Development of dentition / oral surgery courses

DEVELOPMENT OFDEVELOPMENT OF
DENTITIONDENTITION
INDIAN DENTAL ACADEMYINDIAN DENTAL ACADEMY
Leader in continuing DentalLeader in continuing Dental
EducationEducation
www.indiandentalacademy.comwww.indiandentalacademy.com

CONTENTSCONTENTS
 Introduction.Introduction.
 Evolutionary concept.Evolutionary concept.
 Development of tooth & its supportingDevelopment of tooth & its supporting
tissuestissues
 HistophysiologyHistophysiology
 Root formationRoot formation
 ChronologyChronology
 Occlusal developmentOcclusal development
 Predental PeriodPredental Period
 Deciduous Dentition periodDeciduous Dentition periodwww.indiandentalacademy.comwww.indiandentalacademy.com

 Mixed dentition periodMixed dentition period
 Phases of mixed dentitionPhases of mixed dentition
 Permanent dentition periodPermanent dentition period
 Self correcting malocclusionsSelf correcting malocclusions
 BibliographyBibliography

INTRODUCTION
 Purpose of studying the developmentPurpose of studying the development
of dentitionof dentition
1.1. To know the main course of the normalTo know the main course of the normal
development of human dentitiondevelopment of human dentition
2.2. The concept of evolution of toothThe concept of evolution of tooth
developmentdevelopment
3.3. Clinical features of dentitionClinical features of dentition
4.4. The most common developmentalThe most common developmental
disturbancesdisturbances

Stages of Tooth evolutionStages of Tooth evolution
 Graphically there are 4Graphically there are 4
stages of tooth evolution:stages of tooth evolution:
1. Reptilian stage1. Reptilian stage
(Haplodont).(Haplodont).
2. Early mammalian stage2. Early mammalian stage
(triconodont).(triconodont).
3. Triangular stage3. Triangular stage
(trituburcular molars).(trituburcular molars).
4. Quadritubercular molars.4. Quadritubercular molars.

Characteristics of human dentitionCharacteristics of human dentition
Teeth of the vertebrates are characterizedTeeth of the vertebrates are characterized
depending upon:depending upon:
a. a. Mode of attachment .Mode of attachment .
b. b. Number of successive sets.Number of successive sets.
c. Shape of teeth.c. Shape of teeth.
The way teeth are attached to jaws:The way teeth are attached to jaws:
a. Acrodonta. Acrodont
b. Pleurodontb. Pleurodont
c. Thecodontc. Thecodont

Depending on no. ofDepending on no. of successive sets of teeth:successive sets of teeth:
a. Polyphyodonta. Polyphyodont
b. Diphyodontb. Diphyodont
c. Monophyodontc. Monophyodont
According to type or shape of teeth:According to type or shape of teeth:
a. Homodonta. Homodont
b. Heterodontb. Heterodont

Dental FormulaDental Formula
 Permanent dentitionPermanent dentition
 I 3/3, C 1/1, PM 4/4, M 3/3 {11x2 = 44}I 3/3, C 1/1, PM 4/4, M 3/3 {11x2 = 44}
1111
 Deciduous dentitionDeciduous dentition
 I 2/2, C1/1, M 2/2 {5x2 = 20}I 2/2, C1/1, M 2/2 {5x2 = 20}
1111

 Permanent dentitionPermanent dentition
 II 22, C, C 11, PM, PM 22, M, M 33 {8x2 = 32}{8x2 = 32}
2 1 2 3 82 1 2 3 8
 Deciduous dentitionDeciduous dentition
 II 22 , C, C 11, M, M 22 {{ 55x2 = 20}x2 = 20}
2 1 2 52 1 2 5

DEVELOPMENT OF TOOTHDEVELOPMENT OF TOOTH
ANDAND
ITS SUPPORTING STRUCTURESITS SUPPORTING STRUCTURES

The primitive oral cavity or stomodeum isThe primitive oral cavity or stomodeum is
lined by stratified squamous epitheliumlined by stratified squamous epithelium
calledcalled oral ectoderm.oral ectoderm.
 The oral ectoderm contacts the endodermThe oral ectoderm contacts the endoderm
of the foregut to form the buccopharyngealof the foregut to form the buccopharyngeal
membranemembrane..

 The floor of theThe floor of the
stomodeum isstomodeum is
formed by theformed by the
BuccopharyngeBuccopharynge
al membranal membranee
that separatesthat separates
it from theit from the
foregutforegut
 Around 4Around 4thth
wkwk
of IUL thisof IUL this
membranemembrane
ruptures toruptures to
communicatecommunicate
with foregutwith foregut

PRIMARY EPITHELIAL BANDPRIMARY EPITHELIAL BAND
 After about 37After about 37
days ofdays of
development,development,
continuous bandcontinuous band
of thickenedof thickened
epithelium formsepithelium forms
around thearound the
mouth in themouth in the
presumptivepresumptive
upper &lowerupper &lower
jaws.jaws.

