Enamel

Enamel
Dr Urvashi Sodvadiya
I MDS

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ENAMEL
FLOW CHART
▲Introduction
▲Development
Epithelial enamel organ
Amelogenesis
 Life cycle of ameloblast
 Morphogenic stage
 Organizing stage
 Formative/ secretary stage
o Development of Tome’s processes

C O N T. .
 Maturation stage
o Stages of maturation
o Difference between hypoplastic and
hypomineralized enamel
- Molar-incisor hypomineralization (MIH)
o Amelogenesis imperfecta
o Dental fluorosis
 Protective stage
o Importance of reduced enamel epithelium
 Desmolytic stage
▲Chemical properties
Inorganic part
 Structure of hydroxyapatite
 Clinical significance

C O N T. .
Organic part
 Types of protein
Water
▲Basic Structural elements of enamel
 Rods
 Direction of rods
 Interrod enamel
 Rod sheath
 Enamel crystals arrangement and its
importance
 Rodless enamel

C O N T. .
▲Physical characteristics
Density
Thickness
Hardness & Strength
 Compressive and tensile strength of enamel
 Brittleness
 Factors associated with attrition
o Enamel and ceramic restoration
Solubility
 Acid etching of enamel
 Factors affecting acid etching
o Contamination of surface
o Concentration and time of acid
etching
o Type of enamel

C O N T. .
 Effect of bleaching and bleaching agents
on Physical properties of enamel
 Comparison between physical properties
of tooth structure and restorative material
Translucency
Specific gravity
Permeability
 Permeability and structure of enamel
 Factors affecting permeability
Colour
 Factors affecting colour
 White spot lesion
 Deep dentinal caries

C O N T. .
▲Histology
 Hunter- Schreger bands
 Types and its clinical significance
 Incremental lines of Retzius
 Enamel lamellae
 Enamel spindles
 Enamel tufts
 Neonatal line
 Gnarled enamel
 Dentinoenamel junction
 Cementoenamel junction
▲ Difference between Deciduous and Permanent
enamel
▲Repair of Enamel

▲Surface structure
 Prismless enamel
 Perikymata
 Rod ends
 Pits Surface elevation
 Enamel caps
 Enamel brochs
 Enamel cuticle
 Primary enamel cuticle/ Nasmyth’s membrane
 Secondary enamel cuticle
 Pellicle
Age changes
Conclusion
Previously asked questions
References

ENAMEL
INTRODUCTION
 Enamel provides shape and hard
durable outer surface of teeth
Due to high mineral contents and
regular crystalline structure, is the
“HARDEST CALCIFIED TISSUE IN
HUMAN BODY”
Orban’s Oral Histology & Embryology, 13th ed

 vary in thickness and color
Has no blood or nerve supply
Formed by ameloblast; loss of ameloblast before tooth eruption
loss of ability to regenerate or repair

Development
of Enamel

Epithelial Enamel Organ
Outer enamel
epithelium
Stellate reticulum
Intermediate layer
Inner Enamel
Epithelium
Dental papilla
Ameloblast
Odontoblast

Enamel formation
Matrix
formation
Maturation
Lifecycle of ameloblast:
1. Morphogenic stage
2. Organizing stage
3. Formative/ Secretary Stage
4. Maturation Stage
5. Protective Stage
6. Desmolytic Stage

Lifecycle of Ameloblast
• “Bell Stage”
• Short columnar
• Before
ameloblast fully
differentiated &
produce enamel
• Determine the
shape of DEJ &
crown
Morphogenic Stage
Characteristics
1
2
3
4
5
6

• Cell free zone:
disappears
• Differentiates
into Odontoblast
• “Reversal of
nutritional
stream”
Organizing stage
Characteristics
Stage 2: Organizing stage 1
2
3
4
5
6

Stage 3: Formative/ Secretary Stage
• After first layer
of dentin has
been formed
Necessary for
enamel formation
“Mutual
Interaction”
• Formation of
Tome’s process
Characteristics
Important protein secreted by ameloblast:
amelogenins, ameloblastin and enamelin
Undergo degradation: enzymes like
metalloproteinase and serine proleases
-Initial layer of enamel:
on Mantle dentin
-Mineralized
immediately
(rodless enamel)
-Formation of distal part
-Rod and interrod
enamel: result of
Tome’s process Proximal
part
Distal part
Each Tome’s process: Head of 1 prism, Tail of 3
Prism
For formation of one prism: 4 Tome’s process
required
Tome’s process:
diminishes
Last layer of enamel:
not from Tome’s
process
“Aprismatic Enamel”
1
2
3
4
5
6

Ameloblast in
formative stage

Stage 4: Maturation Stage
Characteristics
Maturation:
once enamel
matrix formed
in occlusal/
incisal area
1
2
3
4
5
6

Pattern
of
maturation

Garg N, Jain AK, Saha S, Singh J. Essentiality of early diagnosis of molar incisor hypomineralization in children and review of its clinical
presentation, etiology and management. International journal of clinical pediatric dentistry. 2012 Sep;5(3):190.
Hypoplastic Enamel Hypomineralized Enamel
Type of defect Quantitative defect Qualitative defect
Time of
occurance
Disturbance in Secretory stage Disturbance in Maturation
stage
Characteristic Thin enamel Opacities with altered enamel
translucency
Etiology • Hereditary, Systemic diseases, Prenatal problems, Measles

Appearance a shallow/ deep fossae
with hosrizontal/ vertical
grooves and partial/total
absence of enamel
Appear as yellowish/ brownish area; no
alteration in thickness
Decrease in mineral content: (pathologically
soft enamel) prone to caries
subclinical pulpal inflammation: porosity of the
enamel, lead to hypersensitivity
Diagnosis Borders: smooth Borders: irregular (post-eruptive enamel
breakdown)
Hypomineralized enamel v/s Fluorosis:
- Fluorosis: diffuse opacities (caries resistant)
- Hypomaturation: well-demarcated borders
(more prone to caries)

