DEVELOPMENT OF OCCLUSION

Introduction

Ideal occlusion is not easy to learn as it is not a static condition

but a changing function process, undergoing continued modifications

and adjustments during the whole life of deciduous and permanent

dentition.

The achievement of normal occlusion is the result of so many

interrelated variables starting from the prenatal developmental stages.

The multiplicity and complexity of these factors are such that often

malocclusion exists but occasionally there can be found a mouth without

orthodontic problems.

The active supervision of the developing dentition is a

responsibility of the pedodontists. Seeing things from the beginning is

the most advantageous. By making a detailed studies of dentition from

initiation through eruption till functional occlusion, we may be able to

obtain a clear concept of how occlusion develops and how its

development can be guided.

Occlusion is the approximation of upper and lower teeth, centric

occlusion is the maximum intercuspation between upper and lower

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teeth. Centric relation is defined as the contact of teeth (U & L) in most

retruded position of the mandible so that condyle is in its most posterior

position with respect to glenoid fossa for the maximum comfort of the

patient.

The development of the concepts of occlusion:

There are various trends in the development of the concept of

occlusion. the trend ranges from static to dynamic.

The various periods in the development of concept of occlusion

are:

- Fictional period.

- Hypothetical period.

- Factual period.

Fictional period – 18 th century:

According to Talbot, concept of normal occlusion was that it was

a historical event and passed in the decline of the species this hardly

served as an inspirator for those to follow who were helpful of

preventing, intercepting and treating developing malocclusion.

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Hypothetical period:

a. Edward H. Angle in 1899

Put a hypothesis stating that in the normal occlusion, it will be

seen that each dental arch describes a graceful curve, and that all the

teeth in the arches are so arranged as to be in harmony with their follows

int eh same arch, as well as with opposite arch. Each tooth helps to

maintain every other tooth in these harmonies relations for the cusps to

interlock and each inclined plane serves to prevent each tooth from

sliding out of position.

This basis created the impression of static relationship.

b. Mathew Cryer and Calvin Case: 1905

According to them occlusion refers to the closure of the teeth,

one upon the other, and normal dental relations, normal occlusion and

typical occlusion refers to the standard anatomical occlusion. He

rejected the first molar for the basis of normal occlusion. He told normal

occlusion and normal facial lines are inseparable. He used nose, chin

button areas in reference to the relative position of the teeth.

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c. Lischer and Paul Simon:

They broadened the concept of occlusion by relating the teeth to

the rest of the face and cranium.

Lischer introduced the act of mastication as requisite part of the

definition.

Sinon made an approach to normal occlusion only through

biometry i.e. the anthropometric approach.

d. Milo Hellman

He showed a racial variations in normal occlusion. he studied the

number of skulls. But this still remained as static occlusion.

Factual period:

This concept divides the line between static and dynamic concept

of occlusion.

In 1930, Broadbent introduced an accurate technique of

roentgenographic cephalometry, which eliminated most of the

disadvantages of anthropologic measurements. He followed

longitudinally the orofacial developmental pattern, tooth formation,

eruption and adjustment.

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In his concept, he considered the psychologic rest position, which

means that it is the position of mandible, where the muscles are in a

relaxed position. It is constant throughout life. On the other hand, it may

become smaller even disappear entirely. This is of utmost importance,

because once it reduces, patients often complains atleast the tiredness in

chewing muscles. The patients often complain of clicking of the joint

too.

This gives a concept of dynamic occlusion.

This shows the evolutionary changes of occlusion

Anthrolopithecus Ramapithicus

Evolutionary changes:

The primitive cartilage of the jawless fish developed into the jaws

of the palacoderm, and as evolution continued it developed into jaws of

modern mammals.

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The mammalian dentition goes back to 75 million years. The

dental formula of the early primates consisted of 2 incisors, 1 canine, 4

premolars, 3 molars.

The theories behind this are:

a. Theory of concrescence

i.e. mammalian dentition was produced by the fusion of 2 or

more primitive conical teeth.

b. Theory of trituberculy

Each mammalian tooth was derived from single reptilian tooth by

a secondary differentiations of the tubercles and roots.

c. Theory of multituberculy:

The mammalian dentition is the result of reduction and

condensation of primitive multituberculate teeth.