 Each band of epithelium ,called PRIMARYEach band of epithelium ,called PRIMARY
EPITHELIAL BAND, gives rise to twoEPITHELIAL BAND, gives rise to two
subdivisions:subdivisions:
1.1. Dental lamina.Dental lamina.
2.2. Vestibular laminaVestibular lamina

Vestibular laminaVestibular lamina

DENTALDENTAL
LAMINALAMINA
Dental lamina isDental lamina is
a band ofa band of
epithelium thatepithelium that
has invaded thehas invaded the
underlyingunderlying
ectomesenchymeectomesenchyme
along each of thealong each of the
horse shoehorse shoe
shaped futureshaped future
dental arches.dental arches.

 It serves as aIt serves as a
primordium for theprimordium for the
ectodermal portionectodermal portion
of the teethof the teeth

 The distal proliferation of dental lamina isThe distal proliferation of dental lamina is
responsible for location of germs of permanentresponsible for location of germs of permanent
molars in ramus of mandible & tuberosity ofmolars in ramus of mandible & tuberosity of
maxillamaxilla
 The successors of deciduous teeth developThe successors of deciduous teeth develop
from a lingual extension (successional laminafrom a lingual extension (successional lamina
develops 5develops 5th _th _
1010thth
month of IUL) of free end ofmonth of IUL) of free end of
dental lamina opposite to enamel organ ofdental lamina opposite to enamel organ of
each deciduous tootheach deciduous tooth
 Remnants of dental lamina persist as epithelialRemnants of dental lamina persist as epithelial
pearls or islands within the jaw & gingivapearls or islands within the jaw & gingivawww.indiandentalacademy.comwww.indiandentalacademy.com

DEVELOPMENTAL STAGESDEVELOPMENTAL STAGES
 Bud stageBud stage
 Cap stageCap stage
 Bell stage – advanced bell stageBell stage – advanced bell stage

BUD STAGEBUD STAGE

Cap stageCap stage

Enamel nicheEnamel niche

ENAMEL KNOTENAMEL KNOT

Enamel cordEnamel cord

BELL STAGEBELL STAGE

Inner enamel epitheliumInner enamel epithelium
 Inner enamel epithelium differentiate prior toInner enamel epithelium differentiate prior to
amelogenesis into Ameloblasts – 4-5 microns inamelogenesis into Ameloblasts – 4-5 microns in
diameter & about 40 microns highdiameter & about 40 microns high
 Cells of inner enamel epithelium exert anCells of inner enamel epithelium exert an
organizing influence on the underlyingorganizing influence on the underlying
mesenchymal cells in dental papilla which latermesenchymal cells in dental papilla which later
differentiate into odontoblastsdifferentiate into odontoblasts
 Basement membrane that separates theBasement membrane that separates the
enamel organ & the dental papilla just prior toenamel organ & the dental papilla just prior to
dentin formation is called membranadentin formation is called membrana
preformativapreformativa

Stratum intermediumStratum intermedium
 These cells haveThese cells have
well developedwell developed
cytoplasmiccytoplasmic
organelles, acidorganelles, acid
mucoploysaccharidmucoploysaccharid
es & glycogenes & glycogen
 It is absent in theIt is absent in the
part of the toothpart of the tooth
germ that outlinesgerm that outlines
root portions ofroot portions of
tooth but does nottooth but does not
form enamelform enamel

BREAK UP OF DENTAL LAMINABREAK UP OF DENTAL LAMINA

HistophysiologyHistophysiology
InitiationInitiation
 Requires ectomesenchymal – epithelialRequires ectomesenchymal – epithelial
interactioninteraction
 Specific cells within horseshoe shapedSpecific cells within horseshoe shaped
dental laminae have the potential to formdental laminae have the potential to form
enamel organ of certain teethenamel organ of certain teeth
 Lack of initiation – partial anodontia/Lack of initiation – partial anodontia/
anodontiaanodontia
 Abnormal initiation- supernumerary teethAbnormal initiation- supernumerary teethwww.indiandentalacademy.comwww.indiandentalacademy.com

ProliferationProliferation
 Enhanced proliferation after initiationEnhanced proliferation after initiation
results in bud, cap & bell stageresults in bud, cap & bell stage
 Causes regular changes in the size &Causes regular changes in the size &
proportions of the growing toothproportions of the growing tooth
germgerm

