Bjork's contribution to implant studies and facial growth. /certified fixed orthodontic courses by Indian dental academy

BJORK’S CONTRIBUTION
TO IMPLANT STUDIES AND
FACIAL GROWTH
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

• Arne Bjork- The Man and his work.
• Method and application of use of metallic
implants.
• Three dimensional growth of the maxilla
• Growth of the Mandible and Growth
Rotations
• Growth Rotation of the Frontal Bone.
• Study of RME using metallic implants.

Arne Bjork- The Man and his Work.
• Arne Bjork is internationally known for his
contributions to the understanding of craniofacial
growth.
• His early publication, The Face in Profile, 1947,
made him known all over the world.
• Bjork practiced as a clinician in Sweden for 14
years before moving to Denmark in 1951, where
he chaired the Dept of Orthodontics,Royal Dental
College, Copenhagen.

• There, Bjork combined the methods of metallic
implantation and serial cephalometric
roentgenography to unravel the secrets of facial
growth.
• His sample consisted of children attending the
Department of Orthodontics, who were willing
to take part in the study.
• Around 100 persons of each sex were included
in this study, having different types of
malocclusions, and ranging from 4-25 years of
age.

• The implant method was used and annual
radiographs were obtained from childhood
to adulthood.
• The systematic superimposition of these
serial radiographs with the help of implants
form the basis of Bjork’s studies.
• The results of these studies have been
published in the major American and
European journals since the 1950s and have
become classics on the subject of facial
growth.

Method and application of the use of metallic
implants.
• Small pins of hard
tantalum are
hammered into
bone under local
analgesia with a
special pencil-
shaped instrument
in which the
implant is placed.

• The tantalum pins are
more radiopaque than
chrome cobalt alloy and
retain their position in
bone well.
• These measure 1.5mm
in length and 0.5mm in
diameter.
• A smaller pin has also
been designed,
measuring 1.2 x 0.37
mm.
• The instrument is made
of stainless steel and
has a hard, replaceable
tip, into which the pin
fits.

• The instrument is pressed through
the periosteum to secure a firm basis
before the pin is hammered in.

Sites for Implant placement
The mandible:
Before the pins are
inserted, the form
of the mandible and
position of the
dental germs are
studied on the
profile radiographs.
Usually, 5 or 6 pins
are inserted in 4
regions.

• Region 1: One pin is placed on the anterior aspect of the
symphysis, as low down as possible in the midline beneath
the germs or root tips. This pin has proved to be highly
stable, but may be exposed by resorption, if placed too
high in the supramental region.
• Region2: Two pins are inserted on the right side of the
basal part of the mandible, under the 1st
premolar and 2nd
premolar (or 1st
molar), beneath their germs or root apices.
• Region 3: One pin is placed on the external aspect of the
right ramus, on a level with occlusal surfaces of the
molars. This may be gradually exposed by resorption and a
new one needed.
• Region 4: One or two pins are also inserted in the
mandibular base on the left side, under the 2nd
premolar or
1st
molar.( By using small pins on the right side and larger
ones on the left, they can be recognized easily.)

The Maxilla
• There are 4 regions in which implants are unlikely to be disturbed.
• It is usual to use six implants, preferably small ones on the right
side.
• Region 1: Before eruption
of permanent incisors, pins
are inserted, one on each
side of the hard palate,
behind the deciduous
canines, near the median
plane of the face.(Their
stability depends on the
extent to which the nasal
floor is lowered by
resorption process.)

• Region 2: After eruption
of the permanent central
incisors, an implant is
placed on each side of
the median suture, below
the anterior nasal spine
• Useful for analyzing
sutural growth of upper
face in sagittal plane as
well as transverse growth
of maxilla.
Region 3: Even at an early age, 2 implants can be placed in the
zygomatic processes of the maxilla on each side of the head.

• In order not to be disturbed
by erupting teeth, these
must be placed lateral to
the alveolar process.
• Occasionally when there
is a thin bone wall and
maxillary sinus increases
greatly during growth, one
implant may be lost
through the nose.)
•These implants are particularly useful for measuring growth in
the width of the maxilla in the median suture.www.indiandentalacademy.com

• Region 4: Implants have also been placed with
good results at the border of the hard palate and
the alveolar process, medially to the 1st
molar.
• It is standard technique to insert pins in both jaws
as described.

