Growth rotations /certified fixed orthodontic courses by Indian dental academy

GROWTH
ROTATIONS

INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

Introduction

Traditional view : mandible grows in a
downward and forward direction via
posterior growth and anterior
displacement.

Rotation: Bjork ( 1955)
Since then , the concept has been an
issue of debate!!
Rotational aspect greatly influences
therapeutic result of orthodontic
treatment.

General concepts of
craniofacial bone growth







Articular growth
Remodelling growth
Increased volume of craniofacial
cavities surrounding bones
displaced differential articular bone
growth occurs.
Overall change in shape and size due
to both articular & remodelling growth
3 Dimensions: Rotation + Translation
Assessed by superimpositions.



Bjork’s studies on
growth rotation




Mixed longitudinal study begun in
1951 at Dept of Orthodontics, Royal
Dental College, Copenhagen.
Sample: 100 persons of each sex.
Age range 4-24 years.
Normal Healthy children with
&
without
malocclusion, & also children with
pathologic conditions.

Mandibular Growth pattern:
 Condylar growth  increased length of
mandible.
 Ant. Aspect of chin : stable
Thickening of symphysis: lower border
and posterior surface.
 Ant part of lower border of mand :
periosteal apposition.
 Below Angle: resorption



Apposition + Resorption  individual
shaping of lower border, which
characterizes the type of growth.



Mand. Canal curvature: reflects earlier
shape of mandible



Lower border of developing molar tooth
germ: relatively stationary till root
formation begins. Can act as natural
reference structure for growth analysis.

Two types of rotation



( I)FORWARD

ROTATION
Type I :
- Center in the joint.
- lower dental arch
pressed into upper;
underdeveloped ant.
face height.
- Cause: occlusal
imbalance due to loss
of teeth or powerful
muscular pressure.







Type II:
Center at incisal
edges of lower
anteriors.
Cause: combination
of marked
development of the
posterior face
height, and normal
increase in the
anterior height









Vertical direction of condylar growth 
mandible lowered more than it is carried
forward.
Muscular & Ligamentous attachments 
forward rotation with center at incisal
edges.
Eruption of molars keeps pace with
rotation.
Resorption below gonial angle 
remodelling.








Type III:
In Case of large
maxillary overjet or
mandibular overjet, CRot
no longer at incisors, but
displaced backward to
premolar region.
Ant. Face height
underdeveloped,
posterior face height
increases.
Basal deep bite




In Growth Rotations of Type II and III,
symphysis swings forward to a marked
degree and chin becomes prominent.








(II) BACKWARD
ROTATION
Type I:
CRot lies in TMJ
Eg.: when bite is
raised by
orthodontic means,
change in
intercuspation or
bite raising
appliance.





Increase in Ant. Face height.
May occur in connection with growth
of cranial base:

Flattening of cranial base  Middle
cranial fossa raised in relation to
anterior one 
Incomplete development in
height of MCF
--- mandible
raised







Type II:
Center at most distal
occluding molars.
Growth in sagittal
direction at mand.
condyle; curves
increasingly backward
As the mandible grows
in the direction of its
length, it is carried
forward more than it is
lowered, and because of
muscular and ligament
attachments, it rotates
backward.




Symphysis swung backward, chin
drawn back below face.
Soft- tissues may not follow  doublechin



Basal open bite can develop, with lip
strain.

BJORK’S 7 STRUCTURAL SIGNS
OF GROWTH ROTATION






Help to detect extreme patterns of
rotation during growth.
Not all signs are present in 1
individual; greater the no., more
reliable the prediction.
Not so clearly developed before
puberty.

1)

Inclination of condylar head:
forward  forward rotation
backward  backward rotation

2)

Curving of Mand. Canal:
forward rotators  curve greater than that of contour
backward rotators  canal straight or curved in opp.
direction.

3) Shape of lower border:
forward rotators  apposition below symphysis
produces anterior rounding & thick cortical layer, while
resorption at angle produces typical concavity.
backward rotators ant. rounding absent, cortical layer
thin, lower contour at www.indiandentalacademy.com
jaw angle convex.

4) Inclination of symphysis:
forward rotators  symphysis swung forward, prominent chin.
backward rotatots  symphysis swung back, receding chin.

5) Inter-incisal angle:
increased in forward rotation.
decreased in backward rotation.

6) Inter-molar angle:
increases in forward rotation ( lower posteriors upright)
decreases in backward rotation ( lower posteriors mesially inclined)

7) Anterior lower face height:
decreased in forward rotation.
increased in backward rotation.