HistodifferentiationHistodifferentiation

MorphodifferentiationMorphodifferentiation
 The basic form or the relative size of theThe basic form or the relative size of the
future tooth is establishedfuture tooth is established
 Occurs by differential growth–Occurs by differential growth–
proliferationproliferation
 DEJ & DCJ are characteristic for eachDEJ & DCJ are characteristic for each
type of tooth & act as blueprint patterntype of tooth & act as blueprint pattern
 Ameloblast- enamelAmeloblast- enamel
 Odontoblast- dentinOdontoblast- dentin
 Cementoblast- cementumCementoblast- cementum
 This gives completed tooth itsThis gives completed tooth its
characteristic form & sizecharacteristic form & sizewww.indiandentalacademy.comwww.indiandentalacademy.com

AppositionApposition
 It is the deposition of matrix of hardIt is the deposition of matrix of hard
dental structuresdental structures
 Characterized by rhythmic depositionCharacterized by rhythmic deposition
of extracellular matrix which is ofof extracellular matrix which is of
itself incapable of further growthitself incapable of further growth

TIME LINE OF HUMAN TOOTHTIME LINE OF HUMAN TOOTH
DEVELOPMENTDEVELOPMENT
AGE DEVELOPMENTALAGE DEVELOPMENTAL
(IUL) CHARACTERISTCS(IUL) CHARACTERISTCS
42-48 days dental lamina formation.42-48 days dental lamina formation.
55-56 days bud stage:deciduous I,C&M.55-56 days bud stage:deciduous I,C&M.
14weeks bell stage for deciduous teeth;14weeks bell stage for deciduous teeth;
bud stage for permanent teeth.bud stage for permanent teeth.
18weeks dentin &functional ameloblasts in18weeks dentin &functional ameloblasts in
deciduous teeth.deciduous teeth.
32weeks dentin & functional ameloblast in32weeks dentin & functional ameloblast in
permanent first molars.permanent first molars.

Root formationRoot formation

Life cycle of tooth (Schour I &Life cycle of tooth (Schour I &
Massler M 1940)Massler M 1940)

(NOLLA 1952)(NOLLA 1952)

Stages of tooth eruptionStages of tooth eruption
1.1. Pre-Emergence eruption-Pre-Emergence eruption- during early part ofduring early part of
tooth formation called follicular phase, thetooth formation called follicular phase, the
follicle enlarges concentrically in everyfollicle enlarges concentrically in every
direction.direction.
 It may slightly move facially within alveolarIt may slightly move facially within alveolar
bone but with no or little eruptive movementbone but with no or little eruptive movement
 The tooth starts to erupt & the pre-emergentThe tooth starts to erupt & the pre-emergent
spurt phase of eruption begins, when crownspurt phase of eruption begins, when crown
formation is complete & root formation startsformation is complete & root formation starts

2. Post emergent eruption2. Post emergent eruption
a. The tooth emerges through gingiva & movesa. The tooth emerges through gingiva & moves
into occlusal contact with its antemere. Duringinto occlusal contact with its antemere. During
this phase, a tooth typically erupts about 4 mmthis phase, a tooth typically erupts about 4 mm
in 14 wksin 14 wks
b. Thereafter there is relatively slower velocity ofb. Thereafter there is relatively slower velocity of
eruptioneruption
c. After the teeth are in function they continue toc. After the teeth are in function they continue to
erupt at the same rate as jaws unless there iserupt at the same rate as jaws unless there is
occlusal wear or loss of opposing toothocclusal wear or loss of opposing tooth
d. Pdl is the major contributor of eruptive forces.d. Pdl is the major contributor of eruptive forces.
Principal fibers are now well oriented &Principal fibers are now well oriented &
attached firmly to alveolar boneattached firmly to alveolar bonewww.indiandentalacademy.comwww.indiandentalacademy.com

d. The primary eruption mechanism isd. The primary eruption mechanism is
thought to be either contraction ofthought to be either contraction of
collagen as it matures or tractioncollagen as it matures or traction
from contractile fibroblasts.from contractile fibroblasts.
e. Vascular effects similar to pree. Vascular effects similar to pre
emergent eruption may alsoemergent eruption may also
contributecontribute

Stages of tooth eruptionStages of tooth eruption
Essentials of Oral Histology and Embryology. James Avery, 2Essentials of Oral Histology and Embryology. James Avery, 2ndnd
editionedition

FACTORS AFFECTING DEVELOPMENT OFFACTORS AFFECTING DEVELOPMENT OF
DENTITIONDENTITION
A. Systemic factors:A. Systemic factors:
An accelerating effect on whole dentition isAn accelerating effect on whole dentition is
very rare but has been reported to be due tovery rare but has been reported to be due to
1.hyperthyroidism1.hyperthyroidism
2.hyperpituitarism2.hyperpituitarism
3.Turner’s syndrome3.Turner’s syndrome
A retarding effect :A retarding effect :
Delayed eruption in both primary andDelayed eruption in both primary and
permanent dentition.permanent dentition.