Nolla C (1960) studied different stages of the permanent tooth

development. He arbitrarily divided the development of each tooth into

ten stages:

0 absence of crypt.

1 Presence of crypt.

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2 Initial calcification.

3 1/3rd crown completion.

4 2/3rd crown completion.

5 Crown almost completed.

6 Crown completed.

7 1/3rd root formed.

8 2/3rd root formed.

9 Root almost completed but open apex.

10 Root completed.

In stage 6 most teeth being eruptive movements and in stage 8 most

teeth pierce alveolar crest.

The humans have two sets of teeth:

a. Primary teeth.

b. Permanent teeth.

The dental formulae for primary dentition is 2102 and permanent

teeth is 2123.

Stages of occlusal development

According to Barnett 1978

a. Ist stage (3years) – primary dentition.

b. 2nd stage (6 years) – eruption of first permanent molars.

c. 3rd stage (6-9 years) – exchange of incisors.

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d. 4th stage (9-12 years) exchange of canine and premolars.

e. 5th stage (12 years) – eruption of 2nd molars.

Post natal development of occlusion:

Can be divided into (according to Vander Linden)

1. Birth to complete primary dentition.

2. First intertransitional period.

3. First transitional period.

4. Second intertransitional period.

5. Second transitional period.

6. Adult dentition.

Birth to Complete eruption of primary dentition

At birth the alveolar processes are covered by gumpads, which

are firm and pink. The basic form of the arches is determined in intra-

uterine life around 4 months.

Thus the gumpads are alveolar arches at the time of birth. They

develop in two distinct parts, a labio-buccal and a lingual portion of

these labiobuccal part is differentiated first and grows more rapidly and

gets divided into ten segments by transverse grooves. Lingual portion

which is differentiated later remains entirely smooth.

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The buccal part is divided into ten segment by transverse

grooves, each corresponding to a deciduous tooth sac. It is

papillomatous at first. The groove between canine and first deciduous

molar crypts is important in assessing the relation of two pads. Their

groove is referred to as lateral sulcus.

The lingual groove portion which develops later is separated by

dental groove which is the site of origin of dental lamina. Lingual

portion is limited lingually by gingival groove. In the upper jaw,

gingival groove separates from the palate and is related to inner alveolar

plane. The grooves are more clear in upper arch than the lower arch.

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The dental groove of the upper gum pad passes from the incisive

papilla and moves laterally and lingually, to join the gingival groove in

canine region and then continues distally and buccally across the

segment of the gum pads corresponding to the first deciduous molar

tooth crypt.

The lower gum pad is U-shaped and is limited on the lingual

aspect by a continuous groove. The gum pad is divided by transverse

grooves into ten segments not as clearly as upper anteriorly gum pad is

slightly everted. The lateral sulcus again passes at canine region.

The size of the gumpads at birth is determined by the following

factors:

- State of maturity of infant at birth.

- Size at birth as expressed by birth weight.

- Size of the developing primary teeth.

- Purely genetic factors.

The mandibular gum pad is distal to maxillary gum pad average

2.7mm in males and 2.5mm in females. The labial frenum varies in its

attachment at birth and may be found at the crest of gum pad, high

above the crest or even continuous with the incisive papilla.

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During the first year, gumpads grow rapidly in the lateral

direction, with development of deciduous teeth, there is an increase in

labio-lingual dimensions of the gum pad.

Relationship of gumpads:

At rest gumpads are separated by the tongue and protrudes over

the lower gum pad to lie immediately behind lower lip. At this age,

upper lip appears very short. The gum pads do not have a definite

relationship when occluded. The antero-posterior movements vary and

there are no lateral movement. The upper gum pad is wider than lower

and when two are approximated, there is a complete overjet all around

the lower gum pad. The lateral sulcus of lower is usually posterior to

that of upper. The contact is only seen in first deciduous molar region.

It is common for a vertical space to exist between upper and

lower incisor segment even when they are pressed into occlusion. this

appears to be linked with the position of tongue.

