Tissue reaction to dentofacial orthopedic appliances /certified fixed orthodontic courses by Indian dental academy

Tissue reaction to dentofacial
orthopedic appliances
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


Introduction
In the past 20 yrs have seen an increasing
awareness of the potential of functional
appliances as valuable tool in
armamentarium of orthodontist.
They are not the only tools anymore than
fixed edgewise brackets are able to answer
all therapeutic demands in orthodontics, but
they are important weapons in the arsenal
and can accomplish results not possible
without such appliances.

The effects of altered function on the growing
craniofacial complex have been studied
extensively by various authors.
Various types of appliances have been
constructed that influence upper and lower
jaw resulting craniofacial adaptations.

Breitner, Haupl and Psansky, Baume and
Derichsweiller, and Stöckli and Willert
studied that the condylar cartilage exhibits
compensatory tissue response to
alterations of the postural position of the
mandible.
In histochemical studies, Vogel and Pignanelli
have found that protrusion of the mandible
in rhesus monkeys also results in an
increase in chondrogenic activity at the
head of the mandibular condyle.

Dentofacial orthopaedic appliances have
been designed for :
To affect neuro-muscular and functional
changes
To impede or enhance growth or growth
direction
To achieve tooth movement.


The goal of functional orthopedic appliances
is to elicit a proprioceptive response in the
stretch receptors of the orofacial muscles
and ligaments, and as a secondary
response to influence the pattern of bone
growth correspondingly to support an new
functional environment for the developing
dentition.


Bone
 Dense outer sheet of compact bone
 Central medullary cavity (bone marrow).

Periosteum
 Outer layer
 Inner layer

Endosteum………
This membrane consists of a layer of loose
connective tissue, with osteogenic cells
that physically separates the bone surface
from the marrow within .


Woven bone
The first bone formed in response to
orthodontic loading.
It is compacted to form composite bone,
remodeled to lamellar bone, or rapidly
resorbed if prematurely loaded.


Lamellar bone
A strong, highly organized, well-mineralized
tissue, makes up more than 99% of the
adult human skeleton.
The full strength of lamellar bone is not
achieved until approximately 1 year after
completion of active treatment.
This is an important consideration in planning
orthodontic retention, as well as in the
postoperative maturation period that follows
orthognathic surgery.

Composite bone
Composite bone is an osseous tissue
formed by the deposition of lamellar bone
within a woven bone lattice, a process
called cancellous compaction.
Composite bone is an important
intermediary type of bone in the
physiologic response to orthodontic
loading.



Osteoblast



Osteoclast



Osteocytes


• Bone development :
• Three mechanism
1) Endocondral : when cartilage is replaced
by bone.
2) Intramembranous : bone formation
occures directly within mesenchyme.
3) Sutural : bone formation along sutural margins.


1) Endocondral : rapid growth of the
cartilage analogue ensues by interstitial
growth within its core (as more and more
cartilage is secreted by each condroblast)
and by appositional growth through cell
proliferation and matrix secretion within
the expanding pericondrium.


2) Intramembranous :
• Bone develops directly within the soft
connective tissue. The mesenchymal cells
proliferate and condense, concurrently
with an increase in vascularity at these
sites of condensed mesenchyme,
osteoblasts differentiate and begin to
produce bone matrix.

Sutures
Outer fibrous layer
Inner cellular or osteogenic layer (cambium)

The collagen of suture tissue is type III

Piezoelectricity :
Piezoelectricity in bone is an electric change
produced by the deformation of crystalline
structure such as hydroxyapetite crystals,
collagen and fibrous proteins, which is
believed to stimulate bone cells and thus
bone formation.