 Due to syndromes and systemic factors,Due to syndromes and systemic factors,
the most common are :-the most common are :-
 HypopitutarismHypopitutarism
 HypothyroidismHypothyroidism
 Cleidocranial dysostosisCleidocranial dysostosis
 Downs syndromeDowns syndrome
 AchondroplasiaAchondroplasia
 Hypovitaminosis (A&D)Hypovitaminosis (A&D)
 Amelogenesis imperfectaAmelogenesis imperfecta
 Osteopetrosis.Osteopetrosis. www.indiandentalacademy.comwww.indiandentalacademy.com

B. Local factors:B. Local factors:
 Aberrant tooth positionAberrant tooth position
 Lack of space in the archLack of space in the arch
 Very early loss of predecessorVery early loss of predecessor
 Ectopic eruptionEctopic eruption
 Congenital absence of teethCongenital absence of teeth
 Ankylosis of predecessorAnkylosis of predecessor
 Retained toothRetained tooth
 Persisting deciduous root remnantsPersisting deciduous root remnants
 Arrested tooth formation (trauma)Arrested tooth formation (trauma)
 Supernumerary toothSupernumerary tooth
 TumorTumor
 CystCyst
 Abnormal habit exerting muscular forces.Abnormal habit exerting muscular forces.

 The development of occlusion can beThe development of occlusion can be
divided into the following phases:-divided into the following phases:-
[1] PREDENTATE PHASE[1] PREDENTATE PHASE
(0 to 6 months)(0 to 6 months)
[2] THE DECIDUOUS DENTITION[2] THE DECIDUOUS DENTITION
(6 months to 6 yrs)(6 months to 6 yrs)
[3] THE MIXED DENTITION[3] THE MIXED DENTITION
(6 yrs to 12 yrs)(6 yrs to 12 yrs)
[4] THE PERMANENT DENTITION[4] THE PERMANENT DENTITION
(12 yrs onwards)(12 yrs onwards)
Phases of occlusalPhases of occlusal
developmentdevelopment

PREDENTATE PRIODPREDENTATE PRIOD
 Refers to the time from birth till theRefers to the time from birth till the
eruption of the first deciduous teeth ineruption of the first deciduous teeth in
oral cavity.oral cavity.
 The alveolar arches of an infant areThe alveolar arches of an infant are
called gum padscalled gum pads
 They are firm & pink structures with aThey are firm & pink structures with a
definite formdefinite form
 Each gum pad is divided into 10Each gum pad is divided into 10
segments by transverse groovessegments by transverse grooveswww.indiandentalacademy.comwww.indiandentalacademy.com

Upper gum padUpper gum pad

Lower gum padLower gum pad

 At rest the gum
pads are separated
by tongue lying
over lower gum
pad
Relationship of gum padsRelationship of gum pads

 Lower gum pad being smaller, the lateralLower gum pad being smaller, the lateral
sulcus of lower gum pad lies distal to thatsulcus of lower gum pad lies distal to that
of upperof upper
 There is variable overjet with contactThere is variable overjet with contact
only in first molar segmentsonly in first molar segments
 During function- mainly verticalDuring function- mainly vertical
movement, little A-P & no lateralmovement, little A-P & no lateral
movementmovement

Growth of gum padsGrowth of gum pads
 At birth the width of gum pads are inadequateAt birth the width of gum pads are inadequate
to accommodate all incisorsto accommodate all incisors
 Growth is rapid during first year after birthGrowth is rapid during first year after birth
 Growth is more in transverse direction & inGrowth is more in transverse direction & in
labio- lingual directionlabio- lingual direction
 Due to growth, segments of each gum padsDue to growth, segments of each gum pads
becomes prominentbecomes prominent

 When teeth are
present at the time of
birth they are called
natal teeth
 When they erupt
during the period
between birth & 30
days they are called
neo natal teeth
 INCIDENCE-INCIDENCE-
NATAL-1:1000NATAL-1:1000
NEONATAL-1:30000NEONATAL-1:30000www.indiandentalacademy.comwww.indiandentalacademy.com

DECIDUOUS OR PRIMARYDECIDUOUS OR PRIMARY
DENTITIONDENTITION
 The stage starts after eruption of theThe stage starts after eruption of the
first primary teeth until the eruptionfirst primary teeth until the eruption
of the first permanent tooth.of the first permanent tooth.
 Various features that can be seen inVarious features that can be seen in
deciduous dentition are-deciduous dentition are-