At birth, the incisors are crowded and rotated in their crypts and

as the gumpads grow during first year of life now they are in good

alignment and spaced. Inspite of this incisors may erupt in irregular

relation to each other. But, this however is temporary and later gets

corrected by the tongue and lip pressure.

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Clinch (1934) in Jr of Orthodontics demonstrated the increase in

the size of the alveolar arches from birth to the time just before the

eruption of the incisors. The arches increase in both length and breadth.

At birth no teeth are visible usually. The upper gum pad usually

overlaps the lower anterior pad by about 0.5mm.

At birth, the tooth buds of all primary teeth are present and in

various stages of development. The incisors are somewhat crowded at

this time for two reasons.

1. The arches have not yet complete rounded out anteriorly. Only

during the first 8-12 after the birth are the jaws are capable of

significant anterior apposition thereafter posterior growth and

anterior displacement accounts for the increase in jaw size.

2. The development of posterior teeth takes later hence follicles are

slower in achieving their complete size.

Usually, by the end of first year, sufficient jaw growth has

occurred that the primary teeth are seldom crowded or overlapped.

Infact a normal desirable dentition at this stage will exhibit spacing. The

extensive early transverse development of both jaws can be realized as

mainly because of the presence of mid-palatine suture in maxilla and in

mandible, the mandibular synchondroses. The mandibular

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synchondrosis calcifies at around 1 year of life but maxilla maintain its

transverse growth potential till about 12 years of age.

The growth in the both arches is not coordinated till the occlusion

is established in the posterior region after which the development of

both dental arches are coordinated.

Characteristics of Primary dentition:

The cardinal feature of primary dentition in contrast to the

permanent teeth is that they drop almost vertically into the mouth

requiring very little mesiodistal or bucco-lingual adjustments in their

eruptive movement.

At this age, the roots of primary cuspids and molars are not yet

complete and the crowns of the permanent central incisors, lateral

incisors, cuspids and first molars are in various stages of formation.

By 30 months of age, 70% of all children have their primary

dentition fully erupted but a great deal of variation exists.

Eruption sequence of primary dentition according to ‘Bjork’.

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CI, LI, Ist molars, canines, 2nd molars.

CI

(mth)

LI

(mth)

C

(mth)

IM

(mth)

IIM

(mth) According to Logen and

KronfeldUpper 71/2 9 18 14 24

Lower 6 7 16 12 20

Primary dentition can be broadly classified into two types:

a. Spaced arches.

b. Closed arches.

Spacing was first described by Dellabarre in the year 1819 in the

deciduous dentition between the ages of 4-6 years. The absence of

spacing in the primary dentition is an indication that crowding of teeth

can occur later when larger teeth erupt.

If 6mm of total space is there no crowding develops. If 3-6mm,

20% may develop crowding. If less than 5mm, 50% may develop

crowding. If no spaces, 70% may develop crowding. If crowding, 100%

develop crowding.

Spaces in primary dentition

It is very common to find the physiological spaces in the primary

dentition, with the most prevalent spaces mesial to the primary canines

in maxilla and distal to the primary canine in the mandible. These spaces

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are called the primate spaces or simian spaces as they are commonly

seen in the primates and are characteristics of the primary dentition.

Boyko (1968) in American Jr. of Orthodontics found that 78%

had bilateral primate spaces in both upper and lower arches, 98% of

boys had bilateral primate spaces in the maxilla and 86% in the

mandible.

The primate (simian or primate) space is about 2mm and

generalized interdental spacing is seen between teeth which measures

about. These are also called as developmental or physiological spacs.

Occlusal relationships of the second primary molars:

The primary dentition is complete after the eruption of the 2nd

primary molars. This means that the location for the eruption of the

permanent teeth in the future has already been determined at this stage.

The relation of the distal surface of the maxillary and mandibular second

primary molar is, therefore, one of the most important factors that

influence the future occlusion of the permanent dentition. The mesio-

distal relation between the distal surface of the upper and lower second

primary molars is called the terminal plane when the primary teeth

contact in the centric occlusion. the terminal plane can be classified into

three types:

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Flush or vertical plane type:

The distal surfaces of the upper and lower teeth are on the same

vertical plane. This plane would produce end-on relationship of the first

permanent molars. The change from a flush terminal plane to a mesial

step plane is desirable.