Amelogenesis imperfecta (AI) v/s
Hypomineralized enamel
- AI: affect all teeth may be
detected pre-eruptively on
radiograph. Usually positive
family history
- Hypomaturation: teeth affected
are assymetrical.
Treatment Preventive:
- Fluoride application, Desensitizing toothpaste, CPP-ACP, Glass
inomer sealant
Direct restoration
Full coverage restoration

Almuallem Z, Busuttil-Naudi A. Molar incisor hypomineralisation (MIH)–an overview. British dental journal. 2018 Oct 12;225(7):601.
- One enamel alteration of great clinical significance affecting the first
permanent molars (FPM): described in four presentations at the
European Academy of Pediatric Dentistry Congress in 2000.
- “Hypomineralized FPM”, “Idiopathic enamel hypomineralization in FPM”,
“Nonfluoride hypomineralization in FPM” and “Cheese molars”
- A single clinical entity
- Defined as hypomineralization of systemic origin affecting one, two, three
or all first permanent molars and the permanent incisors.
Molar Incisor Hypomineralization (MIH)

Aldred MJ, Savarirayan R, Crawford PJ. Amelogenesis imperfecta: a classification and catalogue for the 21st century. Oral diseases. 2003
Jan;9(1):19-23.
Amelogenesis imperfecta
“A group of conditions, genomic in origin, which affect the structure and
clinical appearance of the enamel of all or nearly all the teeth in a more
or less equal manner, and which may be associated with morphologic or
biochemical changes elsewhere in the body .”
 Etiology
- Genetic mutation
 Associated syndrome
- Tricho-dento-osseous syndrome

Jan;9(1):19-23.
• CLASSIFICATION:
Jan;9(1):19-23.

Patel M, McDonnell ST, Iram S, MF WY C. Amelogenesis imperfecta-lifelong management. Restorative management of the adult patient. British
dental journal. 2013 Nov;215(9):449.
MANAGEMENT
Oral hygiene
Dietary advice
Desensitization and stabilization
Restorative treatment
o Bleaching and microabrasion
o Crown lengthening
o Crowns
o Direct and indirect composite
- Pre-treatment with 5% NaOCl followed by etching with
37% phosphoric acid

Sundfeld RH, Sundfeld-Neto D, Machado LS, Franco LM, Fagundes TC, Briso AL. Microabrasion in tooth enamel discoloration defects: three cases
with long-term follow-ups. Journal of Applied Oral Science. 2014 Aug;22(4):347-54.
Microabrasion
in tooth enamel
discoloration
defect

Akpata ES. Therapeutic management of dental fluorosis: A critical review of literature. Saudi Journal of Oral Sciences. 2014 Jan 1;1(1):3.
Dental fluorosis
Dental fluorosis is a specific disturbance due to chronic
ingestion of excessive fluoride during the formative period
of the dentition.
Fluoride level (in drinking water) Clinical features
>1.5 ppm esthetically objectionable dental
fluorosis
4-8 ppm Increased density of bone
>8 ppm Osteosclerosis (if exposed for more
than 10 years)

Matalová E, Lungová V, Sharpe P. Development of Tooth and Associated Structures. InStem Cell Biology and Tissue Engineering in Dental Sciences 2015 Jan 1 (pp. 335-
346). Academic Press.
Very mild fluorosis Opacities follow perikymata White flakes
Moderate opacities with pits
and brown mottling
Discrete pitting
Severe form with loss of
enamel

Dean’s fluorosis index (1934)

Richards A, Fejerskov O, Baelum V. Enamel fluoride in relation to severity of human dental fluorosis. Advances in dental research. 1989
Sep;3(2):147-53.
ETCHING AND FLUOROSED ENAMEL
 Hydroxyapatite replaced by acid resistant fluoapatite
 Critical pH:
- Normal enamel crystals: 5.5
- Fluoroapatite: 4.5
 Etching time: doubled
- For mild fluorosis: similar to that in non-fluorosed teeth

Stage 5: Protective Stage
Characteristics
-After complete
development:
Ameloblast no longer
be differentiated
-S. Intermedium &
OEE: Reduced
enamel epithelium
-Protects mature
enamel
“anomalies”
1
2
3
4
5
6

Secretary stage After maturation of enamel

Goldberg M. Ultrastructure of the Enamel-Cementum Junction. InUnderstanding Dental Caries 2016 (pp. 153-159). Springer, Cham.
Formation of
Cemento-Enamel Junction
(overlap type)

Stage 6: Desmolytic Stage
REE: Proliferates and induce atrophy of connective tissue
Fusion of oral epithelium & REE
Facilitate eruption
Premature degeneration
of REE
Prevents tooth
eruption
1
2
3
4
5
6

Formation of junctional epithelium from REE
Primary epithelial attachment (REE-Tooth) Secondary epithelial attachment(JE-Tooth

Removal of REE: (before eruption)
Either resorption of enamel surface : pitting of enamel surface
Formation of afibrillar cementum : overlap junction of CEJ
(when it is retracted from cervical area)
Vandana KL, Haneet RK. Cementoenamel junction: An insight. Journal of Indian Society of Periodontology. 2014 Sep;18(5):549.

Chemical
properties

ENAMEL
INORGANIC
(96%)
ORGANIC WATER (4%)
Hydroxyapatite
Ca₁₀(PO₄)₆(OH)₂
Proteins
- Amelogenins
- Nonamelogenin

INORGANIC
(96%) C
a
C
a
C
a
C
a
C
a
C
a
C
a
C
a
C
a
P
PP
OH

C
a
C
a
C
a
C
a
C
a
C
a
C
a
C
a
C
a
P
PP
OH
Mg
Mg
CO₃-2
Concentration
F-
Increases
: Increases

Nanostructure of enamel crystallites
Enamel crystallite strength and wear: nanoscale responses of teeth to chewing loads Jing Xia1 , Z. Ryan Tian2,3, Licheng Hua1,2,3, Lei Chen1 , Zhongrong Zhou1 , Linmao Qian1 and
Peter S. Ungar4
 Clinical significance

Ion Concentration
Oxygen 43.4%
Calcium 36.6%
Phosphorus 17.7%
3.2%
Sodium 0.67%
Carbo 0.64%
Magnasium 0.35%
Carbonate
- First to be solubilized
- Attacked by acid in
caries