Periosteal pull:
The bone is covered with the periosteum.
Differentiated from the surrounding connective
tissue. The contiguous mesenchymal cells
acquire the character of osteoblasts. The matrix
producing and proliferating cells in the cabium
layer are subject to mechanical influence. When
ever the pressure exceeds a certain threshold ,
reducing the blood supply to thsese cells,
osteogenesis ceases. If on the other hand the
periosteum is exposed to tension, it responds
with bone deposition. Therefore the periosteum
continues to function as an osteogenic zone
through out life, although regenerative capacity
is extremely high in the young child.

Bone mineralization
• Osteoblasts deposit 70% to 85% of the eventual
mineral complement by a process called primary
mineralization.
• Secondary mineralization (mineral maturation)
completes the maturation process in about 8
months by a crystal growth process. Because
the strength of bone tissue is directly related to
mineral content, the stiffness and strength of an entire bone
depends on the distribution and relative degree of mineralization of

ultimate strength of bone is
dictated by secondary mineralization. Which is
the physiochemical process of crystal growth.
its osseous tissue, thus


Methods of studying Bone physiology
• Accurate assessment of the orthodontic or
orthopedic response to applied loads
requires time markers (bone labels) and
physiologic in-dices (deoxyribonucleic acid
[DNA] labels, histochemistry, and in situ
hybridization) of bone cell function.


1) Mineralized sections :
• Mineralized are an effective means of accurately
preserving structure and function relationships.
• Fully mineralized specimens are superior to
routine demineralized histologic sections
because fully mineralized specimens experience
less processing distortion.
• Furthermore, the inorganic mineral and organic
matrix can be studied simultaneously.
• Even without bone labels, micro radiographic
images of polished mineralized sections provide
substantial information about the strength,
maturation, and turnover rate of cortical bone.

2) Polarized light :
• Polarized light birefringes detects the
preferential orientation of collagen fibers in the
bone matrix.
• It appears that loading conditions at the time of
bone formation dictate the orientation of the
collagen fibers to best resist the loads to which
the bone is exposed.
• The important point is that bone formation can
adapt to different loading conditions by changing
the internal lamellar organization of mineralized
tissue.

3) Fluorescent labels
• Fluorescent labels permanently mark all sites of bone
mineralization at a specific point in time.
• Histomorphometric analysis of label incidence and
interlabel distance is an effective. method of determining
the mechanisms of bone growth and functional adaptation
(Figure 3-17, C vanersd).

•

Because they fluoresce at different wavelengths (colors),
six bone labels can be used:
(1) tetracycline (10 mg/kg, bright yellow);
(2) calcein green (5 mg/kg, bright green);
(3) xylenol orange (60 mg/kg, orange);
(4) alizarin complexone (20 mg/kg, red);
(5) demeclocyclin (10 mg/kg, gold); and
(6) oxytetracycline (10 mg/kg, dull or greenish yellow).

4) Microradiography:
• Microradiography assesses mineral density
patterns.
• Provides substantial new physiologic information
about the growth and adaptation of the skeletal
sites most affected by orthodontic and facial
orthopedic treatment.
• These sites are the midfacial sutures, the PDL,
the alveolar process, the mandibular condyle
and the temporal fossa of the TMJ.

5) Autoradiography
• Autoradiography detects radioactively
tagged precursors used to mark
physiologic activity
• Specific radioactive labels for proteins,
carbohydrates, and nucleic acids are
injected at a known interval before tissue
sampling is done.
• The autoradiographic labeling procedures
most often used in bone research are 3Hthymidine labeling of cells synthesizing
DNA (S phase cells) and 3H -proline
labeling of newly formed bone matrix.

• 6) Nuclear volume morphometry:
• Nuclear volume morphometry differentially
assesses os-teoblast precursors in a variety of
osteogenic tissues.
• Measuring the size of the nucleus is a
cytomorphometric pro-cedure for assessing the
stage of differentiation of osteoblast precursor
cells.
• This method has been particularly useful for
assessing the mechanism of osteogenesis in
orthodontically activated PDLs

7) Cell kinetics
• Cell kinetics is a quantitative
analysis of cell physiology based
on morphologically
distinguishable events in the cell
cycle.
• The increase in nuclear size (A' + C) that occurs as committed
osteoprogenitor cells (A' cells)
differentiate to preosteoblasts (C
cells) is the rate-limiting step in
osteoblast histogenesis.
• A localized mechanical stimulus
(orthodontic force), on the other
hand, creates a reciprocal pulse
of A + A/ and C + D waves that
generate huge numbers of
osteoblasts.

