ENAMEL_S / orthodontic courses by Indian dental academy

ENAMEL*****************************************INTRODUCTION

DEVELOPMENT

LIFECYCLE OF AN AMELOBLAST

AMELOGENESIS

ORGANIC MATRIX FORMATION

MINERALISATION AND MATURATION

COMPOSITION

PHYSICAL CHARACTERISTICS

ENAMELSTRUCTURE

A SINGLE ROD UNIT

STRUCTURAL FEATURES

SURFACE FEATURES

DEJ

CEJ

AGE CHANGES

CLINICAL CONSIDERATIONS

ENAMEL DEFECTS

CONCLUSION

INTRODUCTIONImagine walking out into a cold, wintry morning without wearing a sweater. Imagine

crashing head-on into a wall without wearing a helmet. Imagine holding a live wire

without its insulation. Now, imagine the tooth without enamel. The importance of

enamel will strike you surely…….

Enamel can be defined as a highly mineralized, acellular, inert, hard tissue of

ectodermal origin covering the anatomic crown of the tooth, which once destroyed

cannot be physiologically regenerated or replaced.

DEVELOPMENTThe enamel organ or the tooth bud originates from the stratified epithelium of the

primitive oral cavity.

Just before enamel and dentin formation, the enamel organ consists of 4 distinct layers

- Outer enamel epithelium (OEE)

- Stellate reticulum

- Stratum intermedium

- Inner enamel epithelium (IEE) / Ameloblastic layer

The borderline between the IEE and the connective tissue of the dental papilla is the

subsequent Dentino-Enamel Junction (DEJ).

The IEE reflects onto the OEE at the cervical loop.

OEE: it is made up of a single layer of cuboidal cells separated from the surrounding

dental sac by a basement membrane.

Capillaries are present in the adjacent connective tissue, which proliferate and

protrude towards it and may even indent the stellate reticulum. These ensure that there

is plentiful supply of nutrients during enamel formation once dentin formation cuts off

the supply from the papilla to the IEE.

During enamel formation, these cells undergo structural changes like villi formation,

vesicle inclusion, increase in mitochondria etc, to aid in the active transport of

nutrients.

Stellate Reticulum = It is made up of loosely arranged star-shaped cells having

desmosomal connections with each other and the adjacent OEE and stratum

intermedium.

They basically function as a shock absorber and help the tooth germ to resist any force

that may distort the configuration of the developing DEJ. They also aid in transporting

nutrients from the dental follicle to the IEE.

Stratum intermedium: This layer consists of 2-3 layer of polyhedral cells, which

become spindle shaped once enamel formation reaches its maturative stage. They

exhibit a high activity of enzyme alkaline phosphatase, which helps to increase the

mineral content of enamel.

IEE: Consists of a single layer of short coloumnar cells, which differentiate into tall

coloumnar cells termed “ameloblasts” once enamel matrix production begins.

They define the shape of the future crown and also interact with the adjacent dental

papilla to produce dentin-forming odontoblasts.

These cells contain a high amount of glycogen, which nourishes the ameloblast once

dentin is laid down.

LIFE CYCLE OF AN AMELOBLASTFunctionally, the life cycle of the IEE is divided into 6 stages:

- Morphogenic

- Organizing / Differentiation

- Formative / Secretory

- Maturative

- Protective and

- Desmolytic stages

MORPHOGENIC STAGE:

The shape of the future DEJ is determined by the interaction between the IEE and the

adjacent mesenchymal cells. The cells are short, columnar with large oval nuclei

filling almost the entire cell body.

The cell organelles are located proximally (i.e., towards the stratum intermedium)

while the mitochondria are dispersed throughout the cell.

The adjacent pulpal layer is a cell free zone

ORGANIZING STAGE: OR DIFFERENTIATION STAGE:

The IEE cells became longer (the distal end becoming as long as the nucleus

containing proximal end) and there is a reversal of functional polarity with the

organelles moving distally. Because of the increase in length of the cells towards the

papilla, the now differentiated ameloblasts interact with the connective tissue cells

directly (the cell free zone disappears) and the latter differentiate into odontoblasts.

