Bjork’s Concept of Jaw Rotation

Bjork’s
Concept of
Jaw rotation
U N D E R T H E G U I DA N C E O F :
D R . M R I D U L A T R E H A N
P RO F ES S O R A N D H EA D
P R ES E N T E D BY:
D R . D E E KS H A B H A N OT I A
P G I I Y EA R

CONTENTS
 INTRODUCTION
Spiral growth of mandible
MANDIBULAR GROWTH ROTATION
 BJORK’S STUDY
BJORK AND SKEILLER’S METHOD
GROWTH ROTATION OF MAXILLA
MUTUAL RELATIONSHIP OF ROTATING JAW BASE
CONCLUSION
REFERENCES

INTRODUCTION
Every individual has a certain basic pattern of craniofacial growth.
As the craniofacial region grows, many intricate events occur with in and
outside the mandible to maintain its structural integrity and function.
As the facial bones grow, they cause downward and backward rotation of
mandible.
Premkumar S . Text book of Craniofacial Growth 2011, 220-234.

INTRODUCTION
This is compensated by ramus growth and internal remodeling
within the corpus.
To understand growth rotations, the mandible must be imagined
as a long bone which is bent at both ends to join the skull.
The central diaphysis part, hence, is free to rotate.
Premkumar S . Text book of Craniofacial Growth 2011, 220-234.

Moyer RE: Handbook of Orthodontics 2nd Ed; 60

INTRODUCTION
The phrase growth rotation was introduced in 1955 by Bjork. In reporting a case he
states that the lowering of the mandible during growth was “considerably greater
posteriorly than anteriorly, Bjork drew attention to what he called the mandibular
rotation”.
This was based on the fact metallic implants, had given Bjork precise markers from
which he could infer the sites and amount of growth and resorption in a given
mandible.
Bjork A. Prediction of mandibular growth rotation. Am J Orthod.1969;55:585-99.

INTRODUCTION
By superimposing two consecutive tracings of the child's
mandible registered on the implants, the image of the older
mandible appeared to have rotated during the intervening
period relative to its original shape.
The direction of growth and inclination of jaw bases is unique
and no two individuals are alike.
Leonardi M et al Mandibular growth in subjects with infraoccluded deciduous molars. A superimposition study. Angle Orthod 2005;75:927-934.

INTRODUCTION
The rotation of maxillary and mandibular jaw bases is a major
factor in etiological assessment, determining the nature of
anomaly, the prognostic evaluation, determining the possible
forms of treatment, in choosing the principles of treatment and
also in assessing the stability of treatment results.

INTRODUCTION
Certain rotational patterns of jaw bases can be manipulated
quite effectively by means of functional and orthopedic devices
while certain extreme rotations are very difficult to treat and
surgical correction has to be performed at a later stage.

The growth at the condyles shows large variations in amount and direction,
especially during the pubertal spurt and usually does not occur in the direction
of the growth of the ramus.
Instead, it occurs in a direction which is slightly forward, with a curved path, and
varies significantly among individuals.
SPIRALGROWTHOFMANDIBLE1974inajo

Moss and Salentejin predicted that mandible’s rotational growth was along a
spiral path.
Its inspiration is derive from the concept of “gonomic growth”by D’Arcy
Thompson.
He has explained the two fundamental features of chambered nautilus:-
The shell grows in size and there is no change in shape.
SPIRALGROWTHOFMANDIBLE1974inajo
Moss ML, Moss-Salentijn L, Ostreicher HP. The logarithmic properties of active and passive mandibular growth. AJO 1974; 66(6):645-64.

The original shape is maintained
despite the asymmetric growth.
This portion of increment, which even
added, does not alter the shape but
only produces an increase in size is
called as gnomon.(in greek)
Thompson called the growth along
spiral as “gnomonic growth”.
SPIRALGROWTHOFMANDIBLE

The next feature of chambered nautilus is that the
gonomic growth can be described by a curve.
This curve is called as logarithmic or equiangular spiral.
The important feature of this spiral is the movement of
a point away from the pole along the radius vector with
the velocity increasing with the distance from the pole.

The angles formed with the pole will be equal.
The formula ɵ = k log r implies that the vector angles about the pole are
proportional to the logarithms of the successive radii. Hence they are called the
logarithmic spiral.
Moss and Salentijn conducted study on mandibles acquired at various stages
from the skull of dead American Indians.
Moss postulated that growth of mandible could be influenced by the inferior
alveolar nerve and its direction depends on the course of the nerve.