• 8) Finite element modeling (FEM)
• Finite element modeling (FEM) is a powerful
analytic tech-nique for calculating stresses and
strains within mechanically loaded structures.
• The response of the entire structure to loading
can be estimated.
• The estimates of initial stress have been useful
for defining the mechanical conditions for
initiating or-thodontically induced bone
resorption and formation.

9) Microelectrodes
• Microelectrodes inserted in living tissue such as
the PDL can detect electrical potential changes
associated with mechanical loading.
• This technique is used to measure changes in
electrical potential in the extracellular space of the
PDL during the initial response to orthodontic
force.
• In general, widened areas of the PDL have a more
negative electrical potential, and compressed
areas have a more positive electrical potential.

Bone modeling and remodeling
• Bone grow, adapt and turn over by
means of two fundamentally
distinct mechanisms: modeling
and remodeling.
• Bone Modeling, (change the
intrinsic form of a bone) is
produced with headgears, rapid
palatal expansion, functional
appliances.
• Remodeling is a reshaping of the
outline of a bone by selective
resorption and apposition.
• In remodeling, coupled sequence
of resorption and formation occurs
to replace previously existing
bone, so that its thickness is
generally maintained.www.indiandentalacademy.com

• The mechanism for internal remodeling (turnover) of
dense compact bone involves axially oriented cutting
and filling cones.
• Cones, an important determinant of turnover.
• Modeling changes can be seen on cephalometric
tracings, but remodeling events, are apparent only at
the microscopic level.
• The alveolar process but not basilar mandible, have
a high remodeling rate.

Suture

• Sutures are fibrous joint between those bones of
the cranium that are formed by intramembranous
ossification.
• They therefore represent an extension of the
periosteal layer of the bone and participate the
design of the bone by their remodeling capacity.
• These periosteum lined areas do not contain
cartilage but fibrous connective tissue and in
mature state they allow no movement of the joined
parts.
• The maturing suture tissue in the growing individual
demonstrates changes with age that eventually end
with a bony obliteration of the sutural space.

The density and thickness of the fibrous component
of the suture increases with age, and when growth
ceases, bundles of fibers can be seen running
transversely across the suture, increasing the
mechanical strength of the joint.
Osteogenesis tends to be restricted to areas of
transversely arranged collagen bundles.
The intense oxidative enzyme activities in the bony
bridges and areas of densely arranged collagen
bundles support the idea that the bundles are
preliminary to bony bridging.
Tensional forces may stimulate the formation of bony
bridges across the suture.

• Closure progresses more rapidly in the oral than
in the nasal part of the palatal vault, and the
intermaxillary suture starts to close more often in
the posterior than in the anterior part.
• Owing to the increased inclusion and bone
locking (interdigitation), the possibility for
influencing the suture area by orthopedic
treatment gradually decreases with age.


Temporomandibular joint
• Compound joint
• Also called as ginglymoarthodial joint because it
provides hinging movement in one plane
(ginglymoid joint) and at the same time it also
provide gliding movement (arthrodial joint).
• The TMJ is formed by the mandibular condyle
fitting into the mandibular condyle fitting into the
mandibular fossa of the temporal bone ,
separating these two bones from direct
articulation is the articular disc.

