Presented by :Piyush VermaDepartment of Pedodonticsand preventive dentistry

27 – 09 - 2012

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Contents Introduction Eruption Pre eruptive tooth movement Eruptive tooth movement Theories of tooth eruption Post eruptive tooth movement Shedding of teeth Pattern of shedding Tooth resorption and repair Conclusion References

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Introduction The timely initiation and eruption of teeth into the

oral cavity is very important for healthy dentition .

It is the process by which tooth moves within the

Jaw bone comes into the oral cavity and comes up to

the occlusal contact and maintains its clinical position.

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Eruption

Eruption refers to the axial or occlusal movement of the

tooth from its developmental position within the jaw to

its functional position in the occlusal plane.

Physiological tooth movements consists of the

following:

Pre eruptive tooth movement

Eruptive tooth movement

Post eruptive tooth movement4

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Primary dentition: - 2 to 6 years of age

Permanent dentition: > 12 years

DIPHYODONT

Phases of tooth eruption

Preeruptive phase: made by the deciduous and permanent tooth

germs within tissues of the jaw before they begin to erupt.

Eruptive phase: Starts with initiation of root formation and

made by teeth to move from its position within bone of the jaw

to its functional position in occlusion. Has an intraosseous and

extraosseous compartments.

Posteruptive phase: Takes place after the teeth are functioning

to maintain the position of the erupted tooth in occlusion while

the jaws are continuing to grow and compensate for occlusal

and proximal tooth wear.

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Made by the deciduous and permanent tooth germs within tissues of the jaw before they begin to erupt.

tooth germs grow rapidly

crowded

relieved by lengthening of jaws

deciduous second molar tooth germs move backward

anterior tooth germ moves forward

Pre eruptive tooth movement

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Permanent anterior tooth germs

develop lingual to the primary

anterior teeth and later as

primary teeth erupt, the

permanent crowns lie at the

apical 3rd of primary roots.

Premolars tooth germs are

finally positioned between the

divergent roots of deciduous

molars.

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Histologic features

Remodeling of the bony wall of crypt by selective

deposition and resorption of bone by osteoblasts and

osteoclasts.

Normal skeletal morphogenesis might be involved in

determining tooth position

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Eruptive tooth movement

The axial or occlusal movement of the tooth from its

developmental position within the jaw to its final functional

position in the occlusal plane.

The actual eruption of the tooth when it breaks through the

gum is only one stage of eruption.

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Histology

Degeneration of connective tissuesimmediately overlying the erupting teeth.

Eruption pathway – altered tissue areaoverlying the teeth.

Macrophages destroy cells and fibers bysecreting hydrolytic enzymes.

Gubernacular cord: The connective tissueoverlying a successional tooth that connectswith the lamina propria of the oral mucosa bymeans of a strand of fibrous connective tissuethat contains remnants of dental lamina

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Gubernacular canal: Holes

noted in a dry skull noted

lingual to primary teeth in

jaws that represent openings

of gubernacular cord .

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• As the tooth moves occlusally it creates space underneath the tooth to

accommodate root formation

• Fibroblasts around the root apex form collagen that attach to the newly formed

cementum

• Bone trabeculae fill in the space left behind as the tooth erupts in the pattern of a

ladder which gets denser as the tooth erupts

• After tooth reaches functional occlusion periodontal fibers attach to the apical

cementum and extend into the adjacent alveolar bone

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Stages of tooth eruption

Essentials of Oral Histology and Embryology. James Avery, 2nd edition 15

The rate of tooth eruption depends on the type of movement

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• 1 to 10 µm/dayINTRAOOSEOUS

PHASE

• 75 μm/dayEXTRAOSSEOUS

PHASE

are those movements made by the tooth after it has reached its functional position in

the occlusal plane.

