ENAMELClick to edit Master subtitle style

PRESENTED BY: MANVA MOHNISH ZULFIKAR P.G STUDENT DEPARTMENT OF CONSERVATIVE DENTISTRY & ENDODONTICS5/13/12 1 1

CONTENTS

Introduction properties

Composition Physical

Structure Amelogenesis Clinical Defects

consideration of enamel formation5/13/12 2 2

INTRODUCTION DEFINITION:Enamel is the hard mineralized tissue which forms a protective covering of variable thickness over the entire surface of crown.

5/13/12

3

3 3

Also called substantia adamantia.

Hardest tissue in the body from ectoderm

Derived

The only mineralized tissue that is totally acellular. cannot renew itself as5/13/124

Enamel

4 4

Highly

calcified tissue

Organic

content is non collagenous in nature crystals are

Hydroxyapatite

extremely largeEnamel5/13/12 is translucent and varies in55

5

COMPOSITIONMature

enamel (weight %)-

96% minerals 3% water 1% proteins & lipids

5/13/12

6 6

Minerals (96%)

Calcium- 37% 55%

Phosphate-

Carbonate-3.5% Magnesium-0.5%

Traces of Strontium Lead Fluoride The5/13/12 percentage of Ca and P is lower in7 7

Calcium phosphate salts ( hydroxyapatite crystals ) Crystals - large, elongated, ribbon like hexagonal in shape HA= Ca10(PO4)6(OH)2

small amounts of carbonates, magnesium, potassium, sodium and fluoride

Enamel primary mineralization and secondary mineralization increase mineral content in a relatively smooth 5/13/12 curve

8 8

Formation ,mineralization and maturation of enamel , dentin and bone

5/13/12

9 9

ProteinsAmelogenins

-Tryosine rich Amelogenin polypeptide -Lysine rich Amelogenin polypeptideEnamelins Tufetlins

5/13/12

10 10

Physical propertiesProtection

Color

Thickness

Permeability

Specific

Gravity 5/13/12

11 11

Protection:- Forms a resistant covering over

the tooth

Ability to withstand masticatory forces High mineral content hardest but Brittle5/13/12 Dentin is necessary to maintain 12 12

ColorDetermined by differences in translucency

Yellowish white Thin translucent enamel underlying dentin is visible Grayish white 5/13/12 More opaque enamel less of

13 13

Translucency

depends on the degree of calcification & homogenicity on enamel matrix. becomes temporarily whiter within minutes when tooth is isolated from moist environment. change in color is explained by temporary loss of loosely bound water CONSIDRATION:5/13/12 14 14

Enamel

This

CLINICAL The

shade must be determined before

ThicknessThicker

at incisal & occlusal areas thinner until it terminates at CEJ (almost knife edge) incisal edge of incisors to 2.5mm- cusps of5/13/12 15 15

Progressively

2mm-

2.3

PM

Primary

teeth have thinner enamel as compared to permanent teeth decreases towards the junction of the developmental cuspal lobes of posterior teeth nearly zero where junction is

Thickness

Sometime

fissured

CLINICAL This

CONSIDERATION:16 16

fissured5/13/12 junction are prone to food lodgement and caries , hence to be

Hardness

-

Extremel y hard5/13/12

17 17

BrittleDue

to hardness & crystalline structure is brittle with high elastic modulus & low tensile strength requires a base of dentin, a highly compressive tissue acts as a cushion for overlying enamel, to withstand masticatory forces 5/13/12

Enamel

Enamel

18 18

Enamel

rods that fails to posses a dentine base because of caries or improper cavity preparation, are easily fractured away from neighbouring rods

5/13/12

19 19

Permeability- Can act as a semi permeable membrane- Allows complete or partial passage of certain molecules:

14 C-labeled urea 5/13/12 Iodine, etc

20 20

Density

approximately. 2.8 - 3 g/ml .from Surface to DEJ

. from Incisive edge to cervical margin .Permanent teeth > Deciduous teeth .Upper incisors > PM & lower incisors 5/13/1221 21

Variability

due to degree of calcification, prism & crystalline orientation & distribution of metallic ions.