Condylar cartilage:
•

Histomorphologicaly following layers can usually be
seen:
1) A fibrous connective tissue layer, richly vascularized
prenatally and during the first period of life, but
acquiring a dense, fibrous character with increasing
age (surface articular zone)
2) A highly cellular intermediate layer containing
proliferating cells. This layer, at a deeper level, is a
transitional stage between undifferentiated cells
and cartilage cells (transitional or proliferative
zone)
3) A cartilage layer with irregularly arranged
chondrocytes, which are not forming columns as in
the epiphyseal cartilage; a zone with hypertrophic
cartilage cells and a deeper layer of mineralized
cartilage (hypertrophic zone)

4) A zone with endochondral bone ossification (bone
formative zone).
• During the juvenile period the condyle becomes
progressively less vascularized and the entire growth
cartilage layer becomes significantly thinner,
primarily because of reduction in the hypertrophic
zone.
• The articular layer becomes thicker, whereas the
cartilage layer continues to decrease in thickness
during the period of early mixed dentition.
• By the time the patient reaches the age of 10 years,
the mandibular condyle is characterized by a
relatively thick ar-ticular tissue layer.
• After 13 to 15 years, the cartilage layer decreases
further in thickness. By the age of 19 to 22 years,
only islands of cartilage cells remain in the superior
and anterior regions.

Articular disc
• Composed of dense fibrous connective tissue
devoid of any blood vessels or nerve fibers.
• Advantage of having fibrous connective tissue
are, less susceptibility to the effect of ageing and
therefore less likely to breakdown over time and
greater ability to repair than hyaline cartilage.
• In saggital plane, it is divided into intermediate
zone, thinnest central area and anterior and
posterior to intermediate zone the disc become
thicker.
• In the normal joint the articular surface of the
condyle is located on the intermediate zone of
the disc.

• The articular disc is attached posteriorly to
a region of loose connective tissue that is
highly vascularized and innervated. This is
known as the retrodiscal tissue.
• During movement the disc is somewhat
flexible and can adapt to the functional
demands of the articular surfaces.


• Histology of articular
surface
• Composed four distinct layers
or zones.
• Most superficial layer is called
the articular zone, outermost
functional surface adjacent to
the joint cavity. This articular
layer is made of dense fibrous
connective tissue rather than
hyaline cartilage. Most of the
collagen fibers are arranged in
bundles and oriented nearly
parallel to the articular
surface. The fibers are tightly
packed and are able to
withstand the forces of
movement .

• Second layer is called the proliferative
zone and is mainly cellular.
• Undifferentiated mesenchymal tissue is
found.
• This tissue is responsible for the
proliferation of articular cartilage in
response to the functional demands
placed on the articular surfaces during
loading.

• The third zone is the fibrocartilaginous
zone.
• The collagen fibrils are arranged in
bundles in a crossing pattern.
• Offers resistance against compressive
and lateral forces


• The fourth and deepest zone is the
calcified zone.
• This zone is made up of chondrocyte and
chondroblasts.
• The chondrocytes become hypertrophic,
die, and have their cytoplasm evacuated,
forming bone cells.


• Muscles :
• Types : – Skeletal
– Cardiac
– Smooth

• PROPERTIES OF MUSCLE
•
Muscle has 2 physical properties that
are important in its kinetic activity.
• 1. ELASTICITY
• 2. CONTRACTILITY

• ELASTICITY:
• Is the ability of any object to increase in length
within its elastic limit.
• . Normal relaxed muscle withstands only a
certain amount of elongation (about 6/10 of its
natural length) before rupturing. This is an
approximation and is dependent on the muscle
involved, type of stress, individual resistance,
age and possible pathologic conditions

• CONTRACTILITY
• Is the ability of a muscle to shorten its length
under innervational impulse.
• The strength of the contraction of a particular
muscle depends on the number of fibers
engaged in this activity at a particular time.
• Maximum contractility of muscle brings into
action all the available muscle fibres.
• Sherrington has pointed out that individual fibers
have no variable contraction status, but are
either relaxed or go into maximum contraction by
virtue of adequate stimulus. (All or None Law).

