Development of occlusion

DEVELOPMENT OF
OCCLUSION
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DEVELOPMENT OF TEETH
 The first sign of tooth developmentThe first sign of tooth development
appears late in the third embryonicappears late in the third embryonic
week. Both ectodermal and mesodermalweek. Both ectodermal and mesodermal
tissue contribute to the formation of thetissue contribute to the formation of the
teeth. The epithelial dental organ whichteeth. The epithelial dental organ which
molds the shape of the entire tooth andmolds the shape of the entire tooth and
is responsible for the formation ofis responsible for the formation of
Enamel is derived from the ectoderm ofEnamel is derived from the ectoderm of
oral cavity. The other parts of the toothoral cavity. The other parts of the tooth
including dentin, pulp, cementum andincluding dentin, pulp, cementum and
periodontal ligament arise fromperiodontal ligament arise from
mesodermmesoderm www.indiandentalacademy.com

 The teeth progress through a series ofThe teeth progress through a series of
developmental stages which have beendevelopmental stages which have been
arbitrarily defined as followsarbitrarily defined as follows
a)a) The dental lamina and bud stageThe dental lamina and bud stage
b)b)The cap stageThe cap stage
c)c) The Bell stageThe Bell stage
d) The Hertwig’s epithelial root sheath andd) The Hertwig’s epithelial root sheath and
root formation stageroot formation stage

Bud Stage
 During the 6During the 6thth
week inutero, a thickening ofweek inutero, a thickening of
the oral epithelium in the area of futurethe oral epithelium in the area of future
dental arch occurs as a result of Cellulardental arch occurs as a result of Cellular
Proliferation and extends along the entire freeProliferation and extends along the entire free
margin of Jaw. This represents themargin of Jaw. This represents the
Primordium of ectodermal portion of teethPrimordium of ectodermal portion of teeth
called the dental lamina from each dentalcalled the dental lamina from each dental
lamina 10 oval swellings, the buds, which arelamina 10 oval swellings, the buds, which are
precursors of Primary dentition arise at 10precursors of Primary dentition arise at 10
different points corresponding to futuredifferent points corresponding to future
position of the primary teeth.position of the primary teeth.

Cap Stage
 By differential proliferation, the budsBy differential proliferation, the buds
progress into cap stage which isprogress into cap stage which is
characterized by shallow invagination oncharacterized by shallow invagination on
deep surface of bud. The peripheral cells ofdeep surface of bud. The peripheral cells of
cap stage appear in two portions, outer andcap stage appear in two portions, outer and
inner enamel epithelium. Outer cells of theinner enamel epithelium. Outer cells of the
cap are cuboidal and are called O.E.E. Thecap are cuboidal and are called O.E.E. The
cells lining the concavity of the cap becomecells lining the concavity of the cap become
tall columnar and called I.E.E. Between the 2tall columnar and called I.E.E. Between the 2
layers, the cells of epithelial dental organlayers, the cells of epithelial dental organ
separate by an increase in intercellular fluidseparate by an increase in intercellular fluid
and become arranged in stellate patternand become arranged in stellate pattern
called stellate Reticulum (or) Enamel pulp.called stellate Reticulum (or) Enamel pulp.

 Under the influence of proliferatingUnder the influence of proliferating
epithelium of dental organ, the mesodermalepithelium of dental organ, the mesodermal
tissue, which is partly covered by invaginatedtissue, which is partly covered by invaginated
portion of inner dental epithelium. Proliferatesportion of inner dental epithelium. Proliferates
and condenses to form dental papilla, whichand condenses to form dental papilla, which
is formative organ of dentin and precursor ofis formative organ of dentin and precursor of
pulp. The cells adjacent to inner dentalpulp. The cells adjacent to inner dental
epithelium eventually differentiate intoepithelium eventually differentiate into
odontoblasts.odontoblasts.
During this developmental period, thereDuring this developmental period, there
is a marginal condensation of mesenchymalis a marginal condensation of mesenchymal
tissue surrounding the outside border oftissue surrounding the outside border of
enamel organ and the dental papilla whichenamel organ and the dental papilla which
becomes organized into dental sac. Enamelbecomes organized into dental sac. Enamel
organ, dental papilla and dental follice areorgan, dental papilla and dental follice are
collectively called tooth germ.collectively called tooth germ.www.indiandentalacademy.com

Bell Stage
 With continued invagination and growth enamelWith continued invagination and growth enamel
organ progresses into bell stage. In this stage, cells oforgan progresses into bell stage. In this stage, cells of
inner dental epithelium which assume a positioninner dental epithelium which assume a position
similar to future crown of tooth differentiate intosimilar to future crown of tooth differentiate into
Ameloblasts. The peripheral influence of epitheliumAmeloblasts. The peripheral influence of epithelium
differentiates into odontoblasts.differentiates into odontoblasts.
 The dental lamina for all teeth except 1The dental lamina for all teeth except 1stst
permanentpermanent
molar, Proliferates at deep and to produce dentalmolar, Proliferates at deep and to produce dental
organ of permanentorgan of permanent successor.successor. The invaginatedThe invaginated
aspects of enamel organ covers most of dental papilla,aspects of enamel organ covers most of dental papilla,
which produces dentin in outer layers. As primarywhich produces dentin in outer layers. As primary
dentin is produced, dental papilla is converted todentin is produced, dental papilla is converted to
dental pulp. In later part of bell stage connectiondental pulp. In later part of bell stage connection
between dental and enamel organs begin tobetween dental and enamel organs begin to
disappear.disappear. www.indiandentalacademy.com

Root formation stage
 After enamel and dentin formation reachesAfter enamel and dentin formation reaches
future CEJ, roots of teeth begin to form. Thefuture CEJ, roots of teeth begin to form. The
shape of root is governed principally byshape of root is governed principally by
Hertwig’s epithelial sheath, which is formed inHertwig’s epithelial sheath, which is formed in
epithelial dental organ. After odontoblastepithelial dental organ. After odontoblast
produces dentin along contour established byproduces dentin along contour established by
sheath, the sheath disappears.sheath, the sheath disappears.
 This generally takes place between 6This generally takes place between 6thth
–14–14thth
week until 6week until 6thth
month and both enamel andmonth and both enamel and
dentin grow by bone apposition.dentin grow by bone apposition.

