Arcial growth of mandible final /certified fixed orthodontic courses by Indian dental academy

Arcial growth of mandibleArcial growth of mandible
► A normal human mandible grows byA normal human mandible grows by
superior anterior (vertical) apposition atsuperior anterior (vertical) apposition at
the ramus on a curve or arc which is athe ramus on a curve or arc which is a
segment formed from a circle.segment formed from a circle.
► The radius of this circle is determined byThe radius of this circle is determined by
using the distance from mentalusing the distance from mental
protuberance (Pm) to a point at the forkingprotuberance (Pm) to a point at the forking
of the stress lines at the terminus of theof the stress lines at the terminus of the
oblique ridge on the medial side of theoblique ridge on the medial side of the
ramus. (point Eva )ramus. (point Eva )
Angle Ortho,1972,42:368Angle Ortho,1972,42:368
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► Several attempts has been made to study andSeveral attempts has been made to study and
predict the growth of mandible.predict the growth of mandible.
► Roentgenographic study by RickettRoentgenographic study by Rickett
► Implant method by BjorkImplant method by Bjork
► Histological evidence of surface characteristics by EnlowHistological evidence of surface characteristics by Enlow
► After found the relationship of the neurovascular orAfter found the relationship of the neurovascular or
neurotrophic bundle led moss to speculated that theneurotrophic bundle led moss to speculated that the
phenomenon of growth of the mandible was predictablephenomenon of growth of the mandible was predictable
because ,because ,
► foramen ovale, mandibular foramen and mental foramenforamen ovale, mandibular foramen and mental foramen
behaved in an orientation to a logarithmic spiral during thebehaved in an orientation to a logarithmic spiral during the
growth process.growth process.

► Clinical Investigation and Prediction ofClinical Investigation and Prediction of
Mandibular GrowthMandibular Growth
► Early Laminagraphic studies of RickettsEarly Laminagraphic studies of Ricketts suggested that,suggested that,
► Tendencies toward squareness, heaviness and strength ofTendencies toward squareness, heaviness and strength of
the mandibular ramusthe mandibular ramus tended to be associated withtended to be associated with
forward development of the chin and deep faces.forward development of the chin and deep faces.
► Obtusity, fragility and weakness of the mandibleObtusity, fragility and weakness of the mandible seemed toseemed to
contribute to more downward to backward development ofcontribute to more downward to backward development of
the Symphysis in the face.the Symphysis in the face.

► Primary method of predictionPrimary method of prediction
► By plotting a line through the long axis of the condyle andBy plotting a line through the long axis of the condyle and
neck and extending it to the lower border of the mandible,neck and extending it to the lower border of the mandible,
the bending of the mandibular form during growth hadthe bending of the mandibular form during growth had
been studied.been studied.
► short range predictionsshort range predictions
► Limitation of studyLimitation of study
► Earlier studies of bjork suggest that lower border of theEarlier studies of bjork suggest that lower border of the
mandible was resorbingmandible was resorbing
So, mandibular plane was not acceptable as a referenceSo, mandibular plane was not acceptable as a reference
base for growth analysisbase for growth analysis

2)2) Next move towards improving the method was toNext move towards improving the method was to identify aidentify a
“central core” cephalometrically.“central core” cephalometrically.
► To overcome the surface variation and to determine centerTo overcome the surface variation and to determine center
of internal structural phenomenon resulted inof internal structural phenomenon resulted in promulgationpromulgation
of new reference pointsof new reference points as follows:as follows:
► Ricketts, using a trial and error procedure with longitudinalRicketts, using a trial and error procedure with longitudinal
cephalometric records and computers, has developed acephalometric records and computers, has developed a
method to determine the arc of growth of mandible. Thismethod to determine the arc of growth of mandible. This
arcial analysis not only helps in prediction, but also hasarcial analysis not only helps in prediction, but also has
many biologic and clinical implications.many biologic and clinical implications.

► To overcome this drawback, aTo overcome this drawback, a
new point Xi was developed.new point Xi was developed.
► Point XiPoint Xi
► Represents the geometricRepresents the geometric
centre of the ramus.centre of the ramus.
► It is point of intersection of theIt is point of intersection of the
diagonals of the rectanglediagonals of the rectangle
formed by drawing tangents toformed by drawing tangents to
the four borders of the ramus.the four borders of the ramus.
► This point precisely locates theThis point precisely locates the
opening of the mandibularopening of the mandibular
canal.canal.