 Overjet- is theOverjet- is the
horizontalhorizontal
relationship or therelationship or the
distance betweendistance between
the most protrudedthe most protruded
maxillary centralmaxillary central
incisor and theincisor and the
oppositeopposite
mandibular centralmandibular central
incisor. Theincisor. The
average in primaryaverage in primary
dentition isdentition is
between 1-2 mm.between 1-2 mm.

 overbite- amount ofoverbite- amount of
vertical overlapvertical overlap
between thebetween the
maxillary andmaxillary and
mandibular centralmandibular central
incisor.incisor.
The average is 2mmThe average is 2mm

 Canine relationship- relationship ofCanine relationship- relationship of
the maxillary and mandibularthe maxillary and mandibular
deciduous canines. Can be classifieddeciduous canines. Can be classified
asas
 -Class I when mandibular canine-Class I when mandibular canine
interdigitates in embrasure betweeninterdigitates in embrasure between
the maxillary lateral and caninethe maxillary lateral and canine
 -Class II when mandibular canine-Class II when mandibular canine
interdigitates distal to embrasure.interdigitates distal to embrasure.

SpacingSpacing
 Two types of dentition are presentTwo types of dentition are present
[A] spaced dentition-spaced is[A] spaced dentition-spaced is
supposed to be good as spaces insupposed to be good as spaces in
between the teeth can be utilized forbetween the teeth can be utilized for
adjustment of permanent successorsadjustment of permanent successors
which are always larger in sizewhich are always larger in size
compared to the deciduous teethcompared to the deciduous teeth

a. primate spaces ora. primate spaces or
Anthropoid or Simian spacesAnthropoid or Simian spaces

- A- Are generalizedre generalized
spaces, which varyspaces, which vary
fromfrom
0 TO 8mm with0 TO 8mm with
average of 4mm inaverage of 4mm in
maxillary archmaxillary arch
1 TO 7mm with1 TO 7mm with
average of 3mm inaverage of 3mm in
mandibular archmandibular arch
b. Physiologic or developmentalb. Physiologic or developmental
spacesspaces

[b] Nonspaced dentition-[b] Nonspaced dentition-

Molar relationshipMolar relationship
 Described in terms of the relationshipDescribed in terms of the relationship
between terminal planes.between terminal planes.
 Terminal planes are the distal surfaces ofTerminal planes are the distal surfaces of
the maxillary and mandibular secondthe maxillary and mandibular second
primary molars.primary molars.
 It is of great importance to the clinicianIt is of great importance to the clinician
because the erupting first permanentbecause the erupting first permanent
molars are guided by the distal surfacesmolars are guided by the distal surfaces
of the second primary molars as theyof the second primary molars as they
erupt into occlusion.erupt into occlusion.

[1][1] Flush TerminalFlush Terminal
or vertical planeor vertical plane
type-the distaltype-the distal
surface of thesurface of the
upper and lowerupper and lower
teeth are in ateeth are in a
vertical straightvertical straight
plane.(59.1%)plane.(59.1%)
Terminal planesTerminal planes

 Mesial stepMesial step –the–the
terminal plane ofterminal plane of
the mandibularthe mandibular
second deciduoussecond deciduous
molar is situatedmolar is situated
anterior to that ofanterior to that of
the maxillarythe maxillary
second deciduoussecond deciduous
molar (19.1%)molar (19.1%)

 3]3] Distal stepDistal step
type- the distaltype- the distal
surface of thesurface of the
lower primarylower primary
molar is distalmolar is distal
to distal surfaceto distal surface
the upperthe upper
molar(4.8%)molar(4.8%)

ARCH DIMENSIONARCH DIMENSION
 Dimension of the arch can be defined inDimension of the arch can be defined in
the form of the termsthe form of the terms
-Arch length-Arch length
-Arch circumference-Arch circumference
-Intercanine width-Intercanine width
-Intermolar width-Intermolar width

Safety Valve MechanismSafety Valve Mechanism
 Mandibular intercanine width - complete by 9-Mandibular intercanine width - complete by 9-
10 years of age in both boys and girls.10 years of age in both boys and girls.
 Maxillary intercanine width - complete by 12Maxillary intercanine width - complete by 12
years of age in girls but continues to grow untilyears of age in girls but continues to grow until
18 years of age in boys.18 years of age in boys.
 The final horizontal growth increments in theThe final horizontal growth increments in the
mandible causes a forward movement of themandible causes a forward movement of the
mandibular base with its teeth. This basalmandibular base with its teeth. This basal
change eliminates any flush terminal planechange eliminates any flush terminal plane
tendencies that have persisted beyond thetendencies that have persisted beyond the
mixed dentition.mixed dentition.