Development of Dental Arch
 It represents the changes that occur in mandible,It represents the changes that occur in mandible,
maxilla and their alveolar regions to providemaxilla and their alveolar regions to provide
adequate space and bone for teeth. Sinceadequate space and bone for teeth. Since
approximate time span for tooth eruption is from 6approximate time span for tooth eruption is from 6
months to 18 yrs dental arch developmental time ismonths to 18 yrs dental arch developmental time is
atleast 18 yrs.atleast 18 yrs.
 Most dimensional changes in dental arches occurMost dimensional changes in dental arches occur
during the time of eruption (or) exfoliation of teeth,during the time of eruption (or) exfoliation of teeth,
otherwise they are reasonably static. The greatestotherwise they are reasonably static. The greatest
rate of increase of dental arches occurs betweenrate of increase of dental arches occurs between
birth and 3 yrs. further increments from 4 to 18 yrsbirth and 3 yrs. further increments from 4 to 18 yrs
are comparatively small.are comparatively small.

Cont…
 The arch length mesial to 1The arch length mesial to 1stst
permanent molar maypermanent molar may
be longest during early primary dentition, in partbe longest during early primary dentition, in part
because of Posterior inter dental spaces. Changes inbecause of Posterior inter dental spaces. Changes in
the dental arch are measured by using archthe dental arch are measured by using arch
dimensions.dimensions.
 The usual arch dimensions areThe usual arch dimensions are
 1) widths at the canines, primary molars and 11) widths at the canines, primary molars and 1stst
permanent molars.permanent molars.
 It is important to keep in mind 3 important factsIt is important to keep in mind 3 important facts
when studying width changeswhen studying width changes
 a)Width dimensional increase involves alveolara)Width dimensional increase involves alveolar
process growth almost totally since there is littleprocess growth almost totally since there is little
skeletal width increase at this time.skeletal width increase at this time.

b)b) There are important clinical differences inThere are important clinical differences in
the magnitude and manner of width changesthe magnitude and manner of width changes
in maxilla and mandible. Dental arch widthin maxilla and mandible. Dental arch width
increases highly with vertical alveolarincreases highly with vertical alveolar
process growth. maxilla alveolar processprocess growth. maxilla alveolar process
diverse while mandible alveolar process arediverse while mandible alveolar process are
more parallel.more parallel.
c)c)Increase in dental arch width is closelyIncrease in dental arch width is closely
related to events of dental development, lessrelated to events of dental development, less
to endocrinally mediated events of overallto endocrinally mediated events of overall
skeletal growth.skeletal growth.

Cont…..
 The inter canine diameter increases onlyThe inter canine diameter increases only
slightly in the mandible and some of thisslightly in the mandible and some of this
increase is result of distal tipping of primaryincrease is result of distal tipping of primary
cuspids into primate space. In mandible thecuspids into primate space. In mandible the
only significant increase in inter canine widthonly significant increase in inter canine width
occurs during the eruption of incisors whenoccurs during the eruption of incisors when
the primary cuspids are moved distally intothe primary cuspids are moved distally into
primate spaces. It does not widen significantlyprimate spaces. It does not widen significantly
thereafter.thereafter.

Cont…
 Maxillary 1Maxillary 1stst
premolar width increasespremolar width increases
significantly more than the mandible,significantly more than the mandible,
especially in males. Although the alveolarespecially in males. Although the alveolar
process growth is almost vertical in theprocess growth is almost vertical in the
mandible, the crowns of first molarsmandible, the crowns of first molars
erupt tipped somewhat lingually and doerupt tipped somewhat lingually and do
not upright fully until the time ofnot upright fully until the time of
eruption of the second molars. As the 1eruption of the second molars. As the 1stst
molars upright, they cause an increasemolars upright, they cause an increase
in bimolar width, but this is not anin bimolar width, but this is not an
increase in the diameter of mandibleincrease in the diameter of mandible
itself.itself. www.indiandentalacademy.com

2. Arch length (Depth)
 It is measured at the midline from aIt is measured at the midline from a
point midway between the centralpoint midway between the central
incisors to a tangent touching the distalincisors to a tangent touching the distal
surfaces of the second primary molarssurfaces of the second primary molars
(or) second premolars. This does not(or) second premolars. This does not
have the clinical importance of thehave the clinical importance of the
circumference. Sometimes one-half ofcircumference. Sometimes one-half of
the circumference is referred to as ‘archthe circumference is referred to as ‘arch
length’.length’.

3. Circumference (Perimeter)
 This is usually measured from the distal surface ofThis is usually measured from the distal surface of
2nd primary molar around the arch over the contact2nd primary molar around the arch over the contact
points and incisal edges in a smoothed curve to thepoints and incisal edges in a smoothed curve to the
distal surface of 2nd primary molar of the oppositedistal surface of 2nd primary molar of the opposite
side.side.
 The reduction in mandible arch circumferenceThe reduction in mandible arch circumference
during the transitional and early adolescentduring the transitional and early adolescent
dentition is result of a) late mesial shift of the 1dentition is result of a) late mesial shift of the 1stst
permanent molars as leeway space is preempted b)permanent molars as leeway space is preempted b)
mesial drifting tendency of posterior teethmesial drifting tendency of posterior teeth
throughout the life c) slight amounts of interthroughout the life c) slight amounts of inter
proximal wear of teeth d) lingual positioning ofproximal wear of teeth d) lingual positioning of
incisors as a result of the differential mandibularincisors as a result of the differential mandibular
maxillary growth e) original tipped positions ofmaxillary growth e) original tipped positions of
incisors and molars.incisors and molars.