ORGANIC
Amelogenin Non-amelogenin
90% 10%
Low molecular weight protein High molecular weight protein
Proline, histidine, glutamine,
leucine
Glycine, aspartic acid & serine
- Accumulates: Secretory stage of
ameloblast
- Degradation
- Function: prevents crystals from
fusing
Eg:
- Enamelin
- Ameloblastin
- Tuftelin
Enamel protein : Do not contribute to structure
unlike collagen fibres in dentin

Geng S, White SN, Paine ML, Snead ML. Protein interaction between ameloblastin and proteasome subunit α type 3 can facilitate redistribution of ameloblastin domains
within forming enamel. Journal of Biological Chemistry. 2015 Aug 21;290(34):20661-73.
♦ Most abundant of the non-amelogenin
♦ Expressed: Secretory-stage
♦ Diminishes: Maturation stage
♦ Processed by matrix metalloproteinase 20 (enamelysin or MMP20)
AMELOBLASTIN
Amelin / sheathlin
♦ Cleavage products: redistribute, produces a pattern.
♦ C-terminal: within the newly formed rods - “reverse honey-comb”
♦ N-terminal: Peripheral boundaries - “honeycomb” pattern

Challenges in engineering and testing of bioceramics, High-strength Ceramics: Interdisciplinary Perspectives pp.1-16 timothy g bromage
Water
Filled the pores: present between crystals,
at boundaries of rods
small pores: 6% by volume of the space thought to reside in the
centers of prism heads
larger pores: 0.3% by volume at prism boundaries
Diffusion of ions : Ca, P, F
Self healing : caries and fracture

Basic Structural
elements of
Enamel

Basic structure
ROD
(PRISM)
INTERROD RODSHEATH

https://www.researchgate.net/publication/261566958_Finite_element_analysis_of_the_cyclic_indentation_of_bilayer_enamel
ROD
(PRISM)
Basic structural unit
Origin
Diameter
outer surface: inner
surface – 2:1
Number
Length > thickness
Arrangement/ direction
1/3rd

Number of rods:
30000 – 40000 rods/ sq mm of enamel
Bondable surface area : 10-20 fold
Surface energy increases
Micromechanical interlocking- extremely strong

Area in between rods: interrod
enamel/ interrod cement.
Crystal composition: same
Crystal orientation: different,
distinguishing rods from interrod
enamel
Rod sheath: around 3/4th of each
rod
Organic: protein matrix of
enamelins.
INTERROD & RODSHEATH

Isthmus between rod and interrod: “key hole shaped”,
“fish-scale”
5 µm: breadth
9 µm: length
1
3
Head
Tail
2

• Resistant to abrasion (prism):
Perpendicular to enamel surface >>> parallel to prepared
surface (Osborn JW,1965)
• Angle between prism and tooth surface: determine its
resistance to wear
Silverstone LM, Saxton CA, Dogon IL, Fejerskov O. Variation in the pattern of acid etching of human dental enamel examined by scanning electron microscopy. Caries
research. 1975;9(5):373-87.
Osborn JW. The nature of the Hunter–Schreger bands in enamel. Arch Oral Biol. 1965;10:929–935.
Arrangement/ direction of crystals
Spacing & divergent orientation of crystals in rods and interrod
enamel
Enamel rod: differentially soluble exposed to weak acid
Acid Contact time
Plane of
cavity
preparation
Not significant

Crystals :
Parallel – to length of rods
Perpendicular – to external surface of enamel
Cavity preparation:
Sides of enamel
rods
Resin bond strength:
2 (Ends of the crystal) = (Sides of the crystals)
Perpendicular
Cavosurface bevel: 45 degree to expose the ends of enamel crystals

Orientation:
o Right angle to dentin
 Similar in occlusal third
 Cervical third:
- Permanent teeth:
apically directed
- Primary teeth:
horizontally directed
While preparing cavity
Remove unsupported enamel
Reduces microleakage
Reduces secondary caries
Reduces chances of failure of
restoration
Deciduous teeth
Permanent teeth

Kodaka T, Mori R, Miyakawa M. Sequential observations followed by acid etching on the enamel surfaces of human teeth under scanning electron
microscopy at low vacuum. Microscopy research and technique. 1993 Apr 1;24(5):429-36.
Prismless enamel
Hypermineralized
Maturation
stage
Pathological
formation
Secondary
mineralization
Surface prismless enamel:
 type 2 etching pattern
 no type 1 nor type 1-2 etching patterns.
Thus deciduous and permanent teeth can be distinguished from
successive etching patterns on their surface enamel.
Prismless structure
Deep acid
etching
Silverstone
(1975) and
Marshall et al.
(1975)
Removal of
surface layer by
grinding
Sheykholeslam
and Buonocore
(1972), Conniff and
Hamby (1976)
RODLESS ENAMEL
♦ Outermost layer: 30 µm
♦ Seen: all deciduous, 70% permanent teeth
♦ Least: cusp tips
♦ Maximum: cervical area
♦ Highly mineralized:
♦ being formed during the maturation
♦ abnormal or pathological formation-or
secondary mineralization

Physical characteristics

PHYSICAL CHARACTERISTICS
Density
Varies from 2.8-3 gm/sq cm
Characterizes hardness of
enamel
Low enamel density High enamel density

Thickness
Enamel found to be thicker on:
Palatal aspect : Maxillary molars
Buccal aspect : Mandibular molars
C O N T. .
Supporting cusp
Adaptation to functional demand
Summitt’s Fundamentals Operative Dentistry A Contemporary approach, 4th ed (Indian Edition)
Cusp (molars/premolars) : 2-2.5 mm
Thinning down to almost knife edge at the
neck of the tooth

Permeability
C O N T. .
At maturity,
Inorganic hydroxyapatite crystals: 96% (%wt) / 86% (%vol)
Organic structure: small amount
Water: 4-12%
Intercrystalline structure
Network of micropores: opening to external surface
•Dynamic connection

C O N T. .
“SEMIPERMEABLE”
Various fluids, ions and low molecular substances
When teeth become dehydrated
Empty micropores: enamel becomes chalky and lighter in color
Reversible condition
Decreses with age & may be affected by various dental procedures
BleachingAcid etching Physical removal