Radiographic Method:
• Reproducibility of head positioning in the
cephalostat is very necessary in implant studies.
• Any discrepancies in this procedure from year to
year will result in differences in projection,
causing large and unacceptable errors.
• Bjork used a specially designed X-ray cephalostat
with a built-in 5” image intensifier which would
enable the position of the head to be monitored by
television.

•The setting of the head in the
cephalostat is carried out by
traditional 3 point contact,
(two ear rods and a nose rest),
and in addition, a vertical and
horizontal beam of light,
delineating the median plane
and the level of the ear rods.
•Setting by means of ear rods
is not rigid. Fine adjustment
is monitored by television.

Evaluation of facial growth using serial
radiographs:
• In order to avoid
the errors
associated with
the tracing
procedure, a
printer called the
Log-Etronic
printer combined
with an enlarger
is used.

• By copying
superimposed films
by the Log-Etronic
technique, a picture
of the growth of the
face or of a single
jaw is obtained in a
lateral view.
• These pictures are
obtained by
superimposing the
positive films of the
radiographs to be
compared and
making a negative
Log-Etronic film of
the superimposed
films. www.indiandentalacademy.com

Method of Superimposition:
• Evaluation of facial growth is based on superimposition of
film from various stages of development, on the anterior
cranial base.
• The films are superimposed so as to obtain the closest
coincidence for the maximum number of structures in the
anterior cranial fossa.: cribriform plate, medial border of
orbital roof, trabecular system, anterior walls of median
fossae,and anterior contours of pterygopalatine fossae. These
are used to obtain a negative composite Log-Etronic film.
• This orientation shows remodeling of the sella from late
juvenile to adult age, as well as forward movement of nasion.
• This is called the structural method of superimpositionwww.indiandentalacademy.com

.
• In execution of the growth tracing, positive Log-
Etronic film is made and traced for each of the
radiographs in the series, and the positives are
superimposed as described.
• The Nasion –Sella line can be used in growth
analysis only after adjustments have been made
for forward displacement of Nasion and
remodeling of Sella.
• The practical method consists in placing a sheet
of cellophane, with printed cross-lines on the top
of the first film of a series, passing through the
nasion with the center of the cross-lines at the
Sella point

.
• The tracings are superimposed according to the
negative composite Log Etronic film, from which
the position of the implants is transferred to the
tracings.
• Only the principal implants are marked, using a
point.
• The orientated cross-lines from the first film are also
transferred to these tracings.

Evaluation of jaw growth
• The original radiographs are placed and projected on a
tracing table, and with the help of an enlarger , the tracing
of the mandible is enlarged by a factor of three.
• These negative Log Etronic copies are superimposed and
oriented by means of implants in the mandible, and are
copied together in the Log Etronic printer to give a
composite negative film.
• With the help of the composite film, the tracings are
oriented correctly in relation to one another.
• Similarly, one may obtain a radiographic growth tracing of
the maxilla, oriented with respect to the implants in this
jaw.
• On the basis of these tracings, the paths of eruption of the
teeth in each jaw may be analyzed in relation to the
implants, by means of eruption diagrams.

Superimpositions of mandibular tracings made at 5yrs 8 mos and 10y 8 mo

Superimposition of maxillary tracings at ages 7y 5 mo and 18y
5mo.

Evaluation of dental arch development
• The eruptive movements of the teeth in the occlusal view
are studied in the two jaws by means of tracings of the
respective dental casts.
• The dental casts from the different stages of development
are inserted in the enlarger and drawn in three fold
magnification.
• The enlarged tracing of the cast is transferred to the
enlarged radiographic growth tracing and oriented with
respect to the corresponding teeth.
• A composite tracing will show the movements of the teeth
in relation to the implants.

