2. TABLE OF CONTENTS
Introduction : Enamel
Properties of Enamel
Hydroxyapatite (HAP) Crystal
Enamel Rods
Direction of Enamel Rods
Gnarled Enamel
Hunter Schreger Bands
Cross Striations
Striae of Retzius
Perikymata
Enamel Lamellae
Prismless/ Aprismatic Enamel
Aging
Enamel Rods & Fluoridation
Enamel Rods in Dental Caries
Enamel Rods in Cavity Preparation
Enamel Rods in Acid Etching
Enamel Rods in Erosion
3. INTRODUCTION : ENAMEL
- Protective covering of the crown
- Hardest calcified tissue in the body
- Maximum thickness : Cusps of Premolars & Molars
- Minimum thickness : Neck of the tooth
- Hardness : 343 KHN
Content of mineral salt + Crystalline arrangement = ENAMEL
Orban’s Oral Histology &
4. PROPERTIES OF ENAMEL
Maximum thickness at cusp 2-2.5 mm
Specific Gravity 2.8
Temperature resistance 5-13 Hz
Electrical resistance 1015 – 105 Ohms
Permeability Semipermeable
Color Yellowish white to grayish white
Orban’s Oral Histology & Embryology
6. HYDROXYAPATITE
- Ca10(PO4)6(OH4)2
- Rod with an equilateral hexagonal base = HAP Crystal
- Group of crystals Enamel Rods (Enamel Prisms)
Base of a Rod
Orban’s Oral Histology & Embryology 15th
10. C. R. G. Torres (ed.), Modern Operative Dentistry, Textbooks in Contemporary Dentistry
11. ENAMEL RODS
- k/a Enamel prisms
- Shape : Cylindrical with a hexagonal base
- 5 million to 12 million
- Wavy & torturous course (from DEJ to the surface of enamel)
- Longest at the cusps & shortest at the cervical region
- Average Diameter = 4 µm
- Ratio = 1:2 ( DEJ to Enamel Surface)
Orban’s Oral Histology & Embryology 15th
16. Orban’s Oral Histology & Embryology
Keyhole
Pattern
Stacked
Arches
Staggere
d Arches
Irregular
rods
near DEJ
17. WHY ENAMEL RODS & NOT
“PRISMS” ?
Ten Cate’s Oral Histology 9th Ed
18. DIRECTION OF RODS
- Rods are oriented at 90º to the dentin. (Generally)
Deciduous
•Horizontal - Cervical
& Central parts
•Increasingly Oblique
- Incisal area
•Almost Vertical -
edges or tip of the
cusps
Permanent
•Deviate apically-
cervical region
•Same (as deciduous)
- occlusal thirds
Studervant’s Art and Science of Operative Dentistry 7th Edition
22. GNARLED ENAMEL
Over the cusps of teeth, the rods
appear twisted around each
other in a seemingly complex
arrangement known as gnarled
enamel.
-
• is not subject to fracture as much as is regular enamel.
• does not yield readily to the pressure of bladed, hand-cutting
instruments in tooth preparation.
• orientation of the enamel rod heads and tails and the gnarling of
enamel rods provide strength by resisting, distributing, and
dissipating impact forces
Studervant’s Art and Science of Operative Dentistry 7
23. Enamel Spindles : hypocalcified structures that result due to extension of odontoblastic processes
beyond the DEJ into the enamel.
Studervant’s Art and Science of Operative Dentistry 7
24. HUNTER-SCHREGER BANDS
- An optical phenomenon
produced by changes in
direction between adjacent
groups of rods
- Longitudinal ground
sections viewed by reflected
light
- Inner two thirds of the
enamel
- Dark and light alternating
zones (that can be reversed
by altering the direction of
incident illumination)
Orban’s Oral Histology & Embryology 15th Edition
25. PARAZONES & DIAZONES
- Longitudinal sections of rods cause the
formation of Parazones.
- Diazones contribute to the arrangement
of packed rods in transverse sections.
Atlas of Oral Histology 2nd edition
31. - Hunter-Schreger bands optimise resistance to attrition, abrasion
and tooth fracture.
- play beneficial roles in clinical techniques such as enamel bonding
- Abfraction and cracked tooth syndrome appear to be passively
facilitated by HSB packing density and distribution patterns.