Color
Primarily related to:
Thickness of enamel
Shorter wavelength:
blue range; from
enamel
Color of underlying dentin
Long wavelength: Warm
colors predominantly from
dentin
Chromatic
yellow/orange shade
Translucent grey
or
slightly bluish hue

C O N T. .
Conditions can alter the natural color of teeth:
Developmental
defects of tooth
Extrinsic stain Excessive fluoride
Thomas MS, Denny C. Medication-related tooth discoloration: a review. Dental update. 2014 Jun 2;41(5):440-7.
Pulpal necrosis Pulpal bleeding
Antibiotic therapy Meta-morphosis calcification
Drinks such as
coffee, tea and cola
Tobacco or cigarette
smoking

C O N T. .
Etiology of tooth discoloration
Natural/ Acquired Iatrogenic
Extrinsic Intrinsic
( patient related ) ( dentist related )
- Foods
- Beverages
- Tobacco products
- Chemicals in
mouth rinses
- Chromogenic
bacteria
Pre-eruptive
- Diseases
(Hypophosphatemic
rickets)
- Certain medication
- Fluorosis
Post-eruptive
- Aging
- Pulp necrosis
- Calcific
metamorphosis
Short textbook of endodontics; Aarti Daswani,1st Ed
( patient related ) ( dentist related )
- Metallic
restorations
- Composite resin
restoration
Related
toendodontic
treatment
- Remnants of pulp tissue
- Use of Phenol or iodoform
based intracanal
medicament
- Obturating material
Related to
coronal
restoration

Short textbook of endodontics; Aarti Daswani,1st Ed
Management of discoloured teeth
 Teeth bleaching
 Enamel microabrasion
 Restorative treatment
- Composite veneers/ restoration
- Ceramic veneers/ laminates
- Crowns

White spot lesion:
- Subsurface enamel demineralization
- In later stage of demineralization;
White spot opacity: not only when tooth is dried but
also in “wet enamel”
Plaque removal Remineralization
“Lesion may arrest and
enamel may appear normal
again”
If carious lesion extends into dentin:
- Deep discoloration of enamel and cavitation of
enamel to dentin

Hardness & Strength
Structural and compositional characteristics of organic matrix
surrounding the enamel rod and individual crystals:
significantly affect mechanical properties of enamel
Properties value
Knoop hardness number 343
Brinell hardness number 300
Vickers hardness number 294
Tensile strength 1700 PSI
Compressive strength 55000 PSI

Hardness
 Degree of mineralization
 Orientation of the enamel rods and crystals within rods
 Distribution of metallic ions which occur in trace amounts
- Fluoride ions

Modulus of elasticity:
Higher on the surface of enamel
Tensile strength & Compressive strength:
Dentin > Enamel
Brittle
frictional contact with
opposing teeth
Harder restorative
material
“Attrition”

Age
 Factors associated with attrition:
“ Exposed
dentin”
Vertical Dimension
Active tooth
eruption
Parafunctional
habit
Malocclusion Diet
 Normal physiologic wear rate : 15-29 µm/ year

Teeth whitening
procedure
Acid etching
Mechanical
properties of enamel
Tooth preparation
Margin of the restoration
Avoid occlusal contact

Attrition
Olivera AB, Marques MM. Esthetic restorative materials and opposing enamel wear. Operative dentistry. 2008 May;33(3):332-7.
 Non-carious cervical lesion:
Erosion
Different shape of abfraction
Mechanism

Preventive interventions:
• Patient Counseling;
- diet
- brushing technique
- night guards to reduce clenching or bruxism
- chewing gums to increase salivary flow
- medical attention, intrinsic medical or mental condition.
Other treatment options:
• Monitoring of lesion progression
• Occlusal adjustments
• Occlusal splints
• Techniques to alleviate hypersensitity
• Placement of restorations
• Root coverage surgical procedures in combination with
restorations.
Nascimento MM, Dilbone DA, Pereira PN, Duarte WR, Geraldeli S, Delgado AJ. Abfraction lesions: etiology, diagnosis, and treatment options. Clinical, cosmetic and investigational
dentistry. 2016;8:79.

 Wear of enamel due to restorative material:

Translucency
 Degree of calcification and homogeneity of
enamel
Increased by Decreased by
Increasing
wavelengt
h
Dryness
(reversible
)
Specific gravity : 2.8

Solubility
 Normally, resistant to dissolution by oral fluid
 Surface of enamel << DEJ
 Spacing & divergent orientation of crystals
Rods Interrod

Silverstone LM, Saxton CA, Dogon IL, Fejerskov O. Variation in the pattern of acid etching of human dental enamel examined by scanning electron microscopy. Caries
research. 1975;9(5):373-87
Type 1
“Honeycomb
appearance”
Type 3
“Combination of
type 1 & 2”
Type 4
“Random
distribution of
depression”
Prismless enamel Cervical area; rarely
on occlusal
Type 2
“Cobblestone
appearance”
Type 5
“Flat & smooth
enamel”
High fluoride
areas

Cerci BB, Roman LS, Guariza-Filho O, Camargo ES, Tanaka OM. Dental enamel roughness with different acid etching times: atomic force microscopy study. European Journal of General
Dentistry. 2012 Sep 1;1(3):187.
Rods Interrod
Differentially
soluble
Control group
Acid etching for 15 sec
Acid etching for 30 sec
Cerci B B et al;
2012
Gardner A; 2001
Gardner A, Hobson R. Variations in acid-etch patterns with different acids and etch times. American Journal of Orthodontics and Dentofacial Orthopedics. 2001 Jul
1;120(1):64-7.