Study of mandibular dental arch developmentwww.indiandentalacademy.com

Arch development of the maxillawww.indiandentalacademy.com

3 dimensional growth of the maxilla as
revealed by the implant method.
• In an article published in BJO 1977, by Arne Bjork and V.
Skieller, they described the growth of the maxilla studied
by the implant method with the help of lateral and PA
cephalograms, in nine 4 year old boys with normal
primary occlusion who were followed annually up to the
age of 21 years.
• The implant method used was as described earlier.
• The pins inserted in the zygomatic process of the maxilla
at 4 years of age were referred to as the lateral implants.
• The increase in distance between these measured on a PA
cephalogram indicated the increase in width of median
suture at level of 1st
molars.

• The implants placed in the anterior aspect of the
maxilla after full eruption of permanent incisors
(10-11yrs) were referred to as anterior implants.
• The increase in distance between these implants
measured on the frontal film indicates the growth
in width of the median suture anteriorly, at level of
incisors.
• A line drawn from one of the anterior implants to
the midpoint between the lateral implants on one
side, on a lateral cephalogram, was referred to as
the implant line.

• A change in inclination
of implant line at
different ages in relation
to Nasion-Sella line
indicates vertical rotation
of the maxilla in relation
to the cranial base.
• Also, superimposition of
various radiographs on
implant line is used to
analyse remodeling of
maxilla.

Growth of Maxilla analysed by means of Lateral
Implants from age of 4 years.
Maxillary height:
• Earlier implant studies by Bjork have shown that increase
in maxillary height takes place by sutural growth at its
frontal and zygomatic processes, and by apposition on the
lower aspect of alveolar process, in relation to eruption of
teeth.
• There is also apposition at the floor of the orbits, with
resorptive remodeling of the lower surface.
• Simultaneously, the nasal floor is lowered by resorption
and apposition takes place at the hard palate.
• In their study in 1977, Bjork and Skieller clarified the
mean magnitudes of these growth changes from 4 years of
age to adulthood. www.indiandentalacademy.com

• Using the lateral implants as fixed reference points ,
vertical growth of the maxilla was calculated at right
angles to the Nasion-Sella line.
• Sutural lowering of the maxilla was found on average to be
11.2 mm (range 9-13.5mm).
• Orbits do not increase in height from childhood to
adolescence to the same extent as the nasal cavity, and
apposition at the floor of the orbit is on average, 6.4 mm
( range 5-8 mm)
• The height of the nasal cavity increased up through
puberty as result of resorptive lowering of nasal floor of
the order of 4.6 mm ( range 1.5-7.5 mm). This was about
one-third of the increase in sutural height of nasal cavity.
• Appositional growth in the height of the alveolar process
was about 14.6 mm, which was one third greater than the
increase in alveolar process height as a result of resorption
of nasal floor. www.indiandentalacademy.com

Mean growth changes from 4 yrs to adulthood.www.indiandentalacademy.com

Maxillary width:
• There was considerable controversy regarding the role of
the median palatal suture in maxillary growth, which was
resolved by the histological studies of Melsen and the
implant studies of Bjork.
• Bjork showed that growth in the suture continues until
puberty.
• By measuring the distance of separation between the
lateral implants on the frontal cephalogram over time, it
was shown that sutural growth was the most important
factor in the development of the width of the maxilla.
• The mean transverse growth in the median suture,
measured between the lateral implants, from childhood to
adulthood was 6.9mm.
• The curves for cumulative growth in the width of the
median suture from year to year followed the same pattern
as the curves for the growth in body height.www.indiandentalacademy.com

• The curves also showed that the time of the pubertal
growth spurt and sutural growth coincided, but that sutural
growth terminated earlier than growth in body height.
• The pubertal growth spurt in the median suture however
coincided exactly with growth maximum in the facial
sutures in the sagittal plane.
Bimolar width:
• A question of clinical interest is “ How far is the increase
in the width of the dental arch of upper jaw related to
growth in the median suture?”
• Bjork’s implant studies show that though growth in the
median suture from eruption of 1st
permanent molars to
adulthood is 4.8 mm, increase in arch width during this
period was on average, 3.1 mm.

• The reason for this difference in growth in width is related
to transverse rotation of the maxillae.
Bicanine width:
• The development in width of the dental arches between the
canines was different from that of molar region. Though
there was an overall increase of 3.1 mm in intercanine
width from 4 years to adulthood, most of this increase
occurred early, with only 1.1 mm increase from age 6
years to adulthood.