 The last point is a reflection of skeletalThe last point is a reflection of skeletal
pattern, steepness of occlusal plane andpattern, steepness of occlusal plane and
vertical alveolar growth which in some casesvertical alveolar growth which in some cases
i.e. where incisors are tipped lingually andi.e. where incisors are tipped lingually and
molars are tipped mesially, shortens archmolars are tipped mesially, shortens arch
perimeter markedly.perimeter markedly.
 The mandibular arch perimeter showsThe mandibular arch perimeter shows
great variability during natural development.great variability during natural development.
The variation is caused by differences inThe variation is caused by differences in
skeletal pattern, sex (women’s arches shortenskeletal pattern, sex (women’s arches shorten
more) and caries experience (it increasemore) and caries experience (it increase
perimeter loss).perimeter loss).

 Maxillary arch perimeter typicallyMaxillary arch perimeter typically
increases slightly although it has anincreases slightly although it has an
equal chance to either increase (or)equal chance to either increase (or)
decrease. The very markeddecrease. The very marked
difference in angulation of maxillarydifference in angulation of maxillary
permanent incisors as comparedpermanent incisors as compared
with the primary and greatwith the primary and great
increases in width probably accountincreases in width probably account
for tendency to preserve thefor tendency to preserve the
circumference of upper jaw evencircumference of upper jaw even
though the permanent molars arethough the permanent molars are
drifting mesially.drifting mesially.

 Dental development can be dividedDental development can be divided
intointo
 (1)(1) CalcificationCalcification
 (2)(2) EruptionEruption

Calcification
 Calcification of primary teeth are as follows:Calcification of primary teeth are as follows:
 Central incisorsCentral incisors -- 14 weeks14 weeks
 11stst
molarsmolars -- 15½ weeks15½ weeks
 Lateral incisorsLateral incisors - 16 weeks- 16 weeks
 CanineCanine - 17 weeks- 17 weeks
 22ndnd
molarmolar - 18 weeks- 18 weeks
 Maxillary teeth calcify before the mandibular teethMaxillary teeth calcify before the mandibular teeth
with the exception of mandibular canine whichwith the exception of mandibular canine which
calcifies before maxillary canine.calcifies before maxillary canine.

Calcification of permanent teeth
 It begins at birth, with the calcification of cusps of 1It begins at birth, with the calcification of cusps of 1stst
permanent molars and extends as late as 25permanent molars and extends as late as 25thth
year.year.
 At 5½ to 6 yrs, calcification of maxillary permanentAt 5½ to 6 yrs, calcification of maxillary permanent
canine is complete and the clinical emergence takescanine is complete and the clinical emergence takes
place soon after the completion of 1/3place soon after the completion of 1/3rdrd
of root isof root is
completed.completed.
 Girls are more advanced in calcification of permanentGirls are more advanced in calcification of permanent
teeth than boys. Permanent teeth eruption beginsteeth than boys. Permanent teeth eruption begins
between 6-8 yrs and extends to 21between 6-8 yrs and extends to 21stst
yr and frequentlyyr and frequently
much later. The teeth in mandible with the exceptionmuch later. The teeth in mandible with the exception
of 2nd premolars erupt in a short period of time thanof 2nd premolars erupt in a short period of time than
the maxillary teeth.the maxillary teeth.

Eruption of permanent teeth
 Pre emergent eruptionPre emergent eruption
 Two process are necessary i) there must beTwo process are necessary i) there must be
resorption of bone and primary tooth rootsresorption of bone and primary tooth roots
overlying the crown of erupting tooth. ii) theoverlying the crown of erupting tooth. ii) the
eruption mechanism itself then must moreeruption mechanism itself then must more
the tooth in the direction of where the paththe tooth in the direction of where the path
has been cleared.has been cleared.
 Although, the 2 mechanisms normallyAlthough, the 2 mechanisms normally
operate in concert, in some circumstancesoperate in concert, in some circumstances
they do not. The rate of bone resorption andthey do not. The rate of bone resorption and
tooth eruption are not controlledtooth eruption are not controlled
physiologically by the same mechanism.physiologically by the same mechanism.

 Despite many yrs of study, the precise mechanismDespite many yrs of study, the precise mechanism
through which the eruption force is generatedthrough which the eruption force is generated
remains unknown. From animal studies, it seemsremains unknown. From animal studies, it seems
clear that the major eruption mechanism is localizedclear that the major eruption mechanism is localized
within periodontal ligament.within periodontal ligament.
 Other possibilities for eruption mechanism areOther possibilities for eruption mechanism are
localized variations in B.P (or) flow, forces deliveredlocalized variations in B.P (or) flow, forces delivered
from contraction of fibroblasts and alterations infrom contraction of fibroblasts and alterations in
extracellular ground substances of periodontalextracellular ground substances of periodontal
ligament.ligament.
 Normally the rate of eruption is such that theNormally the rate of eruption is such that the
apical area remains at same place while the crownapical area remains at same place while the crown
mores occlusally, but if eruption is mechanicallymores occlusally, but if eruption is mechanically
blocked, proliferating apical area will move inblocked, proliferating apical area will move in
opposite direction, inducing resorption where itopposite direction, inducing resorption where it
usually doesn’t occur. This causes distortion of rootusually doesn’t occur. This causes distortion of root
form which is called dilaceration.form which is called dilaceration.

Post emergent eruption
 Once tooth emerges into mouth, it eruptsOnce tooth emerges into mouth, it erupts
rapidly until it approaches the occlusal levelrapidly until it approaches the occlusal level
and is subjected to forces of mastication. Atand is subjected to forces of mastication. At
this point, the eruption slows and than as itthis point, the eruption slows and than as it
reaches occlusal level of other teeth and is inreaches occlusal level of other teeth and is in
complete function, eruption halts.complete function, eruption halts.
 The stage of relatively rapid eruption fromThe stage of relatively rapid eruption from
the time a tooth first penetrates gingiva untilthe time a tooth first penetrates gingiva until
it reaches the occulsal level is called the postit reaches the occulsal level is called the post
emergent spurt, in contrast to the following,emergent spurt, in contrast to the following,
phase of slow eruption is termed the juvenilephase of slow eruption is termed the juvenile
occlusal equilibrium.occlusal equilibrium.