 But , the bodily mandibular thrustBut , the bodily mandibular thrust
forward is unmatched by comparableforward is unmatched by comparable
maxillary horizontal growth changes.maxillary horizontal growth changes.
Hence, the maxillary intercanineHence, the maxillary intercanine
dimension serves as a "dimension serves as a "safety valvesafety valve""
for pubertal growth spurts.for pubertal growth spurts.

 Not many changes occur till theNot many changes occur till the
eruption of the permanent teeth.eruption of the permanent teeth.
 Intermolar width changes during 3 toIntermolar width changes during 3 to
5 years of age5 years of age
2.0mm2.0mm in maxillain maxilla
1.5mm1.5mm in mandiblein mandible

MIXED DENTITIONMIXED DENTITION
PERIODPERIOD
 It starts with eruption of the firstIt starts with eruption of the first
permanent tooth and ends till all thepermanent tooth and ends till all the
deciduous teeth shed off.deciduous teeth shed off.
 During this period both theDuring this period both the
deciduous and permanent teeth aredeciduous and permanent teeth are
present in the mouth.present in the mouth.

VARIOUS PHASES OF MIXEDVARIOUS PHASES OF MIXED
DENTITION PERIODDENTITION PERIOD
[1] The first transition period[1] The first transition period
[2][2] Inter transitional periodInter transitional period
[3][3] Second transitional periodSecond transitional period

• Characterised byCharacterised by
1.1. Emergence of the first permanentEmergence of the first permanent
molarsmolars
2.2. Exchange of the deciduous incisors withExchange of the deciduous incisors with
the permanent incisors.the permanent incisors.
1. The first transitional period1. The first transitional period

[1][1] Emergence of the firstEmergence of the first
permanent molarspermanent molars
The mandibular first permanent molar is theThe mandibular first permanent molar is the
first permanent tooth to erupt at aroundfirst permanent tooth to erupt at around
6years of age.6years of age.
They are guided into the dental arch by theThey are guided into the dental arch by the
distal surface of the deciduous second molardistal surface of the deciduous second molar

MOVEMENT OF PERMANENT MOLARMOVEMENT OF PERMANENT MOLAR
TAKES PLACE IN TWO WAYSTAKES PLACE IN TWO WAYS
 EARLY MESIAL SHIFTEARLY MESIAL SHIFT
 The eruptive force of the first permanentThe eruptive force of the first permanent
molar pushes the deciduous first andmolar pushes the deciduous first and
second molars forward in the arch to closesecond molars forward in the arch to close
the primate space and establish a class Ithe primate space and establish a class I
molar relationship.molar relationship.
 Since this occurs early in the mixedSince this occurs early in the mixed
dentition period it is called “ early shift”.dentition period it is called “ early shift”.

 LATE MESIAL SHIFT – When no spacesLATE MESIAL SHIFT – When no spaces
exists the erupting permanent molars areexists the erupting permanent molars are
unable to move forward to establish classunable to move forward to establish class
I relationship.I relationship.
 In these cases when the deciduous secondIn these cases when the deciduous second
molars exfoliate the permanent firstmolars exfoliate the permanent first
molars drift mesially utilizing the leewaymolars drift mesially utilizing the leeway
space.space.
 This occurs in the late mixed dentitionThis occurs in the late mixed dentition
period hence called “ LATE SHIFT”.period hence called “ LATE SHIFT”.

Leeway space-the sumLeeway space-the sum
of the mesiodistalof the mesiodistal
width of the primarywidth of the primary
canine and 1canine and 1stst
& 2& 2ndnd
molar is larger thanmolar is larger than
the sum of theirthe sum of their
succedaneous teethsuccedaneous teeth
This difference isThis difference is
called leeway space ofcalled leeway space of
Nance.Nance.

According toAccording to NanceNance
MAXILLA : 0.9mm/ segment= 1.8mmMAXILLA : 0.9mm/ segment= 1.8mm
MANDIBLE : 1.7mm/ segment= 3.4mmMANDIBLE : 1.7mm/ segment= 3.4mm
According toAccording to MoyersMoyers
2.6 mm in maxilla and 6.2 mm in mandible.2.6 mm in maxilla and 6.2 mm in mandible.
However, this leeway space varies considerablyHowever, this leeway space varies considerably
and should be measured on each patient.and should be measured on each patient.