They may be divided in three categories:

Post Eruptive Tooth Movements

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Accomodation for growth

Compensation for occlusal wear

Accomodation for interproximal wear

ACCOMMODATION FOR GROWTH - Mostlyoccurs between 14 and 18 years by formation of newbone at the alveolar crest and base of socket to keeppace with increasing height of jaws.

COMPENSATION FOR OCCLUSAL WEAR -Compensation primarily occurs by continuousdeposition of cementum around the apex of the tooth.However, this deposition occurs only after toothmoves.

ACCOMMODATION FOR INTERPROXIMALWEAR - Compensated by mesial or approximal drift.

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FACTORS CONTROLLING MESIAL DRIFT:

(a) Contraction of the transseptal fibers: As the proximal tooth

surfaces of adjacent teeth become worn from functional tooth

movement, the transseptal fibers of the periodontal ligament

become shorter (due to contraction) and thereby maintain tooth

contact .

(b) Adaptability of bone tissue: The side of pressure on PDL fibers

causes bone resorption, whereas pull on the fibers causes bone

apposition. Therefore, as the contact areas of the crowns wear,

the teeth tend to move mesially, thereby maintaining the

contact.

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(c) Anterior compartment of occlusal force: An anteriorly

directed force is generated when teeth are clenched, due

to the mesial inclination of most teeth and the forward-

directed force generated from inter-cuspal forces.

Eliminating opposing teeth results in elimination of

biting forces, causing a slowing down of the mesial

migration

(d) Pressure from soft tissues: Buccal mucosa and tongue

push teeth mesially

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Theories of resorption

Root formation ( tomes 1872 )

Bone remodeling ( brash 1928 )

Dental follicle ( marks and cahill 1984)

Periodontal ligament ( thomas 1967 )

Hydrostatic pressure ( sutton and graze 1985 )

Pulpal pressure ( v . Korff 1935 )

Cellular theory ( eidmann 1923)

Molecular theory ( marks et al )

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Active eruption

Passive eruption

Genetic factors

Local factors ( steggerda and hill 1942)

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Root Formation :

Root formation would appear to be the obvious cause of tooth

eruption since it causes an overall increase in the length of the

tooth along with the crown moving occlusally.

Clinical observation, experimental studies and histologic

analysis argue strongly against such a conclusion as rootless

teeth do erupt

some teeth erupt more than the total length of the roots and the

teeth still erupt after completion of root formation.

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Bone remodeling

The growth pattern of the maxilla and the mandible moves teeth

by selective deposition and resorption of bone.

Major proof is when a tooth is removed without disturbing its

follicle tooth germ, an eruptive pathway still forms within bone

as osteoclasts widen the gubernacular canal.

If the dental follicle is also removed no eruption path develops.

It establishes absolute requirement for a dental follicle to

achieve bony remodeling and tooth eruption.

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Dental Follicle

Studies have shown that the reduced dental epithelium

initiates a cascade of intercellular signals that recruit

osteoclasts to the follicle.

By providing a signal and chemoattractant for osteoclasts,

it is possible that the dental follicle can initiate bone

remodeling which goes with tooth eruption. Teeth eruption

is delayed or absent in and human diseases that cause a

defect in osteoclast differentiation.

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Experiments done by Cahill & Marks says that viable dental follicle is required for the eruption.

Further studies by them has shown that tooth eruption is a series of metabolic events in alveolar bone characterized by bone resorption and formation on opposite sides of the dental follicle and the tooth does not contribute to this process.

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Periodontal ligament

Available evidences strongly indicate that the force for eruptive

tooth movement lies in PDL.

the PDL and dental follicle from where it forms are implicated

in the process of tooth eruption linked to contractility of

fibroblasts.

PDL fibroblasts are able to provide a force sufficient to move

the tooth and certainly the proper structural elements exist to

translate such force into eruptive tooth movement.

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Cellular and molecular basis of tooth eruption

Cellular basis

prior to onset of eruption

influx of mononuclear cells into coronal

portion of dental follicle

cellular events

influx of mononuclear cells

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Required for formation of osteoclasts

Resorb bone for the eruption pathway

Dental follicle is interposed between the alveolar bone and tooth ,

it is an ideal location to regulate the cellular events of eruption

and receive signals from the tooth.