Co-ordinated 3 dimensional growth of maxilla
analyzed by means of anterior and lateral implants
from age of 10-11 years.
• Maxillary length:
• Growth in length of the maxilla occurs by sutural growth
toward the palatine bone and by apposition at the
tuberosities.
• Bjork’s implant studies show that the anterior surface of
the maxilla is stable sagittally, with the anterior surface of
the maxilla retaining its close relation to the anterior
implants.
• The anterior surface of the maxilla may be described as an
area “ under continuous remodeling in connection with
resorptive lowering of the nasal floor.”

Transverse mutual rotation of the two maxillae:
• Comparison of increase in width between the anterior
and the lateral implants showed that increase in width
between the lateral implants was on average, 3.5 times
greater than that between the anterior implants.(3 mm
and 0.9 mm respectively).
• This indicates that the two maxillae rotate in relation to
one another in the transverse plane, which results in
decreased length of the maxilla in the mid sagittal
plane.

• Mutual transverse rotation of maxillae also
results in greater separation of lateral
segments of dental arch posteriorly,than
anteriorly.
• There is thus, greater increase in intermolar
width than intercanine width, and also a
corresponding decrease in arch length.
• Thus, shortening of arch length is related to
transverse growth of the maxilla.

Changes in maxillary arch form between ages of
10 and 21. www.indiandentalacademy.com

Vertical rotation of the maxillary complex
• Early studies by Brodie
(1941) suggested that
maxilla is lowered without
rotation in the vertical plane.
• The implant studies of Bjork
and Skieller (1972) however
have shown that downward
and forward displacement of
the maxilla during growth is
associated with varying
degrees of forward rotation.
• The inclination of the nasal
floor to the anterior cranial
base is however maintained
as a result of compensatory
differenciated resorption.

• Forward rotation of the maxilla is associated
with greater resorption of the nasal floor
anteriorly than posteriorly, and vice versa.
• Because of this differential remodeling of the
nasal floor, it cannot be used as a reference
structure in analysis of the growth of the
maxilla.
• Forward rotation of the face occurs because
of greater facial growth posteriorly than
anteriorly, associated with development in
height of the cranial base.

The Zygomatic process
• Orientation of
successive lateral
films on the implant
line clearly showed
that no striking
remodeling of the
anterior surface of the
zygomatic process
takes place in the
antero posterior
direction.

• The posterior surface however is appositional,
with the greatest apposition downwards.
• The infrazygomatic crest is also appositional,
being displaced downward and backward on the
maxillary corpus.
• Thus, the anterior contour of the zygomatic
process is strikingly stable and should be regarded
as a natural reference structure in the growth of
the maxilla.
• These findings are in contrast to those of Enlow
and Bang (1965) who stated that the anterior
surface was resorptive in nature

The Growth of the Mandible as studied by the
implant method
• In two classic articles, by Bjork (AJO 1969) and
Bjork and Skieller (AJO 1972) respectively, the
growth of the mandible as well as the nature of
mandibular growth rotations were described.
• This was done on the basis of superimposition of
follow up radiographs from the original implant
sample.
• Growth of the mandible was assessed by orienting
the serial tracings according to the implant line
drawn through two principal implants in mandible.

• The position of articulare point was marked with a
cross in the serial tracings.
• These points were used to calculate the direction
of condylar growth.
• The findings showed that in a majority of cases
there was a forward (negative) rotation of the
mandible, while in only two cases there was a
backward (positive) rotation of the jaws.
• There was strong correlation for the rotation of the
maxilla and the mandible, but mandibular rotation
was more than thrice as great, with a mean of - 6°
• Thus, forward rotation seems to be a general trend
of facial growth.