Dentin formation begins which cuts off the nutritional supply via the papilla and the

ameloblasts start relying or the surrounding capillaries for their nutrition. This result

in proliferation of capillaries and the gradual reduction and disappearance of stellate

reticulum, which brings the OEE closer to the stratum intermedium IEE.

FORMATIVE STAGE or SECRETORY STAGE,

Blunt cell processes develop on the distal end of ameloblast, which penetrate the pre-

dentin. The presence of dentin is necessary for the formation of enamel matrix. Thus,

reciprocal induction / mutual induction is the phenomenon behind enamel formation.

IEE differentiate into ameloblasts interacts with C/T differentiate

into odontoblasts Lays down dentin to lay down enamel.

which stimulate

Formation of enamel matrix and partial mineralization occurs.

MATURATIVE STAGE:

Full mineralization or maturation occurs as matrix is formed occlusally /incisally and

is getting laid down in the cervical portions. Cells changes include shortening of

ameloblasts development of micro villi and cytoplasmic vacuoles distally indicating

absorptive functions. The stratum intermedium cells became spindle shaped.

PROTECTIVE STAGE:

The ameloblastic layers lose their well-defined structure, and together with the OEE

and stratum intermedium form a stratified epithelial covering of the enamel termed

Reduced Enamel Epithelium(REE).

The REE helps to protect the mature enamel from contacting the connective tissue

until the tooth erupts. If contact does occur, then anomalies may occur such as

resorption / cemental deposition.

DESMOLITIC STAGE:

The REE cells produce enzymes that destroy connective tissue fibers by desmolysis

resulting in separation of the connective tissue oral epithelium and a fusion between

the REE and the oral epithelium.

AMELOGENESIS The development of enamel can be divided into 2 processes:

1) Organic matrix formation

2) Mineralization and maturation

FORMATION OF ENAMEL MATRIX:

Once a small amount of dentin has been laid down, ameloblasts lose the projections

into the pre-dentin. The synthesis of the matrix proteins occurs is the rough

endoplasmic reticulum, which are transported to the golgi bodies, which in turn

package them into secretory granules and deposit them along the pre- dentin. The first

thin layer of enamel formed is termed dentino-enamel membrane and this gets

partially mineralized immediately. This mineralization is supposed to occur via

nucleation via nucletion from the apatite crystals located within the dentin. This first

enamel layer is structureless.

DEVELOPMENT OF TOMES PROCESS:

As the first increment of enamel is formed, the ameloblasts begin to move away from

the dentin surface, and as they do each cell forms a conical projection. These

projections called ‘tomes processes’ jut into the newly forming enamel, giving the

junction between the enamel and the ameloblast a picket fence or saw-toothed

appearance. Tomes process primarily contains secretary granules.

At least 2 ameloblasts are involved in the synthesis of each enamel rod. According to

another interpretation, the head of each rod is formed by one ameloblast while 3

others contribute to the ‘tail’ part. Thus, each rod is made from 4 ameloblasts.

DISTAL TERMINAL BARS: Are localized cytoplasmic condensations, which

separate the tomes process from the rest of the cell.

When tomes process is established enamel protein secretion becomes staggered and

gets confined at 2 sites:

-One site is adjacent to the proximal part of process which results in matrix wall

formation and subsequent ‘inter-rod’ substance / tail.

-Another site is one surface / side of tomes process which fills the pit formed by the

insertion of the process and later goes onto form enamel rod / head.

A difference between these 2 occur only in the orientation of the crystallites

The prism sheath is the last area of withdraws by the tomes process. The organic

content is higher and the crystals, which eventually grow originate from adjacent

prisms and are, therefore, differently oriented and are less closely packed.

Ameloblasts covering the maturing enamel are considerably shorter and have a

‘ruffled border / villi on the enamel side. They are packed with mitochondria

indicating an absorptive function of transporting organic components from the matrix

back into themselves. Over 90% of the initially secreted protein is lost and that which

remains is in the prism sheath area.

MINERALIZING AND MATURATION OF ENAMEL MATRIX.

It is a 2-stage process:

1st stage: immediate partial mineralization contributing to 25-30% of total mineral

content occurs.

2nd stage: Is characterized by completion of mineralization from height of crown

towards cervical region.

