Development of occlusion

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DEFINITION :-DEFINITION :-
OcclusionOcclusion:- It is the way the maxillary and:- It is the way the maxillary and
mandibular teeth articulate.mandibular teeth articulate.
Occlusion is much more complex relationshipOcclusion is much more complex relationship
because it involves the study o the teeth theirbecause it involves the study o the teeth their
morphology and angulations, the muscles ofmorphology and angulations, the muscles of
mastication, the skeletal structures, the temporomastication, the skeletal structures, the temporo
mandibular joint and the functional jawmandibular joint and the functional jaw
movements in addition it involes the relationshipmovements in addition it involes the relationship
of the teeth in centric occlusion, in centricof the teeth in centric occlusion, in centric
relation and during functionrelation and during function

Stages of dental developmentStages of dental development
Pre dental periodPre dental period
The deciduous dentition periodThe deciduous dentition period
The mixed dentition periodThe mixed dentition period
The permanent dentition periodThe permanent dentition period

Pre dental period:Pre dental period:
lasts for 6 months after birthlasts for 6 months after birth
Gum padsGum pads:-The alveolar arches of an:-The alveolar arches of an
infant at the time of birth are called guminfant at the time of birth are called gum
pads. They are pink in color and firm inpads. They are pink in color and firm in
consistency of and covered by dense layerconsistency of and covered by dense layer
of fibrous periosteum.of fibrous periosteum.

MAXILLARY GUM PAD
MANDIBULAR GUM PAD

Gum pads are greatly thickened oralGum pads are greatly thickened oral
mucous membranes of the gum whichmucous membranes of the gum which
soon become segmented and eachsoon become segmented and each
segment is a developing tooth site.segment is a developing tooth site.
The pads get divided into labial/ buccalThe pads get divided into labial/ buccal
and a lingual portion. These are separatedand a lingual portion. These are separated
from each other by a groove called thefrom each other by a groove called the
dental groove.dental groove.

Transverse grooves divide gum pads into 10Transverse grooves divide gum pads into 10
segment each segment consists of onesegment each segment consists of one
developing deciduous tooth sac.developing deciduous tooth sac.
Gingival groove separates the gum pads from theGingival groove separates the gum pads from the
palate and floor of the mouth.palate and floor of the mouth.
Transverse groove of the canine and firstTransverse groove of the canine and first
deciduous molar segment is called lateral sulcusdeciduous molar segment is called lateral sulcus
which is useful in judging inter arch relation shipwhich is useful in judging inter arch relation ship
at very early stage.at very early stage.
Lateral sulcus of mandibular arch is normallyLateral sulcus of mandibular arch is normally
more distal to that of maxillary arch.more distal to that of maxillary arch.
Upper gum pad is horse shoe shaped while lowerUpper gum pad is horse shoe shaped while lower
is ‘U’ shaped and rectangular.is ‘U’ shaped and rectangular.

Relationship of gum padsRelationship of gum pads
Anterior open bite is seen at rest whichAnterior open bite is seen at rest which
contacts only in the molar region, tonguecontacts only in the molar region, tongue
protrudes anteriorly through this space.protrudes anteriorly through this space.
This is considered normal and it helps inThis is considered normal and it helps in
sucklingsuckling
Complete over jet all aroundComplete over jet all around
Class II pattern with max gum pad isClass II pattern with max gum pad is
more prominent.more prominent.

The status of dentitionThe status of dentition
Neonate is without teeth for about 6 month atNeonate is without teeth for about 6 month at
birth gum pads are not sufficiently wide tobirth gum pads are not sufficiently wide to
accommodate developing incisors which areaccommodate developing incisors which are
crowded In their crypts during 1st year of lifecrowded In their crypts during 1st year of life
they grow rapidly permitting incisors to erupt.they grow rapidly permitting incisors to erupt.
Natal teeth are present at birth incidence inNatal teeth are present at birth incidence in
1:10001:1000
Pre erupted teeth erupt during the second orPre erupted teeth erupt during the second or
third month.third month.
Natal and neonatal teeth are almost alwaysNatal and neonatal teeth are almost always
mandibular incisors which frequently displaymandibular incisors which frequently display
enamel hypoplasia and have familial tendency.enamel hypoplasia and have familial tendency.

