Develpoment of dentition

A Seminar on
“Development of
Dentition”
www.indiandentalacademy.com

Contents
•Introduction
•Evolution
•Development of tooth
•Development of occlusion
4 phases- Dentition at birth (upto 2years)
Deciduous dentition (from 2-6 years)
Mixed dentition (transitional) period
(from 6-12 years)
Permanent dentition (after 12 years)
•References

Introduction:
Knowledge of the normal development of the
dentition and an ability to detect deviation from the
normal are essential prerequisites for orthodontic
diagnosis and a treatment plan.

Evolution:
During evolution several significant changes took
place in the jaws and teeth.
When the Reptilian evolved to mammalian, the
dentition went from "polyphydont" to "diphydont" and
then to "homodent" to heterodent”.

Dental formula originally in mammals was
I 3/3, C 1/1, PM 4/4, M 3/3 a total of 44 teeth.
The present dental formula is
I 2/2, C1/1, PM 2/2, M 3/3 a total of 32 teeth.
The deciduous dental formula remained the same as;
I 2/2, C1/1, M 2/2 a total of 20 teeth.

Common evolutionary trends in the primates:
1. There was shortening of the jaw.
2. There was decrease in the tooth size to be
accommodated in these jaws. With subsequent
elimination of some teeth from the dentition.
3. There was progressive shortening of the arch
(infront) and relative widening.
4. Canines reduced in size

5. Lower premolar crowns became more
symmetrical from oval.
6. First molars became the dominant cheek
teeth.
7. In the upper second and third molars, the
distolingual cusp reduced and often
disappeared.
8. Third molars, which were larger than the first
molars, were reduced in size and often eliminated.

In modern man:
1. There is a decrease in the tooth-bearing
portion of the face. This decrease is partly due
to a reduction in tooth size.
2. In some primitive and pre historic human
skulls the second permanent molars usually
succeeds the 1st molar.
3. The occlusal length of the lower molars is
reduced in modern man and the ramus width
is even more reduced, less than the occlusal
length of the lower molars.

Development of tooth:
Tooth development involves many processes,
specialized structures that differentiate as part of
closely integrated pattern of events from genetically
potential fertilized ovum to complex stomatodeum,
the primitive oral cavity.

At about 28-30day of embryo, a continuous
band of thickened epithelium located on the
inferolateral border of the maxillary process and the
superolateral borders of the mandibular arches in
the area forming the lateral margins of the
stomatodeum, called the 'primary epithelium band'.

A continuous band of thickened epithelium
forms presumptive of upper and lower jaws, which
are roughly horseshoe shaped and correspond to
future dental arches.

These bands of epithelium are called the
primary epithelium band which gives rise to 2
subdivisions; namely Vestibular lamina, and
Dental lamina (DL).
Vestibular lamina: The Vestibular lamina
proliferates into ectomesenchyme resulting in
vestibule.

Dental lamina:
There is a continuous and localized
proliferative activity leading to epithelium ingrowth
into ectomesenchyme at sites, which are the
positions of the future deciduous teeth. There are
10 successional swellings on both upper and lower
lamina.

Importance:
This DL serves as primodium for ectodermal
portion of deciduous teeth. During development of jaw,
permanent molar arise from distal extension of DL.
The successors of deciduous teeth develop from
lingual extension of free end of the DL opposite to the
enamel organ of each deciduous tooth. The lingual
extension of DL is named successional lamina.
Fate of DL:
The activity of dental lamina extends over period
of 5years, later begins to degenerate. The remnants
are called 'cell rest of serre'.

The tooth development proceeds into 3 stages.
Bud stage,
Cap stage and
Bell stage.

Bud stage:
The epithelium of DL is separated from
ectomesenchyme by a basement membrane. On
differentiation of DL, round/ovoid swelling arise from
the basement membrane, which are the primordia of
tooth bud and enamel organ.