Maturation, which begins from the DEJ, is characterized by growth of the ribbon-

shaped crystals. Each rod matures from the depth to the surface and from height of

crown to the cervical area.

Mineralization starts even before the matrix has reached its full thickness

COMPOSITIONEnamel is the most highly mineralized tissue known making it also the hardest

calcified tissue in the human body.

Enamel is basically composed of 96% inorganic material and 1% organic material and

3% water.

INORGANIC: Out of the 96% inorganic matter, 90-92% is composed of

hydroxyapatite which is slightly different from the basic formula of

Ca10 (PO4)6 (OH)2. The rest consists of trace elements and other minerals. Minor ion

substitutions and slight deficiency in calcium make these crystals different from those

present in other mineralized tissues

The crystals are hexagonal is cross section with dimensions:

Width: 65nm

Length: 0.05- 1(160-1000nm)

Thickness = 30nm

These crystals are almost 10 times larger than those present in bone or dentin. The

space between these crystals in mature enamel is less than 2nm.

These crystals are arranged parallel to the long axis of the rod in the center of the rod

and flare laterally towards the periphery.

ORGANIC: The organic matrix surrounds each crystal as a fine lacy network. Of the

1% matrix, 58% is protein, 42% liquid and trace amounts of lactate, sugars and

citrate.There are 2 types of enamel proteins depending on which stage the enamel

development has reached. Amelogenin is present in the developing enamel while

enamelin is present in mature enamel

PHYSICAL CHARACTERISTICS: THICKNESS: The thickness of enamel varies with the shape of the tooth and its

location on the crown. For example:

-The thickest enamel is always found at the crest of cusps or incisal edges averaging

about 2-2.5mm (molars 3mm)

- It thins down to a knife-edge; sometimes less than 100m at the cervix or within the

fissures and pits of multi cusped teeth.

Clinical signification:

The variable thickness influences the color as underlying yellow dentin is seen

through the thinner regions.

Caries progress is faster within the fissures / near cervical 1/3 with faster chances of

pulpal involvement.

HARDNESS: Since enamel is highly mineralized, it is extremely hard with hardness

comparative to mild steel. Thin enables it to withstand mechanical forces. Enamel has

a high modulus of elasticity and low tensile strength categorizing it as a rigid, brittle

material. This is compensated by the cushioning effect of underlying dentin which

enables enamel to withstand the crushing and grinding forces of mastication. The

hardness of enamel decreases from the surface towards the DEJ.

Clinical significance:

Unsupported enamel will chip off if underlying dentin is lost due to caries or

improper cavity preparation.

COLOUR: It ranges from yellowish white to grayish white. It has been suggested

that colour is determined by-

Differences in translucency

Color of underlying dentin

Thickness of enamel

Amount of stain in enamel

The cervical areas show a yellowish tinge due to reflection of dentin through the thin

enamel.

Incisal edges have a bluish tinge due to double layer of enamel and no dentin.

TRANSLUCENCY: Translucency of enamel is related to the variation in the degree

of calcification and homogeneity.

Clinical significance:

The shade of the tooth must be determined before isolation for tooth preparation for a

tooth colored restoration as it tends to look whiter when isolated due to temporary loss

of loosely bound water (< 1% by weight)

PERMEABILITY: Enamel acts like a semi permeable membrane permitting

complete or partial passage of certain molecules like iodine, etc

ENAMEL STRUCTURE:The study of enamel structure is difficult due to its high mineral content as

conventional sections will reveal only empty spaces. Thus, sections of developing

enamel are used as it contains more organic content.

The planes of sections used in studying enamel are:

Longitudanal / sagittal sections

Horizontal / transverse sections

Tangential /longitudinal facial

Structurally, enamel is composed of millions of the repetitive basic unit ‘enamel rod’.

The enamel rod is the largest structural component. The other component is the rod

sheath and a cementing inter- rod substance in some areas.

LIGHT MICROSCOPE:

Under this, the rods appear as hexagonal, round or oval interlocking rows surrounded

by a sheath giving a typical “fish-scale” appearance.

ELECTRON MICROSCOPE:

The sub microscopic structure of the rod observed in cross section reveals various

types of rod patterns:

Irregular / structure less pattern = observed near the DEJ.