• Study of growth rotation by conventional
cephalometry without the aid of implants is
complicated by compensatory remodeling at the
lower border.
• Using the mandibular line as reference showed a
rotation of only –3.4°, masking upto half the
growth rotation.
Nature of compensatory remodeling:
• In forward rotation, there is marked apposition
below the symphysis and anterior part of lower
mandibular border, and resorption below the
angle.
• In backward rotation, there is only slight
apposition below symphysis and anterior lower
border, and marked apposition below the angle.www.indiandentalacademy.com

• Ramus growth:
• The inclination of the ramus in relation to the
Nasion-Sella line was practically unchanged over
the observation period (mean change -1°)
• Also there was no significant correlation with
mandibular rotation.
• This constancy is ascribed to remodeling of the
ramus to maintain its functional relation to neck
muscles and spinal column.
• This compensatory remodeling at posterior border
of ramus is on average -5°

Posterior remodeling of the ramus depends on
• Condylar growth direction
• Degree of appositional growth behind the angle.
Gonial angle decreases by apposition at posterior
border of the ramus and increases by resorption at
lower border of mandible.
Resorption at anterior border of ramus is generally
small, with development of arch length being more
dependent on increase in height against the slope of
the ramus.

Condylar growth
• The condyles are the center of greatest growth in the
craniofacial complex during the pubertal period.
• Growth in length of the mandible in man occurs
essentially at the condyles.
• The growth in the condyle in most cases follows a
curved path (forward) through an average angle of
-8°(range 22°).
• In a small number of cases there may be
backward(positive) curvature of mandibular growth.
• There is also a strong correlation between condylar
curavature and the rotation of the mandible.
• There is a correlation also between condylar growth
direction and maxillary rotation, but it is weaker.www.indiandentalacademy.com

Prediction of Mandibular Growth
Rotation:
• Mandible may be regarded as an
unconstrained bone, which may change its
inclination in several ways.
• A critical factor is the site of rotation which
may be located at posterior or anterior end
or somewhere in between.
• Forward rotation as studied by the implant
method may occur in one of three ways:

Type I Forward Rotation:
• Forward rotation takes
place about centers in the
joints.
• Gives rise to deep bite in
which the lower dental
arch is pressed into the
upper.
• Leads to under
development of anterior
facial height.
• Cause: Occlusal imbalance
due to loss of teeth , or
powerful musculature.
• May occur at any age.

Type II Forward Rotation:
• Occurs about a center
located at the incisal edges
of lower anterior teeth.
• Cause: Combination of
marked development of
posterior face height and
normal increase in anterior
height.
• The increase in the
posterior face height occurs
due to lowering of middle
cranial fossa and increase
in height of ramus.
• Mandible is lowered more
than it is carried forward.

Type III Forward Rotation:
• Occurs in case of
anomalous occlusion of
anterior teeth e.g. large
overjet.
• Center of rotation lies at
level of premolars.
• Anterior face height
becomes under-developed
and posterior face height
increases.
• Dental arches are pressed
into one another and basal
deep bite develops.

Influence of jaw rotation on inclination of teeth:
• Position of lower incisors is functionally related to the
upper incisors.
• Incisors in their eruption are guided forward with an
increase in alveolar prognathism.
• Jaw rotation also displaces the path of eruption of all
teeth in a mesial direction, tending to create crowding
anteriorly.
• Forward growth rotation causes the lower posterior
teeth to be more upright in relation to the posteriors,
with an increase in inter molar and inter premolar
angles.

Backward Rotation Type I:
• Center of rotation lies in the
TMJ’s.
• Occurs when the bite is raised
by orthodontic means.
• Results in increase in anterior
face height.
• May also be associated with
cranial base growth in case of a
flat cranial base (where
posterior cranial base is raised )
and mandible is also raised.
• Leads to over development of
anterior facial height and
possible anterior open bite.