 During juvenile equilibrium, teeth that are inDuring juvenile equilibrium, teeth that are in
function erupt at a rate that parallels the rate offunction erupt at a rate that parallels the rate of
vertical growth of mandibular ramus. As thevertical growth of mandibular ramus. As the
mandible continues to grow, it moves away from themandible continues to grow, it moves away from the
maxilla, creating a space into which the teethmaxilla, creating a space into which the teeth
erupts.erupts.
 Since the rate of eruption parallels the rate of jawSince the rate of eruption parallels the rate of jaw
growth, it is not surprising that a pubertal spurt ingrowth, it is not surprising that a pubertal spurt in
eruption of teeth accompanies pubertal spurt in jaweruption of teeth accompanies pubertal spurt in jaw
growth. This reinforces the concept that after a toothgrowth. This reinforces the concept that after a tooth
is in occlusion, the rate of eruption is controlled byis in occlusion, the rate of eruption is controlled by
forces opposing eruption not promoting it. The forcesforces opposing eruption not promoting it. The forces
opposing eruption in mouth are those from chewing,opposing eruption in mouth are those from chewing,
soft tissue pressures from lip, cheeks (or) tonguesoft tissue pressures from lip, cheeks (or) tongue
contacting the teeth.contacting the teeth.

 When the pubertal growth spurt ends, a finalWhen the pubertal growth spurt ends, a final
phase in tooth eruption called adult occlusalphase in tooth eruption called adult occlusal
equilibrium is achieved. During adult life,equilibrium is achieved. During adult life,
teeth continue to erupt at on extremely slowteeth continue to erupt at on extremely slow
rate. It its antagonist is lost at any age, arate. It its antagonist is lost at any age, a
tooth can again erupt more rapidly,tooth can again erupt more rapidly,
demonstrating that the eruption mechanismdemonstrating that the eruption mechanism
remains active and capable of producingremains active and capable of producing
significant tooth movement even late in lifesignificant tooth movement even late in life

 In studies of denitions of AustralianIn studies of denitions of Australian
aborigines, begg noted severe interproximalaborigines, begg noted severe interproximal
and occlusal attrition and concluded that thisand occlusal attrition and concluded that this
attritional process produced the “onlyattritional process produced the “only
anatomically correctanatomically correct occlusion”. He said “Theocclusion”. He said “The
accepted text book normal occlusion ofaccepted text book normal occlusion of
civilized man is anatomically incorrectcivilized man is anatomically incorrect
because his food is too soft and concentratedbecause his food is too soft and concentrated
to cause tooth Attrition (Begg, 1954).to cause tooth Attrition (Begg, 1954).

 High unworn cusps are wrongly considered to haveHigh unworn cusps are wrongly considered to have
evolved to maintain stability of occlusion throughoutevolved to maintain stability of occlusion throughout
life, whereas the only advantage of high cusps is thatlife, whereas the only advantage of high cusps is that
they help to guide the teeth into their occlusalthey help to guide the teeth into their occlusal
relationships at the time the teeth are erupting andrelationships at the time the teeth are erupting and
then to hold them only for a short time afterthen to hold them only for a short time after
eruption”. He concluded that high rate of attrition iseruption”. He concluded that high rate of attrition is
supposed to occur in modern humans and is resultsupposed to occur in modern humans and is result
of natural evolutionary process.of natural evolutionary process.
 Beyron also studied Australian aborigine dentitionBeyron also studied Australian aborigine dentition
and masticatory movements of live subjects, findingsand masticatory movements of live subjects, findings
the same severe occlusal and inter proximal wearthe same severe occlusal and inter proximal wear
that seems common in primitive culture with theirthat seems common in primitive culture with their
abrasive diets and more frequent use of teeth asabrasive diets and more frequent use of teeth as
tools.tools.

 Relationship between calcification andRelationship between calcification and
eruptioneruption
 Permanent teeth do not begin eruptivePermanent teeth do not begin eruptive
movements until after, the crown ismovements until after, the crown is
completed. They pass through the crest ofcompleted. They pass through the crest of
alveolar process at varying stages of rootalveolar process at varying stages of root
development. It takes from 2-5 yrs for thedevelopment. It takes from 2-5 yrs for the
posterior teeth to reach the alveolar crustposterior teeth to reach the alveolar crust
following the completion of their crowns andfollowing the completion of their crowns and
from 12-20 months to reach occlusion afterfrom 12-20 months to reach occlusion after
reaching the alveolar margin. The roots arereaching the alveolar margin. The roots are
usually completed a few months afterusually completed a few months after
occlusion is attained. The moment ofocclusion is attained. The moment of
emergence into oral cavity often is spoken asemergence into oral cavity often is spoken as
the “time of eruption”.the “time of eruption”.

 Periods of occlusal developmentPeriods of occlusal development
 a) Pre-dental perioda) Pre-dental period
 This is the period after birth where the neonateThis is the period after birth where the neonate
does not have any teeth. It usually lasts for 6 monthsdoes not have any teeth. It usually lasts for 6 months
after birth.after birth.
Gum padsGum pads
 The alveolar processes at the time of birth are knownThe alveolar processes at the time of birth are known
as gum pads. They are pink, firm and are covered byas gum pads. They are pink, firm and are covered by
a dense layer of fibrous periosteum. They are horse-a dense layer of fibrous periosteum. They are horse-
shoe shaped and develop in two parts. They are theshoe shaped and develop in two parts. They are the
labio-buccal portion and the lingual portion. The 2labio-buccal portion and the lingual portion. The 2
portions are separated from each other by a grooveportions are separated from each other by a groove
called dental groove. The gum pads are divided intocalled dental groove. The gum pads are divided into
ten segments by grooves called transverse grooves.ten segments by grooves called transverse grooves.
Each of these segment consists of one developingEach of these segment consists of one developing
deciduous tooth sac.deciduous tooth sac. www.indiandentalacademy.com

 The gingival groove separates the gum fromThe gingival groove separates the gum from
palate and floor of the mouth. The transversepalate and floor of the mouth. The transverse
groove between canine and first deciduousgroove between canine and first deciduous
molar segment is called lateral sulcus. Themolar segment is called lateral sulcus. The
lateral sulci are useful in judging the interlateral sulci are useful in judging the inter
arch relationship at a very early stage.arch relationship at a very early stage.
 The upper gum pad is both wider as well asThe upper gum pad is both wider as well as
longer than the mandibular gum pad. Thuslonger than the mandibular gum pad. Thus
when upper and lower gum pads arewhen upper and lower gum pads are
approximated, there is a complete overjet allapproximated, there is a complete overjet all
around. Contact occurs between upper andaround. Contact occurs between upper and
lower gum pads in the 1lower gum pads in the 1stst
molar region and amolar region and a
space exists between them in the anteriorspace exists between them in the anterior
region. This infantile open bite is consideredregion. This infantile open bite is considered
normal and it helps in suckling.normal and it helps in suckling.