Stacked arches = the rods are arranged one over the other with definite inter

rod substance present continuously.

Staggered arches = the rods are not exactly one over the other

Keyhole / Paddle shape = the rod with its arch shaped head and tail interpose

between subjacent rod heads.

A SINGLE ROD UNIT:It is shaped somewhat like a cylinder. In transverse section it possesses a rounded

“head / body” and a “tail”. The head measures 5 in width and 9 in length while the

tail is 5 in length. The head is oriented incisally / occlusally while the tail is

cervically oriented. Apatite crystals, present centrally within the rod head, are

arranged almost parallel to the long axis of the rods. The crystals deviate at a 650

angle from this axis as they fan out into the tail region. The orientation of the crystals

is a property of the ameloblast and their tomes processes.

The inter rod region or the tail is an area surrounding each rod having crystals

arranged differently than those making up the rods. In longitudinal sections, it is

seen more clearly because the section passes through the heads of one row and the

tails of the adjacent row giving the appearance of some definite inter rod material.

The rod sheath is the boundary where crystals of rod head meets that of the inter rod

region at sharp angles. It is high in organic matrix and thus more resistant to acid

dissolution.

The Number of enamel rods ranges from 5 million in lower lateral incisor to 12

million in upper first molar.

The Length of most rods is greater than the thickness of enamel due to the oblique

direction and wavy course of the rods. The length of the rods in the cuspal area is

greater than those at the cervical area.

The Diameter of the rod average’s 4. It apparently increases from the DEJ to the

surface at a ratio of 1:2.This could be due to the fact that outer surface of enamel is

greater than the dentinal surfaces where they originate.

Rod direction: In general, rods are arranged perpendicular to the dentin surface and

the external surface. In the cervical region, where the crown contours become

constricted, the perpendicular orientation results in a gingival inclination of the rods.

In primary teeth, the central and cervical rods are almost horizontal.

The occlusal or incisal rods become gradually oblique and become almost vertical at

the cusp tip/ incisal edges. This angulation displays an orientation more directly

opposed to the forces of mastication. The course of the rods is not straight but rather

wavy or undulating. They bend right and left in the transverse plane and up and down

in the vertical plane. Cervically, they have a straighter course. Rods in successive

rows also shown a change in direction of about 20

Structural Features: Enamel possesses features that characterize the tissue as more complex than the

schematic view of enamel rods presented so far.

The features are presented in 3 groups:

1) Structures related to incremental growth patterns.

Cross Striations:

Seen in longitudinal sections running perpendicular to enamel rods, cross

striations mark the daily growth increments of enamel. Human enamel is known to

form at a rate of 4 / day. This produces periodic variation in rod width, which appear

as alternating bulges and constrictions. Sometimes, oblique sectioning of the enamel

reveals the inter rod substance giving an illusion of a band.

Incremental lines of Retzius:

Seen both in longitudinal and transverse sections, the stria of Retzius represent

incremental growth lines, which occur every 7 or 8 days. Rods crossing these lines are

deficient in mineral content and a shift in the rod direction has also been observed. In

L/S, they are seen as a series of brown lines of varying widths and color intensity.

They form concentric arcs at cusps and incisal edges. The incomplete arcs emerge on

the surface in a stepwise fashion creating shallow grooves or troughs called “

Imbrication lines of Pickerill” In C/S, the striae appear as concentric rings much like

the growth rings of a tree.

Significance: if broad and prominent striae are present, it shows that same bind of

metabolic disturbance caused prolonged rest periods

Neonatal Line:

It is an accentuated line of Retzius in primary teeth demarcating enamel

before birth and after birth. It is wider due to disturbance, which occurs during several

days of enamel formation.

2) Structures with organic content higher than the enamel tissue as a whole.

Enamel Lamellae:

They are thin leaf-like structures extending from the surface towards the DEJ

Lamella basically consists of linear longitudinal defects filled with organic material. 2

major categories of lamellae are – pre- eruptive and post eruptive. To former appear to

be caused due to aberrations in the developmental process. These can be of two types:

Type A: Which contains poorly calcified rod segments

Type B: Which contains degenerated cells.

The post-eruptive lamellae (Type C) result from various physical and thermal forces

to which teeth are subjected. These contains salivary organic matter.