Hormati AA, Fuller JL, Denehy GE. Effects of contamination and mechanical disturbance on the quality of acid-etched enamel. The Journal of the
American Dental Association. 1980 Jan 1;100(1):34-8.
 Contamination with saliva:
Contaminated with saliva for 60secWithout contaminated with saliva
Factors affecting acid etching

Smear layer on the dentin surface of a primary (A) and a
permanent (B) tooth
20% phosphoric acid: 7 seconds.
20% phosphoric acid: 15 sec
37.5% phosphoric acid: 7 seconds
37.5% phosphoric acid: 15 seconds
32% Phosphoric acid 15% Phosphoric acid
 Type of dentition, Concentration and time of acid used:

 Acid conditioning affects the enamel in the following ways:
 Removes residual pellicle - 10 µm of surface
 Creates porous layer - Depth of pore: 5.0-50.0 µm
 Wettability and surface area
 Surface energy

Lopes GC, Bonissoni L, Baratieri LN, Vieira LC, Monteiro Jr S. Effect of bleaching agents on the hardness and morphology of enamel. Journal of Esthetic and Restorative Dentistry. 2002 Jan;14(1):24-30.
Schiavoni RJ, Turssi CP, Rodrigues JA, Serra MC, Pécora JD, Fröner IC. Effect of bleaching agents on enamel permeability. American journal of dentistry. 2006 Oct;19(5):313-6.
 Effect of bleaching and bleaching agents on physical properties of enamel:
Properties of enamel Effect on enamel
Surface Microhardness Decreases
Permeability Decreases
Enamel surface Changes are seen (exposure of
enamel prism, dissolution of surface,
irregular depression)
Bond strength with restorative
material
Significantly reduced
Chemical changes:
Calcium concentration
Reduces; negligible quantity for
clinical aspect
Concentration and exposure time
Pimenta-Dutra AC, Rodrigo-de Castro Albuquerque LF, dos Santos-Alves Morgan GM, Pereira EN, Martinho-Campolina-Rebello Horta FF. Effect of bleaching agents on enamel surface

Comparison between physical properties of tooth structure and
restorative material:
Properties Enamel Dentin Amalgam Composite Ceramics Glass Inomer
cement
Knoop hardness
number
343 68 90-110 22-80 460 48
Tensile strength 10 MPa 52 MPa 48-70 MPa 30-35 MPa 20-60 MPa 3.9- 8.3
Compressive
strength
384 MPa 297 MPa 343-510 Mpa 200-300 Mpa
(nano-composites: 450
Mpa)
350-550
MPa
150 MPa
Modulous of
Elasticity
84 GPa 19 GPa 11-12 GPa 13-14 GPa 69 GPa 3.5- 9 GPa
Co-efficient of
thermal expansion
( ̊/C)
11.4 × 10-6 8.3 × 10-6 24-25 × 10-6 25-40 × 10-6 12 × 10-6 11 × 10-6

HISTOLOGY

Characteristics Clinical implication
• Due to: variation in
calcification of
enamel
• Variation in
permeability and
organic content of
enamel
- Dark band: Parazones
- Light band: Diazones
• Extension
• Regular change in
direction of rods
• Functional adaptation
• affects development
and prevention of
tooth surface loss
• Affects enamel
bonding
• associated with crack
tooth syndrome
Hunter- Schreger bands
Originally figured by Hunter (1778) and Schreger
(1800) for humans
Von Koenigswald W, Holbrook LT, Rose KD. Diversity and evolution of Hunter-Schreger band configuration in tooth enamel of perissodactyl mammals. Acta Palaeontologica Polonica.
2011 Mar;56(1):11-33.

Von Koenigswald W, Holbrook LT, Rose KD. Diversity and evolution of Hunter-Schreger band configuration in tooth enamel of perissodactyl mammals. Acta
Palaeontologica Polonica. 2011 Mar;56(1):11-33.
Transverse HSB:
generally parallel
to the occlusal
surface
Curved HSB:
• Transverse HSB curved
towards occlusal surface
• Strictly related to specific area:
prominent crest
• Combined with transverse
HSB
Compound HSB:
• Transverse: inner side
• Vertical: outer side
• Occurrence- related to
thickness of enamel, not to the
area
Vertical HSB:
• Vertically oriented
• Not related to tooth
morphology
• No intersection present
Different configuration of HSB

HSB and tooth wear (attrition, abrasion & abfraction):
 Density of HSB: high in specific area
 Cervical region: relatively HSB-devoid high susceptibility to
wear (abrasion)
HSB and fracture resistance of enamel:
• Masticatory force: 100-500 N (parafunctional: 500-800 N)
• Minimum force is required: weakest point
-along a plane parallel to the alignment of prisms
• High density of HSB: high fracture resistance
Lynch CD, O’sullivan VR, Dockery P, McGILLYCUDDY CT, Rees JS, Sloan AJ. Hunter–Schreger Band patterns and their implications for clinical dentistry. Journal of Oral Rehabilitation.
2011 May;38(5):359-65.

HSB and crack tooth syndrome:
 Location:
 Teeth with large restoration: at line angle at the base of
restoration
 Starts usually in cervical region
 Usually travels: laterally
- Diminished HSB packing
densities
- Parallel prism arrangement
2011 May;38(5):359-65.

2011 May;38(5):359-65.
HSB and enamel bonding:
 Prisms: preferentially dissolved in acid etchant
 Depending on the orientation and angle
 HSB-rich regions of enamel: rapidly changing orientation of prisms
etched surface: many etched pits of varying depth and orientation
Increases the surface area
Increases potential for micromechanical retention
 Weakest bond strength: poorly organized or parallelly
aligned prisms
• Adhesion in cervical enamel: inferior
• Characteristic of cervical enamel: low density of HSB
• Enamel prisms: poorly organized than
incisal/occlusal area

Dean MC. Growth layers and incremental markings in hard tissues; a review of the literature and some preliminary observations about enamel structure in Paranthropus
boisei. Journal of Human Evolution. 1987 Feb 1;16(2):157-72.
Incremental line of Retzius
Described as lines by Retzius (1837)
Appearance  Transmitted light: orange to brown
 Reflected light: bluish white
Radiolucent: indicative of hypomineralization (Gustafson &
Gustafson;1967)
Represent incremental pattern of enamel deposition during formation
slight accentuations of prism cross striations or marked step-like
deviations of those prisms cervically
• Resulted from: “feast days”; sundays
- Large quantities of food and sweets were consumed by
children, consequently resulted in indigestion and disturbance of
enamel formation (Gysi; 1931)
Intensity Moderate: normal, broadening of bands: abnormal
Longitudinal Section
Transverse Section

One rhythmic disturbance: every 3 or 4 pm apart
Another: on average every 25 pm apart,
Indicates a greater disturbance every 7 or 8 days.
(Bradford; 1967)
Clinically: “perikymata” or “imbrication lines of Pickerill”
Disappears with the age
Dean MC. Growth layers and incremental markings in hard tissues; a review of the literature and some preliminary observations about enamel structure in Paranthropus
boisei. Journal of Human Evolution. 1987 Feb 1;16(2):157-72.