Structural signs of mandibular
growth rotation demonstrated in
two craniums-one with basal
deep-bite and one with basal
open-bite.




Skieller, Bjork & Linde Hansen (AJO 1984):
- 21 individuals from original
implant study.
-44 morphologic variables evaluated.
- 4 variables gave best prognostic estimate (86%)
of mand. growth rotation:
1) Mandibular inclination, represented by
3 alternatives:
(a) Index 1 ( proportion between PFH & AFH)
(b) Lower gonial angle.
(c) Inclination of lower border (NL – ML1)
2) Intermolar angle
3) Shape of lower border
4) Inclination of symphysis.





Limitations: represented cases with
extreme growth patterns.
Leslie et al (AJO 1998) : not clinically
useful to predict mandibular rotation in
a general population.


COMPONENTS OF ROTATION


Bjork & Skieller ( EJO 1983):
emergence of different patterns when
different registrations for
superimposition were used.

Superimposition on cranial base

Superimposition on metallic implants
Superimposition on metallic implants

Striking contrast



1)

Divided the
phenomenon of rotation
into 3 components:
TOTAL ROTATION
- Rotation of the mand
corpus measured as a
change in inclination of
implant line relative to
the anterior cranial
base.
- largely determined by
amount & direction of
growth in the condyles.

2) MATRIX ROTATION:
-Rotation of the soft
tissue matrix of the
mandible relative to
cranial base ( soft
tissue matrix defined
by
tangential
mandibular line).
- center at condyles.
- articular growth +
remodelling.

3) INTRAMATRIX
ROTATION :
Change in the inclination of
an impalnt line or
reference line in the
corpus relative to the
tangential mandibular
line.
Difference between the total
rotation and the matrix
rotation; expression of
remodelling at the lower
border







Center somewhere in the corpus.
Independent rotation of the corpus within
the outer contour of the mandible.
Concept based upon local behaviour of
sites of deposition & resorption.
According to Rune et al (EJO 1987), the
defining of various centers of rotation for
bone contours affected by remodelling is
inappropriate, as only displacements that
satisfy the concept of rigid body model can
be accounted for, and not those due to
remodelling.

Schudy’s studies ( Fred Schudy,
Angle 1965)






Clockwise & counterclockwise rotation
Hypo- & hyper-divergence.
Final vector of growth of the chin is a
resultant of the struggle between
horizontal growth ( growth at condyles)
& vertical growth (vertical growth of
molars)
Resultant  downward, forward
direction.





A > I + II + III + IV 
-Hypodivergent facial
pattern.
- Mand plane becomes
flatter.
- Pogonion moves
forward more than
Nasion.
A < I + II + III + IV
-Hyperdivergent pattern
- mand. Plane becomes
steeper
- Pogonion moves back.








“ It is not the growth pattern of the mandible per
se which primarily determines its posture, but
instead the vertical growth if the maxilla”.
Clockwise rotation ( viewed from right): more
posterior vertical growth than condylar growth,
point of rotation being the condyles. ( Bjork’s
Backward Rotation)
Counterclockwise rotation : more condylar
growth than combined vertical growth, point of
rotation is most distal molar in oclusal contact.
( Bjork’s Forward Rotation)


Lavergne & Gasson: Metal implant study
of mandibular rotation ( Angle 1976)
Defined rotation as positional &
morphogenetic.
 Morphogenetic : concerns the shape
of the mandible itself
The angle between 2 implant lines
when 2 cephs are superimposed on a
line through Condylion & Pogonion.
 Similar to Bjork’s concept of
intramatrix rotation.





Positional rotation : Deals with position
of mandible within the head.

Degree of
rotation

Difference in rate of growth
between jaws




Unlike Bjork & Skieller, they do not
consider the key factor in intramatrix
rotation to be found in corpus; they locate
the effective mechanism in the ramus and
its forward or backward growth, thereby
shortening or elongating the effective
length of the mandible.



Opening/ closing of gonial angle 
minimizes manxillary-mandibular sagittal
discrepancy.

Dibbets’s concept of
counterbalancing rotation ( AJO
1985, AJO 1990)


1)

Based on 2 diverging patterns of
mandibular growth:
A circular growth pattern, resulting
only in intramatrix rotation, & marked
by absence of actual mandibular
enlargement.
( condylar growth as the segment of a
circle with its center at the chin).

2) Linear growth curve of the condyle
along Pogonion-Condylion diagonal,
resulting in maximum enlargement,
without any “intramatrix” rotation.
 Most children fall between these 2
postulated extreme patterns.