Neonatal
Natal

The deciduous dentition periodThe deciduous dentition period
This stage starts from eruption of the firstThis stage starts from eruption of the first
deciduous tooth (usually mandibular centraldeciduous tooth (usually mandibular central
incisors ) and ends with the eruption of the firstincisors ) and ends with the eruption of the first
permanent molar i.e. from 6 months to 6 yearspermanent molar i.e. from 6 months to 6 years
of post natal life.of post natal life.
By 2.0 year to 3.5 year of age when the secondBy 2.0 year to 3.5 year of age when the second
deciduous molar come into occlusion, thedeciduous molar come into occlusion, the
deciduous dentition is completed.deciduous dentition is completed.
Eruption age & sequence of deciduous dentitionEruption age & sequence of deciduous dentition

Chronology of human primaryChronology of human primary
dentitiondentition
ToothTooth EruptionEruption Root CompletedRoot Completed
MaxillaryMaxillary
Central incisorCentral incisor 71/2 mos71/2 mos 11/2 yrs11/2 yrs
Lateral incisorLateral incisor 9mos9mos 2yrs2yrs
CuspidCuspid 18mos18mos 31/2yrs31/2yrs
First molarFirst molar 14 mos14 mos 21/2yrs21/2yrs
Second molar 24mosSecond molar 24mos 3yrs3yrs

MandibularMandibular
Central incisorCentral incisor 6mos6mos 11/2yrs11/2yrs
Lateral incisorLateral incisor 7mos7mos 11/2yrs11/2yrs
CuspidCuspid 16mos16mos 31/4yrs31/4yrs
First molarFirst molar 12mos12mos 21/4yrs21/4yrs
Second molarSecond molar 20mos20mos 3yrs3yrs
A variation of 3 month from the mean age has been
accepted as normal
Sequence of eruption is:-A-B-D-C-E

Normal signs of primaryNormal signs of primary
DentitionDentition
– Spaced anterior :- spacing usually existsSpaced anterior :- spacing usually exists
between deciduous teeth these spacesbetween deciduous teeth these spaces
are called physiological or developmentalare called physiological or developmental
spaces. They accommodate the largerspaces. They accommodate the larger
permanent teeth in the jawspermanent teeth in the jaws..

Spacing invariably is seen mesial to the maxillary canines andSpacing invariably is seen mesial to the maxillary canines and
distal to the mandibular canines. These physiological spacesdistal to the mandibular canines. These physiological spaces
are called primate/simian/anthropoid spaces seen commonlyare called primate/simian/anthropoid spaces seen commonly
in primates. They help in inter digitations of opposing caninesin primates. They help in inter digitations of opposing canines
and used for early mesial shift.and used for early mesial shift.

– Shallow over jet and overbite. (Edge to edgeShallow over jet and overbite. (Edge to edge
bite)bite)
– Flush terminal planeFlush terminal plane:- When the distal:- When the distal
surfaces of maxillary and mandibularsurfaces of maxillary and mandibular
deciduous see and molars are in the samedeciduous see and molars are in the same
vertical plane, this is the normal motorvertical plane, this is the normal motor
relationship in the primary dentition becauserelationship in the primary dentition because
the M-D width of mandibular molar is greaterthe M-D width of mandibular molar is greater
than M-D width of maxillary molar.than M-D width of maxillary molar.

