. gastroesophageal reflux, vomiting) or
extrinsic sources (e.g. acidic beverages,
citrus fruits).

96.  Refers to the localised defect in the crown
portion of the tooth caused by the injury to
ameloblasts during the enamel matrix
formation stage.

98.  Refers to the localised defects in the crown
of a tooth due to injury to ameloblasts during
mineralization stage.
 In these defects, the enamel is normal in
structure but its mineralization is defective.
 The color of lesion varies from chalky to
yellow brown, dark brown or grayish.

100.  Also termed as mottled enamel.
 It is an extremely common disorder,
characterized by hypomineralization of tooth
enamel caused by ingestion of excessive
fluoride during enamel formation.

102.  Application of enamel matrix derivative (Endogain)
in endodontic therapy: Researchers suggest that
EMD can be applied in direct pulp capping and
pulpotmy. And EMD may have potential in
treatment of traumatized and immature teeth.
 Enamel matrix proteins in the regenarative therapy
of deep infrabony defects: A multicentre
randomized clinical trial was designed to know the
role of EMP to promote new bone cementum, pdl
and regeneration.

103.  Enamel regeneration: According to the research there are
some bioactive nanofibres (BRGD-PA) present with
enamel proteins participate in integrin- mediated cell
binding to the matrix with delivery of intstructive signals for
enamel formation.
 Enamel Gel ( painting instead of drilling): Recently
Moradin oldak, a researcher, and her team engineered a
string of amino acids that contained only the parts needed
for enamel crystal creation. These shorter peptides could
be incorporated into gel. Such a product could be painted
on teeth eroded by early cavities or erosion causing pain
and tooth hypersensitivity, effectively replacing lost
enamel.

104.  Orban’s oral histology and embryology. 12th
edition
 Shafer’s textbook of oral pathology. 7th
edition
 Journal of endodontic, Vol 44, issue 7
 Journal of clinical periodontology 29(4), 317-
325, 2002
 http://doi.org/10.1359/jbmr.080705