TAKE HOME MESSAGE (ABOUT
HSB)
32. CROSS-STRIATIONS
Enamel rods
Segments separated by dark
lines
Striated appearace
- these demarcate rod
segments
- more visible by the action of
mild acids
- seen in Insufficiently calcified
enamel
These cross striations seen in light microscope is suggested to be due to a diurnal
rhythm in the enamel formation.
Orban’s Oral Histology & Embryology 15th
33. STRIAE OF RETZIUS
Dark brown lines
Representing a 6- to 11-day
rhythm of enamel deposition
Also k/a Incremental lines of
Retzius
Atlas of Oral Histology 2nd
35. PERIKYMATA
The striae of Retzius often extend from the DEJ to the outer surface
of enamel, where they end in shallow furrows known as Perikymata
Run in circumferentially horizontal lines across the face of the crown
Consists of a structureless surface layer (final enamel) that is lost
rapidly by abrasion, attrition, and erosion in erupted teeth.
37. PERIKYMATA
(From Hoffman S: Histopathology of caries lesions. In Menaker L,
editor: The biologic basis of dental caries, New York, 1980, Harper &
Row.)
38. ENAMEL LAMELLAE
Linear leaf-like hypocalcified structures
Extending from the enamel surface to the DEJ to varying depths
These are of three types—A, B, and C.
• Type A is made up of poorly calcified rods.
• Type B contains degenerated cells.
• Type C is filled with organic matter from saliva.
Lamellae act as pathways for entry of bacteria resulting in dental caries.
Studervant’s Art and Science of Operative Dentistr
39. Enamel Tufts : ribbon-like structures made up
of hypocalcified enamel rods that arise from
the DEJ
predispose the tooth to the entry of bacteria and
subsequent development of dental caries.
Studervant’s Art and Science of Operative Dentistry
40.
41. PRISMLESS/ APRISMATIC ENAMEL
On the outer surface of the enamel, at
completion of the enamel surface, the
ameloblasts degenerate and leave a
featureless layer, called prismless enamel.
This layer is more often observed in
deciduous teeth and is often worn off in
permanent teeth.
Craig’s Restorative Dentistry 14th E
42. However, if present, this causes some difficulty in getting
an effective etching pattern and may require roughening
of the surface or additional etching treatments.
There are no visible rod (prism) outlines in this area and
all of the apatite crystals are parallel to one another and
perpendicular to the striae of Retzius.
PRISMLESS/ APRISMATIC ENAMEL
Craig’s Restorative Dentistry 14th E
52. ROLE OF ENAMEL RODS IN
FLUORIDATION
If the fluoride ion is incorporated into or adsorbed on the HAP
crystal, the crystal becomes more resistant to acid dissolution.
This reaction partly explains the role of fluoride in caries prevention,
because the caries process is initiated by demineralization of enamel.
Obviously, if fluoride is present as enamel is being formed, all the
enamel crystals will be more resistant to acid dissolution.
Understanding Dental Caries by Gordon
53. Rate of
dissolution of
partially
fluoridated
synthetic
hydroxyapatite
< pure
hydroxyapatite
Improves
the
crystallinit
y of
enamel
apatite.
The
apatite
structure
is more
stable
fewer
imperfecti
ons and
dislocatio
ns within
the
crystals
an
increase
d
stability
of the
substitut
ed
lattice
structure
Cariostati
c activity
of
fluorides
Understanding Dental Caries by Gordon
Lower acid
solubilities
Increased
rates of
reminerali
zation
Decrease
d rates of
demineral
ization
54. ENAMEL RODS & CARIES
Core Defects
-Increased intercrystalline space
- Preferential loss of core minerals
- Preferentially dissolved in an acidic environment
Higher
concentrati
on of
Carbonate
in the
crystal
center
Increased
dislocations
in the form
of lattice
defects in
the core
Chemical
reactivity at
these
dislocation
points
increases
Understanding Dental caries Nikiforuk, G. Vol. 1
57. Demineralization due to initiation of
caries follows the direction of the
enamel rods, spreading laterally as it
approaches the dentinoenamel
junction (DEJ).
C. R. G. Torres (ed.), Modern Operative Dentistry, Textbooks in Contem
58. C. R. G. Torres (ed.), Modern Operative Dentistry, Textbooks in Contem
59.