Mesial stepMesial step:- distal surface of mandibular:- distal surface of mandibular
deciduous 2nd molar is mesial to the distaldeciduous 2nd molar is mesial to the distal
surface of maxillary deciduous 2nd molar.surface of maxillary deciduous 2nd molar.
Distal stepDistal step:- distal surface of mandibular:- distal surface of mandibular
deciduous 2nd molar is more distal thandeciduous 2nd molar is more distal than
the distal surface of max. deciduousthe distal surface of max. deciduous
second molarsecond molar

Distal step:- 10:/:Distal step:- 10:/:
Flush terminal plane:- 29:/:Flush terminal plane:- 29:/:
Mesial step of 1 mm:- 42:/:Mesial step of 1 mm:- 42:/:
Mesial step > 1.0 mm :-19:/:Mesial step > 1.0 mm :-19:/:

DISTAL STEP TERMINAL
PLANE
FLUSH TERMINAL
PLANE
MESIAL STEP TERMINAL
PLANE

Sequalae of Mesial and distal step –Sequalae of Mesial and distal step –
Distal step terminal planeDistal step terminal plane :- The:- The
permanent 1st molar will erupt into apermanent 1st molar will erupt into a
class II relation this is not self correctingclass II relation this is not self correcting
Mesial step terminal planeMesial step terminal plane :-:-
permanent molars erupt directly intopermanent molars erupt directly into
class I occlusion or may develop in classclass I occlusion or may develop in class
III Occlusion.III Occlusion.

Almost vertical inclination of the anteriors.Almost vertical inclination of the anteriors.
Ovoid arch formOvoid arch form

The mixed dentition periodThe mixed dentition period
Period where teeth of both deciduous andPeriod where teeth of both deciduous and
permanent dentition are seen it extendspermanent dentition are seen it extends
from 6 to 12 year of age. Mostfrom 6 to 12 year of age. Most
malocclusions make then appearancemalocclusions make then appearance
during this stage. This stage can beduring this stage. This stage can be
divided into three transitional periodsdivided into three transitional periods
First transitional periodFirst transitional period
Inter transitional periodInter transitional period
Second transitional periodSecond transitional period

First transitional periodFirst transitional period
emergence of the first permanent molarsemergence of the first permanent molars
and transition of incisors.and transition of incisors.
Eruption of permanent first molars :- 1stEruption of permanent first molars :- 1st
permanent molars erupt at 6 yearspermanent molars erupt at 6 years
Antero posterior positioning of theAntero posterior positioning of the
permanent molars is influenced by:-permanent molars is influenced by:-

Terminal plane relationshipTerminal plane relationship
when deciduous second molars are in a flushwhen deciduous second molars are in a flush
terminal plane, the permanent 1st molar eruptsterminal plane, the permanent 1st molar erupts
initially into a cusp to cusp relationship whichinitially into a cusp to cusp relationship which
later transforms into a class I ,molar relegationlater transforms into a class I ,molar relegation
using the primate spaces (early shift)using the primate spaces (early shift)
This is brought about by mesial shift of theThis is brought about by mesial shift of the
permanent first molar following exfoliation of thepermanent first molar following exfoliation of the
primary molar and this making use of leewayprimary molar and this making use of leeway
space (late shift)space (late shift)

The exchange of incisorsThe exchange of incisors :- The:- The
deciduous incisors are replaced by thedeciduous incisors are replaced by the
permanent incisors, permanent are larger thanpermanent incisors, permanent are larger than
deciduous the difference between the amount ofdeciduous the difference between the amount of
space need for the accommodation of thespace need for the accommodation of the
incisors and amount of the space available forincisors and amount of the space available for
this is called incisal liability. It is 7.6 mm inthis is called incisal liability. It is 7.6 mm in
maxilla and 6 mm in mandible. This space ismaxilla and 6 mm in mandible. This space is
provided by -provided by -

Inter dental physiologic spacing in the primaryInter dental physiologic spacing in the primary
incisor region - 4 mm in maxillary arch, 3 mm inincisor region - 4 mm in maxillary arch, 3 mm in
mandibular arch.mandibular arch.
Increase in the intercanine arch width :Increase in the intercanine arch width :
significant amount of growth occurs with thesignificant amount of growth occurs with the
eruption of incisors and canines.eruption of incisors and canines.
Permanent incisors erupt labial to the primaryPermanent incisors erupt labial to the primary
incisors to obtain and added space of 2-3 mm.incisors to obtain and added space of 2-3 mm.
Primary teeth are upright but permanent teethPrimary teeth are upright but permanent teeth
incline to the labial surface thus decreasing theincline to the labial surface thus decreasing the
inter incisal angle from about 150° in theinter incisal angle from about 150° in the
deciduous dentition to 123° in the permanentdeciduous dentition to 123° in the permanent
dentition. This increases arch perimeterdentition. This increases arch perimeter