► TheThe 2nd point2nd point chosen waschosen was
suprapognionsuprapognion
(Protraberence Menti),(Protraberence Menti),
► point at which the shape ofpoint at which the shape of
Symphysis mentalisSymphysis mentalis
changes from convex tochanges from convex to
concave.concave.
► It is located atIt is located at
approximately a stressapproximately a stress
center (Rickett).center (Rickett).
► It is site of reversal lineIt is site of reversal line
(Enlow).(Enlow).
► it is consistent with theit is consistent with the
findings from implantfindings from implant
studies (Bjork).studies (Bjork).
bone crest located at the superior
aspect of the compact bone on the
anterior contour of the symphysis
was accepted as the most stable
landmarkwww.indiandentalacademy.com

► TheThe 3rd point3rd point chosen waschosen was
DC,DC,
► point in the centre at thepoint in the centre at the
bisection of the condylarbisection of the condylar
neck as high as visible inneck as high as visible in
the ceph film below thethe ceph film below the
fossa along Ba-N Plane.fossa along Ba-N Plane.
► A line drawn from ,A line drawn from ,
► DC to Xi is condyle axisDC to Xi is condyle axis
► from Xi to Pm is Corpusfrom Xi to Pm is Corpus
axisaxis

►By studying the linear growth on theseBy studying the linear growth on these
planes and the form change as a change inplanes and the form change as a change in
angulation between the two, will determineangulation between the two, will determine
the mandibular growth characteristics.the mandibular growth characteristics.
►The objective of further, reaserch was stillThe objective of further, reaserch was still
toward finding a method to critically predicttoward finding a method to critically predict
future form and size of mandible over thefuture form and size of mandible over the
long range or to maturity as a basis forlong range or to maturity as a basis for
treating deformities in the child.treating deformities in the child.

Computer study of mandibleComputer study of mandible
► When an averageWhen an average
mandible at time 1 wasmandible at time 1 was
superimposed on ansuperimposed on an
average mandible at timeaverage mandible at time
2,2, using point Xi andusing point Xi and
Corpus axis as referenceCorpus axis as reference,,
the mandible was found tothe mandible was found to
bend about one-halfbend about one-half
degree each year. ( time 1degree each year. ( time 1
during 8yrs and time 2=during 8yrs and time 2=
13yrs of age )13yrs of age )

► The next step involved a experiment wereThe next step involved a experiment were
undertaken to determined a method by which theundertaken to determined a method by which the
form and size of the mandible can be predicted.form and size of the mandible can be predicted.
► It finally led to the development of three curvesIt finally led to the development of three curves
were drawn - A, B and C and analyzed which bestwere drawn - A, B and C and analyzed which best
fits the true arc of growth of the mandible, thatfits the true arc of growth of the mandible, that
described this bending.described this bending.

► Curve A,Curve A,
► which passed throughwhich passed through
DC, Xi and PM, did notDC, Xi and PM, did not
produce enoughproduce enough
bending, so that in thebending, so that in the
prediction of growthprediction of growth
over a sufficient timeover a sufficient time
span, the mandiblespan, the mandible
would be too obtuse.would be too obtuse.

► Curve B, passing from theCurve B, passing from the
tip of coronoid process,tip of coronoid process,
touching the anteriortouching the anterior
border of the ramus at itsborder of the ramus at its
deepest curve and throughdeepest curve and through
PM .PM .
► Extention of this curveExtention of this curve
exhibited the segment ofexhibited the segment of
circle with too small radiuscircle with too small radius
and resulted in excessiveand resulted in excessive
bending of mandible whenbending of mandible when
the same gradient ofthe same gradient of
growth was employed for agrowth was employed for a
projection.projection.

►These two unsuccessful arcs obviouslyThese two unsuccessful arcs obviously
bracketed the true arcbracketed the true arc, which must be, which must be
somewhere in the mandible between thesomewhere in the mandible between the
condyle and coronoid process and betweencondyle and coronoid process and between
point Xi and anterior border of the ramus.point Xi and anterior border of the ramus.