 Very rarely teeth are present at theVery rarely teeth are present at the
time of birth. Such teeth are calledtime of birth. Such teeth are called
natal teeth. Teeth that erupt duringnatal teeth. Teeth that erupt during
the 1the 1stst
month are called neonatalmonth are called neonatal
teeth. The natal and neonatal teethteeth. The natal and neonatal teeth
are mostly located in theare mostly located in the
mandibular incisor region and showmandibular incisor region and show
a familial tendency.a familial tendency.

b) The deciduous dentition period
 The initiation of primary tooth buds occursThe initiation of primary tooth buds occurs
during the 1during the 1stst
6 weeks of intra uterine life. The6 weeks of intra uterine life. The
primary teeth begin to erupt at the age ofprimary teeth begin to erupt at the age of
about 6 months and eruption is completed byabout 6 months and eruption is completed by
2½-3½ yrs of age when the deciduous 2nd2½-3½ yrs of age when the deciduous 2nd
molars come into occlusion.molars come into occlusion.
 The mandibular central incisors are the 1The mandibular central incisors are the 1stst
teeth to erupt into oral cavity. They erupt atteeth to erupt into oral cavity. They erupt at
around 6-7 months of age. The sequence ofaround 6-7 months of age. The sequence of
eruption of deciduous dentition is A-B-D-C-E.eruption of deciduous dentition is A-B-D-C-E.
The primary dentition is established by 3 yrsThe primary dentition is established by 3 yrs
of age. Between 3-6 yrs of age, dental arch isof age. Between 3-6 yrs of age, dental arch is
relatively stable and very few changed occur.relatively stable and very few changed occur.

 Spacing usually exists between deciduousSpacing usually exists between deciduous
teeth. These spaces are called physiologicalteeth. These spaces are called physiological
(or) developmental spaces. The presence of(or) developmental spaces. The presence of
spaces in the primary dentition is necessaryspaces in the primary dentition is necessary
for the normal development of permanentfor the normal development of permanent
dentition. Absence of spaces is an indicationdentition. Absence of spaces is an indication
that crowding of teeth may occur when largerthat crowding of teeth may occur when larger
permanent teeth erupt.permanent teeth erupt.
 Spacing is seen mesial to maxillary caninesSpacing is seen mesial to maxillary canines
and distal to mandibular canines. Theseand distal to mandibular canines. These
physiological spaces are called primate (or)physiological spaces are called primate (or)
simian (or) Anthropoid spaces as they aresimian (or) Anthropoid spaces as they are
commonly seen in primates. These spacescommonly seen in primates. These spaces
help in the placement of canine cusps of thehelp in the placement of canine cusps of the
opposing arch.opposing arch.

Deep bite
 A deep bite may occur in initial stages ofA deep bite may occur in initial stages of
development. This is accentuated by thedevelopment. This is accentuated by the
fact that deciduous incisors are morefact that deciduous incisors are more
upright than their successors. The lowerupright than their successors. The lower
incisal edges often contact the cingulumincisal edges often contact the cingulum
area of the maxillary incisors. The deeparea of the maxillary incisors. The deep
bite is later reduced due to i) Eruptionbite is later reduced due to i) Eruption
of deciduous molars. ii) Attrition ofof deciduous molars. ii) Attrition of
incisors. iii) forward movement ofincisors. iii) forward movement of
mandibular due to growth.mandibular due to growth.

 c) The mixed dentition periodc) The mixed dentition period
 It begins approximately at 6 yrs of age with theIt begins approximately at 6 yrs of age with the
eruption of 1eruption of 1stst
permanent molars. It can be classifiedpermanent molars. It can be classified
into 3 phases.into 3 phases.
 i) First transitional periodi) First transitional period
 This is characterized by the emergence of 1This is characterized by the emergence of 1stst
permanent molars and exchange of deciduous molarspermanent molars and exchange of deciduous molars
with permanent incisors. The location andwith permanent incisors. The location and
relationship of 1relationship of 1stst
permanent molar which is firstpermanent molar which is first
permanent tooth depends much upon the distalpermanent tooth depends much upon the distal
surface relationship between upper and lower 2surface relationship between upper and lower 2ndnd
deciduous molars. The 1deciduous molars. The 1stst
permanent molars arepermanent molars are
guided into dental arch by distal surface of 2guided into dental arch by distal surface of 2ndnd
deciduous molars. The mesio-distal relationshipdeciduous molars. The mesio-distal relationship
between distal surfaces of upper and lower 2between distal surfaces of upper and lower 2ndnd
deciduous molars can be of 3 types.deciduous molars can be of 3 types.www.indiandentalacademy.com

 a) Flush terminal planea) Flush terminal plane
 The distal surface of upper and lowerThe distal surface of upper and lower
deciduous 2deciduous 2ndnd
molars are in 1 vertical plane.molars are in 1 vertical plane.
This is called flush (or) vertical terminalThis is called flush (or) vertical terminal
plane. This is a normal feature of deciduousplane. This is a normal feature of deciduous
dentition. Thus the erupting 1dentition. Thus the erupting 1stst
permanentpermanent
molars may also be in flush (or) end onmolars may also be in flush (or) end on
relationship. For the transition of such an endrelationship. For the transition of such an end
on molar relation to a class I molar relation,on molar relation to a class I molar relation,
the lower molar has to move forward by aboutthe lower molar has to move forward by about
3-5 mm relative to upper molar. This occurs3-5 mm relative to upper molar. This occurs
by utilization of physiologic spaces and leewayby utilization of physiologic spaces and leeway
space in mandibule and differential growth ofspace in mandibule and differential growth of
mandibule.mandibule.