For the transition from end-on to Class I relation, the lower

molars have to move forward by 3-5mm. This is achieved by two

principles.

1. Early mesial shift : Occurs in children with spaced arches.

Eruptive force of the first permanent molar is sufficient to

mesialize the E and D in the arch to close the primate space. This

occur in the early mixed dentition stage.

2. Late mesial shift : Occurs in children with closed arches. The first

permanent molar drifts mesially by utilizing lee-way space of

nance. This occurs in the late mixed dentition stage.

Mesial step:

The distal surface of the lower molar is more mesial to that of the

upper. This is highly desirable as it would permit an immediate Class I

first permanent molar relationship upon eruption. The mesial step most

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commonly occurs due to the early forward growth of the mandible, if the

differential growth of the mandible continues it can lead to Angle’s

Class II molar relation and if the forward mandibular growth is minimal

it can establish Angle’s Class I molar relationship.

Distal step:

The distal step of the lower molar is more distal to that of the

upper. The persistence of distal step would be consistent with

establishing an Angles Class II first permanent molar relationship.

Among Japanese children, the vertical type is the most prevalent

and also Caucasian children.

Alexander and Prabhu (1998), IJ of Ped. Dentistry, conducted a

study on 1026, 3-4 years old children to assess the profile, occlusal

relationships and presence of spacing or crowding of teeth in South

India males had a higher incidence of straight profiles, but it was not

statistically significant. 75% of both sexes had both physiologic and

primate spaces and 3% population were devoid of spacing. The convex

profiles were significantly correlated with flush and distal step terminal

planes in both sexes.

Foster T.D. and Hamilton in 1969 in Br. Dent. Jr. stated after the

completion of the primary dentition, the ideal features are the following:

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- Spacing of incisor teeth.

- Anthropoidal spaces.

- Flush terminal plane.

- Deep bite and decreased overjet.

First intertransitional period:

This period is between the completion of primary dentition and

the emergence of first permanent teeth and is marked by little obvious

intraoral changes and multiple intrabony activities.

The arches by this time are capable of significant growth leading

to space for the first permanent molars, which is achieved posteriorly by

tuberosity apposition in the maxilla and ramal resorpting in the

mandible.

During the early part of this period, the tooth buds for 1st and 2nd

premolar begin to form between furcations of the primary molar roots.

The first permanent molar crowns are fully developed and roots are

starting to form.

At the stage there is some indication of the future occlusion.

There may be excessive overbite and retrognathic tendency of the

mandible.

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At 5-6 years of age, just before shedding of deciduous incisors,

there are more teeth in the jaws than any other time.

Description of occlusal contacts in primary dentition:

All the maxillary teeth except the maxillary second molars

occlude with two opposite teeth in the mandibular arch. The maxillary

second molar only occludes with the mandibular second molar. All

mandibular teeth except the central incisors occlude with two opposite

teeth in the maxillary arch. The lower central incisors only occlude with

the maxillary centrals.

Each mandibular tooth is one-half cusp mesial to the

corresponding maxillary tooth, there by establishing the following

dental relationship. The primary maxillary cuspid occludes distally to

the mandibular cuspid and mesially to the mandibular first primar molar.

The maxillary first primary molar occludes between the distal aspect of

the mandibular second primary molar.

The contacts between the upper and lower teeth can be described

as surface contact, or as cusp point contact with a fossa, groove or

embrasure, or ridge contact with embrasure, or ridge contact with

groove.

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Factors guiding normal occlusion in primary:

The achievement of a normal occlusion is dependent upon a

number of factors.

Neuro-muscular considerations:

The action of the muscles of mastication on TMJ and also tongue

and cheek muscles are largely responsible for this relationship.

These masticatory muscles are controlled by a system of

complex-neuronal circuit consisting of sensory input to the CNS, and

formation, generation of appropriate motor responses.