Area of condensation, which is immediately
subjacent of the enamel organ, is 'dental papilla'.
While the condensed ectomesenchymal cells
surrounding tooth bud and dental papilla is 'dental
sac'.
The dental papilla forms tooth pulp and dentin
whilst dental sac forms cementum and periodontal
ligament.

Cap stage:
As tooth buds continue to proliferate, there is
shallow invagination on deep surface that marks the
onset of cap stage.

Stellate reticulum:
Centrally located polygonal cells of enamel
organ separate as more intercellular fluid
accumulates forming a cellular network called
'Stellate reticulum' this assumes branched
reticulum form.
The intercellular fluid is rich in albumin, which
provides cushion like consistency protecting
delicate enamel forming cell.
Enamel knot
Enamel cord

Dental papilla:
Due to increased proliferating epithelium of
the enamel organ, the ectomesenchyme (neural
crest cells), which is partially enclosed by inner
enamel epithelium, start to proliferate and
condenses to form 'dental papilla'. This papilla also
has budding of capillaries and mitotic figures near
to peripheral cells adjacent to inner enamel
epithelium, which begin to enlarge to be
differentiated into odontoblasts.

Bell stage:
Continued growth of the tooth germ leads to the
next stage of tooth development, the bell stage so called
because the dental organ comes to resemble a bell as
the undersurface of the epithelial cap deepens.

Four different types of epithelial cells can be
distinguished in this stage,
1. the inner enamel epithelium,
2. the stellate reticulum,
3. the stratum intermedium, and
4. the outer enamel epithelium.

The inner enamel epithelium:
The inner enamel epithelium consists of a
single layer of cells that differentiate prior to
amelogenesis into tall columnar cells called
ameloblasts. The cells of the inner enamel
epithelium exert an organizing influence on the
underlying mesenchymal cells in the dental papilla,
which later differentiate into odontoblasts

Stellate reticulum:
The stellate reticulum expands further, mainly
by an increase in the amount of intercellular fluid.
The cells are star shaped, with long processes.
Before enamel formation begins, the stellate
reticulum collapses, reducing the distance between
the centrally situated ameloblasts and the nutrient
capillaries near the outer enamel epithelium.
Its cells then are hardly distinguishable from
those of the stratum intermedium. This change
begins at the height of the cusp or the incisal edge
and progresses cervically.www.indiandentalacademy.com

Stratum intermedium:
A few layers of squamous cells form the
stratum intermedium, between the inner enamel
epithelium and the stellate reticulum. This layer
seems to be essential to enamel formation.
Outer enamel epithelium:
The cells of the outer enamel epithelium
flatten to low cuboidal cells. The outer enamel
epithelium is thrown into folds, which are rich in
capillary network, which provides the nutrition for
the enamel organ.

Dental lamina
Dental papilla
Dental sac

Advanced bell stage:
During the advanced bell stage, the boundary
between inner enamel epithelium and odontoblasts
outlines the future dentinoenamel junction. In
addition, the cervical portion of the enamel organ
gives rise to the epithelial root sheath of Hertwig.

Root formation:
The development of the roots begins after
enamel and dentin formation has reached the future
cementoenamel junction. The enamel organ plays
an important part in root development by forming
Hertwig's epithelial root sheath, which molds the
shape of the roots and initiates radicular dentin
formation.

A
B
Three stages in development of tooth with two roots and
one with three roots. Surface view of epithelial diaphragm.
During growth of tooth germ, simple diaphragm, A,
expands eccentrically so that horizontal epithelial flaps are
formed. B, Later these flaps proliferate and unitewww.indiandentalacademy.com

Development of Occlusion:
Development of occlusion is a genetically and
environmentally conditioned process that shows a
great deal of individual variations, and
Consequently, for the development of an
acceptable occlusion, quite a remarkable co-
ordination of different events is necessary.
Failure in one part of the developmental
process may lead to anomalies, or else may be
compensated for by other developmental process.