 The shift in lower molar from a flushThe shift in lower molar from a flush
terminal plane to a class I relation canterminal plane to a class I relation can
occur in 2 ways which are designated asoccur in 2 ways which are designated as
early and late shift. Early shift occursearly and late shift. Early shift occurs
during early mixed dentition period. Theduring early mixed dentition period. The
eruptive force of 1eruptive force of 1stst
permanent molar ispermanent molar is
sufficient to push the deciduous 1sufficient to push the deciduous 1stst
andand
2nd molars forward in the arch to close the2nd molars forward in the arch to close the
primate space and thereby establish aprimate space and thereby establish a
class I molar relationship. Since thisclass I molar relationship. Since this
occurs in early mixed dentition period it isoccurs in early mixed dentition period it is
called early shift.called early shift.

 Many children lack primate spaceMany children lack primate space
and thus the erupting permanentand thus the erupting permanent
molars are unable to move forwardmolars are unable to move forward
to establish class I relationship. into establish class I relationship. in
these cases, when the deciduousthese cases, when the deciduous
2nd molars exfoliate the permanent2nd molars exfoliate the permanent
11stst
molars drift mesially utilizing themolars drift mesially utilizing the
leeway space. This occurs in lateleeway space. This occurs in late
mixed dentition period and hencemixed dentition period and hence
called late shift.called late shift.

 b) Mesial step terminal planeb) Mesial step terminal plane
 The distal surface of lower 2ndThe distal surface of lower 2nd
deciduous molar is more mesial than thatdeciduous molar is more mesial than that
of upper. Thus the permanent molarsof upper. Thus the permanent molars
erupt directly into angles class I occlusion.erupt directly into angles class I occlusion.
This type of mesial step terminal planeThis type of mesial step terminal plane
most commonly occurs due to earlymost commonly occurs due to early
forward growth of the mandible. If theforward growth of the mandible. If the
differential growth of mandible in adifferential growth of mandible in a
forward direction persists, it can lead to anforward direction persists, it can lead to an
angle’s class III molar relation. If it isangle’s class III molar relation. If it is
minimal it can establish class I molarminimal it can establish class I molar
relationship.relationship.

 c) Distal step terminal planec) Distal step terminal plane
 This is characterized by the distal surface of lowerThis is characterized by the distal surface of lower
2nd deciduous molar being more distal to that of2nd deciduous molar being more distal to that of
upper. Thus the erupting permanent molars may beupper. Thus the erupting permanent molars may be
in Angle’s class II occlusion.in Angle’s class II occlusion.
 During this period the deciduous incisors areDuring this period the deciduous incisors are
replaced by permanent incisors. The mandibularreplaced by permanent incisors. The mandibular
central incisors are usually first to erupt. Thecentral incisors are usually first to erupt. The
permanent incisors are considerably larger than thepermanent incisors are considerably larger than the
deciduous teeth they replace. This difference betweendeciduous teeth they replace. This difference between
the amount of space needed for accommodation ofthe amount of space needed for accommodation of
incisors and the amount of space available for this isincisors and the amount of space available for this is
called incisal liability. It is roughly about 7mm in maxcalled incisal liability. It is roughly about 7mm in max
arch and about 5mm in mandibular arch. The incisalarch and about 5mm in mandibular arch. The incisal
liability is overcome by following factors.liability is overcome by following factors. i)i) UtilizationUtilization
of interdental spaced seen in primary dentition. ii)of interdental spaced seen in primary dentition. ii)
Increase in inter canine width. iii) Change in incisorIncrease in inter canine width. iii) Change in incisor
inclination.inclination.

 ii) Inter transitional periodii) Inter transitional period
 In this period the maxillary andIn this period the maxillary and
mandibular arches consist of sets ofmandibular arches consist of sets of
deciduous and permanent teeth.deciduous and permanent teeth.
Between the permanent incisors andBetween the permanent incisors and
11stst
permanent molars are thepermanent molars are the
deciduous molars and canines. Thisdeciduous molars and canines. This
phase during the mixed dentitionphase during the mixed dentition
period is relatively stable and noperiod is relatively stable and no
change occurs.change occurs.

 iii) Second transitional periodiii) Second transitional period
 This is characterized by replacement ofThis is characterized by replacement of
deciduous molars and canines by premolarsdeciduous molars and canines by premolars
and permanent cuspids respectively. Theand permanent cuspids respectively. The
combined mesio distal width of permanentcombined mesio distal width of permanent
canines and premolars is usually less thancanines and premolars is usually less than
that of deciduous canines and molars. Thisthat of deciduous canines and molars. This
is called leeway space of nance. This is aboutis called leeway space of nance. This is about
1.8mm in maxillary arch and about 3.4mm1.8mm in maxillary arch and about 3.4mm
in mandibular arch. This excess spacein mandibular arch. This excess space
available after the exchange of the deciduousavailable after the exchange of the deciduous
molars and canines is utilized for mesial driftmolars and canines is utilized for mesial drift
of the mandibular molars to establish class Iof the mandibular molars to establish class I
molar relation.molar relation.

 The ugly duckling stageThe ugly duckling stage
 Sometime a transient (or) self – correctingSometime a transient (or) self – correcting
malocclusion is seen in maxillary incisor regionmalocclusion is seen in maxillary incisor region
between 8-9 yrs of age. This is seen during thebetween 8-9 yrs of age. This is seen during the
eruption of permanent canines. As the developingeruption of permanent canines. As the developing
permanent canines erupt, they displace the roots ofpermanent canines erupt, they displace the roots of
lateral incisors mesially. This results in transmittinglateral incisors mesially. This results in transmitting
of force on the roots of central incisor which also getof force on the roots of central incisor which also get
displaced mesially.displaced mesially.
 A resultant distal divergence of crowns of the twoA resultant distal divergence of crowns of the two
central incisor causes a midline spacing. Thiscentral incisor causes a midline spacing. This
situation has been described by broadbent as thesituation has been described by broadbent as the
ugly duckling stage as children tend to look uglyugly duckling stage as children tend to look ugly
during this phase. This condition usually corrects byduring this phase. This condition usually corrects by
itself when the canines erupt and the pressure isitself when the canines erupt and the pressure is
transferred from the roots to the coronal area oftransferred from the roots to the coronal area of
incisors.incisors.