Interdigitation occurs sequentially from the first teeth to erupt i.e.

central incisors. As other new teeth appear the muscles learn to effect

the necessary function occlusal movements. Since the primary occlusion

is established during periods of ready developmental adaptation, there is

less variability in occlusal relationship in primary when compared the

permanent. The primary teeth are guided into their occlusal position by

the functional matrix or muscles during very active growth of facial

skeleton. The low cuspal height and ease of occlusal wear also make the

primary occlusion more adaptable.

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When teeth are erupted and muscles are functioning, the arch

formed by the crowns of the teeth is altered by muscular activities,

although original arch form is not probably determined by the muscles.

First transitional period:

The first exchange of teeth begins around six years of age and is

usually completed within two years. During this time span the

permanent first molars erupt posterior to the primary teeth and this

change usually goes unnoticed and the obvious exchange of eight

incisors occurs. The chronology of exfoliation can be determinant of

maturation in children and sequence of exfoliation can influence the

order of eruption of succedaneous teeth. There is bilateral symmetry of

tooth loss and the mandibular teeth exfoliate earlier than maxillary only

the 2nd molars exfoliate at the same time.

In girls, teeth exfoliate earlier than boys. This difference is

greatest for canines especially. In the mandibular arch (10 months) and

least for maxillary incisors (1-3 months).

The rank of exfoliation of each tooth is the same for both sexes.

In the mandibular arch the teeth are lost in order from anterior to

posterior part of mouth but in maxillary, the posterior progression is

disrupted by the canines which exfoliate after the first deciduous molars

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with the eruption of first permanent molars first of the three assaults on

the excessive overbite occurs. As the upper and lower first permanent

molars erupt, the pad of tissue overlying them creates a premature

contact. The proprioceptive response leads to the increased eruption of

deciduous teeth anterior to first permanent molar, thus reducing the

overbite.

The upper and lower first permanent molars display contrast

pathways of eruption. The tooth buds of the lower first permanent

molars are mesially and lingually inclined. The upper permanent first

molar bud develop with a buccal and distal orientation.

The mesiodistal relationship of the permanent molars is

determined by the alignment of distal surfaces of 2nd primary molars.

The later mesial shift occurs because of Lee-way space of Nance.

The mesiodistal dimension of the primary molars is more than the

mesiodistal dimensions of premolars. This difference of 1.7mm

unilaterally in mandible and 0.9mm unilaterally in the maxilla.

According to Moyers 1.4mm mandible unilaterally.

The permanent incisors will start erupting in the early mixed

dentition period. At 4 ½ years the crowns of permanent central incisors

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will be fully developed and located above and slightly lingual to the

roots of primary incisors.

Usually mandibular central incisors erupt first, followed by

maxillary permanent central incisors. The mandibular incisors erupt

lingual to the deciduous counterparts, while the maxillary permanent

incisors appear as large bulges in the muco-buccal vestibule above the

deciduous incisors before they erupt.

Since the permanent incisors are larger than the primary incisors,

inorder for the anterior tooth buds to fit within the jaws lingual to their

antecedents, they must overlap and assume different vertical levels.

In the maxilla, particularly the lateral incisors are situated behind

the centrals and cuspids in addition to their labial position are located

furthest from the occlusal plane. (The longer the root, the more away

from the occlusal plane is the tooth bud).

In the lower jaw, the cuspids are so inferior as to be almost at the

mandibular border. The labial movement of the anterior teeth effects on

the oblique resorption of the roots of the primary teeth.

Within few months of appearance of the first permanent molars,

the lower central incisors erupt. The upper centrals emerge a few months

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late followed by lower lateral incisors. The upper centrals are the last

teeth to appear in the fist transitional phase.

Because of the discrepancy in the mesiodistal crown width

between the primary and permanent incisors, space available for the

permanent teeth after the exfoliation of the antecedents is barely

sufficient Mayne in 1969 has coined the term “Incisal liability” for this

difference. It is 7.18mm in the maxilla and 5.06mm in mandible. This

will be compensated by:

- The inter dental spacing of primary incisors.

- Increase in the intercanine width (3mm by eruption of LI in

maxilla and mandible and in maxilla further 1.5m by eruption of

canines).

- The average arch position of the maxillary central are 2.2mm

anterior to the primary incisors.

- Change of tooth axis of incisors. The interincisal angle is 150° in

the primary dentition 123° in permanent dentition.