5/13/12

22 22

Comparison of physical properties of enamel and dentine

5/13/12

23 23

Structure

Rods structure

Submicroscopic Striations Direction

of rods bands lines of retzius

Hunter-schreger Incremental Surface Enamel Enamel Enamel

structures cuticle lamellae tufts5/13/1224 24

Enamel rodsAlso

known as PRISMS from approx. 5 million in lower incisor to 12 million in upper molarRuns in tortuous25 25

Ranges

5/13/12

Length of most rods is greater than the thickness of enamel because of the oblique direction and the wavy course

5/13/12

26 26

Submicroscopic structure

Human enamel contains rods surrounded by rod sheaths and separated by interrod substance section of ground section: fish scale hole or paddle-shaped pattern c/s each rod has rounded 5/13/12 head which is oriented to27 27

Cross key In

Cross section of enamel representing rod , rod sheath and interprismatic substancs5/13/12 28 28

Click icon to add picture

In cross section, it resembles a keyhole or a paddle shaped prism

A cross sectional view B-lateral view C-top surface

5/13/12

29 29

In head region crystallites are arranged with their long axis parallel to long axis of rod Towards tail crystallites show a progressive inclination away from this until they are oriented about 65-70 away from long axis5/13/12 30 30

The head of each rod is made up of One The tail is made up of three ameloblast Rods are the secretory product of Rods runs in perpendicular direction

amelobast

Thus each ROD ----->FOUR AMELOBLASTS

ameloblasts

from Dentinoenamel junction to the surface of enamel5/13/12 31 31

Rods

measure 5 micrometre in breadth and 9 micrometre in length crystals are arranged parallel to long axis of prisms, although a deviation of 40 degrees have been reported cross section crystals have an average thickness of 30 nm and 32 5/13/1232

Apatite

In

Direction of rodsRods In At

are oriented at right angles to dentin surface deciduous dentition cervical portion the rods

-Deviate in an occlusal direction

In permanent dentition cervical portion the rods33 33

At

-Deviate in an apical direction 5/13/12

Direction of enamel rods

5/13/12

34 34

Cross striations

Perpendicular to enamel rods enamel forms at rate of 4

Human

m/day

Ground

sections reveal periodic bands or cross striations at 3-6 m intervals Indicates daily variation in the secretory 5/13/12 35 activity of ameloblast. 35

o

SEM

of fractured enamel showing cross striations

5/13/12

36 36

Striae of RetziusCan

be Hypo or hyper mineralized

structure

Brownish bands in ground sections as concentric rings in the structure and mineralization during

Appears

Variation

enamel formation5/13/12 37 37

Illustrate

successive apposition of layers of enamel section----surround the tip of dentin section------arranged concentrically striae in enamel of decidous teeth than permanent teeth ( forming more rapidly )5/13/12 38 38

Longitudinal Transverse fewer

Transverse

section of enamel showing enamel striae 5/13/12

Longitudinal

section of enamel showing 3939

Enamel lamellaThin Run

- Leaf like structures

from the surface to the dentino-enamel junction, sometime time extend to or penetrate into DEJ more of Organic content and less inorganic content cracks40 40

Contains

Resembles On

decalcification lamella persists. 5/13/12

A. Enamel lamella B. Enamel tufts C. Enamel spindle

5/13/12

41 41

Type Type A

Content

Extent

Poorly Enamel calcified enamel rods Degenerated Dentin cells Organic matter originating from saliva5/13/12

Type B

Type C

Dentin

42 42

Enamel tufts

From the dentinoenamel junction

Extends

1/5 to 1/3

thickness of enamelAppear Narrow

as tufts of grass ribbon like5/13/12 43 43

structures that arise

Hunter schreger bandsAlternating

dark and light bands of varying width in longitudinal ground sections under oblique reflected light from the dentino-enamel junction5/13/12 44 44

Seen

Extends

Reaches

4/5th of enamel surface

Regular

change in the direction of the enamel rods adaptation of rods to minimize cleavage in an axial direction light is reflected, rod 5/13/12 orientation causes alternating

Functional

When

45 45

Dark

Diazones (transversely cut rod) Parazones (longitudinally cut

Light

rods)

Zones

can be reversed by altering the direction of incident rays between diazones and parazones is approx 40o5/13/12 46 46

Angle

Hunter schreger bands viewed under incident light

Diazones and parazones

5/13/12

47 47

Enamel spindles Are

produced

by odontoblastic process which gets incorporated b/w cells of Inner Enamel5/13/12

48 48

More

in number in region of

cuspsRun

at right angle to dentin surface not follow direction of rods

Do

Would

serve to improve the anchorage; particularly in critical 49 sites like 5/13/12 region cusp 49

Neonatal line

Neonatal ring Striae of Retzius enamel formed before

Accentuated Demarcates

birth & after birth

Deciduous teeth & perm I molar in occlusal & incisal parts of5/13/12 50 50

Absent

deciduous teeth, present in post natal

Longitudinal section of a deciduous tooth showing neonatal line

5/13/12

51 51

Dentino-enamel junction

Is established as dentin and enamel begin to form as a scalloped profile; convexity towards dentin

Seen

ena mel5/13/12 52 52

Cemento-enamel junction Relation

b/w cementun & enamel at cervical region is variable types seen

3

5/13/12

53 53

In 60% of the teeth cementumOverlaps enamel In 30% of the teeth cementum justMeets enamel In 10% of the teeth there is a smallGap between cementum and enamel