60. Α protective organic film of
strongly adsorbed protein, the
acquired salivary pellicle,
forms on the surface of
enamel mineral. Acquisition of
fluoride in surface enamel and
loss of carbonate from the
enamel surface may also
contribute to the reduced
solubility of the outer enamel
surface
Understanding Dental caries Nikiforuk, G. Vol. 1
61. In the presence of
a suitable
carbohydrate
substrate, such
as sucrose,
cariogenic plaque
bacteria produce
organic acids
(lactic, acetic,
propionic)
localized within
the plaque in
juxtaposition to
STEP 1
Understanding Dental caries Nikiforuk, G. Vol. 1
62. Production of these organic
acids produces a
concentration gradient that
causes the hydrogen ions
(H±) and the undissociated
acid (HA or HL, etc.) to
diffuse into the enamel.
As diffusion proceeds the
undissociated acid
molecules continually
dissociate providing H+
ions. These hydrogen ions
are rapidly used up in the
reaction with enamel,
producing calcium and
STEP 2
Understanding Dental caries Nikiforuk, G. Vol. 1
63. The undissociated
HA and HL form a
reservoir of
hydrogen ions.
Dissociation is
dependent upon the
pH and the
concentration of
undissociated
molecules.
Understanding Dental caries Nikiforuk, G. Vol. 1
64. The H+, attack the
apatite crystals
particularly at vulnerable
lattice points such as
where CO3 - is present.
This causes Cat+, OΗ-,
Ρ04 -, F-, CO3 -, Na+
and Mgt+ to be removed
from the lattice and to
diffuse to the solution
phase between the
crystals.
Fluoride in solution
markedly inhibits this
dissolution stage of the
process
STEP 3
Understanding Dental caries Nikiforuk, G. Vol. 1
65. These ions and their
appropriate complexes
(CaHPO4, CaL+,
CaH2Ρ04 , etc.) will
diffuse according to
their concentration
gradients through the
newly enlarged pores
of the carious enamel
so that calcium and
phosphate are lost to
the external
environment.
Mineral loss, or
demineralization,
proceeds as long as
STEP 4
Understanding Dental caries Nikiforuk, G. Vol. 1
66. If subsurface dissolution continues and
repair cannot keep pace with mineral
loss this leads eventually to more
extensive damage to crystal structure
and cavitation.
Dissolution of mineral salts
eventually exposes the organic
matrix of enamel and dentin to
proteolytic enzymes of the oral flora.
Understanding Dental caries Nikiforuk, G. Vol. 1
67. At an incipient caries stage, and prior to cavitation, repair of a lesion may occur by
remineralization.
If the calcium and phosphate gradients are reversed and these species diffuse
inwards rather than outwards then remineralization results.
Crystal regrowth, or new precipitation, will also occur, of course, as the pH rises.
Fluoride, if present at the crystal surface in the immediately adjacent water phase,
promotes this remineralization by dramatically speeding up the process.
There is now considerable evidence that one of the principal mechanisms of fluoride
action is the enhancement of remineralization.
Understanding Dental caries Nikiforuk, G. Vol. 1
68. Removal of substrate; substitution of
substrate by noncariogenic sweetening;
removal of plaque. These procedures will
reduce formation of organic acids and the
diffusion of acids into enamel
Development of more caries-resistant
enamel by incorporation of fluoride ion
during tooth maturation and
remineralization; formation of
fluorapatite-like material in surface
enamel by topical fluoride applications.
Maintaining a protective pellicle without
the formation of thick, bacterial plaques,
and maintaining an effective concentration
of calcium and phosphate in the plaque
fluid-pellicle-enamel surface interface by
a satisfactory flow of fresh, well-buffered
saliva.
HOW CAN WE
PREVENT
CARIES ?
1
2
3
Understanding Dental caries Nikiforuk, G. Vol. 1
69. • Enhancement of the natural remineralizing action of
saliva by regular and frequent administration of low
levels of fluoride in drinking water, dentifrices
and/or mouthrinses.
• These will also provide fluoride at the dissolution
site at the time of acid challenge.
• Frequent availability of low concentrations of
fluoride at the time of demineralization challenge
by acid and the immediately ensuing
remineralization step are major anticaries
procedures.
4
Understanding Dental caries Nikiforuk, G. Vol. 1
70. The enamel rods, which are
parallel to each other and
perpendicular to the surface
structurally, limit the lateral
propagation of occlusal stress
and transfer it unidirectionally to
the resilient dentinal foundation.