•
•
•
•
•

Contraction of muscle depends on
Striated / smooth muscle
Cross section
Frequency of discharge
Muscle fiber length.


• Contraction are of 2 types : • Isometric contraction: When the muscle does not
shorten during contraction i.e. the muscle will be simply
resisting an external force without any actual shortening
•
e.g. Postural position. Isometric contractions do little
external work, the distance the load is moved is very
small or zero.
• Isotonic contraction: When the muscle does shorten,
and with tension on the muscle remaining constant.
These perform external work.
•
e.g. flexing of biceps, closure of mandible from
physiologic postural position to occlusion. Lifting a
weight involves isotonic contraction holding it is air is
isometric.
• The greatest strength of contraction is elicited when the
muscle approximates its resting length.

Orthopaedic effects
• Effects of mandibular advancement:
• A number of factors contributed to the
mandibular advancement, e.g., anterior glenoid
fossa relocation, condylar displacement in the
glenoid fossa, and proliferation of the posterior
part of the fibrous disk, maxillary and mandibular
tooth movement, changes in maxillary position.
• Some researchers have claimed that the main
effect of functional appliance therapy is
increased condylar growth, other researchers
have contended that the main effect is due to
remodeling of the glenoid fossa that is anterior
relocation of glenoid fossa

• Glenoid fossa response to mandibular
advancement
• The new bone formation appeared to be
localized in the primary attachment area of the
posterior fibrous tissue of the articular disk in the
direction of tension exerted by the stretched
fibers of the posterior part of the disk.
• The posterior part of the articular disk, between
the postglenoid spine and the posterior part of
the condyle, increased in thickness and showed
active cellular and connective tissue response
associated with numerous enlarged fibroblasts
in active stage.
• This response stabilize the anterior condylar
displacement,

• Mandibular protrusion resulted in the
osteoprogenitor cells being oriented in the
direction of the pull of the posterior fibers
of the disc and also resulted in a
considerable increase in bone formation
(wollfs law) in the glenoid fossa .


• Rabie et al in 2001
• Experiments on rats
shows


•
•
•
•
•
•

Cellular response during normal growth in glenoid fossa
The articular surface of the glenoid fossa is covered by a layer of dense
fibrous tissue 7 to 8 cells thick
The fibroblasts were arranged parallel to the bundles of collagen fibers,
which in turn were densely packed parallel to the articular surface.
Underneath the fibrous articular layer, there was a zone of undifferentiated
reserve cells about 4 to 5 cells thick. There was an absence of dense
intercellular collagenous matrix, which was unlike the articular fibrous layer
and the underlying calcified zone. The undifferentiated reserve cells were
densely packed together, which separated the articular fibrous tissue from
the osteoid tissue. In the cancellous bone layer, there were osteoblasts and
lacunae with osteocytes. There was abundant dense collagenous osteoid
substance surrounding the lacunae. The bundles of collagen fibers were
arranged parallel to the articular surface. Marrow spaces were evident in the
bone. The deeper down in the cancellous bone the fewer lacunae were
present.


•
•

•

Cellular response to mandibular protrusion ( by Rabie et al in his study
on rats 2001 AJO 119: 390-400)
Cellular response to mandibular protrusion was most evident in the posterior
aspect of the glenoid fossa. In the fibrous layer, the fibroblasts were found to
be packed parallel to the articular surface on day 3 (Fig 5, A) and became
increasingly oriented towards the direction of the pull by disc fibers from day
7 onwards (Fig 5, C, E, G, I, K). The fibroblasts were round at the beginning
(Fig 5, A, C) and were stretched and flattened by mandibular protrusion (Fig
5, E, G, I, K). The mesenchymal cells beneath the fibrous layer were
arranged in line with the articular surface on day 3 (Fig 5, A). With the
mandibular protrusion, however, the axis of the mesenchymal cells became
increasingly aligned with the presumed direction of pull (Fig 5, C, E, G, I, K).
Mandibular protrusion leads to an increase in the number of replicating
mesenchymal cells in the temporomandibular joint. These mesenchymal
cells differentiate into condrocytes. These hypertropic chondrocytes secrets
type X collagen, which marks the onset of endochondral ossification and the
replacement of the hypertrophic cartilage matrix with bone. In the cancellous
bone layer, the osteoblasts and osteocytes were randomly packed at the
beginning of mandibular protrusion (Fig 5, A).
Bone formation triggered by mandibular advancement in the posterior region
of the glenoid fossa was significantly higher than in the anterior and middle
regions. This could be due to the fact that the primary attachment area for
the posterior fibrous tissue of the articular disc is in this particular zone. The
deposition of bone seemed to correspond to the direction of tension exerted
by the stretched fibers of the posterior part of the disc (Fig 5, C, E, G, I, K).