The Broad bent’s phenomenonThe Broad bent’s phenomenon
Ugly duckling stage (8-14 years )Ugly duckling stage (8-14 years )
Crowns of canines n young jaws impinge on theCrowns of canines n young jaws impinge on the
development of lateral incisor roots thus driving the rootsdevelopment of lateral incisor roots thus driving the roots
medially and causing the crowns to flare laterally.medially and causing the crowns to flare laterally.
Roots of central incisors are also forced together thusRoots of central incisors are also forced together thus
causing max.causing max.
midline diastema.midline diastema.
The period from the eruption of lateral incisors to canineThe period from the eruption of lateral incisors to canine
is termed as ugly duckling stage.is termed as ugly duckling stage.
It occurs around the 8 years age and commonly seen inIt occurs around the 8 years age and commonly seen in
upper archupper arch
It is an unaesthetic metamorphosis which eventuallyIt is an unaesthetic metamorphosis which eventually
leads to an aesthetic result.leads to an aesthetic result.

Chronology of human permanentChronology of human permanent
dentitiondentition
ToothTooth EruptionEruption Root CompletedRoot Completed
MaxillaryMaxillary
Central incisorCentral incisor 7-8 yrs7-8 yrs 10yrs10yrs
Lateral incisorLateral incisor 8-9 yrs8-9 yrs 11yrs11yrs
CuspidsCuspids 11-12yrs11-12yrs 13-15yrs13-15yrs
First bicuspidFirst bicuspid 10-11yrs10-11yrs 12-13yrs12-13yrs
Second bicuspidSecond bicuspid 10-12yrs10-12yrs 12-14yrs12-14yrs
First molarFirst molar 6-7yrs6-7yrs 9-10yrs9-10yrs
Second molarSecond molar 12-13yrs12-13yrs 14-16yrs14-16yrs

MandibularMandibular
Central incisorCentral incisor 6-7yrs6-7yrs 9yrs9yrs
Lateral incisorLateral incisor 7-8 yrs7-8 yrs 10yrs10yrs
CuspidCuspid 9-10yrs9-10yrs 12-14yrs12-14yrs
First bicuspidFirst bicuspid 10-12yrs10-12yrs 12-12-
13yrs13yrs
Second bicuspidSecond bicuspid 11-12yrs11-12yrs 13-14yrs13-14yrs
First molarFirst molar 6-7yrs6-7yrs 9-10yrs9-10yrs
Second molarSecond molar 11-13yrs11-13yrs 14-15yrs14-15yrs

Inter Transitional periodInter Transitional period
(1.5 years)(1.5 years)
This is a stable phase where little changes takesThis is a stable phase where little changes takes
place. Teeth present are permanent incisors andplace. Teeth present are permanent incisors and
first molar along with deciduous canines andfirst molar along with deciduous canines and
molars.molars.
Other features of this stageOther features of this stage :-:-
Any asymmetry in emergence andAny asymmetry in emergence and
corresponding differences in height levels ofcorresponding differences in height levels of
crown lengths between right and left teeth arecrown lengths between right and left teeth are
made up.made up.
Ugly duckling stageUgly duckling stage

Root form of emerged incisors, caninesRoot form of emerged incisors, canines
and molars continue along withand molars continue along with
concomitant increase in alveolar processconcomitant increase in alveolar process
height.height.
Resorption of roots of deciduous molarsResorption of roots of deciduous molars

Second transitional phase:-Second transitional phase:-
It is characterized by the replacement of theIt is characterized by the replacement of the
deciduous molars and canines by the premolarsdeciduous molars and canines by the premolars
and permanent cuspids respectivelyand permanent cuspids respectively
The combined mesio-distal width of permanentThe combined mesio-distal width of permanent
canines and premolars in usually less than thatcanines and premolars in usually less than that
of deciduous canines and molars the surplusof deciduous canines and molars the surplus
space n called leeway space of Nance. Amountspace n called leeway space of Nance. Amount
of space is -of space is -
0.9 mm/segment in max. - 1.8mm total0.9 mm/segment in max. - 1.8mm total
1.7mm/segment in mandible;-3.4 mm total1.7mm/segment in mandible;-3.4 mm total