5/13/12

54 54

Subsurface structuresGnarled enamel Group

of enamel rods may

entwine with adjacent groups of rods & they follow a curving irregular path towards the tooth surface Occurs

near the cervical

region, incisal & cuspal areas5/13/12 55 55

Surface manifestations

PERIKYMATA

Transverse wave-like groove External manifestation of Striae of Retzius

5/13/12

56 56

Are

continuous around a tooth & usually lie parallel to each other at cervical region in no. at cervical region30/mm

More

less occlusally10/mmUsually

regular;

5/13/12

57 57

Enamel Cuticle Nasmyths membrane/Primary enamel cuticleStructureless

membrane seen on crown,

adhering firmly to its surfacePresent

on a newly erupted tooth & lost

due to mastication0.5

to 1.5 mm thick5/13/12 58 58

Acquired Pellicle

Precipitate of salivary glycoproteins Forms within hours of mechanical Within a day or two , becomes

cleansing-Brushing

colonized by micro organism to form a bacterial plaque

5/13/12

59 59

AMELOGENESIS

Amelogenesis, or enamel formation, is a two step process

Stage I: Secretory stage/ Matrix formation Production of partially mineralized enamel (30%) Stage II: Maturative stage/ Mineralization n maturation Significant influx of additional mineral coincident with removal of organic 5/13/12 mineral and water (>96% mineralization)60 60

LM of bell stageOuter Enamel Ep. Stellate Reticulum Stratum Intermedium Inner Enamel Ep.

5/13/12

61 61

Enamel formation lags dentin formation

IEEodontoblastde ntinIEEAMELOBL AST

This dependance is known as reciprocal induction

5/13/12

62 62

ENAMEL MATRIX FORMATION

Once ameloblasts have differentiated, synthesis of organic enamel matrix starts formed enamel- 65% water, 20% organic mat. ,15% inorganic material of the ameloblast, adjacent to the devloping enamel is found to be pyramidal in shape and projects into the enamel matrix processes Tomes process63 63 5/13/12 enamel matrix immediately

Newly

Surface

Pyramidal Formed

MINERALIZATION OF ENAMELMineralization

takes place in four

stages: 1) first stage (primary mineralization) 2) second stage (secondry mineralization) 3) third stage (tertiary mineralization) 4) fourth stage (quaternary mineralization)5/13/12 64 64

FIRST STAGE (PRIMARY MINERALIZATION)

Formation

of a partially mineralized enamel matrix mineralization is achieved overall

30%

Although

a very narrow 8m innermost layer next to the DEJ is heavily mineralized as soon as it is 5/13/12 formed

65 65

SECOND STAGE (SECONDARY MINERALIZATION)Begins

with a secondary increase in mineralization at the surface of the enamel and sweeps rapidly into the deeper layers until it reaches the innermost 8m layer

Starts

5/13/12

66 66

THIRD STAGE (TERTIARY MINERALIZATION)A

tertiary increase in mineral rebounding from the innermost layer out toward the enamel surface

A

surface layer some 15 m wide can be distinguished during this phase, and it mineralizes more 67 slowly 5/13/12 67

FOURTH STAGE (QUATERNARY MINERALIZATION)The

outer layer mineralizes rapidly and heavily the most mineralized part of the enamel

Becomes

5/13/12

68 68

Four stages of mineralization of enamel

5/13/12

69 69

LIFE

CYCLE OF AMELOBLAST

5/13/12

70 70

Morphogenic Cells

are shorter , columner oval nuclei fills the Cell body Golgi bodies, centrioles are located at proximal end evenly distributed

Large

Mitochondria

IEE

is separated from the conn. tissue of dental papilla by delicate basal 5/13/12 lamina

71 71

OrganizingIEEodontoblasts Cells

are longer

Nucleus

shifts to proximal end lies in the proximal part of cell of dentin5/13/12 72 72

Mitochondria

Formation

begins

FormativeFollows

dentin formation formation begins

Enamel

Ameloblast

retain same length & arrangements of blunt cell process5/13/12 73 73

Development

after 1st layer of dentin is laid synthesis of enamel protein Golgi complex (condensed secretory granules) Tomes process secretion of enamel matrix over mantle dentin with immediate mineralization5/13/12

74 74

Though the cytoplasm of the ameloblast continues into Tomes process, the distinction b/w process & cell body is marked by distal terminal web & junctional complex

The Cell

process has secretory granules body has organelles

5/13/12

75 75

Secretory ameloblasts with tomes process5/13/12

Relation

of tomes process and enamel prism76 76

When the distal portion of Tomes' process is established, secretion of enamel proteins becomes staggered and is confined to two sites