 Occlusal relationship of primary & permanent molar
 The amount of differential mandibular growth & molar
shift into the leeway space determines the molar
relation

 Distal step leads to class II in 38.6%Distal step leads to class II in 38.6%
casescases
 Flush terminal leads to class IFlush terminal leads to class I
relationship in 58.9% of casesrelationship in 58.9% of cases
 Mesial step leads to class III in 2.5%Mesial step leads to class III in 2.5%
casescases

[2] INCISAL TRANSITION[2] INCISAL TRANSITION
(ages 6 ½ to 8 ½)(ages 6 ½ to 8 ½)
 The permanent incisors are considerably largerThe permanent incisors are considerably larger
than the deciduous teeth they replace.than the deciduous teeth they replace.
 This difference between the amount of spaceThis difference between the amount of space
needed for the accommodation of the incisorsneeded for the accommodation of the incisors
and the amount of space available for this isand the amount of space available for this is
called “incisal liability”.called “incisal liability”.
It is about 7mm in maxillary archIt is about 7mm in maxillary arch
and about 5mm in mandibular archand about 5mm in mandibular arch

The incisal liability is overcome by :The incisal liability is overcome by :
Utilization of the interdental spaces inUtilization of the interdental spaces in
primary dentitionprimary dentition
Averages :- 4mm in the maxillary archAverages :- 4mm in the maxillary arch
3mm in the mandibular arch3mm in the mandibular arch
Lack of interdental spacing is a seriousLack of interdental spacing is a serious
handicap toward normal incisorhandicap toward normal incisor
alignment.alignment.

INCREASE IN INTERCANINE WIDTHINCREASE IN INTERCANINE WIDTH
 Males – maxilla 6mmMales – maxilla 6mm
(2-18 yrs) mandible 4mm(2-18 yrs) mandible 4mm
 Females – maxilla 4.5mmFemales – maxilla 4.5mm
(2-18 yrs) mandible 4mm(2-18 yrs) mandible 4mm

The interincisalThe interincisal
angle is 150angle is 150
degree in thedegree in the
primary dentitionprimary dentition
whereas it is aboutwhereas it is about
123 degree in123 degree in
permanentpermanent
dentition whichdentition which
makes permanentmakes permanent
intercanine archintercanine arch
length increase bylength increase by
approximatelyapproximately
3mm.3mm. www.indiandentalacademy.comwww.indiandentalacademy.com

The permanentThe permanent
maxillary centralmaxillary central
incisors are flaredincisors are flared
out on theirout on their
longitudinal axis likelongitudinal axis like
an inverse “v”. Thisan inverse “v”. This
is due to theis due to the
presence of thepresence of the
erupting permanenterupting permanent
canines in thecanines in the
developing roots ofdeveloping roots of
the lateral incisors,the lateral incisors,
the crown flarethe crown flare
producing a midlineproducing a midline
diastemadiastema www.indiandentalacademy.comwww.indiandentalacademy.com

 The diastema between the central incisors mayThe diastema between the central incisors may
vary from 1.0-3.0mm.vary from 1.0-3.0mm.
 This stage is called “ the ugly duckling stage”This stage is called “ the ugly duckling stage”
(Broadbent in 1937)(Broadbent in 1937)
 This is a self correcting phenomenon and theThis is a self correcting phenomenon and the
diastema closes by the time the maxillarydiastema closes by the time the maxillary
canine erupt and does not require orthodonticcanine erupt and does not require orthodontic
interventionintervention
 It would be most hazardous to placeIt would be most hazardous to place
appliances at this critical stage.appliances at this critical stage.
 The chances ofThe chances of damage to the apicesdamage to the apices of theof the
maxillary lateral incisors and the possibility ofmaxillary lateral incisors and the possibility of
deflecting the permanent caninesdeflecting the permanent canines fromfrom
their normal path of eruption are great.their normal path of eruption are great.www.indiandentalacademy.comwww.indiandentalacademy.com

2. Inter transitional period
 Lasts for about 1.5 yrsLasts for about 1.5 yrs
 Under the influence of tongue mandibularUnder the influence of tongue mandibular
lateral incisors attain proper sites & theirlateral incisors attain proper sites & their
lingual location is eliminatedlingual location is eliminated
 Small rotations are corrected by pressureSmall rotations are corrected by pressure
exerted by tongue & lipsexerted by tongue & lips
 There is wearing of deciduous teeth withThere is wearing of deciduous teeth with
attrition of cusp tips & occlusal morphologyattrition of cusp tips & occlusal morphology
approaching that of a planeapproaching that of a plane

• Starts around 9-10 yrs of age with theStarts around 9-10 yrs of age with the
shedding of posterior teethshedding of posterior teeth
• After the eruption of incisors there is pause ofAfter the eruption of incisors there is pause of
about 1 to 2 yrsabout 1 to 2 yrs
• Next tooth to erupt is lower cuspid & 1Next tooth to erupt is lower cuspid & 1stst
bicuspid at 9-10 yrs then maxillary cuspids &bicuspid at 9-10 yrs then maxillary cuspids &
bicuspidsbicuspids
• The period is terminated by the appearance ofThe period is terminated by the appearance of
22ndnd
molars at 12 yrsmolars at 12 yrs
3. Second transitional period3. Second transitional period