Overjet and overbite
 Over bite and overjet undergo significantOver bite and overjet undergo significant
changes during primary and transitionalchanges during primary and transitional
dentitions. During primary dentition,dentitions. During primary dentition,
overbite normally decreases a slight amountoverbite normally decreases a slight amount
and overjet is often reduced to zero. Fromand overjet is often reduced to zero. From
the early mixed dentition to the completionthe early mixed dentition to the completion
of permanent occlusion the average overbiteof permanent occlusion the average overbite
increases slightly and then decreases.increases slightly and then decreases.
Overbite is co-related with a number ofOverbite is co-related with a number of
vertical facial dimensions whereas overjet isvertical facial dimensions whereas overjet is
a reflection of anteroposterior skeletala reflection of anteroposterior skeletal

 d) The permanent dentition periodd) The permanent dentition period
 The permanent dentition forms withinThe permanent dentition forms within
the jaws soon after birth, except for thethe jaws soon after birth, except for the
cusps of the 1cusps of the 1stst
permanent molars whichpermanent molars which
form before birth. The permanent incisorsform before birth. The permanent incisors
develop lingual (or) palatal to the deciduousdevelop lingual (or) palatal to the deciduous
incisors and move labially as they erupt. Theincisors and move labially as they erupt. The
premolars develop below the diverging rootspremolars develop below the diverging roots
of the deciduous molars.of the deciduous molars.
 The frequently seen eruption sequences inThe frequently seen eruption sequences in
maxillary arch aremaxillary arch are
 6-1-2-4-3-5-7 (or) 6-1-2-3-4-5-76-1-2-4-3-5-7 (or) 6-1-2-3-4-5-7
 Mandibular archMandibular arch
 6-1-2-3-4-5-7 (or) 6-1-2-4-3-5-76-1-2-3-4-5-7 (or) 6-1-2-4-3-5-7

 Clinical implicationClinical implication
 Determinants of occlusion areDeterminants of occlusion are
 a.a.          Condylar guidanceCondylar guidance
 b.b.          Incisal guidanceIncisal guidance
 c.c.            Plane of occlusionPlane of occlusion
 d.d.          Compensating curveCompensating curve
 e.e.          Cusp heightCusp height
 The exact integration of these determinantsThe exact integration of these determinants
does not apply to a natural dentition wheredoes not apply to a natural dentition where
balance is not a naturally occuring condition.balance is not a naturally occuring condition.
Each has some influence on the attritionalEach has some influence on the attritional
pattern of dentition and in that sensepattern of dentition and in that sense
considered an occlusal determinant.considered an occlusal determinant.

 The teeth are aligned in dental arches withThe teeth are aligned in dental arches with
varying degrees of inclination bothvarying degrees of inclination both
mesiodistally and buccolingually. Whenmesiodistally and buccolingually. When
viewed laterally, a line from tip of canineviewed laterally, a line from tip of canine
touching the tips of buccal cusps of posteriortouching the tips of buccal cusps of posterior
teeth will describe a relatively smooth curve,teeth will describe a relatively smooth curve,
the curve of spee.the curve of spee.
 In transverse plane alignments of long axis ofIn transverse plane alignments of long axis of
posterior teeth cause occlusal surfaces ofposterior teeth cause occlusal surfaces of
mandibular molars to be directed somewhatmandibular molars to be directed somewhat
lingually whereas those of max molars arelingually whereas those of max molars are
directed buccally. For each pair of left anddirected buccally. For each pair of left and
right posterior teeth, a transverse occlusalright posterior teeth, a transverse occlusal
curve the curve of wilson can be described.curve the curve of wilson can be described.

 It was once suggested that curves of spee and wilsonIt was once suggested that curves of spee and wilson
are related three dimensionally so that all cusp tipsare related three dimensionally so that all cusp tips
and incisal ridges of all teeth are aligned on theand incisal ridges of all teeth are aligned on the
curved surface of sphere (sphere of monsoon).curved surface of sphere (sphere of monsoon).
However attempts to demonstrate such sphericalHowever attempts to demonstrate such spherical
curves in natural dentition have failed.curves in natural dentition have failed.
 An accurate diagnosis based on adequate history,An accurate diagnosis based on adequate history,
examination and utilization of relevant information isexamination and utilization of relevant information is
fundamental to treatment of patients. Wheneverfundamental to treatment of patients. Whenever
possible specific causes and effect relationshipspossible specific causes and effect relationships
should be established as a prelude to treatmentshould be established as a prelude to treatment
decisions. These principles apply to management ofdecisions. These principles apply to management of
patients with occlusal and dysfunctional problems ofpatients with occlusal and dysfunctional problems of
masticatory system.masticatory system.

 Theoretically ideal occlusionTheoretically ideal occlusion
 It is a preconceived view of structural andIt is a preconceived view of structural and
functional relationships. Such an occlusionfunctional relationships. Such an occlusion
occasionally represents the characteristics ofoccasionally represents the characteristics of
a given individual. An occlusion anda given individual. An occlusion and
masticatory system should ideally bemasticatory system should ideally be
 a.a. All components of masticatory system areAll components of masticatory system are
present.present.
 b. b. In centric occlusion, the supporting cuspsIn centric occlusion, the supporting cusps
of all posterior teeth occlude with marginalof all posterior teeth occlude with marginal
ridges except disto buccal cusps ofridges except disto buccal cusps of
mandibular molars and mesio lingual cuspsmandibular molars and mesio lingual cusps
of maxillary molars which occlude withof maxillary molars which occlude with
central fossae of opposing teeth.central fossae of opposing teeth.