The development of occlusion may be divided into 4
periods;
1. Period from birth to the complete eruption of the
deciduous teeth (birth to 2 1/2 years),
2. Period from the completion of the deciduous
dentition to the eruption of the 1st permanent
molar (2 1/2 to 6 years),
3. Period from eruption of 1st permanent molar to
the final shedding of the deciduous teeth (6 to 12
years) and
4. The period from the eruption of the second
permanent molars at about 12 years onwards.

Period from birth to the complete eruption of the
deciduous teeth:
Gum pads:
At birth the alveolar arches, also called gum
pads, are horseshoe shaped in the maxilla and U-
shaped in the mandible. They are firm and pink in
colour.
These gum pads develop in two parts, Labio
buccal portion- that differentiates first and grow
more rapidly, Lingual portion- that differentiates
later. The two portions of gum pads are separated
from each other by a groove called the dental
groove. www.indiandentalacademy.com

The gum pads are divided by 10 transverse
grooves that represent the future deciduous teeth as
their tooth sacs, which are papillomatous at first.
Of these grooves those between the canines
and first molars segment are of importance as they
help in assessing the relationship of the gum pads to
each other, they are called lateral sulci, and these
are the only ones to extend on the buccal side.
Normally the mandibular arch is more distal to
that of the maxillary arch.

Upper jaw:
In the upper jaw the gingival groove separates
the gum pad from the palate, and is related to the
inner alveolar plate (floor of the mouth).
The dental groove of the upper gum pad passes
from the incisive papilla laterally and lingually, to join
the gingival groove in the canine region,
Whence, it continues distally and buccally
across that segment of the gum pad which
corresponds to the first deciduous molar tooth crypt.
The gingival groove defines the limits of the palate,
both anteriorly and laterally, by three almost straight
borders forming part of an oblong.www.indiandentalacademy.com

Lower gum pad:
The lower gum pad is 'U' shaped, and once more it
is found that the alveolar pad is limited on the lingual
aspect by a continuous groove.
In the anterior region the gum pad is slightly everted
labially. Here too the pad is divided by transverse
grooves into 10 segments, but it is not as clear as in
upper. The groove distal to the canine is continued
on to the buccal surface and is again called the
lateral sulcus.

At rest the gum pads are separated by tongue,
which protrudes over the lower gum pad to lie
immediately behind the lower lip, and may even
protrude a little between the lips. At this age the
upper lip appears short.
The degree of overjet of the upper gum pad
varies considerably.
Clinch and Sillman (1932) have shown that
there is rarely any contact between the gum pads
anteriorly when they are approximated, wherein the
contact was found in the first molar region. The
presence of anterior open bite is normal and helps
in sucking. www.indiandentalacademy.com

Sillman in 1940 classified space between the anterior
segments of the gum pads as follows :
Class A— The maxillary and mandibular anterior
segments lie in their respective planes.
Class B— In the maxillary, the incisor segments are
higher than the canine segments, while in the
mandibular, the anterior segments are in the same
plane.
Class C— In the maxillary, the incisor segments are
higher than the canine segments, while in the
mandibular the canine segments are higher.
Class D— In the maxillary, the anterior segments are in
the same plane, while in the mandibular, the canine
segments are higher.

At birth, the gum pads are not sufficiently wide to
accommodate the incisors, which are crowded and
rotated in their crypts.
During the first year of life the pads grow rapidly,
and the growth is most marked in the lateral direction.
This increase of width permits the incisors to erupt in
good alignment and to be spaced.
This condition wherein the crowding of incisors
occurs is temporary that gets corrected by the tongue
and lip pressures. The length of the pads increases
more moderately and the second molar segment
becomes clearly defined.

