1. Occlusion refers to the relationship between the teeth of the upper and lower jaws during normal function. Proper occlusion develops through growth of jaws and synchronous eruption of teeth. 2. From birth through adulthood, there are four periods of occlusal development: the neonatal period, primary dentition period, mixed dentition period, and permanent dentition period. Each period involves changes to the gums, eruption of specific teeth, and shifting relationships between teeth. 3. During the mixed dentition period, as permanent teeth erupt to replace primary teeth, the occlusion transitions through three phases involving early and late shifts in molar and canine relationships to achieve optimal occlusion. Space management and sequencing of

1. Introduction:
Term occlusionisderivedfromthe Latinword,“occlusio”;definedasthe relationshipbetweenall the
componentsof the masticatorysysteminnormal function,dysfunctionandparafunction.Anideal
occlusionisthe perfectinterdigitationof the upperandlowerteeth,whichisaresultof developmental
processconsistingof the three mainevents,jaw growth,toothformationanderuption
Evolution:
To developafunctional occlusionitbecame necessaryforthe teethandbonestodevelop
synchronously.Overaperiodof time there waslossor fusionof cranial andfacial bones,the numberof
boneshave reducedandthe dental formulahasalsoundergone changes.
Periods of Occlusal Development
o Neo-natal period.
o Primarydentitionperiod.
o Mixeddentitionperiod.
o Permanentdentitionperiod.
Neonatal Period
(lasts upto 6 months after birth)

2. Gum Pads:
• Alveolarprocessesatthe time of birth- gumpads.
• Pinkincolour,firmand are coveredbya dense layerof fibrousperiosteum.
• The gum pad soongetssegmentedbyagroove called transverse groove,& each segmentisa
developingtoothsite.
• The pads getdividedinto‘labio-buccal’&‘lingual portion’,bya dental groove.
• The groove betweenthe canineandthe 1st
molarregioniscalledthe lateral sulcus, useful for
judgingthe interarchrelationshipataveryearlystage.
• The uppergum pad ishorse shoe shaped& shows:
• Gingival groove:separates gum padfrom the palate.
• Dental groove: startsat the incisive papilla,extends backwardto touch the gingival groove
inthe canine region&then moveslaterallytoendin the molar region.
• Lateral sulcus .

3. • The lowergumpad is ‘U’ shapedandrectangular,characterizedby:
• Gingival groove:lingual extensionof the gum pads.
• Dental groove.
• Lateral sulcus.
Relationship of Gum Pads
o Anterioropen bite isseenatrestwithcontact onlyat the molarregion.
o Complete overjet.
o ClassII patternwithmaxillarygumpadbeingmore prominent.
o Mandible isdistal tothe maxillaof 2.7 mm- male and2.5- female. ( SillmanJH1938)
o The range of variationof thisdistal relationshipisfrom0 to 7 mm. . ( SillmanJH 1938)

4. Relationship of Gum Pads
o Mandibularlateral sulci liesposteriortomaxillarylateral sulci.
o Mandibularfunctional movementsare mainlyvertical,andtoa little extentantero-posterior.
Lateral movementsare absent.
o
Primary DentitionPeriod:
(Fromaroundthe 6th month to 6 years)
Chronology of Primary Dentition
Primary
(upper)
First evidence ofcalcification
(Weeksinutero)
Crown completed
(months)
Eruption
(months)
Root com
(years)
Central 14 (13-16) 11/2
10 11/2
Lateral 16 21/2
11 2
Canine 17 9 19 31/4
1st
molar 151/2
6 16 21/2
2nd
molar 19 11 29 3
Features Of Primary Dentition:
• Spacing- 2 typesof dentitionare seen:

5. • A) Spaced dentition- usuallyseeninthe deciduousdentitiontoaccommodate the larger
permanentteethinthe jaws.
• More prominentinthe anteriorregion,andare called ‘physiological spacing’or
‘developmental spacing’.
• Absence of spacesinthe primarydentitionisanindicationthatcrowdingof teethmayoccur
whenthe largerpermanentteetherupt.
• Most subhumanprimateshave itthroughoutlife anduse itfor interdigitationof the opposing
canines.Thisspace isusedfor earlymesial shift.
 Non- spaced dentition
 Teethare presentwithoutanyspacesinbetweenthe teeth
 Due to narrowdental archesor if teethare widerthanusual
 Usuallyindicatesindevelopingpermanentdentitionbutitisnotalwaysthe case
 Shallowoverjet&overbite.Initiallyadeepbite mayoccurdue to the fact that the deciduous
incisorsare more uprightthan theirsuccessors.The lowerincisal edgesoftencontactthe
cingulumareaof the maxillaryincisors.Thisdeepbite islaterreducedby:
 Eruptionof deciduousmolars.
 Attritionof incisors.
 Forwardmovementof the mandible due togrowth.
Molar Relationship:
The molar relationshipinthe primarydentitioncanbe classifiedinto3types:
o Straight/flushterminal plane.
o Mesial step.
o Distal step.
Flush Terminal Plane
• If the distal surface of maxillaryandmandibulardeciduoussecondmolarsare inthe same
vertical plane;thenitiscalledaflushterminal plane
Normal molarrelationshipinthe primarydentition,becausethe mesiodistal widthof the mandibular
molaris greaterthanthe mesiodistal widthof the maxillarymolar

6. Mesial Step
Distal surface of mandibulardeciduoussecondmolarismesial tothe distal surface of maxillary
deciduoussecondmolar.
Distal Step:
Distal surface of mandibularseconddeciduousmolarismore distal tothe distal surface of the maxillary
seconddeciduousmolar
Canine relationship:
 Relationshipof maxillary&mandibulardeciduouscaninnesisone of the moststable inprimary
dentition
 Classifiedas:
 Class1
 Class2
Mixed Dentition Period
(Around 6 years- 12 years):
The mixeddentitionperiodcanbe dividedintothree phases:
o First transitional period.
o Inter-transitional period.
Secondtransitional period
Eruption of 1st Permanent Molar:
The location& relationof the 1st
permanentmolardependsmuchuponthe distal surface of the upper&
lower2nd
deciduousmolar
Transition to Class I Molar Relation:
The shiftinlowermolarfroma flushterminal planetoa classI relationcanoccur in twoways:
Early shift.
Late shift.
Early Shift:
• Early shiftoccursduringthe earlymixeddentitionperiod.
• Since thisoccurs earlyinthe mixeddentition,itiscalledearlyshift.
Late Shift:
Thisoccurs in the late mixeddentitionperiodandisthuscalled late shift

7. Leeway Space of Nance:
• Describedby Nance in 1947
Maxilla:0.9 mm/segment=1.8 mm. Mandible:1.7 mm/segment=3.4mm
• Althoughthe deciduousposteriorsegmentof teethislargerthanthe permanentsegment,
converse istrue of the anteriorsegments
• Nance didnot consider large difference inmesiodistalsize betweenthe deciduousincisorteeth
& theirpermanentsuccessors–archneedstobe lookedinitstotality
• Maxillaryincisors,asa groupin one quadrant–3.2to 3.5 mm larger
• Mandibularincisors,asa group inone quadrant – 2.4 to 2.5 mm larger
• The latterfiguresbalance outorcancel the 1.7 mm of so calledleewayspace
• Moorrees-- measurementsof deciduous&permanentteethinthe mouthsobtainedby
longitudinalstudies, thereis no leeway space
• Total no.of permanentteethdestinedtoreplace total no.of deciduousteethinanaverage
child– slighlylessthan1mmmore space inmandibulararch,6mm more in maxillaryarch
• 1.7 mm leewayspace takenupbythe largerpermanentincisors,requiresmore distal eruption
of permanentcanines
• Allowsreductionof incisorcrowdinginmandibulararch
• If the permanentmolarswere allowedorevenencouragedtodriftmesiallyandutilize the
leewayspace –no enoughroomin the arch for the incisorsegment
• Initially –permanentincisorsare forcedintoacrowdedposition
• If molarsare heldstable,incisorswillutilizethe leewayspace,ultimatelythe average
mandibulararchwill have enoughroom forproperalignment
Secondary spacing:
• Term wascoinedby Baume
• Observedinclosedprimarydentition
• Secondaryspacingcan alsooccur duringthe eruptionof permanentcentral incisors