Thus, unsupported enamel
causes failure of the restoration
C. R. G. Torres (ed.), Modern Operative Dentistry, Textbooks in Contem
71. CAVITY PREPARATION & ENAMEL
RODS
A cavity wall preparation that is perpendicular to the surface
will expose predominantly the sides of both the enamel rods
and their crystals.
This configuration is recommended for amalgam preparations
because it preserves the dentinal support of the enamel, but it
does not present the optimum bondable enamel substrate.
When the transverse section or face of the crystal, rather than
its side, is exposed to acid, the central core of the crystal is
most susceptible to acid dissolution.
Resin bond strengths are twice as high when adhering to the
acid-etched ends of the crystals as compared with the sides of
the crystals.
Thus, a tangential cut or bevel of approximately 45 degrees
across a 90-degree cavosurface angle of a prepared cavity will
C. R. G. Torres (ed.), Modern Operative Dentistry, Textbooks in Contem
72. C. R. G. Torres (ed.), Modern Operative Dentistry, Textbooks in Contem
73. If a nonadhesive restorative material (such
as the amalgam) is used under
the undermined enamel, the load applied
over the enamel will not be absorbed and
dissipated by the material under it, and
there is a great possibility of enamel
fracture
1) to remove it completely,
even though this represents an
increase of the final
dimensions of the tooth
preparation.
2) to create artificial support to the enamel,
providing its reinforcement, by using a
restorative material that bonds to the tooth
structure and simulate the mechanical
behavior of the dentin
C. R. G. Torres (ed.), Modern Operative Dentistry, Textbooks in Contem
74. GIC can be used as dentin replacement or
full composite resin restorations can be
performed .
For nonadhesive restorations, cavity margins
should hence follow, preferably, the same
direction of the enamel prisms, avoiding that
undermined prism remains.
Otherwise, marginal degradation can occur,
leading to deposition of bacterial biofilm and
caries lesion development.
MANAGEMENT
C. R. G. Torres (ed.), Modern Operative Dentistry, Textbooks in Contem
75. C. R. G. Torres (ed.), Modern Operative Dentistry, Textbooks in Contem
76. SECONDARY CARIES
The fracture
resistance
between
enamel rods
is weakened if
the
underlying
dentinal
support is
pathologically
destroyed or
mechanically
Fracture
dislodgment
of the enamel
rods that
form the
cavity wall or
cavosurface
margin of a
dental
restoration
creates a gap
defect.
Leakage or
ingress of
bacteria and
their by-
products may
lead to
secondary
caries lesions.
C. R. G. Torres (ed.), Modern Operative Dentistry, Textbooks in Contem
77. ENAMEL RODS & ENAMEL
SOFTENING (EROSION)
The critical pH below which
enamel dissolves is about 5.5.
Erosion starts by initial softening
of the enamel surface, followed
by a loss of volume with a
softened layer persisting at the
surface of the remaining tissue.
Exposure to acids combined with
insufficient salivary flow results
in enhanced dissolution.
Goldberg’s Understanding Dental Caries (2016)
78. EROSION
Hydrogen ions or chelating agents begin their
deleterious effects by dissolving enamel crystal,
either in the center of crystallites (central
dissolution affecting a screw-like structure) or at
the lateral border and eventually at the edge of the
crystallite.
This outer screw dislocation occurs at the edge of
the crystallite.
The prism sheath (organic extracellular matrix) and
the prism core are dissolved, leaving apparent a
honeycomb structure mostly identifiable after acid
etching.
If the acidic impact persists (e.g., longer periods of
interaction and/or increased concentrations),
further dissolution of the enamel occurs.
The dissolution becomes irreversible and leads to a
severe alteration associated with a reduction of Goldberg’s Understanding Dental Caries (2016)
79. At the surface, crystallite endings look irregular with a
scalloped profile.
Goldberg’s Understanding Dental Caries (2016)
80. PREVENTION
The direct attack by hydrogen ion combines with the carbonate and
phosphate release of the crystal surface, leading to direct surface
etching. The citrate ion can also form complex with the calcium
removed from the crystal surface.
Preventive strategies of patients suffering from erosion include
1. Dietary counseling
2. Stimulation of salivary flow
3. Optimization of fluoride regimens
4. Modification of erosive beverage
5. Adequate oral hygiene measures
Goldberg’s Understanding Dental Caries (2016)
81. ACID ETCHING
- increases the porosity of exposed surfaces through selective
dissolution of crystals, which provides a better bonding surface for
the restorative and adhesive materials
- etching pattern depends on crystal orientation.