First site adjacent to proximal part (periphery of cell) Interrod enamel

Second site along one face of distal portion of Tomes process Enamel rod

5/13/12

77 77

Maturative Ameloblast

are

reduced in lengthWater

& organic material are removed content is5/13/12 78 78

Inorganic

ProtectiveOnce

the entire thickness of enamel is laid down, ameloblast undergo morphologic changes of SI,SR & OEE reorganize ameloblasts reduced enamel epithelium5/13/12 79 79

Cells

Desmolytic REE

proliferates of OEE &

Fusion

REE

Enzymes

destroy connective (Desmolysis)

5/13/12

80 80

AGE CHANGES

5/13/12

81 81

Nonvital tissue - incapable of regenerationBecomes progressively worn away in regions of masticatory attrition

5/13/12

82 82

Wear facets - in older people

5/13/12

83 83

In some cases substantial portions of the crown (both enamel and dentin) become eroded

5/13/12

84 84

Discoloration

5/13/12

85 85

Reduced permeability Teeth darken with age. caused by a change in the structure of enamel (debatable) addition of organic material to enamel from the environment it also may be due to a deepening of dentin color seen through the progressively thinning layer of translucent enamel Less permeable with age5/13/12 86 86

CLINICAL CONSIDERATIONS

5/13/12

87 87

1)

Enamel rods:

- in cavity preparation , its important that unsupported enamel rods are not left at cavity margins - as enamel is brittle ,does not withstand forces in thin layers or in areas where it is not supported by underlying dentine

5/13/12

88 88

2) Enamel spindles:-

They may serve as pain receptors, may cause sensitivity in enamel during cavity preparation.

3) Enamel tufts:-

This are area of weakness May play a role in spread of dental caries5/13/12

89 89

4) Enamel lamellae -this are the weaker areas -may provide entry to bacteria , leads to dental caries 5)Gnarled enamel: -strengthen enamel5/13/12 -does not yield readily to the 90 90

6)Enamel pit and fissures:-

Areas prone to food lodgement Difficult to clean Prone to dental caries Must be sealed with sealants

5/13/12

91 91

7)Cervical region:-

Should be kept smooth and well polished. If decalcified or roughned, leads to accumulation of food debris & plaque, further leads to cervical caries, gingivitis and later periodontal problem5/13/12 92 92

DEFECTS OF ENAMEL FORMATION

5/13/12

93 93

Defective enamel formation can be classified as -Systemic -Local -Genetic

The most common systemic influences are Nutritional deficiencies Endocrinopathies Febrile diseases Chemical intoxications

5/13/12

94 94

Hereditary Amelogenesis imperfecta Environmental Nutritional deficiency (vitamin A, C and D) Exanthematous diseases ( measles, chicken pox, scarlet fever ) Congenital syphilis Hypocalcemia Local infection or trauma Ingestion of chemicals (fluoride)

5/13/12

95 95

Mulberry molars-congenital syphilis

Hutchinsons teeth

5/13/12

96 96

Local spot due White trauma

to local trauma

5/13/12

97 97

Amelogenesis imperfecta

Hereditary enamel dysplasia Hereditary brown enamel Hereditary brown opalescent teeth

It consists of a group of conditions that demonstrate developmental alterations in the structure of enamel in the absence of a systemic disorder Deciduous/ Permanent teeth Localized / Generalized5/13/12 98 98

Three types of amelogenesis imperfects are recognised

Formative stage deposition of organic matrix- Hypoplastic type Calcification stage this matrix is mineralized Hypocalcification (hypomineralization) type Maturation stage-crystallites enlarge and mature - Hypomaturation type

5/13/12

99 99

Hypoplastic type

Defective formation of matrix Disturbance is differentiation or viability of ameloblasts Clinically enamel has not formed to full thickness on newly erupted developing teeth

5/13/12

100 100

Hypocalcification (hypo mineralization) type

Defective mineralization of formed matrix Defect of matrix structure and of mineral deposition Clinically enamel is so soft that it can be removed by a prophylaxis instrument

5/13/12

101 101

Hypomaturation type

Enamel crystallites remain immature Alteration in enamel rod and rod sheath structure Clinically enamel can be pierced by an explorer point under firm pressure and can be lost by chipping away from underlying normal appearing 5/13/12

102 102

Environmental Enamel HypoplasiaNutritional defeciency and exanthematous fevers

Congenital syphilis -Hutchinson teeth -Mulberry molars Hypoplasia due to Hypocalcemia Birth injuries Local infection/Trauma -Turners tooth5/13/12

103 103

Fluorosis

Fluoride ion can interfere with amelogenesis Chronic ingestion of F- con. >5 ppm Mottled enamel White patches to sever brown discol. & pitting

Such enamel, though unsightly, is still resistant to caries

5/13/12

104 104

Flourosis

5/13/12

105 105

5/13/12

106 106