The sequence of deciduous teeth eruption is
A B D C E.
The sequence of eruption:

PRIMARY
DENTITION
Hard
Tissue
Formation
Amount of
Enamel
Formed at
Birth
Ename
l
comple
tion
Erupti
on
Root
Compl
etedMaxillary Begins
Central
incisor
4 mos.
Inutero
Five sixths 1 1/2
mos.
7 1/2
mos.
1
-1/2Yrs
Lateral
incisor
4 1/2 mos.
Inutero
Two thirds 2 1/2
mos.
9 mos. 2 Yrs
Cuspid
5 mos.
Inutero
One third
9 mos.
18
mos.
3 1/4
Yrs
First molar
5 mos.
Inutero
Cusps
united
6 mos.
14
mos.
2 1/2
Yrs
Second
molar
6 mos.
Inutero
Cusp tips
still isolated
11
mos.
24
mos.
3 Yrswww.indiandentalacademy.com

Mandibular
Central
incisor
4 1/2 mos.
Inutero
Three fifths
2 1/2
mos.
6 mos.
1 1/2
Yrs
Lateral
incisor
4 1/2 mos.
Inutero
Three fifths 3 mos. 7 mos.
1 1/2
Yrs
Cuspid 5 mos.
Inutero
One third 9 mos.
16
mos.
3 1/4
Yrs
First molar
5 mos.
Inutero
Cusps
united
5
1/2mos
12
mos.
2 1/4
Yrs
Second
molar
6 mos.
Inutero
Cusp tips
still isolated
10
mos.
20
mos.
3 Yrswww.indiandentalacademy.com

At two year of age, a large number of children
have 20 teeth that are clinically present and
functioning
- is the good place to begin a more
detailed analysis of the age-linked status of the
dentition.
Is important, because preventive and interceptive
measures are possible,
As when the orthodontist knows the normal range
and timing of developmental phenomena.

Deciduous incisor root formation is finished and
root formation of the deciduous canines and first
molars approaches completion.
The permanent first molars continue to develop
with a shift in their position within their respective
bones toward the occlusal plane.
Calcification is also proceeding in the
developing permanent teeth, anterior to the first
permanent molars.
By two and a half years of age the deciduous
dentition is usually complete and in full function.

Anomalies:
Usually the neonate is tooth less for about
6months after birth, but rarely teeth are found to
have erupted at the time of birth, which are called
natal teeth. Whilst those which erupt during the first
month of age are called neonatal teeth. These teeth
have shown prevalence mostly in the lower incisor
region showing familial tendency.

Self correcting malocclusion:
a) Retrognathic mandible:
Corrects with differential and forward growth of the
mandible.
b) Anterior open bite:
Eruption of primary incisors
c) Infantile swallowing pattern:
During the first year of life with introduction of solid
foods in diet.

Period from the completion of the deciduous
dentition to the eruption of the 1st permanent
molar:
The calcification of the deciduous teeth begins
early in the fourth month in the incisor region, and four
weeks later in the canine and molar regions.
About one-quarter to a half of the crowns are
formed before birth, its for this reason that any
condition which interferes with development or
calcification of the deciduous teeth does not
necessarily involve the permanent teeth, which are
calcified after birth, and vice versa.

The maxillary central incisors erupt at 9
months of age with spaces between them, followed
by the lateral incisors at the age of 1 year.
By 1 to 1 1/2 years, the first molars erupt,
resulting in a vertically supported occlusal contact
between the two arches.
The mandibular canines erupt at 16 months
and the maxillary canines follow at around 18
months.
By the age of 2 1/2 months to 3 years the full
compliment of deciduous dentition is present.

Spacing:
Spacing in the deciduous dentition occurs
between all the teeth as they erupt or subsequently
as they erupt.
Spaced dentition
Non-spaced dentition
2 types
Physiologic/developmental spaces
Primate/simian/anthropoid spaces

Non-spaced dentition
According to Leighton B. C. the chances of
crowding in permanent dentition is 100% when there is
crowding in the deciduous dentition.
Deciduous dentition Chances of crowding
in permanent
Crowding 100%
No spaces 70%
Below 3mm of total spacing 50%
3-6mm of total spacing 20%
Over 6mm of total spacing 0%

Primary molar relationship:
The relationship of the distal surface of the
maxillary and mandibular second primary molars is,
one of the key factors that influences the future
occlusion of the permanent dentition.
The mesio-distal relation between the distal
surface of the upper and lower second primary
molars usually can be classified into the three types:
      Flush terminal or vertical plane type,
      Mesial step type and
      Distal step type