Line of Retzius

Risnes S. Structural characteristics of staircase‐type Retzius lines in human dental enamel analyzed by scanning electron microscopy. The Anatomical Record. 1990
Feb;226(2):135-46.
Visibility can be attributed to:
 Hypomineralization or hypermineralization of enamel
(Gustafson, 1959)
 Altered mineral composition (Woltgens et al., 1980)
 Altered organic composition (Ducroc and Proust, 1973)
 Increased width or density of prism sheaths (Osborn, 1973)
 Reduced width of prisms (Bergman and Engfeldt, 1954)
 Change in prism direction
 Cervically (Gustafson and Gustafson, 1967; Helmcke and
Schulz, 1968)
 Transversely (Osborn, 1973; Weber and Ashrafi, 1979)

Qualities:
•artifacts in enamel (not found in dentin): created by
incremental steps of ameloblasts
•comparable to the contour "lines of Owen" in dentin
•have increased organic content and show the variations
in rhythm as the tooth enamel matrix calcifies
•follow an appositional or side-by-side growth pattern

Walker BN, Makinson OF, Peters MC. Enamel cracks. The role of enamel lamellae in caries initiation. Australian dental journal. 1998 Apr;43(2):110-
6.
Enamel lamellae
Bodecker; 1906
Leaf like structure
Extends from enamel towards DEJ
Difference between lamellae and
enamel cracks
- Decalcification of section;
- Lamellae: persist
- Crack: disappears
Development: in planes of tension
Dentin lesion associated with
enamel lamellae

Bodecker CF. Enamel lamellae and their origin. Journal of dental research. 1953 Apr;32(2):239-45.
Most common
Clinical
significance
Harbour
microorganisms
Caries
Believed to be
associated with
hidden caries

Lams, H.: Histogenese de la dentine et 1 'mail de las mammiferes, Soc. de Biol. Belge, Compte Rendu 83: 800-2, 1920.
Enamel Spindles
Extension of odontoblastic processes
across DEJ into the enamel
Thickened at their ends
“Enamel spindles”
 Absence of peritubular structure
 Hypocalcified area
- Before hard substances formed
 Direction:
- Corresponds: original direction of
ameloblast
- Divergent: enamel rods
Serve as pain receptors
“enamel sensitivity”

Enamel tufts
Due to overlapping of imperfection
present in different planes when
viewed in a single plane
Ribbon-like structure; inner end of
which arises at dentin
Arise from DEJ towards enamel
Resembles: “tuft of grass”
Hypomineralized area

Enamel rods at the region of cusps/incisal edges seem
to interwine irregularly
interwining & twisting of enamel rods: special optical
appearance called gnarled enamel
Twisted rods increases the strength resists
load
 Resists tooth cutting while preparation
Gnarled Enamel

Janardhanan M, Umadethan B, Biniraj KR, Kumar RV, Rakesh S. Neonatal line as a linear evidence of live birth: Estimation of postnatal survival of
a new born from primary tooth germs. Journal of forensic dental sciences. 2011 Jan;3(1):8.
Neonatal Line
Enamel partly formed before birth and partly
formed after birth
Boundary: “Neonatal line”
Marked by: accentuated incremental line of
Retzius
Due to: abrupt change in environment & nutrition
More distinct than neonatal line present in dentin
Absent: Boys >> girls (less dentally premature
than girls)
Location:
-Present in cervical part of tooth
- Varies in pre-term and post-term birth
Quality
Prenatal enamel >> postnatal
enamel

Losee FL, Jennings WH, Lawson Jr ME, Forziati AF. Microstructure of the human tooth: A. the dentinoenamel junction. Journal of dental research.
1957 Dec;36(6):911-21.
Complex structure; junction between two
dissimilar calcified structure
Scalloping structure
- Convexities: towards dentin
- Concavities: towards enamel
- Proximal surfaces >> buccal and lingual
surfaces
Act as a crack-stopping mechanism
- lower mineralization (Wang and Weiner, 1998)
- higher collagen content (Lin and Douglas, 1994),
- prevent stress concentration
Dentino-Enamel Junction (DEJ)
“Crack tends to run parallel rather than through the DEJ”
(Rasmussen, 1984; Lin and Douglas, 1994; White et al., 2005)

Stress distribution in teeth due to DEJ (Fong et al.,2000):
 Vertical load : in enamel
 Hosrizontal load: in dentin
creates “shear stress”
 Locking mechanism: Reduction in
dentin-enamel sliding
 Increases the area: due to scalloped
structure
 Cavity preparation and DEJ:
 Initial depth- 0.2 mm inside DEJ
Dentin
Enamel
Losee FL, Jennings WH, Lawson Jr ME, Forziati AF. Microstructure of the human tooth: A. the dentinoenamel junction. Journal of dental research.
1957 Dec;36(6):911-21.