CLINICAL SIGNIFICANCE – These can serve as avenues for caries invasion.

Enamel Tufts:

Seen in transverse sections resembling tufts of grass, enamel tufts are actually

ribbons of organic material arising from the DEJ and extending 1/5 to 1/3 of enamel

thickness. The base of each tuft is in a straight line along the DEJ while its free end

undulates right to left in synchrony with the rod paths. They are believed to occur due

to abrupt changes in direction of rods that arise from different regions of the scalloped

DEJ

Enamel Spindles:

Seen in longitudinal sections, spindles are bulbous club-shaped irregular blind

canals filled with air or debris. They once housed the ends of odontoblastic processes.

They do not follow the path of the enamel rods. At times it is seen that the enamel

spindles is continuous with the dentinal tubule [it could be the reason behind increase

in sensitivity once tooth preparation approaches the DEJ]

3) Structures observed due to shift in the rod orientation.

Hunter schreger Bands:

When longitudinal sections are viewed by reflected light, enamel displays

alternating light and dark bands coursing from the DEJ towards the surface and

disappearing in the outer 1/3 of the enamel. These zones are an optical phenomenon

resulting from the orientation of rod groups relative to the plane of sectioning. Due to

the undulating course of the rods, there is differential reflection of light creating dark

‘diazones’ and light ‘parazones’.

Gnarled Enamel:

It is so called because of its complex, twisted, irregular rod arrangement. It is

found throughout the entire thickness of the pulp and represents very hard enamel,

which is difficult or impossible to cleave by hard instruments or carbide burs.

SURFACE STRUCTURES

Aprismatic / structureless enamel: Many teeth exhibit a superficial layer of

enamel that is devoid of typical rod structure. It is found in the outer 30 of all

primary teeth and in the cervical region of many (around 70%) permanent

teeth. It is believed to be caused by the cessation of the secretary activity by

the ameloblast and the retraction of the Tomes process, thus halting the

characteristic shift in crystal orientation. No prism outline in visible and all

appatite crystals are parallel to one another perpendicular to the striae of

retzius. This enamel is also present near the DEJ.

CLINICAL SIGNIFICANCE: The layer of prismless enamel in primary teeth poses

difficulties in etching. A longer etching time is needed.

Perikymata: are transverse wave-like grooves believed to be external

manifestation of striae of Retzius. They appear as corrugations and are seen

clearly in teeth not exposed to abrasive forces. These ridges alternate with the

troughs called ‘imbrication lines of pickerel’. Perikymata are continous around

the tooth lieing parallel to each other and the CEJ. Their number varies from

30/mm near the CEJ gradually decreasing to 10/mm occlusally. Over the cusps

they are absent as the lines of Retzius do not reach the surface. With age, these

ridges are worn away.

Enamel rod ends: are concave depressions of variable depth and shape. They

are shallowest in the cervical region and deepest near occlusal / incisal edges.

Cracks: are fissure-like outer edges of lamellae. They extend for varying

distances along the surface perpendicular to the DEJ. The length varies from a

few mm to the entire length of the crown

Enamel cuticle/Nasmyths membrane : is a delicate organic membrane

covering the entire crown of the newly erupted tooth but is soon removed by

mastication. This membrane may represent the final organic matrix secreted

by the ameloblast or it could be the degenerated remains of the REE. It

represents a typical basal lamina.

Pellicle: Within hours after eruption, a secondary deposit derived from

salivary proteins forms on all the exposed surfaces of the tooth. Unlike the

cuticle, the pellicle can be constantly replenished within 1-2 days. The pellicle

gets colonized to form microbial plaque consisting of oral flora, cellular debris

and food remains. If remained uncleaned, caries and gingival problems can

occur.

Pits and Fissures: are defects in the enamel surface usually associated with

the lines of fusion between cusps and other major divisions of the crown.

Enamel formation in multi-cuspal teeth proceeds from the growth centers

corresponding to the cusps tips and proceeds over the inclines towards the

center of the tooth. When inclines are steep “ strangulation” of ameloblast

occurs at the center of the tooth due to collision of ameloblasts from adjacent

cusps colliding as they retreat from the DEJ. The secretary activity of these

cells ceases in there compressed cells leading to a fissural defects in enamel.

