Growth rotations 1 /certified fixed orthodontic courses by Indian dental academy

Growth Rotations

www.indiandentalacademy.com

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INDIAN DENTAL ACADEMY
Leader in continuing dental education


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“An intensive study of the growth of the human
head will inevitably lead to the realization that it
involves the most complicated anatomical
complex in all creation.
The interrelationships are infinite and the
causes and effects of these relationships are
almost imponderable. The more our knowledge
increases the more our ignorance unfolds.
The vast stretches of the unanswered and the
unfinished still outstrip our collective
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comprehension. It is little wonder that the allied

 Introduction
 Terminologies
 Concepts of Mandibular Rotations
 Concepts of Maxillary Rotations
 Tooth eruption and facial development
 Prediction of growth rotations
 Clinical implications of Rotations
 Conclusion


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Introduction
 First publication on the
growth of the face-18th
century.
 Hunter suggested that
mandible lengthens due
to resorption of the
anterior surface of ramus
and deposition
posteriorly.

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Introduction

Growth was studied www.indiandentalacademy.com
using stains and inserting metal wires 6

Introduction
 Cephalometrics introduced in 1930s.

 Originally used to reveal the anatomy of head.

 Since longitudinal study is possible it was used
to test various concepts concerning the
mechanisms of postnatal enlargement of head.

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Introduction
 Measurements and
tracings showed little
changes in the facial
form.
 The development in the
form of the face was
considered static.


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 With the use of metallic implants as markers it
was seen that mandibular corpus rotates during
growth but the shape is kept stable by surface
remodeling.


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Introduction
 Lande in 1952 observed that the lower border
becomes less steeply inclined with growth.
 The phrase ‘growth rotation’ was introduced by
Bjork in 1955.
 Metallic implants were precise markers from
which sites and amount of growth and
resorption could be found.
 Superimposing two consecutive tracings showed
that the older mandible had rotated.

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Types of rotation
 Forward rotation (Bjork)/
Counterclockwise (Schudy)

 Backward rotation (Bjork) /
Clockwise (Schudy)

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Posterior growth is greater than the anterior growth

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Anterior growth is greater than posterior growth.

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Terminologies.
 1965-Schudy introduced clockwise and
counterclockwise rotation.
 1969-Bjork discussed different directions of
rotation of the mandibular implant line and the
relation of these to mandibular form.


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 1970-Odegard described rotation as the change
in the orientation that can occur between
implant line and lower border of the mandible.
 1977-Lavergne and Gasson described the terms
Positional and Morphogenetic rotations.
 1983-Bjork and Skieller gave the termsTotal rotation.
Matrix rotation.
Intramatrix rotation.

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 1985-Dibbets introduced the term
Counterbalancing rotation.
 1988-Solow,Houston
True rotation.
Apparent rotation.
Angular remodeling of the lower border.
 Proffit- used the terms
Internal rotation.
Total rotation .

External rotation.

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Core


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Total / True /
Internal
 Is the rotation of the mandibular corpus
and is measured as a change in inclination
of the implant line, in the mandibular
corpus relative to the anterior cranial base.


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When implant line rotates forward relative to the
S-N , total rotation is designated negative.
Converging S-N lines-forward rotation.


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MATRIX / APPARENT
/TOTAL
 Rotation of the soft tissue matrix of the
mandible relative to the anterior cranial
base.
 Soft tissue matrix is defined by a tangential
mandibular line .

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Negative when mandibular line rotates forward
relative to S-N line.
‘Pendulum movement’.
Centre of rotation at the condyle.


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Intramatrix / Angular remodeling
of lower border / External
rotation-

Defined by the change in inclination of the
implant line relative to the tangential
mandibular line.


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 Rotation of the corpus inside the soft tissue
matrix.

 Forward rotation of the corpus relative to the
tangential line is negative.
 Centre of rotation some where in the corpus.
 Dependent on the rotation of maxilla and
occlusion of teeth.

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-----

+

+++
++


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+
-----

+++
++

-


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According to Bjork and Skieller


The mandible “wiggles” within the matrix



This wiggling is associated with the corpus but
is caused by the growing condyle.



Rotation results from or compensates for, a
genetically determined program.


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ANGULAR REMODELING OF LOWER
BORDER
 Rotation should be used to describe the angular
movement of one rigid body relative to another.
 Single body changes in form-surface accretion
and removal- Angular changes
 Makes a terminological distinction between-the
measure of the amount of remodeling that
occurs at the mandibular border and the
rotational process that causes it.

