enamel structure

1. Enamel & Amelogenesis
By
Amira Mohsen Elsherbini

2. Objectives
•Def 
•External factor 
Properties (Chemical or Physical)
•Developmental 
(Amelogenesis and life cycle of ameloblast) 
•Surface structure 
Structure of enamel , surface structure and
Hypocalcified structures.

3. •Enamel structure can be related to
•DEJ and initial
enamel formation
•Appositional growth
•Change in Enamel
rod directions
•Surface coating
(developmental or acquired)

4. Structural features of Enamel
• I.Basic structural unit… Enamel Rod
• Change in Enamel rod directions
• Gnarled enamel
• Hunter schreger band
• II. Structures related to Appositional growth
• Brown striae of Retzius
• Cross striation
• Neonatal line
III. DEJ and initial enamel formation
DEJ
E.Tuft
E.spindle
IV.Surface stratructures
• E.Lamella
• Perikymata
• Rod end
• Surface coating
developmental or acquired
Afibrillar cementum Salivary Pellicle
1ry&2ry e.cuticle Plaque & calculus
V.Age changes and clinical considerations

5. How to examine the enamel Structures

6. Light microscope
Decalcified section
• Only a space is left
• Minerals are
dissolved
• But during
Development
Enough organic
materials are retained
Ground section
Minerals are retained
Either
•Longitudinal sections.
•Cross sections.

7. Electron microscope

8. Ameloblast

9. I.Basicstructuralunit…EnamelRod
Rods
 LM&EM
 Number
 Direction
 Course
 Diameter
 Hunter-Schregerbands
 Perikymata
InterRods
Rodsheath

10. Enamel Rods
•By light microscope:
• the enamel rods whether cut
longitudinally or transversely appear clear and
structureless, because they are formed of tightly
packed mass of hydroxyapatite crystals that allow
light to pass through.

11. Enamel Rods
• By electron microscope (EM):
• LONG. SEC ..it appears cylindrical separated
by less calcified dark lines “cross striations”.
• T .S Oval, fish scales, rounded, hexagonal
or Key hole with the head directed occlusally and
the tail points cervically.

12. Enamel Rods (EM)
• The rod is made up of crystals
whose long axes run for the
most part parallel to the
longitudinal axis of the rod.
• Crystals more distant from
the central axis flare laterally
to an increasing degree as
they approach the rod
periphery.
• The difference in the
angulation is the function of
toms process and causes
difference in the reflective
index.

13. Long. sec

14. trans.sec
For each pattern
One ameloblast form
the the rod
Three for the interrod

15. •Enamel Rods
•Course
The course is wavy from ADJ till the
enamel surface it become straight.
At the incisal edge or cusp tip:
• It has a twisted course and braided
together
to give maximum strength to the areas
which
are more subjected to the masticatory forces

gnarled enamel
(grain pattern)

17. Enamel Rods
•Diameter
• because of the marked difference in the surface area between the inner and outer enamel surfaces
• Diameter increase from ADJ to the surface (Ratio !:2)
• 3-4 micron  8 micron
•Number
Varies 5 millions at lower central and up to 12 millions at the upper 1st permanent molar.

18. • Enamel Rods
Direction
General direction of the enamel is perpendicular on dentin.
At cusp tip or incisal
ridge regions  roughly vertical
middle third become oblique
(towards the occlusal surface)
deciduous teeth
cervical region  horizontal
where the enamel ends abruptly as a thick layer.
permanent teeth
while in the cervical region the rods deviated from horizontal to be directed obliquely rootwise. This is
because the enamel of permanent teeth ends as a knife

19. Hunter-Schreger
bands

20. Hunter-Schregerbands
• alternatedarkandlightbands extending fromDEJ
towardstheenamelsurface.
Darkband(l.srods)Diazones(absorb)
lightband(c.srods)parazones(reflect)
•Theselines arecurvedwiththeconvexitiesfacing
thecervicalregion.
•Hunter-Schregerbands areconsidered asoptical
phenomenon .
•observedingroundlongitudinalsection ofenamelunder

21. It may be due to:
1. Change in the direction of enamel rods.
2. Variation in calcification of the enamel.
3. Alternate zones having different permeability and
organic material
4. Optical phenomenon.

22. Enamel main unit structure  Enamel Rods
Rods 
 LM & EM
 Number
 Direction
 Course
 Diameter
Inter Rods
Rod sheath


23. Inter-rodregion:
Is an area surrounding each
crystals are oriented in a
direction from those
Ithasa differentrefractive
In human teethitappears to
minimum orevenabsent in
areas.