When the mandibular lateral incisors emerge, not only they push

the primary lateral incisors labially but also more the primary cuspids

distally and laterally, closing the primate space or an unusual resorption

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of the primary cuspid root. When the mandibular primary cuspids are

lost prematurely, the anterior arch loses its stability and incisors may tip

lingually by the hyperactivity of the mentalis muscle. This lingual

tipping of incisors permits the developing cuspid to slide labially where

it may erupt later in labioversion.

In maxilla, there is a diastema often found between central

incisors this may be because the central incisors often erupt with a slight

distal inclination. The maxillary lateral incisors on the other hand,

experience more difficulty in assuming their normal position, for as they

are erupting, the developing crown of the maxillary cuspids lies just

labial and distal to their roots. This position often causes the lateral

incisors to erupt more palatally than central incisors. After the erupting

cuspid has changed its course the lateral incisors correct itself and come

into position besides the central incisors.

Thus, as the end of first transitional phase the incisors are present

sometimes slightly crowded in the mandible and spaced in the maxilla

with more labial inclination than their antecedents.

The first permanent molars are erupted usually with an end on

relationship.

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Gellin and Haley (1982) Int. J. Dent. Child conducted a clinical

study to determine if removal of the corresponding primary tooth is

necessary when the lingual eruption pattern of permanent incisor is

identified. They monitored 57 lingually positioned permanent central or

lateral incisors in 44 children. They concluded that the spontaneous

correction of lingually erupted mandibular incisor occurred in 95% of

cases by the age 8 years, 2 months to 4 months.

Ugly duckling stage:

Children tend to look ensued during the time of exchange of their

incisors, especially in the upper arch. Because of the presence of

diastema the parents become worried; and often frenum is sacrificed in

an effort to remove the cause of the space between the centrals. This

transitional malalignment during the exchange period of upper incisors

is called as ugly duckling stage, the term coined by Broadbent in 1937.

This is corrected later when the canines erupted and the pressure

is transferred from the roots to the crown of the incisors.

If diastema is very much abnormal (> 4mm) investigations has to

be carried out to rule out the presence of midline pathologies.

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2 nd intertransition period:

Almost 1 year gap between 1st and 2nd transitional period. During

this in space dentition the end-on will correct to the Class I molar

relation.

Lo and Moyers in 1953, American Jr. Of Orthodontics, studied

the sequence of eruption of maxillary and mandibular permanent teeth

on a sample of 236 children.

The most frequent in the maxilla was 6124537 appeared 48.72%

of the time. There were 18 possible sequences.

- 6124357 16.01%

- 6124573 11.87%

In mandible, 17 different sequences were noted:

- 6123457 was found in 45.77%

- 6123475 were found in 18.64%

- 6124357 were found in 8.47%

They reported the combination of eruption sequences of 6124537

in maxilla and 6123457 in mandible provides the greatest incidence of

normal molar relationship.

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Nanda (1973) in Jr. of Dental Research, reported that most

common sequence of tooth emergence is 6124357 in maxillary arch and

6123457 in the mandibular arch:

The factors affecting the sequence of eruption:

- Endocrine (GH, TH).

- Familial tendency.

- Mental development.

Second transitional period:

The primary cuspids and molars are shed and permanent cuspids

and premolars erupt and 2nd permanent molars erupt.

It is commonly occurs between the ages 10-12 years.

Occasionally maxillary cuspid and second premolar will erupt

simultaneously and mandibular cuspid and first premolar erupt

simultaneously.

The maxillary and mandibular 2nd permanent molars are the last

teeth to erupt.

They start erupting at the age of 12-13 years and this delay may

be due to lack of space.

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The maxillary 2nd molar is tilled distally and buccally and

mandibular 2nd molar is tilted mesially and lingually with the emergence

of teeth, they are guided into occlusion by the “cone funnel” mechanism

and not until contact is attained do these teeth start to upright.

If the 2nd molar erupts before 2nd premolar, there is tipping of first

molar thus reducing space for the erupting second premolar.

The eruptive force of the 2nd molar helps in late mesial shift and it

also acts as bite-opener.