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BJORK

SOLOW,HOUSTON

PROFFIT

Rotation of the
mandibular core
relative to cranial
base.

Total
Rotation

True Rotation

Internal
Rotation

Rotation of
mandibular plane
relative to cranial
base.

Matrix
Rotation

Apparent
Rotation

Total
Rotation

Rotation of
mandibular plane
relative to core of
the mandible.

Intramatrix
Rotation

Angular
External
Remodeling of Rotation
lower border


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TOTAL ROTATION = MATRIX ROTATION
+
INTRAMATRIX ROTATION


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 Direction of total rotation more forward
than the matrix rotation pronounced
remodeling takes place at the lower border
of the mandible.
 Forward intramatrix rotation lifts up the
anterior part of the corpus from the soft
tissue matrix-APPOSITION.
 Posterior part pressed down into the
matrix-RESORPTION.

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 The center of rotation for total rotation depends
on the other 2 centers.
 The vertical facial development is strongly
related to the rotation of both the jaws.
 Average individual-rotation 4-adult life
Total rotation: -15.4o
Matrix

: -4.1o (27%)

Intramatrix : -11.3o (73%)

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 Total Rotation- Matrix Rotation
=Intramatrix Rotation

 Expression of remodeling at the lower
border.

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Positional and Morphogenetic
Rotation.
 Introduced by Lavergne and Gasson.

Positional Rotation Describes the position of mandible within the
head.


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Morphogenetic Rotation Concerns the shape of the mandible.
 Superimposition done on line through condylion
and pogonion.
 The angle formed between the 2 implant linesdegree of morphogenetic rotation.
 Similar to Bjork’s intramatrix but not identical.

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 Bjork considered key factor of
intramatrix to be found in a
rotation of mandibular corpus
inside the matrix.
 Lavergne and Gasson –
consider the forward and
backward growth of the ramus
the main mechanism for
shortening and elongating the
effective length.

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 Sagittal discrepancies-minimized by opening and
closing the mandible.


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 “It is a compensating mechanism which is
capable of enlarging or reducing
mandibular length as measured along the
condylion-pogonion diagonal”


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The Third Option-Dibbets
 The first option-Bjork and Skieller’s
Intramatrix rotation-rotation of the
mandibular core relative to the lower
border is the result of genetically
determined condylar growth.
 The second option-Hunterian concept or
the Morphogenetic rotation .

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Bjork’s Approach
•SUPERIMPOSITION SUGGESTS A ROTATION.


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Superimposed on the implants
Change in the inclination of
the implant line relative to
the mandibular plane. www.indiandentalacademy.com
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 This suggests1.when the mandibles are superimposed on the
their contours they are identical in shape and size.
2.The condyle grows on a circular arc (c-c’) with
radius from the chin to condyle.
 This concludes1.The external configuration need not change.
2.Any depositional-resorptive activity maintains the
original contours.

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The painting may be rotated within the frame but the
external outline, configuration and dimensionality, of
the frame is not lost.

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 ‘Every deflection of condylar growth direction
creates the possibility of compensatory
remodeling mostly of the lower border resulting
in intramatrix rotation’.

 Actual effect of growth of the condylar cartilage is
neutralized to a given extent.


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 The second option-The Hunterian concept or
principle of Morphogenetic rotation.
Superimposition based on
traditional Hunterian
conception of Posterior
ramal deposition and
Anterior ramal resorption.
Enlarging and reducing the
mandibular length
measured along the Co-Pog
line.

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 The third option-Based on 2 divergent patterns
of mandibular growth.
1.Intramatrix rotation with absence of
enlargement.
2.Linear condylar growth-evidencing mandibular
enlargement.
Suggested mechanism -

COUNTERBALANCING ROTATION

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COUNTERBALANCING ROTATION“It pertains to the circular condylar growth,
accompanied by selective co-ordinated remodeling ,
which does not contribute to the incremental growth
of the mandible”.
1.The actual path of the condyle relative to fixed and
stable points inside the mandible is accompanied by
selective remodeling-neutralizes growth.
2.Resuts in selective enlargement of the mandible,
apart and distinct from mechanisms that have been
described in literature.

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Counterbalancing
Proportion

 It is the quotient between mandibular and
condylar incremental growth and is expressed as
a percentage.
 Condylar growth and mandibular growth are
weighted in relation to one another.
 The proportion gives a percentage of condylar
relocation that has contributed to actual
mandibular enlargement.