Lead shots were implanted at three foramina along the path of the nerve,
namely the foramen ovale, mandibular foramen, mental foramen.
Mandibles at 4 different stages of development were included in the study:
Fetal, deciduous, mixed dentition, adult mandible.
The X rays were superimposed ad it was found that the path of inferior
alveolar nerve was along a logarithmic curve and that the four curves of all
mandibles were superimposed.

As the bone increases in size, the spiral
itself does not change, instead, the
mandible changes in position and the
base appears to rotate along the spiral,
moving to a position where there is
less curvature of a spiral because as
the bone lengthens with growth, the
distance between foramina increases.

Mandibular rotations assume an important role in orthodontics
treatment planning because mandibular rotations are more common
than maxillary rotations.
Mandibular inclination drastically affects facial morphology, and
treatment planning and treatment outcome and mandibular
inclination to a certain extent can be effectively guided by certain
functional or orthopedic appliances during growth period.
Premkumar S . Text book of Craniofacial Growth 2011. 220-234.

Bjork study
Started his study in 1951
Mixed longitudinal study of 100 children between the age group of 4 – 24 yrs.
Used metal implants
- to find the sites of growth and resorption in individual jaws.
- examined individual variation in direction and intensity.
- Analyzed mechanism of changes in intermaxillary relations during growth.
Bjork A. Prediction of mandibular growth rotation. AJO 1969;55:585-99.

Bjork study
Implants were placed in the following sites of
mandible:-
◦ Anterior aspect of symphysis, in the midline below the
root tips.
◦ Two pins on the right side of mandibular body. One pin
under the first premolar and the other below the second
premolar on the first molar.
◦ One pin on the external aspect of the right ramus in level
with the occlusal surface of the molars.
Bjork A. Prediction of mandibular growth rotation. AJO.1969;55:585-99.

Resultsof study
Growth in length of the mandible in
man occurs essentially at the
condyles.
The anterior aspect of the chin is
extremely stable.
The thickening of the symphysis
normally takes place by apposition on
its posterior surface. On its lower
border there is likewise apposition,
which contributes to the increase in
height of the symphysis.

Below the angle of the mandible there
is normally resorption, which may be
very pronounced.
The growth at the condyles usually
does not occur in the direction of the
ramus.
The mandibular canal is not
remodeled to the same extent as the
outer surface of the jaw. The
curvature of the mandibular canal,
therefore, reflects the earlier shape of
the mandible.

BJORK’SCLASSIFICATION
FORWARD
ROTATION
TYPE I
TYPE II
BACKWARD
ROTATION
TYPE I
TYPE II
TYPE III

Centre of rotation
Centers in the joints.
The lower dental arch is pressed into the upper,
resulting in
- deep bite
- under development of the anterior face
height.
Cause
occlusal imbalance due to loss of teeth powerful
muscular pressure.
TYPE I (ForwardRotation):

Centre of rotation
Center located at the incisal edges of the lower
anterior teeth.
Due to the combination
- marked development of the posterior face height
- normal increase in anterior face height.
2 Components of posterior facial height
1. Lowering to middle cranial fossae in relation to
anterior one
2. Increase in height of ramus
TYPEIIFORWARDROTATION

Centre of rotation
TYPEIiiFORWARDROTATION
Occurs in anomalous occlusion of
the anterior teeth where there is a
large overjet.
Center of rotation displaced
backward to the level of the
premolars.
Dental arches are pressed into each
other - basal deep bite develops
- the anterior face height becomes
underdeveloped

TYPEIBACKWARDROTATION
Centre of rotation
Centre of rotation lies in the TMJ
Occurs when bite is raised by orthodontic means.
- Flattening of the cranial base, the middle cranial
fossae are raised in relation to the anterior one, and
the mandible is also raised.
- Incomplete development in height of the middle
cranial fossa ( as in oxycephaly),the underdeveloped
posterior facial height leads to a backward rotation of
mandible.
Open bite as a consequence.