THE PERMANENT DENTTIONTHE PERMANENT DENTTION
The permanent dentition forms within the jawsThe permanent dentition forms within the jaws
soon after birth calcification begins at birth withsoon after birth calcification begins at birth with
the calcification of the cusps of the firstthe calcification of the cusps of the first
permanent molar and extends as late as thepermanent molar and extends as late as the
25th year of life. Complete calcification of incisor25th year of life. Complete calcification of incisor
crowns takes place by 4to 5 years and of thecrowns takes place by 4to 5 years and of the
other permanent teeth by 6to8 years except forother permanent teeth by 6to8 years except for
the third molars. Therefore the total calcificationthe third molars. Therefore the total calcification
period is about 10 years. The permanentperiod is about 10 years. The permanent
incisors develop lingual to the deciduousincisors develop lingual to the deciduous
incisors and move labials as they erupt. Theincisors and move labials as they erupt. The
premolars develop below the diverging roots ofpremolars develop below the diverging roots of
the deciduous molars.the deciduous molars.

At approximately 13 years of age all permanentAt approximately 13 years of age all permanent
teeth except third molars are fully erupted. Beforeteeth except third molars are fully erupted. Before
the deciduous incisors are shed, there are 48the deciduous incisors are shed, there are 48
teeth/parts of teeth present in the jaws.teeth/parts of teeth present in the jaws.
Features of the permanent dentitionFeatures of the permanent dentition::
Co-inciding midline.Co-inciding midline.
Class I molar relationship of the permanent firstClass I molar relationship of the permanent first
molar.molar.
Vertical overbite of about one third the clinicalVertical overbite of about one third the clinical
crown height of the mandibular central incisors.crown height of the mandibular central incisors.
OverjetOverjet : over jet and over bite decrease: over jet and over bite decrease
throughout the second decade of life due tothroughout the second decade of life due to
greater forward growth of the mandible.greater forward growth of the mandible.
Curve of speeCurve of spee : develops during transition and: develops during transition and
stabilizes in adulthood.stabilizes in adulthood.

ERUPTIONERUPTION
Eruption is the developmental process that movesEruption is the developmental process that moves
a tooth from its crypt position through the alveolara tooth from its crypt position through the alveolar
process into the oral cavity and to occlusion withprocess into the oral cavity and to occlusion with
its antagonist. During eruption of succedaneousits antagonist. During eruption of succedaneous
teeth:teeth:
Primary tooth resorbsPrimary tooth resorbs
Root of the permanent tooth lengthensRoot of the permanent tooth lengthens
Increase in the alveolar process heightIncrease in the alveolar process height
Permanent tooth moves through the bone.Permanent tooth moves through the bone.
Teeth do not begin to move occlusally untilTeeth do not begin to move occlusally until
crown formation is complete. It takes 2-5 years forcrown formation is complete. It takes 2-5 years for
posterior teeth to reach the alveolar crestposterior teeth to reach the alveolar crest
following crown completion and 12-20 months tofollowing crown completion and 12-20 months to
reach occlusion after reaching alveolar margin.reach occlusion after reaching alveolar margin.

SEQUENCE OF ERUPTIONSEQUENCE OF ERUPTION
There is wide variability in the sequence ofThere is wide variability in the sequence of
arrival of teeth in the mouth.arrival of teeth in the mouth.
Maxilla 6-1-2-4-3-5-7-or 6-1-2-4-5-3-7Maxilla 6-1-2-4-3-5-7-or 6-1-2-4-5-3-7
(most common)(most common)
Mandible 6-1-2-4-5-3-7 or 6-1-2-3-4-5-Mandible 6-1-2-4-5-3-7 or 6-1-2-3-4-5-
7(most common)7(most common)

Development of occlusion

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