Pits are similar manifestations found at the ends of developmental grooves or

at the intersection of 2 / more grooves.

Pits and fissures are present in multicuspid teeth but are also frequently seen

on the palatal surface of upper incisors.

CLINICAL SIGNIFICANCE: Susceptibility to caries

Dentino Enamel Junction / (DEJ)The irregular surface that separates the enamel from the dentin is clinically reffered to

as the DEJ. The surface of the DEJ is pitted into which rounded projections of enamel

fit in ensuring a firm hold of the enamel cap on the dentin. In sections, DEJ is seen as

a scalloped line with convexities towards dentin. The pitted DEJ is preformed even

before development of hand tissues. The DEJ provides a zone in which irritating

agents / fluids are able to permeate through enamel lamellae defects and gain rapid

access to pulp via dentinal tubules.

Cemento Enamel Junction / CEJ:The enamel and cementum may bear any one of the 3 relationships:

1. Cementum may overlap Enamel (65%)

2. Edges of Cementum and Enamel may simply abut (30%) or

3. They may not contact at all.

Sometimes all 3 may exist on the same tooth because the CEJ is irregular

CLINICAL SIGNIFICANCE: Dentinal Sensitivity occurs when Cementum and Enamel do

not contact each other.

AGE CHANGESEnamel is a non-vital tissue incapable of regeneration physiologically.

With age teeth get progressively altered or worn out occlusaly & proximally

as a result of masticatory forces. Wear facets are pronounced in older people.

There is a loss of vertical dimension & flattening of proximal contours.

Teeth also tend to discolor or darken due to either addition of organic matter

from the environment or due to reflection of the underlying yellow dentin

through the thinned translucent enamel.

Enamel permeability decreases because the pores between the crystals

diminish in size as the crystal acquires more ions and increase in size. Water

content also decreases. This can account for lower caries rate as well.

Teeth absorb fluoride ions from the environment making teeth less prone to

caries.

CLINICAL CONSIDERATIONS:Although enamel is the hardest tissue in the human body, it comprises one of the

weakest points in a preparation wall, especially when it loses its dentinal support.

Whenever enamel is stressed, it tends to split along the length of the rod. Splitting is

easier when rods are parallel to each other rather than twisted together. Fortunately,

enamel rods are twisted upon each other in the inner 1/2 - 2/3 of their thickness’ while

the remaining outer portion is parallel. According to Noy, the ideal enamel wall has

the following structural requirements:

1. Enamel wall must rest upon sound dentin or else undermined enamel will fracture

2. Enamel rods, which form the cavosurface angle, must have their inner ends resting

on sound dentin

3. The rods forming the cavosurface angle must have their outer ends covered by

restorative material: This can be produced only via:

a bevel (applicable when restorative material is stronger than the tooth

structure [such as direct gold/ cast metal / ceramic])

Plane of enamel wall is parallel to length of rods [Applicable when

restorative material is weaker than the tooth structure such as in amalgam]

4. The cavosurface angle must be trimmed / beveled so that the margins will not be

exposed to injury while condensing the restorative material against it.

Not all material can perform well when placed in cavities with such walls. The rules

should be applied whenever feasible.

A knowledge of the direction of enamel rods is very important during cavity

preparation. For example :

In a class II SAF, the gingival seat is beveled at an angle of 200 or 6 centigrade

with a GMT to ensure full length enamel rods forming the gingival margins

because the rods bend apically in this area.

When preparation margins came to an area of abrupt directional changes of

enamel rods or an area where no rules for enamel rod direction exist (mesio

incisal angle of incisor / cuspal area), this area should be included in the

preparation and margins placed in areas of a more predictable rod pattern.

Enamel walls should be smooth and junction between enamel walls should be

rounded.

Thickness of enamel at different locations should be kept in mind to avoid injudicious

cutting of dentin

Enamel structures:

1. Lamellae, cracks, pits and fissures are predisposed to caries

2. Gnarled enamel is difficult to cleave with hand instruments

3. DEJ: Sensitivity is high because of spindles and dentinal anastamosis

4. Striae of Retzius gets accentuated due to caries

5. CEJ: if no contact exists then sensitivity or caries can occur.

ACID ETCHING: Discovered by Bounocore in 1955, acid etching transforms the

smooth enamel into a very irregular surface and also increases its surface free energy.