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Molecular basis

Eruption molecules

the molecules that initiate eruption , their localization and the

regulation of the cellular events of eruption all must fit within the

context that each tooth erupts independently

Determination of the molecules that may be required for eruption

began with the isolation of –

EGF (epidermal growth factor )

TGF α (transforming growth factor )

Colony stimulating factor 1

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TGF α , EGF ↑ in incisor eruption

colony stimulating ↑ in molar eruption

factor 1

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Nakchbandi IA et al (june 2000)

experiments in vivo have established that tooth eruption fails in

the absence of parathyroid hormone (PTH)-related protein

(PTHrP) action in the microenvironment of the tooth because

of the failure of osteoclastic bone resorption on the coronal

tooth surface to form an eruption pathway.

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Localization of eruption molecules:

Studies have demonstrated that the eruption genes and their

products are localized primarily in either the dental follicle or

stellate reticulum.

The tissue required for eruption , the dental follicle produces

the majority of the potential eruption molecules.

The remainder of the molecules reside in the stellate reticulum

adjacent to the dental follicle.

E.g IL – 1 – resides in dental follicle

DF -95 resides in stellate reticulum

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Pulp theory

It suggests that the tooth is moved lingually by the pressure

from the pulp the explosive effect of pulpal bulge is produced

by the osmotic pressure of the briskly proliferating and

differentiating mesenchymal cells.

Alveolar bone deposition Deposition of bone beneath the tooth during eruption is

unlikely to be the cause rather than consequence of the tooth

erupting.

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The classic experimental model for studying eruption is the rat’s incisor , where continuous eruption occurs without any additional bone being formed at the base of tooth.

However, it is quite likely that bone growth is partly responsible for the pre eruptive phase during which growth of the entire alveolus and remodeling around the tooth crypt helps to move it into place for the eruptive phase.

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Active eruption

bodily movement of tooth from its site of development to its functional position in the oral cavity.

Passive eruption

Apparent lengthening of the crown due to loss of attachment or recession of gingiva.

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Genetic and environmental factors

The environment, prenatal and maternal factors, social

factors, climate etc. may influence the timing of tooth eruption

but the determinants of this timing are still thought to be more

genetic than environmental.

Lewis and Garn (1960) and Garn et al. (1965) theorized that tooth

formation is genetically determined and in an analysis of

monozygotic twin pairings found strong correlations of tooth

formation

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Local factors

Local alterations frequently form a physical barrier to normal

tooth eruption. In the gingiva, fibromatous or hyperplastic

alterations may hamper the eruption of the underlying tooth .

In the bone, supernumeraries, odontogenous or non-

odontogenous tumours, cysts or cleft anomalies may interfere

with proper eruption.

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Tooth eruption in children with growth deficit.

Barberia Leache E et al

found that children whose delayed growth is accompanied by a

low genetic height or growth hormone deficit presented

retardation in dentition and retardation in bone age.

J Int Assoc Dent Child. 1988 Dec;19(2):29-35

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Shedding of teeth

Physiologic process resulting in the complete elimination of the

deciduous dentition.

Pattern of shedding

Result of progressive resorption of roots of deciduous teeth and

its supporting tissues.

Pressure generated by the erupting permanent tooth guides the

pattern of deciduous tooth resorption.

Initially , pressure is against the root surface of the deciduous

tooth and resorption occurs on the lingual surface.

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Later these developing tooth germs occupy a position directly

apical to the deciduous tooth.

In mandibular incisors the apical positioning of the tooth germs

does not occur and permanent tooth erupts lingually.

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Resorption of deciduous molars

Resorption of the roots of deciduous molars first begin on their

inner surfaces because the early developing bicuspids are found

between them.