► At the same time, Analysis ofAt the same time, Analysis of
the stress lines of mandiblethe stress lines of mandible
revealed an irregular gnarledrevealed an irregular gnarled
area at this area on the lateralarea at this area on the lateral
surface where stress seemedsurface where stress seemed
to divide forward or backwardto divide forward or backward
in respect to coronoid andin respect to coronoid and
condyloid demands.condyloid demands.
► On the inner aspect, (medialOn the inner aspect, (medial
side) greater forking was notedside) greater forking was noted
followed the mylohyoid ridgefollowed the mylohyoid ridge
upward in to a thick mass toupward in to a thick mass to
terminate at a Y- Shape bonyterminate at a Y- Shape bony
prominence. An Area at almostprominence. An Area at almost
the centre of the upward andthe centre of the upward and
forward quadrant of the ramusforward quadrant of the ramus
on the lingual surface thaton the lingual surface that
appeared at the confluence ofappeared at the confluence of
various fields of forcevarious fields of force Ricketts remarked that these
areas were important in the
mandibular growth.www.indiandentalacademy.com

► Two new points identified :Two new points identified :
► The point of medialThe point of medial
confluence was given theconfluence was given the
name Eva.name Eva.
► A new pointA new point TrTr locatedlocated
geometrically, is used asgeometrically, is used as
centre of a circle. This pointcentre of a circle. This point
represents the intersection ofrepresents the intersection of
two arcs with their radii equaltwo arcs with their radii equal
to Eva-PM. Eva constitutesto Eva-PM. Eva constitutes
the centre of one arc, PM thethe centre of one arc, PM the
other.other.
► This curve constructedThis curve constructed
through Eva and PM with Trthrough Eva and PM with Tr
as the centre represents theas the centre represents the
true arc of the mandibulartrue arc of the mandibular
growth.growth. www.indiandentalacademy.com

Amount of growth forecast on theAmount of growth forecast on the
ArcArc
►Annual increase of 2.5 mm/year wasAnnual increase of 2.5 mm/year was
predicted.predicted.
►Growth was found to cease at 14.5 yearsGrowth was found to cease at 14.5 years
for females and 19 years for males.for females and 19 years for males.

► Next study to determine amount of growth of the condyleNext study to determine amount of growth of the condyle
and coronoid process when measured from a point at theand coronoid process when measured from a point at the
crossing of the arc with the sigmoid notch. Point ofcrossing of the arc with the sigmoid notch. Point of
crossing was labeledcrossing was labeled pointpoint MuMu..
►Finding:Finding:
► condyle and coronoid processes grow upward and outwardcondyle and coronoid processes grow upward and outward
in a direction essentially as a function of the curve of thein a direction essentially as a function of the curve of the
original arc.original arc.
► Means sigmoid notches with arc of a small radius tendedMeans sigmoid notches with arc of a small radius tended
to stay small, while widely divergent condyles and coronoidto stay small, while widely divergent condyles and coronoid
processes tends to extended.processes tends to extended.

► k factor ( constant) fork factor ( constant) for
coronoid process growthcoronoid process growth
came to be 0.8 mm percame to be 0.8 mm per
year.year.
► condylar k factor wascondylar k factor was
discover to be variable.discover to be variable.
Small and short condyleSmall and short condyle
or weak condyle wereor weak condyle were
found not to growfound not to grow
► well formed condylewell formed condyle
heads with long necksheads with long necks
found to grow 0.4 mmfound to grow 0.4 mm
per year.per year.

► studies for gonionstudies for gonion
showed thatshowed that gonialgonial
angleangle drifteddrifted
posteriorly on the arcposteriorly on the arc
almost exactly one halfalmost exactly one half
the total increase inthe total increase in
mandibular growth onmandibular growth on
the arcthe arc

► study for forecastingstudy for forecasting
of complete,of complete,
mandibular growthmandibular growth
using RR point as ausing RR point as a
reference pointreference point
oblique ridge of theoblique ridge of the
mandible showsmandible shows
apposition aboutapposition about
0.4mm per year.0.4mm per year.