TYPEIIBACKWARDROTATION
Centre of rotation is situated at the most distal
occluding molars
Occurs in connection with growth in the sagital
direction at the condyles.
As the mandible grows in the direction of its length it
is carried forward more than it is lowered in the face
and because of its attachment to muscles and
ligaments it is rotated backward.
Double chin, Open bite, Difficulty in closing the lips
Centre of rotation

From the clinical standpoint, it is important to detect extreme types of
mandibular rotation occurring during growth.
Seven structural signs of extreme growth rotation will be considered in relation
to the condylar growth direction.
Not all of them will be found in a particular individual, but the greater the
number that are present, the more reliable the prediction will be.
Moreover, it is evident that these signs are not so clearly developed before
puberty.
STRUCTURALSIGNSOFGROWTHROTATION

1.Inclination of the condylar head
2.Curvature of the mandibular canal
3.Shape of lower border of mandible
4.Inclination of the symphysis
5.Inter molar angle
6.Inter incisal angle
7.Anterior lower face height.
STRUCTURALSIGNSOFGROWTHROTATION

These signs are illustrated by the two craniums shown
in Fig.
In one of them there is a basal deep-bite, caused by
extreme forward rotation, Type III, conjunction with
growth at the condyles which is presumed to have been
vertical.
In the other there is a basal open-bite after what is
presumed to have been a backward rotation of the
mandible where the condylar growth must have been
directed backward.

 A forward or backward
inclination of the condylar head
is a characteristic sign, but it
may not be easy to identify on
the cephalometric radiogram,
where part of the condyle is
masked.
1.Inclination of the condylar head

2.Curvature of the mandibular canal
The curving of the mandibular
canal may also be a clear sign.
In the vertical type of condylar
growth, the curvature of the
canal tends to be greater than,
that of the mandibular contour,
including the angle of the jaw,
whereas in the sagittal type the
opposite is generally the case.

3.Shape of lower border
of mandible
The shape of the lower border of the mandible is highly
characteristic.
In sagittal growth, the anterior rounding is absent and the
cortical layer is thin, while the lower contour at the jaw angle is
convex.
In vertical condylar growth, the pronounced apposition below
the symphysis and the anterior part of the mandible produces an
anterior rounding, with a thick cortical layer, while the
resorption at the angle produces a typical concavity.
HORZONTAL
CONDYLAR GROWTH
VERTICAL
CONDYLAR GROWTH

4.Inclination of the symphysis
This is measured as the angle
between the tangent to the
anterior surface of the
mandible and the anterior
cranial base.
◦ In horizontal growers chin swings
forward to become prominent.
◦ In vertical growers symphysis is swung
backward causing a receding chin.

5.Inter molar angle
The inter molar angle tends to increase in forward rotation of the mandible and
decrease when the rotation is directed backward.

6.Inter incisal angle
In backward rotation the inter incisal angle is reduced (b), where as in forward
rotation it is increased (a).
BACKWARD ROTATION FORWARD ROTATION

7.Anterior lower face height.
In forward growth rotation there is deep overbite and reduced lower face
height.
 In backward rotation there is increased lower face height and open bite.
a) Forward growth rotation of the
mandible with normal incisal occlusion
b) Forward rotation with deep over
bite & reduced LAFH
c) Backward rotation with increased
LAFH

LOWER ANTERIOR FACIAL HEIGHT

ACCORDING TO BJORK AND SKIELLER
TOTAL ROTATION
MATRIX ROTATION
INTRAMATRIX ROTATION
Leslie LR et al. Prediction of mandibular growth rotation: assessment of Skeiller, Bjork, & Linear-Hansen method. Am J Orthod Dentofacial Orthop 1998; 114:659-67.

TOTAL ROTATION
Rotation of the mandibular corpus
Measured as change in inclination
of a reference line or a implant
line in the mandibular corpus
relative to the anterior cranial
base

Defined it “as a rotation of the
soft tissue matrix of the
mandible relative to the cranial
base”. The soft tissue matrix is
the tangential mandibular line.
It has its center at the condyles.
MATRIX ROTATION

The difference between the total rotation and matrix rotation is an expression
of the remodeling at the lower border of the mandible.
It is identified by the change in inclination of a reference line/ implant line in the
mandibular corpus relative to the tangential mandibular line. The center of
rotation lies in the corpus.
INTRAMATRIX ROTATION

Change in the inclination of the
implant line relative to the
mandibular plane.
Superimposed on the implants
Schematic illustration of
intramatrix rotation