With continued growth of the jaws and occlusal movement of

the deciduous molars, the successional tooth germs lie apical to

the deciduous molars.

When the bicuspids begin to erupt , resorption of the deciduous

molars is again initiated and continues until the roots are

completely lost and the tooth is shed.

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Resorption occurs on the surface of cementum and dentine .

Resorption involves a loss of the organic as well as the mineral constituent of the matrix .

during resorption the process of disorganization relative to the mineral and the organic components occurs more or less concomitantly.

Resorption of cementum and dentine of deciduous teeth is characterized by the presence of osteoclasts.

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Root resorption seems to be initiated and regulated by the

stellate reticulum and dental follicle of the underlying

permanent tooth via the secretion of stimulatory molecules i. e.

cytokines and transcription factors .

The primary root resorption process is regulated in a manner

similar to the bone remodeling , involving the same receptor

ligand system known as RANK/ RANKL

( receptor activator of nuclear factor – kappa B / RANK ligand)

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PRIMARY ROOT RESORPTION WITH PERMANENT SUCCESSOR

The pressure of erupting tooth is believed to play a contributoryrole in setting of resorption but the presence of permanentsuccessor is not a prerequisite for this process to occur.

Root resorption of primary teeth starts at the site of root that isclosest to the permanent successor. E.g in anterior teethcompleted crown of permanent successor is found lingual toapical third of root of primary predecessor:

Resorption of lingual surface of apical third of primary toothroot.

Resorption of labial surface.

Resorption proceeds horizontally in incisal direction untilprimary tooth sheds & permanent tooth erupts.

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PRIMARY ROOT RESORPTION WITHOUT PERMANENT SUCCESSOR

The root is protected from resorption by presence ofnarrow PDL cell layers which are composed of:

Collagen fibers

Fibroblasts

Cementoblasts

Degradation of PDL precede root resorption & removal ofcollagen fibers of PDL is considered main step in initiationof this process.

As face grows & muscles of mastication enlarge, forces thatare applied on the deciduous teeth become heavier thanprimary tooth periodontal ligament can withstand.

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Histology of shedding

Odontoclasts are resorbing cells derived from monocyte –

macrophage lineage.

Giant multinuclear cells with 4 – 20 nuclei.

Resorption occurs at the ruffled border which greatly increases

the surface area of the odontoclast in contact with bone.

Found on surfaces of the roots in relation to advancing

permanent tooth.

Single rooted teeth shed before root resorption is completed.

Distribution of odontoclasts during tooth resorption

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Odontoclasts are not found in pulp chamber of these teeth.

In molars , the roots are completely resorbed and crown is

partially resorbed.

Odontoblasts layer is replaced by odontoclasts.

Sometimes all the dentine is removed and the vascular tissue is

seen beneath the translucent cap of enamel.

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5 monthsAt birth 1 year

2 years 3.5 years 4.5 years

Shedding of mandibular incisor

Figure Source: Dr. Sandra Meyers 49

Tooth resorption and repair

Resorption is not a continuous process but have also periods of

repair.

Resorption predominates repair.

Repair is achieved by cells resembling cementoblasts.

Final repair tissue resembles cellular cementum but is less

mineralized.

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Mechanism of resorption and shedding

Pressure from the erupting successional tooth and appearance

of odontoclasts at the site of pressure.

Membrane of ruffled borders act as proton pump → adding

hydrogen ions to extracellular region → acidification →

mineral dissolution.