Studies on the Occlusal plane andStudies on the Occlusal plane and
eruption of mandibular teetheruption of mandibular teeth
►Investigation in 1955 on the treatmentInvestigation in 1955 on the treatment
behavior of the Occlusal planebehavior of the Occlusal plane
►Five relations will be useful for clinicalFive relations will be useful for clinical
implications.implications.

► Angle of the Occlusal plane to the corpusAngle of the Occlusal plane to the corpus
axis tended to be regular and orderly.axis tended to be regular and orderly.
► some functional and biological relations tosome functional and biological relations to
the development of the posterior end ofthe development of the posterior end of
the Occlusal plane and xi point. Distal endthe Occlusal plane and xi point. Distal end
of Occlusal plane dropped downwardof Occlusal plane dropped downward
slightly with growth , this is a biologic clueslightly with growth , this is a biologic clue
for the development of curve of spee.for the development of curve of spee.

► Occlusal plane tended to hold its relation to theOcclusal plane tended to hold its relation to the
embrasure of the lips at the forward end. Itembrasure of the lips at the forward end. It
seemed vertical development of the lower dentalseemed vertical development of the lower dental
arch. As this Arc was growing, symphysis orarch. As this Arc was growing, symphysis or
chin was pushed under the denture as the teethchin was pushed under the denture as the teeth
are erupted upward and forward which explainare erupted upward and forward which explain
“chin button” development.“chin button” development.
► Lower incisor relates to the convexity or facialLower incisor relates to the convexity or facial
type in all age groups. Means prediction of lowertype in all age groups. Means prediction of lower
incisor position related to the prediction ofincisor position related to the prediction of
change in convexity of face.change in convexity of face.

► Lower molarLower molar tends to erupt upwardtends to erupt upward
and forward with the Occlusal planeand forward with the Occlusal plane
from the mental protuberance . thisfrom the mental protuberance . this
acquire space for the erupting thirdacquire space for the erupting third
molar.molar.

Discussion
► Arcial growth is dependent on superior-anterioris dependent on superior-anterior
growth of the ramus rather than posterior growth.growth of the ramus rather than posterior growth.
Clearly, the Increase in size involved a vertical and notClearly, the Increase in size involved a vertical and not
a horizontal process.a horizontal process.
► This shift in the direction of growth automatically altersThis shift in the direction of growth automatically alters
the mechanism whereby room is made for the 2nd andthe mechanism whereby room is made for the 2nd and
3rd molars.3rd molars.
► In the conventional view, major resorption is required atIn the conventional view, major resorption is required at
the anterior border of the ramus to provide eruptionthe anterior border of the ramus to provide eruption
space for the distal teeth. The arcial pattern obviatesspace for the distal teeth. The arcial pattern obviates
the need for such resorption because the lower 1stthe need for such resorption because the lower 1st
molar tends to erupt upward and forward with themolar tends to erupt upward and forward with the
Occlusal plane.Occlusal plane.

► The arcial movement of the mandible also pushes theThe arcial movement of the mandible also pushes the
Symphysis under the denture as the teeth erupt forwardsSymphysis under the denture as the teeth erupt forwards
and upwards. This explains theand upwards. This explains the formations of chin-buttonformations of chin-button
despite the minimum apposition in this area.despite the minimum apposition in this area.
► Important clinical decisions currently being predicted on theImportant clinical decisions currently being predicted on the
reality of arcial growth. For instance, anchorage of lowerreality of arcial growth. For instance, anchorage of lower
arch during orthodontic treatment is improved byarch during orthodontic treatment is improved by
positioning the roots of lower first molar to the buccal orpositioning the roots of lower first molar to the buccal or
locking them under cortical bone will prevent upward andlocking them under cortical bone will prevent upward and
therefore forward eruption of the whole lower dental arch.therefore forward eruption of the whole lower dental arch.

Concept of Growth of MandibleConcept of Growth of Mandible
• Superimposition at Po
and at coronoid crest
• Vertical apposition at
superior border of
ramus
• Occlusal plane moving
with Xi point
• Incisors moves upwards
and forwards
• Lower molars moves
upward and forwards

Thank youThank you
For more details please visitFor more details please visit
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Arcial growth of mandible final /certified fixed orthodontic courses by Indian dental academy

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