Craig’s Restorative Dentistry 14th Edition; Ten Cate’s Oral Histolo
82. It is these countless
numbers of minitags,
formed within the
individual crystal
cores, that contribute
most to the enamel-
resin bond.
At the same time, the
internal cores of all
the exposed
individual crystals are
solubilized to create a
multitude of
microporosities.
The acid-treated
enamel surface
has a high
surface energy so
that resin
monomer flows
into, intimately
adapts to, and
polymerizes
within the pores
to form retentive
resin tags that
are up to 20 μm
deep.
Depending on
the acid, contact
time, and plane
of cavity
preparation,
either the ends
or the sides of
the crystals may
be preferentially
exposed.
Craig’s Restorative Dentistry 14th Edition; Ten Cate’s Oral Histolo
84. The crystal dissolution starts
either as screw dislocations
in the central part of
crystallite section
(dissolution of the hollow-
core type), or the initial
dissolution begins at defects
located in the edge of the
crystallite (edge dislocation)
Acidic solutions or gels
spread at the surface and
dissolve the center of the
crystal or enlarge the narrow
intercrystalline structures.
Goldberg’s Understanding Dental Caries (2016)
85. Type I
characterized by
preferential removal of
rods
Type II
interrod enamel is
removed preferentially
and the rod remains
intact
Type III
which is irregular and
indiscriminate
Craig’s Restorative Dentistry 14th Edition;
Ten Cate’s Oral Histology 9th E
92. AGING
Enamel becomes less permeable with age.
Young enamel behaves as a semipermeable membrane,
permitting the slow passage of water and substances of small
molecular size through pores between the crystals. With age
the pores diminish as the crystals acquire more ions and as the
surface increases in size
A progressive increase in the fluoride content affects the surface
layer, thus decreasing the solubility of the enamel as it ages.
94. 1. Understanding the direction of enamel rods and topical fluoride treatments at
the mineralizing stage of enamel helps preventing caries significantly.
2. Following some diet restrictions can avoid enamel softening due to acid
reflux, erosion due to external factors.
3. Removing the unsupported enamel at the cervical region by making a
cavosurface angle helps in preventing secondary caries as well as avoiding
failure of restorations.
95. BIBLIOGRAPHY
Craig’s Restorative Dentistry 14th Edition; Ten Cate’s Oral Histology 9th Edition
C. R. G. Torres (ed.), Modern Operative Dentistry, Textbooks in Contemporary Dentistry
Understanding Dental Caries by Gordon Nikiforuk
Orban’s Oral Histology & Embryology 15th Edition
Hunter–Schreger Band patterns and their implications for clinical dentistry Lynch C. Journal of
Oral Rehabilitation 38 (2011) 359–365
Ten Cate’s Oral Histology 9th Edition
Summit’s Fundamentals of Operative Dentistry 4th Edition
Goldberg’s Understanding Dental Caries (2016)
96. BIBLIOGRAPHY
Studervant’s Art and Science of Operative Dentistry 7th Edition
Atlas of Oral Histology 2nd edition
Understanding Dental caries Nikiforuk, G. Vol. 1
Tetsuo kodaka, Michiyo miyakawa, Sequential Observations Followed by Acid Etching on
the Enamel Surfaces of Human Teeth Under Scanning Electron Microscopy at Low
Vacuum, 24:429-436 (1993)
Elia Beniash,Cayla A. Stifler, The hidden structure of human enamel,(2019)10:43-83
S. Habelitz a, S.J. Marshall, Mechanical properties of human dental enamel on the
nanometre scale, Archives of Oral Biology 46 (2001) 173–183
97.
98. TYPE IV ETCHING PATTERN
i. Pitting enamel
surface
ii. Cervical regions of
the buccal surfaces
iii. No preferential
destruction of either
cores/ peripheries
iv. M/c found in
Prismless enamel
Galil A., Wright Z., Acid etching patterms on buccal surfaces of permanent teeth, Journal of Pediatric
99. TYPE V ETCHING PATTERN
• No evidence of prism
outlines
• Extremely flat & smooth
• Lacks micro-
irregularities (for
penetration & retention
of resin)
• Occurs on teeth which
have received ‘Fluoride’
treatments or Patients
residing in high fluoride
Galil A., Wright Z., Acid etching patterms on buccal surfaces of permanent teeth, Journal of Pediatric