Arch dimensions:
The size of the primary dental arch can be
measured by the dental arch width between the
primary canines and between the second primary
molars.
The dental arch length can be measured from
the most labial surface of the primary central incisors
to the canines and to the second primary molars.
Arch circumference is determined by measuring
the length of the curved line passing over the buccal
cusps or the incisal edges of the teeth, from the distal
surface of the primary second molar around the arch
to the distal surface of the other primary molar.www.indiandentalacademy.com

A - Arch length B1 - Bicanine diameter
B2 - Bimolar diameter C- Arch perimeter/Arch
circumference

Arch length and circumference
A small amount of decrease takes place in
the arch length and arch circumference from the
eruption of the second molars until the eruption of
the first permanent molars due to the mesial
migration of the second primary molars, or the arch
can also be shortened due to interproximal caries.

Arch width:
The primary dentition does not show any
substantial increase in width across the alveolar
arch. Both maxillary and mandibular arches
increase in width by growing posteriorly to
accommodate the eruption of the permanent
molars.
Arch height:
Increase in the height of the alveolar bone
takes place as it grows with time. There is little or no
increase in the arch height during the period of the
primary dentition.

1) Anterior deep bite:
Eruption of deciduous molars
Attrition of incisal edges
Forward and downward growth of
mandible
2) Flush terminal plane
(Early shift) Eruption of the first
permanent molar
(Late shift) Leeway space

3) Spacing
Eruption of first permanent molar
4) Edge to Edge (due to attrition)
Eruption of permanent incisors

Period from eruption of 1st permanent molar to
the final shedding of the deciduous teeth:
This is the period during which both the
primary and permanent teeth are in the mouth
together, so also called period of mixed dentition.
Successional teeth: The permanent teeth erupting in
place of previous deciduous teeth.
Accessional teeth: Those erupting posteriorly to the
primary teeth.

Nolla's stages of tooth calcification:
Nolla divided the development of each tooth into 11
stages, as
0 - absences of crypt,
1 - presences of crypt,
2 - initial calcification,
3 - 1/3rd of crown completed,
4 - 2/3rd of crown completed,
5 - crown almost completed.

6 - crown completed,
7 - 1/3rd root completed,
8 - 2/3rd root completed,
9 - root almost completed, open apex and
10 - apical end of the root completed.
Stage2 wherein there is initial calcification,
Stage 6 is the time most teeth begin eruptive
movements,
Stage 8 wherein the teeth pierce the alveolar crest.

First permanent molars eruption – 6-7 years.
"There are three periods of physiologic raising
of the bite, with the eruption of the first permanent
molars at six, with the eruption of the second
permanent molars at twelve and with the eruption of
the third molars at around 18." - Schwarz
The 'first of three assaults’ on the excessive
overbite.

As the upper and lower first permanent molars
erupt, the pad of tissue overlying them creates a
premature contact.
Permanent first molar as natural "bite opener"
Proprioceptive response conditions the patient
against biting on this natural "bite opener," leading to
reducing the overbite.
Deciduous central incisors are lost and their
permanent successors start their eruptive path toward
contact with the incisors of the opposing arch.

The mandibular central incisors erupt first,
followed by the maxillary centrals.
Mandibular incisors frequently erupt lingual to
the deciduous counterparts and move forward
under the influence of tongue pressure as they
erupt.
Maxillary Central Incisors erupt labially,
appear as large bulges in the mucobuccal vestibule
If inadequate space, the eruption time is
delayed for these teeth, or they erupt markedly to
the lingual or are rotated.

Corrected by removal of canines ahead of time
But Orthodontic consultation is desirable
As, if removal is postponed, the lateral incisors
may erupt palatally and in lingual cross-bite with the
lower incisors.
Permanent canine and its crypt move mesially
toward the midline and encroach on the space that
would normally be occupied by the lateral incisor.

