This document provides information on the physical, chemical, structural, and ultrastructural properties of enamel. It discusses how enamel forms a protective covering on the tooth and consists primarily of calcium hydroxyapatite. Enamel's structure includes enamel rods that run from the dentin-enamel junction to the outer surface. It also describes features like Hunter-Schreger bands, incremental lines of Retzius, and surface structures such as enamel tufts. The document outlines the life cycle of ameloblasts and process of amelogenesis, and discusses implications for clinical applications like fluoridation and acid etching.

1. ENAMEL
Department of Conservative Dentistry and Endodontics
Shubham Parmar
Final year

2. Physical properties
 Forms a protective covering over
the tooth structure
 Variable thickness seen over entire
surface of crown
 Thins down to almost knife edge at
cervical area of crown
 Yellowish white to grayish white in
colour
 Semi permeable in nature i.e. allows
passage of certain molecules

3.  Specific gravity 2.8
 Compressive strength 384Mpa
 Modulus of elasticity 84Gpa
 Knoop hardness number 350-430
KHN
 Tensile strength 10Mpa
 Co-efficient of thermal expansion
11.4

4. Chemical properties
 Inorganic material 96% - Calcium
Hydroxyapatite Ca10(PO4)6(OH4)2
 Organic material 4% - Proteins (
Amelogenins, Non Amelogenins, Enamelin,
Ameloblastin, Tuftelin) lipids
 Water

5. Structure
 Basic structure consists of ENAMEL
RODS or PRISMS
 Diameter of rods averages 4µm
 Prisms are cylindrical in longitudinal
section
 Number of enamel rods ranges
from 5 million to 12 million

6.  Enamel rods move from DEJ to
the outer surface of tooth
 Enamel rods are obliquely
placed and move in a wavy
course
 This leads to increased length
of rods as compared to
thickness of enamel
 Enamel rods resemble fish
scale appearance

7. Ultrastructure
 Enamel seems to be
surrounded by rod sheaths
and separated by interrod
substance
 Key hole or paddle shaped
prism pattern is seen in human
enamel
Key hole pattern

8.  Direction of Rods – rods are
generally oriented at right angles
dentinal surface
 In deciduous and permanent teeth
rods are in oblique direction until
they become almost vertical at
tips and incisal edges
 However in cervical region of
deciduous teeth rods are
horizontal, whereas in permanent
teeth the shift to a more apical
direction

9.  Clinical significance – enamel rods
direction should be followed
cavity preparation to avoid
unsupported enamel

10.  Gnarled enamel - Over the cusps of teeth the rods appear twisted around each
other in a seemingly complex arrangement known as gnarled enamel

11.  Clinical significance - This enamel is not subject to cleavage as regular enamel
 This enamel does not yield readily to pressure of hand cutting instruments

12.  Hunter-Schreger bands – these are
alternating bands of dark and light
strips of varying widths
 Change in the direction of rods is
responsible for the appearance of
Hunter-Schreger bands
 Seen in longitudinal ground section
under oblique reflected light
 Dark bands are called Diazones and
light bands are called Parazones
 Clinical significance - Distribute and
dissipate impact forces

13.  Incremental Lines Of Retzius –
appear as brownish lines in ground
section of enamel
 Illustrate the incremental
apposition of layers of enamel
during crown formation
 Appear as concentric circles in
transverse section

14.  Neonatal line – the boundary
between the two portions of
enamel of deciduous teeth is
marked by an accentuated
incremental line of Retzius called
the Neonatal line
 Appears to be the result of the
abrupt change in the environment
of the infant

15. Surface structures
 Prismless enamel
 Enamel cuticle
 Enamel lamellae
 Enamel tufts
 Enamel spindles

16.  Prismless enamel – a relatively
structureless layer of enamel seen
in almost 70% of deciduous and all
permanent teeth
 30µm thick
 Most commonly seen at cervical
area

17.  Enamel cuticle – a delicate membrane called Nasmyth’s Membrane or the
Primary Enamel Cuticle covers the crown of a newly erupted tooth
 It is almost as a basal lamina found below most epithelium
 Protects the surface of enamel from the resorptive activity of adjacent vascular
tissue prior to eruption of teeth

18.  Enamel lamellae – thin leaf like
structures that extend from the
enamel surface towards the DEJ
 3 types of lamellae are seen
 Type A – composed of poorly
calcified rod segments
 Type B – consisting of
degenerated cells
 Type C – arising in erupted teeth
where cracks are filled with organic
matter

19.  Enamel tufts – these arise at the
DEJ and reach into the enamel to
about one-fifth to one-third of its
thickness
 Tufts consists of hypocalcified
enamel rods and interprismatic
substance
 Clinical significance - play a role in
spread of caries

20. Dentinoenamel
Junction
 The surface of dentin at the
dentinoenamel junction is pitted.
 into the shallow depressions of the
dentin fit rounded projections of
the enamel
 Scalloped appearance
 More pronounced in occlusal area

21. Life Cycle of
Ameloblasts
 Life span of ameloblast cells can be
divided into six stages
1. Morphogenic stage
2. Organizing stage
3. Formative
4. Maturative stage
5. Protective stage
6. Desmolytic stage

22. Amelogenesis
 Amelogenesis involves 2 processes
 Enamel matrix formation
 Mineralization
 It occurs during the advanced bell stage
 Reciprocal epithelial-mesenchymal interactions lead to differentiation of
odontoblasts and ameloblasts

23. Age changes in
enamel
 Attrition
 Wear of occlusal and proximal contacts
 Decreased permeability of enamel
 Discoloration

24. Clinical Implications
 Fluoridation - fluoride ion incorporated into or adsorbed on the hydroxyapatite
crystal becomes more resistant to acid dissolution
 It explains the role of fluoride in caries prevention
 Presence of fluoride enhances chemical reactions that lead to the precipitation of
calcium phosphate
 Acid Etching - Acid etching of the enamel surface, or enamel conditioning is an
important technique in clinical practice
 Fissure sealants, bonding of restorative materials to enamel, and cementing of
orthodontic brackets to tooth surfaces involve acid etching

26. References
 Orban’s Oral Histology and Embryology 14e
 Ten Cate’s Oral Histology 8e

27. Thank You