The dimension pogonion
to articulare represents
mandibular size.
Mandibular growth is
determined by
subtracting Pg-Ar1 from
Pg-Ar2. Condylar growth
is represented by the
dimension Ar1 to Ar2.
Counterbalancing
proportion =
Growth of Ar to Pg X 100%
Condylar incremental growth






Should approximate 100% in
congruous mandibular growth. (In
reality  50-97%)
“Thus, counterbalancing rotation
pertains to circular condylar growth,
accompanied by selective coordinated
remodelling, which does not contribute
to the incremental growth of the
mandible”.

Solow & Houston’s terminology
( EJO 1988)




ROTATION: only displacements that
satisfy the concept of rigid body
model.
ANGULAR CHANGE: change in form
due to surface accretion and removal,
causing change in orientation between
reference lines within that body.



1)

2)

3)

3 changes with respect to growth rotation of
mandible:
True rotation of mandible: Rotation of Mand.
body relative to anterior cranial base. ( Total
Rotation)
Apparent rotation of mandible: Angular change
of mandibular line relative to anterior cranial
base. True Rotation + Remodelling. ( Matrix
rotation)
Angular remodelling of lower border: Angular
change of mand. line when mandible is
registered on implants or stable trabecular
structures. ( Intramatrix rotation)

Proffit’s terminology & comparison with
other authors
Condition

Bjork

Schudy

Post.
Growth>
Anterior

Forward
Rotation

Counter

Ant Growth Backward
> Posterior

clockwise
(Viewed
from right)
Clockwise

Bjork

Rotation of
mand core
relative to
cranial base
Rotation of
mand plane
relative to
cranial base
Rotation of
mand plane
relative to core
of mandible

Solow,
Houston

Proffit

Total Rotation

True rotation

Internal Rotation

Matrix rotation

Apparent
rotation

Total rotation

Intramatrix
rotation

Angular
remodelling of
lower border

External rotation


GROWTH ROTATION OF MAXILLA







Small & variable degree of rotation.
Forward  more usual pattern.
Analogous to intramatrix rotation of
mandible.
Varying degrees of resorption on nasal side
& apposition on palatal side. Similar
variations in the amount of eruption of the
molars & incosors occur. These changes
amount to external rotation.
Mostly, external = internal rotation, Net =0

INTERACTION BETWEEN JAW
ROTATION & TOOTH ERUPTION


Rotation

magnitude
tooth eruption
direction

Translocation within jaw + True eruption 
Movement of teeth relative to cranial base







Maxillary teeth : path of eruption is
downward, somewhat forward.
Forward rotation of maxilla  tends to
tip incisors forward, increasing their
prominence.
Backward rotation  relatively
uprights the ant teeth, decreases their
prominence.








Mandibular teeth: eruption path upward & somewhat
forward.
Forward rotation uprights incisors
Molars migrate furthur mesially than do incisors
decreased mand arch length  crowding tendency.
Incisors carried into overlapping position, hence deep
bite.
Lower Posterior teeth upright, hence increased intermolar
angle.
Backward rotation Ant open bite as AFH increases.
Incisors carried forward, creating dental protrusion.
Reduced intermolar angle.
Brin et al ( AJO 1982) no significant correlations
between molar occlusion & growth rotation.

References
1)
2)

3)

4)

Bjork A. Prediction of mandibular growth rotation.
Am J Orthod 1969;55:585-599.
Skieller V, Bjork A, Linde-Hansen T. Prediction of
mandibular growth rotation evaluated from a
longitudinal implant study. Am J Orthod
1984;86:359-370.
Leslie et al. Prediction of mandibular growth
rotation: assessment of the Skieller, Bjork &
Linde-Hansen method. Am J Orthod Dentofacial
Orthop 1998;114:659-67.
Schudy F.The rotation of the mandible resulting
from growth: its implications in treatment. Angle
Ortho 1965;35:36-50.

5) Diabbets. Mandibular rotation & enlargement. Am J
Orthod Dentofacial Orthop 1990;98:29-32.
6)Dibbets. The puzzle of growth rotation. Am J Orthod
1985;87:473-480.
7)Solow & Houston. Mandible rotations: concepts &
terminology. EJO 1988;10:177-179.
8)Brine et al. Molar occlusion & mandible rotation: a
longitudinal study. Am J Orthod 1982;81:397-403.
9) Lavergne & Gasson. Metal implant study on
mandibular rotation. Angle ORthod 1976;46:144150.
10) Rune et al. Growth Rotation– A puzzle? EJO
1987;9:237-239.


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Growth rotations /certified fixed orthodontic courses by Indian dental academy

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