• The highest level of expression of type X collagen, a
marker for endochondral ossification, also occurred at
day 21.
• The expression of type X collagen is specifically
associated with the hypertrophic chondrocytes and
precedes the onset of endochondral ossification.
• Temporal adaptive responses were found to occur later
than the condylar adaptive response. However, it was
stated that this nonparallel adaptive response could be
due to the difference between the periosteal ossification
of the temporal bone and the endochondral ossification
of the condyle.

Condylar response
• expression of Sox 9
• Type II collagen, undifferentiated mesenchymal
cell proliferate, differentiate into condrocytes,
mature, and engage in matrix synthesis leading
to bone growth in the condyles.
• Hypertrophy and hyperplasia of the
prechondroblastic and chondroblastic layers of
the condylar cartilage were seen, particularly
along the posterior border of the condyle, with
rapid bone formation in the condylar head.
Deposition of new bone also occurred along the
anterior surface of the postglenoid spine.

• A mandibular retrusion by chin cap
therapy in the rat revealed a reduced
thickness of the prechondroblastic zone
and a decrease in the number of dividing
cells. Chin cap treatment had a retarding
effect on mandibular growth.


• Muscular response :
• Mechanism of adaptation of
neuromuscular adaptation involves
1) Elongation of the muscule fibers
themselves
2) Establishment of altered neuromuscular
feedback mechanism
3) Migration of muscle attachments along
bony surfaces
4) Occurrence of changed muscular
dimension due to displacement and
rotation of the bony elements.

• Altered form alters function
• The functional position of mandible results
in an immediate alteration of the
neuromuscular activity of orofacial
muscles, which is particularly noticeable in
the lateral pterygoid muscle.
• Charlier(1967) , Petrovic and
associates(1962), suggest that condylar
growth may be dependent on functional
stimulation, especially from lateral
pterygoid muscle.

• Reduced number of serially arranged
sarcomeres of the lateral pterygoid
muscle, indicating the anatomic length of
the muscle was decreased. Histologically
fibers of the lateral pterygoid muscles,
exhibits considerable hypertrophy.
• The superior head of the lateral pterygoid
muscle gradually increased in activity
• These contractions most likely caused (helps) the
anterior positioning and stabilization of the
articular disc and head of the condyle
along the articular eminence.

• The masseter is biomechanically suited
for moderate protrusive movement.
• Decreased participation of the posterior
portion of the temporal muscle was also
noted.


• A general sequence of adaptation can be
postulated. First, the exteroceptive and
proprioceptive stimuli from the orofacial area
were altered by the introduction of the appliance,
Existent functional pattern were interrupted and
reorganized. This, in turn, caused a change in
maxillomandibular functional relationships. This
change in functional pattern altered the orofacial
environment in such a way that tissue structural
adaptations resulted and an anatomic balance
was eventually restored. As this occurred,
neuromuscular compensation correspondingly
declined and functionally more efficient pattern
were developed

HEADGEAR :
• Extraoral forces can restrict maxillary horizontal
growth or direct the growth of the maxillary
complex in a more posterior and inferior
direction.
• Headgear treatment has been shown to produce
mandibular remodeling and dentoalveolar
changes, which are considered by some to be
the main component of Class II correction.
• By the use of vigorous extraoral forces, he was
able to show a reduction of point A on the
maxilla and a similar retraction of the anterior
nasal spine.
• Change in direction of growth of the maxilla with
a downward tipping as the palatal plane
descended, as a result of headgear effects.