CONDITION BJORK SCHUDY
Back ward
Rotation
Clockwise
Rotation
Forward
Rotation
Counter
clockwise
Rotation
ANTERIOR GROWTH
GREATER THAN
POSTERIOR GROWTH
POSTERIOR GROWTH
GREATER THAN
ANTERIOR GROWTH
TERMINOLOGIES & SUMMARY OF GROWTH ROTATION

Solow,
Houston
Proffit
Lavergne,
Gasson Enlow Dibbets
Rotation of
mandibular
core
relative to
cranial
base
Total
rotation
Bjork &
Skieller
Condition
True
rotation
Internal
rotation
Rotation
of
mandibular
Plane
relative to
cranial base
Matrix
rotation
Apparent
rotation
Total
rotation
Positional
rotation
Displac-
ement
rotation
Rotation of
Mandibular
plane
relative to
core of
mandible
Intra
matrix
rotation
External
rotation
Morphog-
enetic
Rotation
Remo-
delling
Rota-
tion
Counter
Balan-
cing
rotation
Angular
Remod-
eling
Of lower
border

Generally, the vector of maxillary growth is in
anterior and inferior direction (downward and
forward displacement).
Due to the varying growth activities of middle
cranial fossa, the sutural attachments of
midface and surface remodeling, the maxilla
tends to get rotated by displacement.

Bjork and Skeiller (1972) studied this
rotational growth of maxilla with the
help of implants.
Those sites selected by Bjork include:-
◦ Inferior to anterior nasal spine
◦ In the zygomatic process of
maxilla(lateral implant)
◦ At the border between the hard
and the alveolar process mesial to
molar.

The lateral implant placed on anterior and posterior contour of
zygomatic process seems to give best results when compared
to other sites.
Bjork and Skeiller introduced various terminologies to describe
the growth rotation of maxilla.

Internal rotation
This is the rotational pattern that occurs in the
core of maxilla.
This is also called as intramatrix rotation.

External rotation
Simultaneous to internal rotation of maxilla, varying degrees of
resorption of bone on the nasal side and apposition of bone of
the palatal side in anterior and posterior parts of the palate also
also takes place.
All these changes collectively contribute to external rotation.

External rotation
This external rotation is usually opposite in direction and
equal in magnitude to the internal rotation, so that the two
rotations cancel each other and the net change in jaw
orientation, as evaluated by the palatal plane is zero .

Depending upon the different degrees of combination of internal
and external rotations, Bjork and Skeiller observed two types of
rotational growth.
The terminologies used are forward and backward rotation.
FORWARD GROWTH ROTATION
This condition occurs either due to excessive internal rotation or lack
of normal compensatory external rotation or a combination of both.
The maxilla is inclined upwards and forward, the anterior end is
tipped up.
Schwarz – Ante inclination

This forward rotation also tends to
tip the incisors forward, increasing
their prominence.
The extent of forward tipping in
relation to anterior cranial base is
given in degrees by Schwarz.

The inclination angle is not
measured directly but is defined
as the angle between the Pn-
perpendicular and the palatal
plane (J angle).
In ante inclination, this angle is
greater than 85 degrees where
as in normal inclination it is
equal to 85 degrees.

BACKWARD ROTATION
In this there is downward and backward tipping of the anterior end of the
palatal plane and the maxillary base.
Retroclination – by Schwarz
In this type , the jaw bases are translated posteriorly and upper incisors
appear to tip lingually.
J angle is less than 85 degrees.

Though the growth related rotation does occur in the midface, extreme
rotational patterns are often compounded with various environmental
disturbances.
According to Linder-Aronson, Lowe, and Woodside, various environmental
influences such as neuromuscular dysfunction, occlusal forces etc can cause
extreme rotation of jaw bases.

An upward and forward tipping of
the anterior part of maxiila is often
confirmed in mouth breathers,
while a downward and backward
tipping of anterior part in maxilla is
observed as a natural
compensation in patients with
vertically growing faces.

JAW ROTATION AND TOOTH
ERUPTION
The rotation of the face necessitates compensatory adaptation of the paths
of eruption of the teeth.
When there is full compensatory occlusal development, the lower incisors
retain their inclination in the face practically undisturbed, irrespective of
the rotation of the jaw, because of a forward tipping on the jaw base.
The posterior teeth in the lower jaw, too, involved in this compensatory
occlusal development and are, likewise, tipped forward.
Kharbanda O P. Diagnosis and Management of Malocclusion and Dentofacial Defomities. 2nd Ed 2013. 129-131.