 c.c.The occlusion is stable i.e. teeth do notThe occlusion is stable i.e. teeth do not
migrate (or) change position other than slowmigrate (or) change position other than slow
physiological compensatory movement.physiological compensatory movement.
 d.Teeth do not exhibit attritional weard.Teeth do not exhibit attritional wear
beyond what is expected for the age ofbeyond what is expected for the age of
individual.individual.
 e.During protaction, posterior teethe.During protaction, posterior teeth
disoclude so as not to interfere with ability ofdisoclude so as not to interfere with ability of
opposing incisor teeth to occlude andopposing incisor teeth to occlude and
function properly.function properly.
 f.f.During lateral movements, the teeth on nonDuring lateral movements, the teeth on non
working side disoclude so as not to interfereworking side disoclude so as not to interfere
with the ability of opposing working sidewith the ability of opposing working side
teeth to contact and function properly.teeth to contact and function properly.

 g.All masticatory, deglutition, speechg.All masticatory, deglutition, speech
articulation, esthetics and respiratoryarticulation, esthetics and respiratory
requirements are met and are satisfactory torequirements are met and are satisfactory to
patient.patient.
 h.Minimum parafunctional activity, that ish.Minimum parafunctional activity, that is
little phasic muscle activity occurs.little phasic muscle activity occurs.
 i.No signs (or) symptoms of pain (or)i.No signs (or) symptoms of pain (or)
dysfunction from any component ofdysfunction from any component of
masticatory system can be detected.masticatory system can be detected.

 Physiological occlusionPhysiological occlusion
 Usually found in adults, it deviates in one (or)Usually found in adults, it deviates in one (or)
more ways from theoretically ideal occlusion but ismore ways from theoretically ideal occlusion but is
well adapted, is esthetically satisfactory to patientwell adapted, is esthetically satisfactory to patient
and has no pathological manifestations (or)and has no pathological manifestations (or)
dysfunctional problems. This does not requiredysfunctional problems. This does not require
therapeutic intervention.therapeutic intervention.
 This demonstrated maxillomandibular relationshipsThis demonstrated maxillomandibular relationships
different from theoretical criteria, but no untowarddifferent from theoretical criteria, but no untoward
effects are observed. Para-functional activity may beeffects are observed. Para-functional activity may be
present, but all components of masticatory systempresent, but all components of masticatory system
are responding well and no pain (or)- dysfunctionalare responding well and no pain (or)- dysfunctional
signs (or) symptoms can be demonstrated.signs (or) symptoms can be demonstrated.

 The criteria for physiological occlusion areThe criteria for physiological occlusion are
 a.a.  Occlusal stabilityOcclusal stability
 b.Masticatory function is satisfactory tob.Masticatory function is satisfactory to
patient.patient.
 c.c.  Speech articulation is acceptable to patientSpeech articulation is acceptable to patient
 d.d.  Esthetic considerations are acceptable.Esthetic considerations are acceptable.
 e.e.  Freedom from signs (or) symptoms involvingFreedom from signs (or) symptoms involving
periodontal attachment apparatus.periodontal attachment apparatus.
 f.Freedom from signs (or) symptoms off.Freedom from signs (or) symptoms of
conditions involving the teeth themselves.conditions involving the teeth themselves.
 g.g.  Freedom from signs (or) symptomsFreedom from signs (or) symptoms
involving TMJ or musculature associated withinvolving TMJ or musculature associated with
mandibular function.mandibular function.

 Non-physiologic occlusionNon-physiologic occlusion
 It is one in which there are signs (or)It is one in which there are signs (or)
symptoms of pathology, dysfunction, (or)symptoms of pathology, dysfunction, (or)
inadequate adaptation of one (or) moreinadequate adaptation of one (or) more
components of the masticatory system thatcomponents of the masticatory system that
can be attributed to faulty structuralcan be attributed to faulty structural
relationship (or) mandibular functional (or)relationship (or) mandibular functional (or)
para functional activity. It also includespara functional activity. It also includes
patients non-acceptance of occlusally relatedpatients non-acceptance of occlusally related
esthetics, speech articulation (or)esthetics, speech articulation (or)
masticatory function parameters.masticatory function parameters.

 In addition to subjective criteria forIn addition to subjective criteria for
treatment there are objective criteriatreatment there are objective criteria
like signs (or) symptoms oflike signs (or) symptoms of
 a.a.          Periodontal conditions attributed toPeriodontal conditions attributed to
functional loading.functional loading.
 b.b.          Pathological conditions of teeth thatPathological conditions of teeth that
can be attributed to mandibularcan be attributed to mandibular
functional (or) para functional activity.functional (or) para functional activity.
 c.c.          TMJ disorders.TMJ disorders.

 Therapeutic occlusionTherapeutic occlusion
 It is one that has been modified byIt is one that has been modified by
appropriate therapeutic modalities in order toappropriate therapeutic modalities in order to
change a non-physiologic occlusion to onechange a non-physiologic occlusion to one
that at least falls within the parameters ofthat at least falls within the parameters of
physiologic occlusion, if not theoreticallyphysiologic occlusion, if not theoretically
ideal. Such an occlusion may containideal. Such an occlusion may contain
structural modifications not necessarilystructural modifications not necessarily
found in order to optimize the health andfound in order to optimize the health and
adaptive potential of masticatory system.adaptive potential of masticatory system.
 Eg. cusp to fossae posterior occlusalEg. cusp to fossae posterior occlusal
relationship instead of cusp to marginal ridgerelationship instead of cusp to marginal ridge

Conclusion
 It is apparent that many unassociatedIt is apparent that many unassociated
factors exist in transition from deciduous tofactors exist in transition from deciduous to
permanent dentition. Some can be definedpermanent dentition. Some can be defined
with considerable precision i.e. size of teeth.with considerable precision i.e. size of teeth.
While others such as incremental changes inWhile others such as incremental changes in
anterior arch perimeter as incisors erupt areanterior arch perimeter as incisors erupt are
less clear.less clear.
 Although changes are small, the alignment ofAlthough changes are small, the alignment of
permanent teeth depends on relationshippermanent teeth depends on relationship
between arch perimeter in primary dentition,between arch perimeter in primary dentition,
changes in arch length and breadth in mixedchanges in arch length and breadth in mixed
dentition and the size of succedaneous teeth.dentition and the size of succedaneous teeth.

Thank you

Development of occlusion

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