24. Inter-rodregion
• Thedegreeofdifference issignificant around
approximately three fourthsofthecircumference ofa
rod.
• Theportionofinterred regionlocateddirectly
cervical to aparticular rodisnotseparated fromthat
rodbyasheathbecausethecrystals there are
confluentwiththosemaking up therod.
• InL/Sofenamel rods,thelateralflaringofrodcrystals
continues uninterrupted intothe cervically located
interred region untiltheylienearlyperpendicularto
therod.
• InC/Softherod –interredrelationhasbeencompared
to
theshapeofakeyhole (theheadrepresent partofE.rod

26. EnamelmainunitstructureEnamelRods
Rods 
 LM&EM
 Number
 Direction
 Course
 Diameter
 Hunter-Schregerbands
 Perikymata
InterRods 
Rodsheath



27. Rodsheath
•Thethinstructureformedbythe
accumulationoforganicmaterial
•delineatingthecoronal2/3rdboundaryof
enamelrod.
•Itis lesscalcified thantheroditselfi.e.ithas
ahigherorganiccontent, thusit resists
decalcificationmorethantherod
•thecrosssection.
Thusenamelrodswithdistinct rodsheath
covering coronal2/3rdportionandconfluent

28. • The apatite crystals of the mature human
enamel are the largest of all those of the
other calcified structures in the body. They
are irregular in shape having an average
thickness of 300A, average width of 900A
and their length range from 0.05-0.1
micron and may reach up to one micron

29. But remember
• Both outer and inner most layers of enamel are
structureless enamel
• In these regions, the crystals are arranged uniformly
with their long axis perpendicular to the surface. This
is due to the absence of Tomes’ process during the
formation of innermost and outermost enamel.

30. EnamelmainunitstructureEnamelRods
Rods 
 LM&EM
 Number
 Direction
 Course
 Diameter
 Hunter-Schregerbands
 Perikymata
InterRods 
Rodsheath 




31. cavitypreparation

32. Bleaching&acidetch
• Bleaching:
• food, drinks,tobacco,etc. staintheenamelsurfaceor not
depends ontheattractionofthematerialstothetoothsurface.
• Chromogens fillporesandbindtotheorganicmatrix.
• Whiteningagentsproduce reactivemolecules thatpenetratethe
enamelporesandactasbothanoxygenator andanoxidant,
reducingthelargechromogenic organicmolecules intheenamel
matrixgivingalighterappearance.
• Acid etch:
• Itisinvolvedinfissuresealant,inbondingrestorationsandin
cementingorthodonticbrackets.
• 30-40%phosphoricacidappliedtoenamelfor60seconds
providesanadequateetch
• Crystalsdissolvemorereadilyattheirendsthanontheirsides,
andinsideout.
• areaswithrodless enamel,especiallyindeciduousteeth,slightly

33. Type I
Type II
Type III

36. Forensically it doesn't
add up ???!!

37. Rods embedded in interrod

38. Structural features of Enamel
• I.Basic structural unit… Enamel Rod

• Change in Enamel rod directions
• Gnarled enamel
• Hunter schreger band
• II. Structures related to Appositional growth
• Brown striae of Retzius
• Cross striation
• Neonatal line
III. DEJ and initial enamel formation
DEJ
E.Tuft
E.spindle
IV.Surface stratructures
• E.Lamella
• Perikymata
• Rod end
• Surface coating
developmental or acquired
Afibrillar cementum Salivary Pellicle
1ry&2ry e.cuticle Plaque & calculus
V.Age changes and clinical considerations

39. Structuresrelatedtoapposition

40. Structuresrelatedtoapposition
•The concept of Incremental lines
(lamination or Rhythmic formation)
Incremental growth lines
Periods of activity alternating with periods
of rest.

41. Crossstriations:
short increment
•In GLS of enamel is treated with mild etching solution, the cylindrical clear
crystalline enamel prism appears to be divided horizontally into equal
segments by less calcified dark lines, giving the enamel rods a striated
appearance.
•These lines are called cross striation or short increments.
•Like a ldder (4 micron)
•Represent daily rhythm.
•Scaining electron microscopy reveals
alternating constrictions and expansions of the rods
in some regions.
May represent concavities in the rod structure.

42. • however the cross striations could also result from structural interrelations
among groups of rods rather than the modification of a single rod.(altered
packing of enamel crystals)
• Variation in mineral or organic content or density in enamel rod (ex.
Carbonate and sodium).