Increased forces of mastication with increase in jaw size

leading to trauma to PDL → degeneration of PDL

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Resorb bone for the eruption pathway

Dental follicle is interposed between the alveolar bone and tooth , it is an ideal location to regulate the cellular events of eruption and receive signals from the tooth

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7 years-functional occlusion attainedbut root apex is still not fully formed

15 years – incisal wear

Figure Source: Dr. Sandra Meyers53

Sequence and chronology of tooth eruption

Source: http://www.columbia.edu/itc/hs/dental/d9903/lectures/lecture4.pdf

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According to Hillson (1996), eruption times can be broken into three phases:

Phase One includes the emergence of permanent first molars and incisors (5 to 8 years of age);

Phase Two consists of the emergence of the canines, premolars, and second molars (9.5 to 12.5 years);

Phase Three consists of the emergence of the third molars (late teens to early twenties)

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Chronology of Human Permanent Dentition

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The six/four rule for primary tooth emergenceFour teeth emerge for each 6 months of age

1. 6 months: 4 teeth (lower centrals & upper centrals)

2. 12 months: 8 teeth (1. + upper laterals & lower laterals)

3. 18 months: 12 teeth (2. + upper 1st molars & lower 1st molars)

4. 24 months: 16 teeth (3. + upper canines & lower canines)

5. 30 months: 20 teeth (4. + lower 2nd molars & upper 2nd molars)

1. By 5 months in utero, all crowns started calcification

2. By 1 year old, all crowns completed formation

3. By 2.5 years, all primary teeth erupted

4. By 4 years old, all primary teeth completed root formation

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The rules of “Fours” for permanent toothdevelopment (3rd molars not included)

At birth, four 1st molars have initiated calcification

At 4 years of age, all crowns have initiated calcification

At 8 years, all crowns are completed

At 12 years, all crowns emerge

At 16 years, all roots are complete

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Rules of “sixes” in dental development

6 weeks old in utero: beginning of dental development

6 months old: emergence of the first primary tooth

6 years old: emergence of first permanent tooth

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Problems of Primary Tooth Eruption

Natal and Neonatal Teeth

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Eruption cyst

- follicular enlargement occurring just before eruption.

- blue-black color due to presence of blood

- no specific treatment if uninfected

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Submerged primary teeth

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Failure of eruption of first and second permanent molars

Camila Palma et al

CONCLUSIONS

1. In this series, the failure of eruption of permanent molars was the consequence of impactions and primary retentions.

2. Unfavorable prognosis is associated with advanced age and with molars in the last stages of root formation.

3. Root dilaceration is a major factor limiting eruption and an indicator of poor prognosis.

4. The degree of non-eruption and the inclination axis are not key factors in prognosis.

5. Posterior dento-alveolar discrepancy is associated with impaction of second molars.

J Clin Pediatr Dent 27(3): 239-246, 2003

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Congenital hypothyroidism/ Cretinism

- due to hypo function of thyroid gland

- primary tooth eruption is delayed till 2 years.

- large head, protruding tongue

- as soon as it is detected, treated with thyroxin.

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(Rushton, 1937; Jensen and Kreiborg, 1990,1993

The defects seen in the dentitions of patients affected with

Cleidocranial dysplasia have been thought to arise from a

disruption in the bone remodeling process. In addition to an

increased density in the maxilla and mandible, multiple

supernumerary teeth are present that show a marked delay or

arrest in eruption

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Impaction

due to failure in eruption mechanism

maxillary canine, 3rd molars – commonest form

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(Sauk, 1988; Gorlin et al., 1990; Jones, 1997).

Eruption failure and delayed eruption are conditions that do not naturally involve ankylosis and are associated with craniofacial dysostosis, hypothyroidism, hypopituitarism, and several genetic and medical syndromes.

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Ectopic eruption

describes a path of eruption that causes root resorption of a portion or all of the adjacent primary teeth.

mandibular lateral incisor –commonest

maxillary 1st molar and canine.

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Conclusion

For the clinicians to treat dental problems knowledge of proper eruption and shedding time is very important .

A variety of developmental defects that are evident after eruption and shedding of the primary and permanent teeth can be related to local and systemic factors.

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References

Textbook of oral histology by Ten cate,7 th edition; 268 – 289

Orban‘s textbook of oral histology and embryology –(10 th edition); 372 - 386

Textbook of oral development and histology by James Avery 3. rd. edition : 92-105.

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Thank you

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