When fluid resin material is applied, the resin penetrates into the surface aided by

capillary action. The monomer polymerizes and the material gets interlocked with the

enamel surface. The formation of resin microtags within the enamel surface is the

fundamental mechanism of adhesion between resin and enamel. The effects of acid

etching are:

1. Preferential dissolution of inter- prismatic enamel first followed by cores (or

vice versa). Least dissoluble are the sides (rod sheath area)

2. Increase in surface area up to 2000 times than that of unetched area

3. Etching depth of 25 –m is reached in enamel

4. Exposes proteinacious organic matrix

5. Removal of smear layer to help increase wettability of enamel( thus ensuring

that this fully reacted surface enamel, possessing minimal surface energy to

able to react to an adhesive, is removed)

Etching should done perpendicular to the rod heads to attain etch patterns. The latter

is of 3 types:

Type 1 – Preferential removal of rod cores (Prismatic)

Type 2 – Preferential removal periphery with intact core (inter-prismatic)

Type 3 – Irregular and indiscriminate

ENAMEL DEFECTS:These can be broadly classified as:

Smooth surfaces

1. Carious defects

Pit and fissures

2. Non-carious defects

Developmental:

Amelogenesis Imperfecta

Enamel hypoplasia Hereditary and Environment

Enamel pearl

Regressive :

Attrition

Abrasion

Erosion

Abfraction

3. Others: Discoloration: Extrinsic and intrinsic

Fractures

ENAMEL CARIES:

It is preceded by dental plaque. The smooth surface incipient lesion is seen as a

smooth chalky white area (white spot). On drying the tooth surface certain histologic

changes seen are

- loss of inter rod substance

- presence transverse striations perpendicular to enamel rods

- Accentuation of incremental lines of Retzius

It is a cone shaped lesion with apex at the DEJ

Pit and fissure caries leads to greater and earlier dentinal involvement and thus more

undermining and larger cavitations. The lesion is triangular in shape with base at DEJ

DEVELOPMENTALAMOLOGENESIS IMPERFECTA :

It represents a group of hereditary defects of enamel unassociated with any other

generalized defects. These defects can occur in any of the stages of amelogenesis.

Accordingly they are of 3 types

1. Hypo plastic: (formative Stage): The defects are in the matrix formation

C/F = enamel does not form to its full thickness.

2. Hypo calcified:(Calcification Stage): Defects is in mineralization of matrix

C/F = enamel is soft that it can be flaked off with a hand instrument.

3. Hypo Maturation (Maturation Stage): Enamel crystals remain immature

C/F = enamel can be pierced with an explorer tip.

Others features common to all of them are

May /may not be discolored

Presence of parallel vertical grooves at times

Abrasion and open contacts

ENAMEL HYPOPLASIA:

It is an incomplete or defective formation of the organic enamel matrix of teeth.

It is of 2 types:

1. Hereditary = It is similar to hypoplastic enamel hypoplasia, All primary as

well as permanent teeth are affected.

2. Environmental = either of the dentitions or even just a single tooth can be

defective. A number of factors cause this:

a] Nutritional deficiency of vitamins A, C and D

b] Exanthematous fevers such as in measles, chicken pox

C/F = Pitted, stained, unsightly teeth

Incisors, cuspids 1st & molars are usually affected

c] Congenial Syphilis

C/F Hutchinsons teeth=Permanent incisors are screw driver

shaped and notched

Mulberry molars= First molars have globular masses instead of

cusps and narrow occlusal surfaces.

d] Hypocalcaemia. Pitting of enamel occurs when serum Ca+2 is very low

e] Birth Injuries: The Neonatal line is indicative of trauma at time of birth at

times, enamel formation totally ceases

f] Local infection and Injury =

C/F: Turners teeth occurs due to periapical infection/ trauma to deciduous

tooth, disturbing the underlying ameloblastic layer of permanent tooth bud.