The time between seven and eight years of
age is critical for the developing dentition.
Will there be enough space or not?
Frequent observation by the dentist is
essential at this time.
A mucosal barrier may prevent the
permanent incisors from erupting.
Keeping constant vigilance is essential.
If inadequate space is present can be
corrected by guided extraction.

Phases of mixed dentition can be divided into three
period:
i) The first transitional period:
ii) Intertransitional period:
iii) Second transitional period:

•The first transitional period:
By the time of first permanent molars erupts,
initial spaces between the deciduous molars and
canines will generally have diminished or
disappeared.
In both the jaws, the first permanent molars
erupt more or less in a perpendicular orientation to
the occlusal plane.

The antero posterior relation between the two
opposing first molars after eruption depends on:
Positions previously occupied within the jaws
The sagittal relation between the maxilla and
mandible.
Ratios of the mesiodistal crown dimensions of
the U/L deciduous molars.
The occlusal relationship is established by the
'cone and funnel' mechanism with the upper palatal
cusp (cone) sliding into the lower occlusal fossa
(funnel).

Ideally, the eruption of the permanent molars
into a class I relationship is desired.
The desired class I relationship is established by
the following ways:
a) Early mesial shift
b) Late mesial shift
c) Primary molar guidance of permanent
dentition

Early mesial shift:
Spaced dentition with flush terminal
relationship of second deciduous molars

Late mesial shift
When no spaces exist.
Utilization of Leeway space

Primary molar guidance of permanent dentition:
If the deciduous arches terminate in a mesial
step, the permanent molars may erupt directly into
a normal, angle class I occlusion.

Favourable variations in the size ratio between the
primary and permanent teeth:
Labial inclination:
The interincisal angle between the maxillary
and mandibular incisors is about 1500
in primary
dentition,
Whereas it is about 1230
in permanent
dentition which makes permanent dental arch
circumference wider.

Incisal Liability
The permanent incisors are larger in total width
than the primary incisors they replace, this difference
is called 'incisal liability' .
Corrected by
The utilization of the developmental
spaces, apart from which the labial
inclination also helps.

Leeway space:
Permanent canine, premolars are usually
smaller in total width than primary canine and molars
they replace this difference is called 'Leeway space'.
This averages 1.8 mm in the maxilla and 3.4
mm in the mandible.
Also allows the permanent molars to move
mesially when the deciduous molars are replaced with
the mesio-distally smaller premolars.
Greater Leeway space in lowers helps the
mesial movements of lower 1st
molars which helps
shift from endon relation to normal.

Ugly duckling stage:
This is the stage occurs when there is a
transitional mal-alignment during the exchange period of
the upper anterior teeth.
In the upper arch when the permanent incisors
erupt, these appear much larger compared with the
primary teeth with their longitudinal axes-flared out like
as an inverse 'V'.
This is because of the pressure of erupting
permanent canines in the developing roots of lateral
incisors, the crowns of erupting incisors flare more
laterally producing diastema.

INTER TRANSITIONAL PERIOD
Lasts about 1.5 years, asymmetry in
emergence and associated differences in height
levels and lengths of clinical crowns of the
corresponding left and right teeth are made up.
Influence of the tongue
Wearing of deciduous teeth

SECOND TRANSITIONAL PERIOD
At around 9 to 10 years of age, the second
transitional period starts with shedding of the
primary posterior teeth.
The alignment of the erupting permanent
teeth depends a lot on the order of exchange of the
lateral teeth which takes about 1 1/2 years to
complete the exchange of all the lateral teeth.

After the eruption of incisors, there follows a
pause of about 1-2 years, and the next tooth to
erupt is the lower cuspid and the first bicuspid at 9-
10 years.
The maxillary cuspid and second bicuspid
then erupt, at 11 to 12 years, and the period is
terminated by the appearance of the second molars
at 12 years

Sequence of eruption of permanent
lateral teeth in the maxilla 4-3-5 and
in the mandible 3-4-5
After the exchange of the lateral teeth has
been completed and dental arch upto the first
molar is established, the second permanent molars
begin to erupt.
The dental arch length is reduced just prior to
eruption of the second molar by the mesial force.

