This document provides an overview of enamel structure and composition. It begins with an introduction to enamel as the hardest tissue in the body, composed primarily of hydroxyapatite crystals. It then describes various hypocalcified structures found in enamel, such as rod sheath, incremental lines, enamel lamellae and tufts. Surface structures like perikymata and enamel cuticle are also discussed. In conclusion, it emphasizes that enamel is about 96% inorganic mineral and 4% organic material, with hydroxyapatite crystals forming its primary composition. Hypocalcified zones indicate areas of weakness where dental caries can develop.

1. DEPARTMENT OF ORAL AND MAXILLOFACIAL
PATHOLOGY AND MICROBIOLOGY
BDS I YEAR
25/11/2023
Dr. Shefali
MDS SENIOR LECTURER
ORAL PATHOLOGY

2. CONTENTS
Introduction
Structure of enamel
Hypo calcified structures of enamel
Summary and Conclusion
FAQs
MCQs
Video link
References
Suggested readings

3. INTRODUCTION
Most highly mineralized tissue
Protective structure of crown
Ectodermal in origin
Hardest calcified structure of the body
Components
Organic-4%
Inorganic-96%
Water

4. HYDROXYAPATITE
CRYSTALS
• Inorganic material of enamel
• Hexagonal in shape
• Unite to form enamel rods or prisms
• Chemical formula- Ca10(PO4)6(0H)2
• Comprises-
• 88-90%of tissue by volume
• 95-96% by weight
• Present in form of crystallites

6. Formation, mineralization, and maturation of some
mineralized tissues.

7. HYPOCALCIFIED STRUCTURES OF
ENAMEL
1. Rod sheath
2. Incremental lines (straie) of Retzius
3. Neonatal line
4. Cross striations
5. Enamel lamellae
6. Enamel tufts
7. Enamel spindles
8. cracks
9. Dentino enamel junction

8. SURFACE STRUCTURES
• Aprismatic enamel
• Perikymata
• Enamel cuticle
• Rod ends
• Pits, caps and brochs
• Pellicle

9.  Thin leaf like structures
 From enamel surface towards DEJ, sometimes
penetrate into dentin.
 Consist of organic material with little mineral
content
 Develop in plane of tension, where rod cross such
plane, a short segment may not calcify
 If more severe a crack develop that is filled either by
cells or organic substances

11. ENAMEL LAMELLA
• Enamel lamella extend for varying depths from
surface of enamel & consist of linear, longitudinally
oriented defects filled with organic material
•It is formed as a result of local failure of maturation
process.
•Best seen in transverse section
•Can be seen in decalcified section because of protein
content.
•It may arise developmentally due to incomplete
maturation of a groups of prisms (in which case they
would contain protein) or after eruption as cracks
during function (containing saliva & oral debris).

12. 3 TYPES-
Type A – lamellae composed of poorly
calcified rod segments.
Type B – lamellae consisting of degenerated
cells.
Type C – lamellae arising in erupted teeth
where the cracks are filled with organic matter,
presumably originating from saliva.

13. Type A Type B Type C
Consistency Poorly calcified
rod seg.
Degenerated
cells
Organic matter
from saliva
Tooth Unerupted Unerupted Erupted
Location
Restricted to the
Enamel.
Reach into the
Dentin.
Reach into the
Dentin.
Occurrence Less common Less common More common

14. ENAMEL CRACKS
• The term cracks was used to describe the narrow, fissure-
like structures that are seen on almost all surfaces.
• They are actually the outer edges of lamellae.
• In decalcification of ground sections of enamel, cracks
usually disappear whereas the enamel lamellae still
persist because they contain greater concentrations of
organic material.

15.  Narrow fissure like structure.
 Seen on almost all surfaces.
 They are the outer edges of lamellae.
 Extend for varying distance along the surface.
 At right angles to DEJ.
 Long cracks are thicker than the short one.
 May reach the occlusal or incisal edge.

16. • Careful decalcification of ground sections of
enamel makes possible the distinction between
cracks and lamellae.
• The former disappear whereas the latter persist.
• Cracks don’t contain organic material and
lamellae has higher protein content.

17. ENAMEL TUFTS
 Arise from DEJ.
 Reach to 1/5 – 1/3 the thickness of Enamel
 In ground section: resemble tufts of grass
 The inner end arises at the dentin.
 Consist of hypocalcified E. rods and
interprismatic substance.
 The extend in the direction of the long axis of
the crown (best seen in horizontal sections).

18.  Enamel tufts consist
of several
unconnected
"leaves" of hypo-
calcified enamel.
 They display a
wavy twisted
appearance
 A, Enamel spindle;
B, Enamel tuft

19. BERKOVITZ

20. Transverse ground
section of enamel
Enamel
lamella
Enamel
tufts
ENAMEL LAMELLA & TUFTS

21.  The odontoblasts processes may cross DEJ (before the
hard substance is formed) to the E. and ends as E.
spindles.
 Odontoblasts process trapped in the enamel
 More in the cuspal region
 They are filled with organic matter.
 The processes and spindles are at right angle to the
surface of the dentin.
 The direction of spindles and rods is divergent.
 Spindles appear dark in ground sections under
transmitted light.

23. ENAMEL SPINDLES
 Before the formation of enamel certain odontoblastic
processes project & get trapped b/w the adjacent
ameloblast to form enamel spindles.
 They do not follow the direction of enamel rods.
 Spindles are more prominent in the cuspal region &
generally oriented in a direction perpendicular to the DEJ.