- Can manifest as stain severe pitting

- Single tooth involvement

- Upper incisors and maxillary mandibular premolars are commonly affected.

g] Fluoride: Ingestion of fluoride containing drinking water (> 1ppm) during the

time of tooth formative leads to mottled enamel formation

C/F: Ranges from white specks/ patch to pitting to brownish staining to a totally

corroded appearance

ENAMEL PEARL:

Enamel Pearl/ Enamel Drop/ Enameloma are small masses of enamel found apically

to CEJ occurring of molars. They are formed to CEJ occurring

a position of sheath remains in contact with dentin is stimulated to differentiate

into functional amloblasts

REGRESSIVEATTRITION: is the physiologic wearing away of the tooth as a result of tooth to

tooth contact occlusally, incisally and proximally

C/F

Permanent dentitions affected more than deciduous.

Males > Females

Older > Younger

- Initial change = Small polished facet on cusp tip or flattering of ridge or

incisal edge

- Gradually = reduction of in cusp height and flattening of occlusal inclined

plants there is shortening of dental arch length (due to proximal wear)

- Advanced attrition: enamel gets completely worn away with complete loss of

cuspal interdigitations, there is exposure of dentinal tubules resulting in

secondary dentin formation, at times pulp horns are exposed.

Certain habits like tobacco chewing and bruxism can aggravate attrition

ABRASION: is the wearing away of tooth substance through abnormal mechanical

process. Causes –

- Improper brushing

- Habits (hair pin opening causes incisal notching)

- Occupational – tailors, shoemakers

- Improper flossing / tooth picking- proximal wear

C/F =

o ‘V’ wedge shaped ditch on root side of CEJ

o Sharp angle between depth of lesion + enamel edge

o Exposed dentin is highly polished. Sensitivity and pulp exposure may

occur

EROSION: is wear or loss of tooth surface by chemico- mechanical action. It is

common in adults and increases with age. C/F:

Occurs mostly an facial surfaces. Proximal and lingual erosion is also seen in

same conditions

Enamel, dentin and cementum get affected

3 types of erosive lesions are seen

Dish / Saucer shaped, shallow concavities –gingival 1/3

of incisors

Wedge / notch shaped ‘V’-shaped (PM, M)

Irregular random location

Causes of erosion:

1. Extrinsic - Diet – soft drinks, foods

- Environment – wine tasters, swimmers

- Drugs – Vit. C, mouthwash

- Lifestyle

2. Intrinsic –

- Gastric reflux

- Sphincter incompetence

- Increased gastric pressure

- Increased gastric volume

- Vomiting:

- Psychosomatic – anorexia nervosa, bolemia -

- G.I.T disorders

- Drugs

- Regurgitation

- Rumination

IDIOPATHIC EROSION OR ABFRACTION = some cervical, wedge shaped

defects are caused due to heavy eccentric occlusal forces resulting in micro-fractures

or abfractures. The cervical areas flex under such loads and lead to micro fractures.

OTHERSFRACTURES:Can occur due to:

- Trauma

- Dentinal caries leading to undermining of enamel

- Defective, weak enamel

- Excessive occlusal load

DISCOLORATION:This can be either extrinsic or intrinsic.

Causes of extrinsic discoloration

- Remnants of Nasmyth’s membrane

- Poor oral hygiene

- Existing restorations

- Gingival bleeding

- Food colors

- Chromatic bacteria

- Tobacco stains

- Plaque / calculus

- Esthetic staining (racial)

Causes of intrinsic discoloration

- Caries

- Hereditary Disorders

- Tetracycline and other drugs

- Fluoride

- Age changes

- Non vital teeth / endodontically treatedTeeth

- Internal resorption / “ Pink spot” of mummery

CONCLUSION :

It is said “Do not judge a book by its cover” but in the case of enamel it does not hold

good. Certain conditions of the tooth can certainly be judged by the state of the outer

enamel. A sound knowledge of the basic units of the tooth is important for a clinician

to understand and diagnose tooth related problems for a better comprehensive

treatment plan for his/ her patient

BIBLIOGRAPHY:

- Orbans- Oral histology and embryology

- Oral histology- inheritance and development -Vincent Proverza

- Oral histology -A.R. Ten Cate.

- Oral development and histology- James K Avery

- Art and Science of operative dentistry – Sturdvent

- G.J. Mount and Hume