43. Incremental lines of enamel:-
Striae of Retzius (long increment):-
Represent a weekly rhythm of the ameloblasts.
In L/S: Seen as a series of dark bands reflecting successive
enamel-forming fronts.
It arise from the ADJ upward outward surrounding the tip
of the cusp or incisal edge and not reach the incisal edge or
cusp tip.
At the middle and cervical parts: they run obliquely and
deviate occlusally reach the enamel surface and become
represented as a series of transverse depressions
(perikymata).

44. In GTS it appear as concentric circles like the
growth rings of a tree
Metabolic disturbance leads to prolonged periods
of rest and broadening of the incremental lines.

45. So.. What is
perikymata?

46.  It is the external
manifestation of the
brown striae of retzius.
 Represented as shallow
furrows where the striae
of retzius end in the
outer surface of enamel.
 Continuous around the
tooth and parallel to the
CEJ.
 There are 30 /mm in
cervical area and decrease
to 10/ mm toward the
occlusal surface.

47. CROSS
STRAIATIONS
(short increment)
increment)
Brown striae OF RETZIUS
( long increment)
 
Incremental lines of enamel
Neonatal line

48. Neonatalline
•Anaccentuatedstriaofretzius
thatreflectsthemarked
physiologicchangesoccurring
atbirth.
•Presentonlyindeciduousteeth
andfirstpermenantmolars
(enameldevelopspartlybefore
andpartlyafterbirth).

49. Neonatalline
•Thequalityofprenatalenamelisbetter
thanthepostnatalenamel(moreprotected
conditionandconstantnutritionofthefoetus).
•Perikymataareabsentintheocclusalparts
ofdeciduousteeth,whereastheyarepresent
inthepostnatalcervicalparts.

51. Structural features of Enamel
• I.Basic structural unit… Enamel Rod

• Change in Enamel rod directions
• Gnarled enamel
• Hunter schreger band
• II. Structures related to Appositional growth
• Brown striae of Retzius
• Cross striation
• Neonatal line
III. DEJ and initial enamel formation
DEJ
E.Tuft
E.spindle
IV.Surface stratructures
• E.Lamella
• Perikymata
• Rod end
• Surface coating
developmental or acquired
Afibrillar cementum Salivary Pellicle
1ry&2ry e.cuticle Plaque & calculus
V.Age changes and clinical considerations

52. Structures related to ADJ
• ADJ
• Spindles
• Tufts

53. Structures related to ADJ
•What is ADJ?
•The interface between
different mineralized matrices.
Scalloped nature (undercut)?!
The protein found in the ADJ is
Believed to act as nucleation center
And as cementing substances for enamel
& dentin (interdigitation)

54. Scalloped pattern is not responsible for the
attachment

55. Enamelspindles
• E.Spindlesareformedduringdifferentiation
stage ofameloblast.
•OriginatefromADJ
• Wheretheodontoblasticprocesspassthrough
andbecomeinsinuatedbetweenPreameloblast.
• Astheenamelformitrepresentterminal
extensionofprimarydentinaltubules

57. •InGS;theodontoblasticprocessesdisintegrateandare
replacedbyairwhichappearsdarkintransmitted
light.(hypocal,st,organiccontent)
•Theenamelspindlesappearasshort,straight,thin,dark

60. EnamelTufts
•Tuftsareformedduring
elaboration
ofinitialenamelandtomes’
process
formation.
•Frequent,regular&periodic
featureofADJ
• TheyoriginatefromADJextend
to1/3-1/5

61. EnamelTufts
•theyappeartobebranched
andcontaingreater
concentrationofenamel
proteinsthantherestof
enamel(failtomature).
•Bestseenintransverse
sectionsofenamelmainlyin
G.Sbutcanalsoseenin

62. EnamelTufts
•theyappearasundulatingsheetsinthe
interprismaticareas.
• Itmaybedueto
•Abruptchangesinthedirectionofgroupsofrodsthatarise
fromdifferentregionsofthescallopedDEJ.
• Adifferentratioofinterredandrodenamelinthesegroups
createslessmineralizedandweakenedplanes
•Itissupposedto
• AnchorEnamelanddentin
•Distributethemasticatoryforces
• Preventcracks

63. Structural features of Enamel
• I.Basic structural unit… Enamel Rod

• Change in Enamel rod directions
• Gnarled enamel
• Hunter schreger band
• II. Structures related to Appositional growth
• Brown striae of Retzius
• Cross striation
• Neonatal line
III. DEJ and initial enamel formation 
DEJ
E.Tuft
E.spindle
IV.Surface stratructures
• E.Lamella
• Perikymata
• Rod end
• Surface coating
developmental or acquired
Afibrillar cementum Salivary Pellicle
1ry&2ry e.cuticle Plaque & calculus
V.Age changes and clinical considerations
Hypocalcified
st.
Hypocalcified
st.