The lower dental arch then shifts forward on the jaw base with out undergoing any
appreciable change in shape.
The intermolar inclination remains comparatively constant as the lateral teeth in
both jaws follow the rotation of the face.
In forward rotation of maxilla, the incisors tend to tip forward increasing their
prominence, while in the backward type of rotation, the anterior teeth are directed
more posteriorly, relatively decreasing their prominence and uprighting them.

The eruption path of mandibular teeth is normally upward and forward.
In excessive forward rotation in short faced individuals, the incisors to be
carried in to an overlapping position , hence there is tendency towards
deep bite malocclusion.
Due to the lingual movement of lower incisors, there is reduction in arch
length because of rotational changes and this is more evident in mandible
when compared to the maxilla.

MUTUAL RELATIONSHIP OF ROTATING
JAW BASES
Rotation of mandible decides the vertical proportions of the
face.
Horizontal growers have a
◦ Short lower anterior facial height.
◦ Predisposed to having a deep bite.
vertical growers have a
- long lower anterior facial height.
◦ Predisposed to having a open bite

According to Lavergne and Gasson the mutual rotation of
the upper and lower jaw can be of following 4 types
1. CONVERGENT ROTATION
2. DIVERGENT JAW BASES.
3. CRANIAL ROTATION OF BOTH THE BASES.
4. CAUDAL ROTATION OF BOTH JAWS

1. Convergent rotation.
 True severe deep bite.
 Both maxilla and
mandible converge
towards each other.
 Difficult to treat with a
functional therapy.

2. Divergent jaw bases.
 Severe open bite.
 Maxiila and
mandible move
away from each
other.
 In severe cases
orthognathic
surgery is required.

3. Cranial rotation of
both the bases.
 Horizontal growth
pattern.
 Maxillary cranial
rotation
compensates for
the mandibular
rotation.
 Normal overbite.

3. Caudal rotation of both bases.
 Vertical growth
pattern.
 Maxillary caudal
rotation compensates
for the mandibular
rotation.
 Normal overbite.

Effects of mandibular growth on
the dental occlusion.
In forward rotators, the inter-premolar and
inter-molar angles increased, leading to
posterior teeth being more upright on the jaw
base.
The lower anterior teeth are also guided
forward resulting in the alveolar prognathism.
Proffit W R, Fields H W, Sarver D M. Contemporary Orthodontics 5th Ed 2007.114-119.

However, since all mandibular teeth show
mesial migration on the mandibular base,
the lower incisors have a tendency to show
crowding which is called ‘packing’.
CROWDING

In contrast, in patients with backward rotation pattern, the inter-
premolar and inter-molar angles are small, which means that the
premolars and molars are inclined forward in relation to maxillary
bases, which is an important consideration while planning
anchorage during orthodontic treatment.

The lower teeth also tend to become more upright on the jaw bases, thus
reducing alveolar prognathism and increasing the incisor crowding.

CONCLUSION
Orthodontist are interested in facial growth and development basically
because growth can be altered for the need of application of therapy.
Therefore we should predict future growth changes that occur thereby
avoid making undesirable changes and can alter undesirable growth
pattern.
The rotation of the mandible during growth appears to be a complex
phenomenon showing annual variations in direction & intensity.

CONCLUSION
Such rotation is not only dependent on mandibular factors, but
also is strongly related to the intensity of growth of both jaws.
Clinician should confine his effort to correct the abnormal
growth pattern during the process of correcting the
malocclusion for better prognosis.

•Premkumar S . Text book of Craniofacial Growth 2011, 220-234.
•Moyer RE: Handbook of Orthodontics 2nd Ed; 60
•Bjork A. Prediction of mandibular growth rotation. Am J Orthod.1969;55:585-99.
•Leonardi M et al Mandibular growth in subjects with infraoccluded deciduous molars. A superimposition
study. Angle Orthod 2005;75:927-934.
•Leslie LR et al. Prediction of mandibular growth rotation: assessment of Skeiller, Bjork, & Linear-Hansen
method. Am J Orthod Dentofacial Orthop 1998; 114:659-67.
•Kharbanda O P. Diagnosis and Management of Malocclusion and Dentofacial Defomities. 2nd Ed 2013.
129-131.
•Proffit W R, Fields H W, Sarver D M. Contemporary Orthodontics 5th Ed 2007.114-119.

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