8. Influence of terminal plane on the position of 1st permanent molar:
Exchange of Incisors:
Duringthe firsttransitional periodthe deciduousincisorsare replacedbythe permanentincisors.The
mandibularcentral incisorsare usuallythe firsttoerupt.The permanentincisorsare considerablylarger
than the deciduousteeththeyreplace.Thisdifferencebetweenthe amountof space neededforthe
accomodationof the incisorsandthe amountof space available forthis,iscalled ‘Incisal liability’.
The incisal liabilityisroughlyabout 7.6mm inthe maxillaryarch& about 6 mm inthe mandibulararch
(Wayne).
Transition of Incisors:
The incisal liabilityisovercome bythe followingfactors:
Interdental physiological spacinginthe primaryincisorregion. (4mm inmaxillaryarch& 3 mm in
mandibulararch)

9. Increase in inter-canine arch width:
Significantamountof growthoccurswiththe eruptionof incisorsandcanines.
Increase in anterior lengthof the dental arches:
Permanentincisorseruptlabialtothe primaryincisorstoobtainan addedspace of around 2-3 mm.
Change in inclinationof permanentincisors:
Primaryteethare uprightbut permanentteethinclinetothe labial surface,thusdecreasingthe inter-
incisal angle fromabout151 degreesinthe deciduousdentitionto124 degreesinthe permanent
dentition.Thisincreasesthe archparameter.
Inter-Transitional Period:
Thisis a stable phase where little changestake place inthe dentition.The teethpresentare the
permanentincisorsandfirstmolaralongwiththe deciduouscaninesandmolars.Thisphase prepares
for the secondtransitional phase.Some of the featuresof thisstage are:
o Anyasymmetryinemergence andcorrespondingdifferencesinheightlevelsorcrownlengths
betweenthe rightandleftside teethare made up.
o Root formationof emergedincisors,andmolarscontinues,alongwithconcomitantincrease in
alveolarprocessheight.
o Resorptionof rootsof deciduouscaninesandmolars.
Second Transitional Period:
The secondtransitional periodischaracterizedbythe replacementof the deciduousmolarsandcanines
by the premolarsandpermanentcaninesrespectively.
At around10 yearsof age the deciduouscaninesshed,butjustbefore the sheddingthere isatransient
or self correctingmalocclusionseeninthe maxillaryincisorregionbetweenthe age of 8 – 9 years.
Ugly Duckling Stage
(Broadbent’s phenomenon:
Aroundthe age of 8 - 9 years,a midlinediastemaiscommonlyseeninthe upperarch,whichisusually
misinterpretedbythe parentsasa malocclusion.
Its typical featuresare:
o Flaringof the lateral incisors.
Maxillarymidline diastema

10. Crownsof canineson youngjawsimpinge ondevelopinglateralincisorroots,thusdrivingthe roots
mediallyandcausingthe crownstoflare laterally.
The roots of the central incisorsare alsoforcedtogether,thuscausingamaxillarymidline diastema
Withthe eruptionof the canines,the impingementfromthe rootsshiftincisallythusdrivingthe incisor
crownsmedially,resultinginclosure of the diastemaaswell asthe correctionof the flaredlateral
incisors.
Hence thisunaestheticmetamorphosis,eventuallyleadstoan aestheticresult.
Sequence of Eruption:
The caninesinthe upperarch eruptonlyafterthe premolarshave replacedthe deciduousmolars,
whereasthe canine eruptbefore the premolarsinthe lowerarch
SecondTransitional Period…Favorableocclusioninthisareaislargelydependenton:
Favorable eruptionsequence.
Satisfactorytoothsize toavailable space ratio.
Attainmentof normal
Eruption of permanentsecondmolars
 Before emergence- secondmolars,orientedinamesial &lingual direction

11.  Teeth- formedpalatally,guidedintoocclusionby ConeFunnel mechanism, upperpalatal cusps
(cone) slidesintothe lowerocclusal fossa(funnel)
 Arch lengthisreducedbymesial eruptive forces
 Thereby,crowdingif presentisaccentuated
The Permanent Dentition Period:
The permanentincisorsdeveloplingualtothe deciduousincisorsandmove labiallyastheyerupt.
The premolarsdevelopbelow the divergingrootsof the deciduousmolars
At approximately13yearsof age all permanentteethexceptthirdmolarsare fullyerupted
Vertical overbiteof aboutone thirdthe clinical crownheightof the mandibularcentral incisors.Overjet
and overbite decreasesthroughoutthe seconddecade of life due togreaterforwardgrowthof the
mandible.