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 Mandibular growth=
Pg-Ar1-PgAr2

 Condylar
growth=distance from
Ar1 to Ar2.
Counterbalancing proportion= Growth from Ar-Pg x 100%
Condylar incremental growth

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 According to the concept of congruous
mandibular growth the proportion should be
100%.
 But study done by Dibbets shows that it ranges
from 50% to 90%.
 This percentage strongly correlates type of
malocclusion.
 Class III-85%
 Class I -76%
 Class II-59%

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Concepts of Mandibular
rotations

What causes mandibular rotation ?


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Enlow’s concept.
 The ramus has a sequence of remodeling
changes to provide for 4 basic functions.
1. Elongation of the corpus.
2. Accommodates for horizontal growth of middle
cranial fossa and pharynx.
3. Accommodates for vertical growth of
nasomaxillary complex.
4. To position the mandibular corpus in proper
position to maxillary corpus.

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 The ramus provides intrinsic capacity for
adaptation .
 If its adequate then class I occlusion results.

MANDIBULAR ROTATIONS

Displacement

Remodeling

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Displacement
 Changes in the junctional contact with the
cranial floor and maxilla.
 Cranial base angleOpen-downward and backward rotation of
mandible.
Closed-forward rotation.


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Closed angle


Open angle

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Short nasomaxillary complex-forward
rotations


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Long nasomaxillary complex –
backwad rotations


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Remodeling


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 Mandible has to
remodel to1.Produce a more upright
ramus.
2.To accommodate for
displacement rotations.


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 Opening and closing of the gonial angle
compensates for extreme forward or
backward rotation.


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Ramal remodeling
Ramus moves
posteriorly-increasing
the length of the
corpus.
Grows horizontally to
match the growth of
the pharyngeal space.
Ceases when growth
stops

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 2nd type of remodeling.
 Makes ramus more upright but does not
increase the horizontal dimension.


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Schudy’s concept
 Variation in the growth at the condyles and the
molar area is responsible for the rotation of the
corpus of the mandible.
 Clockwise rotation-More posterior vertical
growth than condylar growth.
 Counterclockwise-More condylar growth than
the combined vertical growth.

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

Vertical ‘elements’ of
growth
Growth at the condyles =
I- AP growth of nasion.
II- Vertical growth of corpus of maxilla.
III-Vertical growth of maxillary alveolar process.
IV-Vertical growth of mandibular alveolar process.

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Posterior growth analysis
 Ratio between the
vertical and
horizontal growth.
 A=I+II+III+IV


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Bjork’s concept
 Implant studies show-growth of the mandible
occurs essentially at the condyles.
 The anterior aspect of the chin-stable.
 Lower border of the mandibleAt the symphysis-apposition.
At the angle
-resorption.
 The appositional and resorptive areas may
change-determining the type of growth.

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 The growth of the condyle occurs in a upward and
forward curving manner.
 The center of rotation may be located-posteriorly
or anteriorly or somewhere in between.
 The center may not always lie at the TMJ.


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FORWARD ROTATION
 THREE TYPES:
TYPE I
-center at the TMJ.

-underdeveloped anterior
face height.
-deep bite.
Cause: occlusalwww.indiandentalacademy.com
imbalance
or powerful musculature.

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 Type II
-center at the incisal edges of the lower teeth.
- marked increase in posterior face
height and normal anterior face height.

Increase in posterior face height

Lowering of the
middle cranial fossa.

Increased height of
ramus


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 Increase in ramus height
maybe due to vertical
growth of the condyle.
 But this vertical lowering
manifestes as forward
rotation –muscular and
ligamentous attachments.
 Eruption of the molars
keep pace with the
rotation.

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Type III
-center of rotation
is at the premolars.
-deep bite occurs.
cause: Anomalous
occlusion-large
overjets.

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 The inclination of teeth influenced by jaw
rotations.
 Path of eruption of teeth-mesial.
 Crowding occurs in the anterior segment‘PACKING’


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BACKWARD ROTATION
 TWO TYPES:
 Type I
-center at the TMJ.
-underdevelopment of
the posterior face height
occurs-open bite.
causes: 1.middle cranial
fossa is raised.
2.orthodontic bite
raising appliance.
3.oxycephaly.

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TYPE II
-center at distal most occluding molars.
Cause: sagittal (backward ) growth of the condyle.
-The mandible is carried forward but due to
muscle and ligaments attachments its rotated
backwards.


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- the eruption of lower
molars was hindered-the
rotation not due to
overeruption.

-seen in condylar
hypoplasia.


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Thank you
Leader in continuing dental education


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