 Transition from ugly duckling to mature stageTransition from ugly duckling to mature stage
dentition is also calleddentition is also called prepubertal periodprepubertal period
 Most commonMost common sequence of eruption ofsequence of eruption of
permanent maxillary teeth 4-3-5 & mandible ispermanent maxillary teeth 4-3-5 & mandible is
3-4-53-4-5
 Crowding is common at this stage but getsCrowding is common at this stage but gets
corrected after exfoliation of 2nd primary molarcorrected after exfoliation of 2nd primary molar
 Second molars begin to erupt after dental archSecond molars begin to erupt after dental arch
upto 1upto 1stst
molar is establishedmolar is established
 Dental arch length is reduced prior to eruptionDental arch length is reduced prior to eruption
of 2of 2ndnd
molar by mesial forcemolar by mesial force

PERMANENT DENTITIONPERMANENT DENTITION
STAGESTAGE
• Starts afterStarts after
shedding of the lastshedding of the last
primary tooth andprimary tooth and
the eruption of allthe eruption of all
the permanentthe permanent
teeth excludingteeth excluding
third molars.third molars.
Sequence of eruption

DEVELOPMENT OF PERMANENT DENTITION
 Permanent dentition forms within the jaws
soon after birth except for cusps of 1st
permanent molars which form before birth
 Permanent incisors develop lingual or palatal to
deciduous incisors
 The premolars develop below the diverging
roots of deciduous molars

 Calcification begins at birth with theCalcification begins at birth with the
calcification of cusps of 1st permanent molars &calcification of cusps of 1st permanent molars &
extends as late as the 25th yr of lifeextends as late as the 25th yr of life
 Complete calcification of incisor crowns takesComplete calcification of incisor crowns takes
place by 4-5 yrs & of other permanent teeth byplace by 4-5 yrs & of other permanent teeth by
6-8 yrs except for the 3rd molars6-8 yrs except for the 3rd molars
 At approximately 13 yrs of age all permanentAt approximately 13 yrs of age all permanent
teeth except 3rd molars are fully eruptedteeth except 3rd molars are fully erupted

Chronology of Human Permanent DentitionChronology of Human Permanent Dentition

Self correctingSelf correcting
malocclusionsmalocclusions

7/2/2008 107www.indiandentalacademy.comwww.indiandentalacademy.com

BibliographyBibliography
 Tencate A.R.; Development of tooth and itsTencate A.R.; Development of tooth and its
supporting tissues; oral histology,supporting tissues; oral histology,
development structure and function;sixthdevelopment structure and function;sixth
edition.edition.
 Orbans oral Histology andOrbans oral Histology and
embryology;development and growth of teeth;embryology;development and growth of teeth;
tenth edition.28-48tenth edition.28-48
 Shobha Tandon text book of pedodontics; firstShobha Tandon text book of pedodontics; first
edition.100-120edition.100-120
 Proffit William R. : ContemporaryProffit William R. : Contemporary
Orthodontics,ed.3,2006, C.V . MosbyOrthodontics,ed.3,2006, C.V . Mosbywww.indiandentalacademy.comwww.indiandentalacademy.com

 Arthi Rao; Principles and Practice of Pedodontics; firstArthi Rao; Principles and Practice of Pedodontics; first
editionedition
 Bishara Sameer E.,Text book of Orthodontics,W.B.Bishara Sameer E.,Text book of Orthodontics,W.B.
Saunders, 2001Saunders, 2001
 Robert E Moyers, Handbook Of Orthodontics,4Robert E Moyers, Handbook Of Orthodontics,4thth
Edition,1973Edition,1973
 Damle S.G.; Text book of pediatric dentistry ;secondDamle S.G.; Text book of pediatric dentistry ;second
edition.edition.
 GLOSSARY OF ORTHODONTIC TERMSGLOSSARY OF ORTHODONTIC TERMS
 Ash & Stanley Nelson, Dental Anatomy, Physiology &Ash & Stanley Nelson, Dental Anatomy, Physiology &
Occlusion, 8Occlusion, 8thth
Edition, ElsevierEdition, Elsevier
 James Avery,Essentials of Oral Histology andJames Avery,Essentials of Oral Histology and
Embryology., 2nd editionEmbryology., 2nd edition
 Graber T.M :Orthodontics Principles And Practice, ThirdGraber T.M :Orthodontics Principles And Practice, Third
ed., Philadelphia 1996, W.B. Saunders Companyed., Philadelphia 1996, W.B. Saunders Company

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