Backward Rotation Type II
Occurs about a center situated at
the most distal occluding molars.
Occurs in connection with growth
in the sagittal direction at
condyles, which is curved
backwards.
The symphysis swings backwards
and the chin is drawn back below
the face.
Lower incisors become
retroclined, crowding may
develop.
Inter premolar angles and inter
molar angles are small: the lower
molars and premolars are inclined
forward more with respect to the
uppers. www.indiandentalacademy.com

Both forward and backward rotation may be
divided into three components
Total rotation : Rotation of the mandibular
corpus (implant line or reference line) relative to
the anterior cranial base.
Matrix rotation: Rotation of the soft-tissue
matrix of the mandible (tangential line to lower
mandibular border) relative to the anterior cranial
base.
Intramatrix rotation: Rotation of the mandibular
corpus within its soft-tissue matrix (or the
difference between reference lines), expressing the
amount of remodeling at the lower border of the
mandible. www.indiandentalacademy.com

Total rotation, which is the sum of matrix
and intramatrix rotation, generally shows a
steady increase with age, forward or
backward, dependent on the case.
Matrix rotation, on the contrary, displays
a pendulum movement, forward or
backward, in the same person during
development.
Intramatrix rotation, like the total rotation,
increases steadily during growth, but with
fluctuations counteracting the pendulum
movements of the matrix.

Bjork’s structural signs of growth rotation
Seven structural signs of mandibular rotation
were given by Bjork:
1. Inclination of condylar head.
2. Curvature of mandibular canal
3. Shape of lower border of mandible
4. Inclination of symphysis
5. Inter incisal angle
6. Inter premolar or inter molar angles.
7. Anterior lower face height.www.indiandentalacademy.com

Clinical relevance of growth rotation:
• More extreme the growth rotation of mandible,
greater the clinical problems it presents.
• Extreme rotation, whether forward or backwards,
influences strongly the paths of eruption of the
teeth.
• Serious risk of extreme migrations following
extractions, which calls for secure anchorage.
• Crowding in the mandible results from both
directions of growth rotation.
• In pronounced forward rotation there is risk of
development of deep bite, while backward rotators
are at greater risk of developing anterior open bite.

Intra Matrix rotation of the frontal bone
• Bjork, Sarnas and Rune (EJO 1995) studied the
growth and dvelopment of the frontal bone using
metallic implants in 5 patients at the Center for
Craniofacial Anomalies, Sweden.
• They were able to detect rotations of the corpus
inside the periosteal matrix from 1 to 9.5 degrees
in the mid sagittal plane.
• However the applicability of this study to patients
without congenital anomalies could not be
elucidated.

Long term effects of RME studied with
metallic implants.
• A study by Sarnas, Bjork and Rune (EJO 1992) was
carried out using metallic implants inserted in the
maxillary bone of a girl who underwent RME for a
narrow maxillary arch.
• A ten year follow up revealed extensive relapse in
maxillary rotations as well as translations, and a limited
effect in the long term.
• The cause for relapse was ascribed to resistance from
circum maxillary sutures as well as soft tissues, and also
inadequate healing of bone.
• This led them to seriously question the rationale for RME
traement.

Conclusion
• The longitudinal implant studies of Arne Bjork,
with their ingenious method, painstaking attention
to detail, and meticulous follow up, have created a
body of literature that has revolutionized the way
orthodontists understand and visualize facial
growth.
• The findings of the implant studies have helped to
solve age old mysteries concerning the pattern of
facial growth and rotations of the jaw bones,
which have important clinical implications.

References:
• Björk A: The use of metallic implants in the study
of facial growth in children: method and
application. Am J Phys Anthropol 1968. 29: 243-
254.
• Bjork A, Skieller V. Growth of the Maxilla in
three Dimensions as revealed radiographically by
the implant method. BJO 1977: 53-64.
• Björk A: Prediction of mandibular growth
rotation. Am J Orthod 1969; 55: 585-599.
• Bjork A, Skiller V. Facial development and tooth
eruption: An implant study at the age of
puberty.Am J Orthod 1972; 62(4): 339-383.

• Skieller V, Bjork A. Prediction of mandibular
growth rotationevaluated from a longitudinal
implant sample.AJO 1984. 86; 5:359-370.
• Bjork A, Sarnas K, Rune B. Intramatrix rotation-
the frontal bone. EJO 1995;17:3-7.
• Long term effect of rapid maxillary expansion
studied in one patient with the help of metallic
implants and roentgen stereometry. EJO 1992;14:
427-432.

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Bjork's contribution to implant studies and facial growth. /certified fixed orthodontic courses by Indian dental academy

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Bjork's contribution to implant studies and facial growth. /certified fixed orthodontic courses by Indian dental academy