Adult dentition:

Although after the exfoliation of last primary tooth, the dentition

is considered as adult, it is only around the 20th years when the 3rd

molars have erupted and finished root development, the adult dentition

is completed.

3rd molars show more variability in calcification and eruption

than do any other teeth.

There is evidence of ethnic differences. The finnish aquire their

3rd molars, later than middle American whites and south Indians show

eruption as early as 13-14 years.

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Andrews – 6 keys to normal occlusion:

Andrew during 1970s put forward 6 keys to normal occlusion. He

considered the presence of these features essential to achieve an optimal

occlusion.

1. Molar inter arch relationship.

2. Mesio-distal crown angulation.

3. Labio-lingual crown inclination.

4. Absence of rotation.

5. Tight contacts.

6. Curve of spee.

Molar inter-arch relationship:

The mesio-buccal cusp of the upper first molar should occlude in

the groove between mesial and medial buccal cusp of the lower firt

molar. The mesio-lingual cusp of upper first molar must be angulated so

that the distal marginal ridge occludes with the mesial marginal ridge of

lower second molar.

Mesiodistal crown angulation:

It is the line that passes along the long axis of the crown through

the most prominent part in the center of labial or buccal surface. For the

normal occlusion, the gingival part of long axis of the crown must be

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distal to the occlusal part of line. Different teeth exhibit different crown

angulation.

The labio-lingual crown inclination:

The crown inclination is determined from a mesial or distal view.

If the gingival area as the crown is more lingually placed from the

occlusal area, it is referred to as positive crown inclination and the

opposite is referred to as negative crown inclination.

The maxillary incisors exhibit a positive crown inclination, while

the mandibular incisors show a very mild negative crown inclination.

The maxillary and mandibular posterior have a negative crown

inclination.

Absence of rotation:

Normal occlusion is characterized by absence of any rotation.

Rotated posterior teeth occupy more space on the dental arch while

rotated incisors occupy less space in the arch.

Tight contacts:

To consider an occlusion as normal, should be light contact

between adjacent tooth.

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Curve of spee:

A normal occlusal plane according to Andrew should be flat, with

the curve of spee not exceeding 1.5mm.

Summary and Conclusion

Guidance of eruption and development of the primary and

permanent dentitions is an integral part of the speciality of pediatric

dentistry. Early diagnosis and successful treatment of developing

malocclusion can have both short term and long term benefits while

achieving the goal of occlusal harmony, function and dental facial

esthetics.

The understanding of the normal occlusion indicate whether

prevalence and interceptive orthodontic procedures can be applied or

not.

References

1. White & Gardner – Book of orthodontics.

2. Moyers.

3. Vander Lindon – Development of occlusion.

4. McDonald – Text book of children through adolescence.

5. Graber – Text book of orthodontics.

6. Wheeler – Text book of Dental anatomy.

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CONTENTS

INTRODUCTION

DEVELOPMENT OF CONCEPTS OF OCCLUSION

a. Fictional Periodb. Hypothetical Periodc. Factual Period

EVOLUTIONARY CHANGES

STAGES OF OCCLUSAL DEVELOPMENT

POST NATAL DEVELOPMENT OF OCCLUSION

BIRTH TO COMPLETE DEVELOPMENT OF PRIMARY DENTITION

RELATIONSHIP OF GUMPADS

CHARACTERISTICS OF PRIMARY DENTITION

SPACES IN PRIMARY DENTITION

OCCLUSAL RELATIONSHIP OF 2ND PRIMARY MOLARS

a. Flush Or Vertical Plane Typeb. Mesial Stepc. Distal Step

FIRST INTERTRANSITIONAL PERIOD

DESCRIPTION OF OCCLUSAL CONTACTS IN PRIMARY DENTITION

FACTORS GUIDING NORMAL OCCLUSION IN PRIMARY DENTITION

a. Neuromuscular Co-ordinations

FIRST TRANSITIONAL PERIOD

UGLY DUCKLING STAGE

SECOND INTERTRANSITIONAL PERIOD

SECOND TRANSITIONAL PERIOD

ADULT DENTITION

ANDREW’S SIX KEYS ON NORMAL OCCLUSION

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