The arch circumference may also become
shortened than that of the primary dental arch by
the utilization of the leeway space with the
exchange of the second primary molar to the
second premolar.
Therefore, it is quite possible that eruption of
second molar may accentuate the crowding if it
was already present in the dentition.
Proximal carious lesions or early extraction
of second primary molars

1) Anterior deep bite:
Proprioceptive response condition of patient
(with the eruption of first permanent molars
and premature contact of the pad of tissue
overlying them as natural bite opener)
2) Mandible anterior crowding:
Tongue pressure, Increase in intercanine
width

3) Ugly duckling stage:
Maxillary canine eruption
4) End-on relation:
With eruption of first permanent
molars, late mesial shift in non spaced
dentition

The period from the eruption of the second
permanent molars at about 12 years onwards:
The permanent dentition is considered when all
the permanent teeth (all 28 teeth) are seen in the
dental arches, often by the age of 12 to 14 years of
age.
The established interrelationship between
permanent dental arches is by no means the final step
in occlusal development.
After the occlusion of the dentition has been
established fairly minor changes related to teeth take
place in sagittal, transverse and vertical
interrelationship. www.indiandentalacademy.com

Horizontal overbite decreases
Dental arches become shorter due to proximal
wear and often crowding develops in mandibular
incisor region by 14 years of age.
Vertical overbite decreases upto the age of
18years by 0.5 mm.
The alveolar process may grow in height
beyond 16 years of age.
Overjet decreases by 0.7mm between 12 and
20years of age. Individual variations are
considerable. The increase in the dental arches is
generally not continuous.

Role of 3rd molars:
Now a day the role of 3rd molars is diminishing,
due to which there has been impaction of these and
even missing.
If the 3rd molars is missing or has not erupted
into the oral cavity then the role played by it in the
malocclusion is quite less compared to that if it is to
erupt and occupy the space.
The 3rd molars impaction cases are frequently
seen in the class II cases.

If present the 3rd molars usually causes;
Arch perimeter shortening,
Incisor crowding increases especially with the
mandibulars,
Mandibule grows forward more than the maxilla,
1st molars move forward and the incisors become
more procumbent.

Overjet and overbite- Decreases with eruption
of all permanent molars
. Differential growth of
mandible.

References
Textbooks
1. Orthodontics Principles and Practice by T.M. Graber, W.B.
Saunders company, 3rd ed.
2. Handbook of Orthodontics, by Robert E. Moyers, 3rd ed.
3. Orthodontics for dental students by TC White, HH. Gardener,
BC. Leighton, MacMillan press 3rd ed.
4. Orbans oral Histology and Embryology by S.N.Bhasker 11th
edition
5. Ten Cate Oral histology, W B saunders company.
6. Contemporary Orthodontics by William Profitt. C V Mosby
Company.
7. Orthodontics the art and science by S I Bhalajhi , 2nd ed.www.indiandentalacademy.com

Journals:
1. Sillman J.H.,: A serial study on occlusion from birth to three years.
AJO-DO.,: 207 - 227,1940.
2. Sillman J.H.,: dimensional changes of dental arches: longitudinal
studies from birth to 25 years. AJO-DO., 50: 824-842,1964.
3. Sillman J.H.,: a serial study of good occlusion from birth to 12 years:
longitudinal studies from birth to 12 years. AJO-DO., 37: 481,1951
3. Dent. Practnr dent. 1971 21: 359-372.] Leighton B. C.
4. Broad-bent, B. H.: Ontogenetic Development of Occlusion, Angle
Orthodontist, 11: 223-241, 1941
5. Moorrees , C. F. A., and Chadha, J.M.,: Available space for the
incisors during dental development. Angle orthodontist., 35;12-22, 1965.
6. Baume, L J : Physiological tooth migration and its significances for
the development of occlusion. J Dent. Res. 29: 123, 331-338, 1950.

Develpoment of dentition

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