Vandana KL, Haneet RK. Cementoenamel junction: An insight. Journal of Indian Society of Periodontology. 2014 Sep;18(5):549.
Cemento-Enamel Junction (DEJ)
Anatomic limit between the crown and root surface
Formation of CEJ
Types I
60%
Types II
30%
Types III
10%
Types IV
1.6%
Types of CEJCurvature of
CEJ

Difference between
primary and
permanent enamel

Primary dentition Permanent dentition
less High
less High
81.3–94.2 wt% 97%
Thin (1); consistant
thickness
-smaller in dimension
Thick (2-3 mm)
-larger in dimension
Color Bluish white in color Greyish white to yellowish
white in color
Mineralization Less mineralized More mineralized
Mamelons Absent Present in incisors
Orientation of enamel rods Right angle to DEJ
throughout
Cervical area: apically
directedDe Menezes Oliveira MA, Torres CP, Gomes‐Silva JM, Chinelatti MA, De Menezes FC, Palma‐Dibb RG, Borsatto MC. Microstructure and mineral composition of dental
enamel of permanent and deciduous teeth. Microscopy research and technique. 2010 May;73(5):572-7.
Crystal density
Amount of Ca and P
Mineral content
Thickness of enamel

CEJ More apically than
permanent dentition
- Protection from caries
- Dentinal hypersensitivity:
rare
At the bottom of gingival
sulcus
Lines of Retzius Less common More common
Prismatic enamel Seen in all deciduous teeth Seen in 70% of permanent
teeth
Neonatal line Present in all deciduous
teeth
Present only in permanent
molars
Dental fluorosis and
dentition
Less involved More involved
De Menezes Oliveira MA, Torres CP, Gomes‐Silva JM, Chinelatti MA, De Menezes FC, Palma‐Dibb RG, Borsatto MC. Microstructure and mineral composition of dental
enamel of permanent and deciduous teeth. Microscopy research and technique. 2010 May;73(5):572-7.

Repair of enamel

Formed by ameloblast; loss of ameloblast before tooth eruption
loss of ability to regenerate or repair
Microstructure of the enamel:
- Promoted repair of microcracks
- reached saturation after approximately 48 hours
- 10% reduction in crack length
- DEJ >> Occlusal surface
- Crack repair ability and fracture toughness …
- female >> male
Organic matter: viscoelastic characteristics
Facilitate crack closure
(Habelitz et al., 2002; Sognnaes, 1949; Svensson et al., 2010)
Rivera C, Arola D, Ossa A. Indentation damage and crack repair in human enamel. Journal of the mechanical behavior of biomedical materials.
2013 May 1;21:178-84.

Reversal of dental fluorosis
Reversal of dental and clinical fluorosis in children
Calcium, vitamin D3 and ascorbic acid
supplementation; below toxic dosage
(Gupta SK; 1994)
Gupta SK, Gupta RC, Seth AK. Reversal of clinical and dental fluorosis. Indian pediatrics. 1994 Apr;31:439-44.

Surface structure
of enamel

Perikymata
Transverse, wave-like grooves
External manifestation of striae of Retzius
Continuous, parallel to each-other and to CEJ
Number:
- 30 perikymata/ mm in CEJ
- 10 perikymata/ mm near occlusal or
incisal third
Course:
- regular; but in cervical region: irregular

Enamel pits
1-1.5 mm in diameter
Represents end of the ameloblast
Enamel caps
Around 10 µm in size
Small elevation
Due to: deposition of enamel on nonmineralized debris
Larger elevation: “enamel brochs”

Enamel cracks/ craze lines
Narrow fissure like structure seen almost on the entire surface
Extends for varying distance
Length : less than 1 mm; some are longer

Some observations on the epithelial attachment and enamel maturation in human incisors C. J. Griffin, D.D.Sc.* and E. J. Gee, M.D.S., F.1.C.D.t
Primary enamel cuticle/ Nasmyth’s
membrane
Secondary enamel cuticle
Covers the entire crown of newly
erupted tooth; soon removed by
mastication
(basal lamina)
Covers only cervical area, extends
subgingivally
Forms initially; before eruption Forms after eruption of the tooth
Protect the surface of enamel; while
eruption
Responsible for primary attachment
of tooth (REE-tooth)
Responsible for secondary
attachment of tooth (JE-REE)
Enamel cuticle

Pellicle
Erupted enamel – normally covered by “pellicle”
Precipitates of salivary mucin
Colonization of microorganism
Plaque formation
Mechanical cleaning: pellicle reforms within short
period of time

Age changes in
enamel

Attrition
 Physiological wear
 Resulting mainly from tooth to tooth contact without any
foreign substance intervention
 Causative agents:
 Parafunctional habits
 Bruxism
 Developmental defects
 Coarse diet
 Natural teeth opposing porcelain
 Signs & Symptoms:
 Sensitivity
 More prone to caries
 Supraeruption of the tooth
 Loss of perikymata
 Rate:
 Depends on location of surface and tooth
 Facial surface >> proximal surface

Abrasion
Loss of tooth structure resulting from direct functional forces between teeth
and external object
Causes:
- Faulty tooth brushing
- Oral hygiene products
- Ill-fitting clasps of RPD
- Interproximal brushing
Most commonly:
Affected area: cervical area
Affected tooth: premolars
Appearance:
- V-shaped defect/ scooped out lesion
- Burnished appearance
- Hard smooth surface
Exhibits hypersensitivity
Treatment:
Diagnosis of cause
Correct iatrogenic force/ factors of cause
Evaluation of abraded area
Restorative treatment
Anterior teeth: tooth-colored restorative material (micro-
filled composites)
Posterior teeth: Resin-modified glass ionomer cement

Erosion
Loss of tooth structure resulting from chemico-mechanical action in
absence of specific microorganisms
Causative agent: intrinsic/ extrinsic

Change in permeability
 Young enamel: semipermeable
 With age:
crystals grow in size
Decreased in size of the pores
Reduces the permeability

Change in organic matrix
with age
chances of caries in teeth with age
F content (mainly from oral fluid)
Requires more time for acid etching in older teeth
Tooth: darker and resistance to decay

Discoloration
Appears darker in color
Loss of enamel structure
Reflects the color of underlying dentin
Appear more darker

Conclusion
Good knowledge of the main four dental tissues and their
relationships to each other and of supporting structures is
necessary for excellence in the performance of operative
dentistry
Physical characteristics of enamel is similarly important to
understand the adhesion (mechanical or chemical) of
restorative material to the structure.

Previously asked questions
Explain development, formation, structure, chemical composition
of enamel.
Explain physical properties of enamel.
Describe various age changes in enamel and its clinical significance.
Development of enamel and dentin and factors affecting physical and
chemical properties of the structure during formation of teeth.
Discussed the etiology and management of discoloured teeth.