64. Surfacestructure
1. E.lamellae&Cracks
2. Outerstructurelessenamel.
3. perikymata. 
4. Rodend.
5. AfibrillarAcellular
cementum,1ry&2rycuticle


65. 1.EnamelLamellae

66. 1.EnamelLamellae
Def
Arethinleaforsheetlikestructures
Extendforvaryingdepthsfromthe
surface
ofenamel
consistoflinearlongitudinaloriented
defectsfilledwithenamelptnor
organicdebrisfromtheoralcavity

67. Type A Type CType B
1.EnamelLamellae
types
Developmentalortrue(typeA)
Nondevelopmental(false)orcracks
TypeB
TypeC

68. Type A Type B Type C
Stimulus Mild stimulus (abnormal
tension)
Sever stimulus Sever stimulus
Time of
incidence
During enamel formation
but before calcification
(disturb calcification and
block ptn reabsorption)
After enamel
formation but before
eruption
After eruption
Extension Enamel May reach ADJ May cross ADJ to
dentine
Content Enamel matrix &
interprismatic
substance
Cells of enamel organ
either die in the depth
Surface hornified
cuticle
cells of c.t diff 
cementum
Organic materials
from saliva,
bacterial plaque
and food depris

69. Type A Type B Type C
Tooth Unerupted Unerupted Erupted
Occurrence Less common Less common More common

70. RoleofE.lamellaincaries
areaofpermeability
hiddencaries

71. E.Lamellavscracks
•Lamellaecanbedifferentiated
fromcrackwhichmaybe
producedduringGS.
• Crackrepresenttheouteredgesof
enamellamellae
•Preparationbycareful
decalcification,wherecrackwill
completelydisappear
•Devofcracktttcrown&
endo
N.B

72. 2.Outerstructureless
(prismless)
enamel

73. 2.Outerstructureless(prismless)
enamel.
•Theoutermost 30microns ofenamel.
•Foundinall deciduous teethan 70%of
permanent teeth.
•Mostcommon in cervical area and
leastoftenin cusptiporincisaledge.
•Norodoutline isvisible;crystals are
arranged parallel toeachother and
perpendicular totheincremental
linesofRetzius.

74. 4.Rodend
•Theyareconcavedepressionvaryin
depthandshape.
•Theyareshallowatthe
cervicalregionanddeepen
nearthe incisalorocclusal
surface

75. 5.AfibrillarAcellularcementum
• Due toretractionor
degeneration ofREE
duringdevelopment
• Inhistologicalsectionsit
mayappearasan"islandor
a"spur"ofcementum
continuous withradicular
cementumandoverlapping
thecervicalenamel.
• Generally,coronal
cementuminhumansis
acellular andafibrillar

76. 6.Salivarypellicle&Dental
plaque(Aquiredcoating)
Salivarypellicle
Thinfilmofsalivary
proteins(organicmat)
Dentalplaque
Softadherentcoatof bact
embeddedinsal.&bac.
products
CalculusorTartar
calcifiedplaque

77. Structural features of Enamel
• I.Basic structural unit… Enamel Rod

• Change in Enamel rod directions
• Gnarled enamel
• Hunter schreger band
• II. Structures related to Appositional growth
• Brown striae of Retzius
• Cross striation
• Neonatal line
III. DEJ and initial enamel formation 
DEJ
E.Tuft
E.spindle
IV.Surface stratructures
• E.Lamella
• Perikymata 
• Rod end
• Surface coating
developmental or acquired
Afibrillar cementum Salivary Pellicle
1ry&2ry e.cuticle Plaque & calculus
V.Age changes and clinical considerations
Hypocalcified
st.
Hypocalcified
st.

78. V.Agechangesand
clinicalconsiderations

79. Age changes
 Attrition
• Occlusal wear is leading to decrease vertical dimensions.
• Proximal wear is leading to decrease in arch length and flattening of contact
points.
• Loss of perikymata and rod ends.
 Discoloration
• Due to addition of organic material or a deepening of
dentin color seen through the progressively thinning layer of translucent
enamel.
 Modification in the surface layer (ionic exchange)
• Increase in the fluoride content of surface enamel.
 Decreased Permeability
• Water content of enamel decreases with age.

80. Clinical consideration
• Acid etching
• Bleaching.
• Fluoridation
• Enamel pearl.

81. Any Questions?

82. Thanks