• Cervical forces
• Produce posterior tipping of the palate and
opening of the mandibular plane angle.
• An extrusion of the upper molars and an
undesirable opening of the mandible.
• Several investigators found a posterior
repositioning of point A by cervical headgear
application. Because the mandible was
displaced forward by growth, the decrease in
ANB angle.
• Brown (liteature on cervical forces) stated that
cervical headgear was more effective in
reducing ANB than high-pull headgear.

• cervical traction produces a shearing force and
the compressive force at the pterygoid suture.
• Stresses developed by cervical traction could be
recorded along the palatine bones, areas where
high pull headgear produces no observable
effects. Only the high pull headgear developed
stress at the anterior junction of the maxillae
(ANS)
• The
generation
of
stresses
at
the
zygomaticotemporal
suture,
the
zygomaticofrontal suture and the palatal plates
and along the frontal process of the maxilla
indicates a downward and backward tipping of
the maxilla under cervical traction.

• High-pull forces
• Recommended to restrict excessive
vertical development in high-angle cases.
• Anterior high-pull headgear may allow
better control of vertical growth by
compressing all three primary sutures of
the maxilla.


• Effects of both cervical and high pull headgears
are
• Pterygoid plates of the sphenoid :
Upon activation of either headgear , high
stresses were developed in the pterygoid plates
of the sphenoid bone. These stresses began in
the middle of the posterior curvature of the
plates and just superior to their anterior junction
with the palatine bone and maxilla. As the forces
was increased, the stresses were seen to
progress superiorly toward the body of the
sphenoid bone.

•
•

Zygomatic arches :
Stresses within the zygomatic arches were similar for
both types of headgear they tended to start at the inferior
border of the zygomaticotemporal suture and proceeded
posteriorly along the zygomatic process of the temporal
bone.
• Junction of the maxilla with the lacrimal and ethmoid
bones :
• Both high pull and cervical traction produces a stress
concentration at the maxillary molars during at the
junction of the maxilla with the lacrimal bones and with
the orbital plates of the ethmoid.

• Maxillary teeth :
• High stresses were recorded around the
maxillary molars during application of cervical
headgear. These forces are located around the
middle third of the mesiobuccal root of the
maxillary first molar and around the distobuccal
root at a position more towards the apex. Some
stresses was demonstrated at the apex of the
second premolar. The high pull headgear
stressed the same areas, but to a much lesser
degree.

• Frontal process of the maxilla :
• With cervical traction , but not with highpull, stress was concentrated along the
frontal process of the maxilla anterior to
the nasolacrimal foramen .With high load
levels, the intensity was increased and the
pattern moved somewhat more cranially.


• Zygomaticofrontal sutures :
Cervical headgear develops stresses at
zygomaticofrontal sutures, the concentration
was in the middle of the suture and tended to
creep laterally. High-pull forces did not produces
any stresses here.
• Palate:
Cervical traction tended to separate the two
palatine bones at the suture. High-pull traction
produces no observable effect here.

• Anterior junction of left and right maxillae :
The anterior junction of the left and right
maxillae showed stress only when high-pull
traction was applied. The forces were
concentrated directly below the anterior nasal
spine and just lateral to the suture between the
two maxillae. These stresses indicates
compression at the suture. Cervical traction
produces no measurable effect here.

• The effect of high pull traction on this
anterior region of the palate combined with
the effect of cervical traction at the
posterior region could help justify the
clinical use of these two types of headgear
in combination.


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