References
• Orban’s Oral Histology & Embryology, 13th ed
• Garg N, Jain AK, Saha S, Singh J. Essentiality of early diagnosis of molar incisor
hypomineralization in children and review of its clinical presentation, etiology and
management. International journal of clinical pediatric dentistry. 2012 Sep;5(3):190.
• Almuallem Z, Busuttil-Naudi A. Molar incisor hypomineralisation (MIH)–an overview.
British dental journal. 2018 Oct 12;225(7):601.
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catalogue for the 21st century. Oral diseases. 2003 Jan;9(1):19-23.
• Patel M, McDonnell ST, Iram S, MF WY C. Amelogenesis imperfecta-lifelong
management. Restorative management of the adult patient. British dental journal. 2013
Nov;215(9):449.
• Sundfeld RH, Sundfeld-Neto D, Machado LS, Franco LM, Fagundes TC, Briso AL.
Microabrasion in tooth enamel discoloration defects: three cases with long-term follow-

• Akpata ES. Therapeutic management of dental fluorosis: A critical review of literature.
Saudi Journal of Oral Sciences. 2014 Jan 1;1(1):3.
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InStem Cell Biology and Tissue Engineering in Dental Sciences 2015 Jan 1 (pp. 335-
346). Academic Press.
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dental fluorosis. Advances in dental research. 1989 Sep;3(2):147-53.
• Goldberg M. Ultrastructure of the Enamel-Cementum Junction. InUnderstanding Dental
Caries 2016 (pp. 153-159). Springer, Cham.
• Vandana KL, Haneet RK. Cementoenamel junction: An insight. Journal of Indian Society
of Periodontology. 2014 Sep;18(5):549.
• Enamel crystallite strength and wear: nanoscale responses of teeth to chewing loads
Jing Xia1 , Z. Ryan Tian2,3, Licheng Hua1,2,3, Lei Chen1 , Zhongrong Zhou1 , Linmao
Qian1 and Peter S. Ungar4

• Kodaka T, Mori R, Miyakawa M. Sequential observations followed by acid etching on the enamel surfaces of
human teeth under scanning electron microscopy at low vacuum. Microscopy research and technique. 1993
Apr 1;24(5):429-36.
• Silverstone LM, Saxton CA, Dogon IL, Fejerskov O. Variation in the pattern of acid etching of human dental
enamel examined by scanning electron microscopy. Caries research. 1975;9(5):373-87.
• Osborn JW. The nature of the Hunter–Schreger bands in enamel. Arch Oral Biol. 1965;10:929–935.
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2;41(5):440-7.
• Summitt’s Fundamentals Operative Dentistry A Contemporary approach, 4th ed (Indian Edition)
• Short textbook of endodontics; Aarti Daswani,1st Ed
• Olivera AB, Marques MM. Esthetic restorative materials and opposing enamel wear. Operative dentistry.
2008 May;33(3):332-7.
• Nascimento MM, Dilbone DA, Pereira PN, Duarte WR, Geraldeli S, Delgado AJ. Abfraction lesions: etiology,
diagnosis, and treatment options. Clinical, cosmetic and investigational dentistry. 2016;8:79.

• Kanemura N, Sano H, Tagami J. Tensile bond strength to and SEM evaluation of ground and intact
enamel surfaces. J Dent. 1999;27:523-530.
• Barkmeier WW, Shaffer SE, Gwinnett AJ. Effects of 15 vs 60 second enamel acid conditioning on
adhesion and morphology. Oper Dent. 1986;11:111-116
• Gateva N, Gusyiska A, Stanimirov P, Kabaktchieva R, Raichev I. Effect Of Etching Time And Acid
Concentration On Micromorphological Changes In Dentin Of Both Dentitions. Journal of IMAB–Annual
Proceeding Scientific Papers. 2016 Apr 5;22(2):1099-110.
• Gardner A, Hobson R. Variations in acid-etch patterns with different acids and etch times. American
Journal of Orthodontics and Dentofacial Orthopedics. 2001 Jul 1;120(1):64-7.
• Lopes GC, Bonissoni L, Baratieri LN, Vieira LC, Monteiro Jr S. Effect of bleaching agents on the
hardness and morphology of enamel. Journal of Esthetic and Restorative Dentistry. 2002 Jan;14(1):24-
30.
• Schiavoni RJ, Turssi CP, Rodrigues JA, Serra MC, Pécora JD, Fröner IC. Effect of bleaching agents on
enamel permeability. American journal of dentistry. 2006 Oct;19(5):313-6.
• Pimenta-Dutra AC, Rodrigo-de Castro Albuquerque LF, dos Santos-Alves Morgan GM, Pereira EN,
Martinho-Campolina-Rebello Horta FF. Effect of bleaching agents on enamel surface of bovine teeth: A

• Von Koenigswald W, Holbrook LT, Rose KD. Diversity and evolution of Hunter-Schreger band configuration in
tooth enamel of perissodactyl mammals. Acta Palaeontologica Polonica. 2011 Mar;56(1):11-33.
• Losee FL, Jennings WH, Lawson Jr ME, Forziati AF. Microstructure of the human tooth: A. the dentinoenamel
junction. Journal of dental research. 1957 Dec;36(6):911-21.
• Janardhanan M, Umadethan B, Biniraj KR, Kumar RV, Rakesh S. Neonatal line as a linear evidence of live
birth: Estimation of postnatal survival of a new born from primary tooth germs. Journal of forensic dental
sciences. 2011 Jan;3(1):8.
• Lams, H.: Histogenese de la dentine et 1 'mail de las mammiferes, Soc. de Biol. Belge, Compte Rendu 83:
800-2, 1920.
• Dean MC. Growth layers and incremental markings in hard tissues; a review of the literature and some
preliminary observations about enamel structure in Paranthropus boisei. Journal of Human Evolution. 1987
Feb 1;16(2):157-72.
• Lynch CD, O’sullivan VR, Dockery P, McGILLYCUDDY CT, Rees JS, Sloan AJ. Hunter–Schreger Band
patterns and their implications for clinical dentistry. Journal of Oral Rehabilitation. 2011 May;38(5):359-65.

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