24. ENAMEL SPINDLES
Enamel
spindles
LONGITUD
INAL
SECTION
SHOWING
ENAMEL
SPINDLES

25. DENTINOENAMEL
JUNCTION
• Scalloped
• Convexity towards dentin
• Firm locking
• More pronounced occlusally

27. STRIAE OF RETZIUS
• The incremental lines of Retzius appear as brownish
bands in ground sections of the enamel.
• They illustrate the incremental pattern of the enamel,
that is, the successive apposition of layers of enamel
during formation of the crown.
• In longitudinal sections, they surround the tip of the
dentin.
• In the cervical parts of the crown, they run obliquely.
From the DE junction to the surface, they deviate
occlusally.

28. STRIAE OF RETZIUS

29. CROSS STRIATIONS
• They demarcate rod segments and
become more visible by the action of mild
acids.
• The rods are segmented because the
enamel matrix is formed in a rhythmic
manner.
• In humans, these segments seem to be
a uniform length of about 4 µm. The
cross-striations seen in light microscope
is suggested to be due to a diurnal
rhythm in the enamel formation and that
in these areas rods show varicosities and
variation in composition.

30. NEONATAL LINE
• The neonatal line is due to the abrupt
change in the environment and nutrition
of the newborn infant. The prenatal
enamel usually is better developed than
the postnatal enamel.
• The neonatal line is an accentuated
incremental line, denoting the prolonged
rest period of enamel formation that
occurs at the time of birth.

31. ROD SHEATH
• The enamel prisms appear as segmental rods in
longitudinal section and in cross-section they
appear as oval, fish scale, or keyhole shaped.
The prisms are covered by prism sheath or rod
sheath and interprismatic substance is said to be
present between prisms.

32. a. Perikymata
b. Rod ends
c. Cracks
d. Pits, caps and brochs
e. Enamel cuticle

33. SURFACE APRISMATIC
ENAMEL
• 30um
• Rodless, aprismatic
• More mineralized
• Crystals parallel to each
other & perpendicular to
striae of Retzius

34. STRUCTURE OF ENAMEL…
 Striae of retzius extend from the
DEJ to the outer surface of
enamel , where they end in
shallow furrows known as
Perikymata.
 Perikymata grooves- seen as
wave like concentric surface
rings.
 Perikymata ridges- grooves are
separated from each other by
ridges.
PERIKYMATA

36. A-PERIKYMATA GROOVES,B-PERIKYMATA
RIDGES
High power view of surface enamel with perikymata grooves separated by
perikymata ridges (SEM)
Perikymata
grooves
Perikymata
ridges

38. SURFACE PITS , CAPS
AND BROCHS
• Pits of about 1–1.5 μm in diameter and small elevations
of about 10–15 μm 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 nonmineralizable debris.
• Larger enamel elevations are termed enamel brochs.

39. 1. Primary Enamel cuticle (Nasmyth’s
membrane).
2. Secondary Enamel cutile (afibrilar
cementum).
3. Pellicle (a precipitate of salivary
proteins.

40.  Covers the entire crown of newly erupted
tooth.
 Thickness: 0.2 µm.
 Removed by mastication (remains intact in
protective areas).
 Secreted by postameloblasts.
 EM: similar to basal lamina.
 Prevent resorption of surface enamel before
eruption

41.  Covered the cervical area of the enamel.
 Thickness: up to 10 µm.
 Continuous with the cementum.
 Probably of mesodermal origin or may be
elaborated by the attachment epithelium.

42. HUNTER SCHREGER
BANDS
• Change in the direction of
rods is responsible for the
appearance of the
Hunter–Schreger bands.
• Alternate Dark
(Diazones) and light
(parazones) bands
• Longitudinal section
(diazones)
• Transverse(parazones)
• Oblique light
• Change in rod direction

43. HUNTER SCHREGER
BANDS

44. Seen due to:
1. Change in the direction of Enamel rods-
Most accepted
2. Variation in calcification of the Enamel
3. Alternate zones having different
permeability and organic material.
HUNTER SCHREGER BANDS

45. When enamel is cut parallel to the long axis of
the tooth, individual crystals will be oriented
differently in the groups of prism cut more
transversely or longitudinally.
Angulation is 40°.
This complex pattern of prisms makes enamel
resistant to fracture.

46. SEM of longitudinally
sectioned enamel lightly
etched to show
alternating bands of
transversely
sectioned(diazones) &
longitudinally
sectioned(parazones)
prism.
Diazones
Parazones

47. GNARLED ENAMEL
• 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 called gnarled
enamel.
• Due to change in rod direction

49. SUMMARY and
CONCLUSION
• Enamel is about 96% inorganic mineral in the
form of hydroxyapatite and 4% water and
organic matter. Hydroxyapatite is a crystalline
calcium phosphate that is also found in bone,
dentin, and Cementum.
• Hypo mineralized zones of Enamel are the weak
areas from where percolation of dental caries
takes place.

50. QUESTIONS
• Long Answer Questions:
• Discuss Hypocalcified structures
of enamel
• Short notes:
• Incremental lines of Retzius
• Neonatal line
• Enamel lamellae

51. MCQs
Hypocalcified structure include all except:
A. Incremental line
B. Neonatal line
C. Enamel lamellae
D. Hunter shreger bands
• Hypocalcified structure of dentinal origin seen in enamel are:
A. Enamel lamellae
B. Enamel spindle
C. Enamel tufts
D. Neonatal line

52. Video Link
• https://youtu.be/Gxy6f0BKgk0

53. REFERENCES
• Orban's Oral Histology and Embryology- 15 th
ed.
SUGGESTED READING
• Ten Cate's Oral Histology, Development,
Structure, and Function- 9th Edition.
• Provenza Text book of Oral Histology.