bio mechanical consideration to orthopedic force

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Dr. Mohammed Alruby
Biomechanical
Consideration
To
orthopedic force
Prepared by:
Dr. Mohammed Alruby
‫أمرا‬ ‫ذلك‬ ‫بعد‬ ‫يحدث‬ ‫هللا‬ ‫لعل‬

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Dr. Mohammed Alruby
Biomechanical consideration to orthopedic force
The effect of orthopedic force on the skeletal bases has been a source of controversy for many
years, this related to methodology and magnitude of force.
Induced deformation of bone has been plasticized in many societies for many centuries, the well-
known examples are the induced deformation of feet in a Chinese girl, and induced cranial
deformity in Colombian Indians.
Perez Martinz 1960 concluded that, application of mechanical force can modify or alter the
direction of bone growth and consequently alter the shape and position of bone, but the genetically
determined total volumes of bone remains constant.
On cranial base:
Wise Lander reported, rotation of sphenoid bone as a result of long term cap traction.
Sassoni, showed that the inter-cranial pressure in cranio-stenosis can deflect the ethmoid bone.
Palatal complex
Transverse palatal expansion
= palatal expansion devices are one of the oldest appliances in orthodontics, rapid expansion can
be achieved by splitting mid palatal suture with 2—3 weeks and this separation is maintained and
new bone formed within 1 to 3 weeks. Several studies by Hass and Posen etal 1963 proved that the
mid-palatal suture is opened in response to tension, the nasal cavities were enlarged, remodeling
adjustment takes place in fronto-maxillary and tempro-zygomatic sutures and new bone is formed
within 1—3 months.
= other studies revealed that after palatal expansion, broadening of the nasal cavity and
remodeling is occurs.
Posterior force against maxilla:
Several studies done by Burston and MacNamara 1972, demonstrate that headgear and cervical
traction against maxilla can restrict forward growth, of maxilla, alveolar process and corpus.
It has been shown radiographically that, application of heavy continuous force 400gm/side on
maxilla during late deciduous dentition can moves the midface posteriorly into Class III
relationship within 3 months provided that the force applied 24 hours/ day
Anterior force against maxillation
Studies by Dlair 1971 and Kanbara 1977 demonstrated that the application of heavy force 300—
400gm/side using facemask produce an extensive anterior displacement of maxillary complex
within 3 months.
There is opening in maxillary suture associated with new bone formation and sutural adjustment,
upward rotation of maxilla is often seen.
So: we can say that, orthopedic force can inhibit, influence or modify the antro-posterior as well
as the vertical maxillary growth.
The mandible
After 1930 with the development of advanced cephalometric technics, it is possible to assess the
effect of orthopedic forces on mandibular growth more accurate by cephalometric studies.
Anterior-posterior influence of orthopedic force on mandible:
1- Functional protrusion:

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Dr. Mohammed Alruby
Breitner 1940: reported that it is possible to produce Class III skeletal pattern by using Class II
elastics, also there is remodeling changes in ramus, gonion, condyle and glenoid fossa.
New bone formation takes place in posterior wall of glenoid fossa with bone resorption at the
anterior wall of glenoid fossa with also new bone at the posterior border of ramus and condyles.
2- Functional restriction and redirection:
= Breitner reported that, Class II relationship can be produced by using Class III elastics.
= Petrovic etal 1975 produced significant alteration in mandibular growth using device similar to
human chin cup
= other studies reported significant posterior displacement of mandible after 140 days, also gonial
angle was reduced as well as facial height, as result of posterior traction by using implant hooks
in symphysis of mokeys.
Vertical influences on mandible:
= Baume 1961, the condylar cartilage is responsive to mechanical stimuli.
= Foster and Alexander found, significant upward and forward rotation of mandibular reduction
in lower face height and protrusion of the chin.
Clinical studies and application
1- Clinical studies and palatal expansion:
= Hass 1961 found 1-11mm widening of the dental arches associate with expansion of the palate
and nasal fossa.
= skiller 1964, by means of implant on both sides of palatal sutures found, the result of palatal
expansion were stable over 7 years post treatment period.
=Fans 1963, very rapid expansion in few hours under anesthesia.
2- Clinical studies on headgear on maxilla:
= Klein 1927 1st
demonstrate a skeletal changes and dental changes by using headgear, and
ANS ----moves posterior 2—3mm
Posterior displacement of maxilla 4—7mm
= Klein also found that cervical headgear cause extrusion of molars which if not compensated by
same amount of downward condylar growth will cause opening of bite due to downward and
backward rotation of the mandible.
=Sassoni recommended use of oblique or partial anchorage in case of open bite which not only
prevent opening the bite but also causes intrusion of molars, upward and forward rotation of the
mandible and closing the bite.
= Petrovic 1984 demonstrate, that alteration of maxillary position automatically affect the position
of mandible and mandibular elevators accommodate the mandible to maxilla during function.
3- Clinical studies on effect of mask on maxilla:
= Dlair 1978 reported that the best results of facemask therapy can be obtained by applying heavy
force as early as from 5 – 8 years of age.
=Petit 1983 reported anterior movement of maxillary complex in patient treated with facemasks.
= there is upward rotation of maxilla in association with facemask therapy.
4- Effect of chin cups on the mandible:
= Sassoni found that, the use of chin cup with cervical anchorage primarily causes downward
rotation of mandible with reduce the chin protrusion but at the same time open bite, while the use

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Dr. Mohammed Alruby
of chin cap with partial anchorage permit the direction of force to pass through the condyle, thus
the pressure can alter condylar growth.
= Graber concluded that, the use of chin caps in children at late primarily and early mixed
dentition periods cause definite alteration in mandibular morphology and mandibular growth.
Ramus height was significantly retarded.
5- Influence of activators on mandible:
The activator is designed to fit the maxillary arch and to guide the mandible to close in
predetermined forward position, thus stretching the masticatory muscles behind their resting
position, it has been suggested that this may be affect:
a- The masticatory muscles exert a backward force on the mandible in an attempt to return to
their posture, consequently, this will exert a forward force on mandibular dentition and
backward force on maxillary dentition thus moving the two dental arches against each other
utilizing reciprocal anchorage.
b- Skeletal effect:
= the postural position of mandible modifies or induce growth at the mandibular condyle and TMJ
fossa which effectively alter the base bone relationship.
= many authors believed that, the mandibular growth can be altered by functional means because
the TMJ and condyles are very responsive growth site.
= Jacobson 1967 reported the, the activator modifies the gonial angle, open the bite, increase the
lower height as well as inhibit the forward growth of maxilla.
= Panchrz report significant changes in the mandibular corpus and overall length of the mandible
by using activator and Herbest appliances.
6- Effect on facial proportion:
= from the previous studies it is clear now that, the orthopedic force can alter the anterior posterior
and vertical proportions of the face by influencing the size and position of maxilla and position of
mandible.
= some orthopedic forces can improve the dental occlusion but worsen the facial esthetics, and the
reverse is true, best example: in Class II open bite cases, in which the application of extra-oral
traction on the mandible would reduce the Class III but at the same time will open the bite due to
downward rotation of the mandible. In the same case if you try reduce the open bite by vertical
traction, the Class III will increase.
Types of orthopedic force and method of transmission
1- Natural forces: the forces of masticatory and circum oral muscles, these forces are
transmitted to the jaws by means of functional appliances.
2- Mechanical orthopedic forces: these forces are transmitted through the use of extra oral
appliance.
Uses of orthopedic forces:
- Effect dento alveolar changes, used to move the teeth through the alveolar bone.
- Anchor the tooth movement.
- Effect changes in the morphology and position of basal bones.
Effect of functional orthopedic appliance on muscle posture:
In regard to construction of wax bite, there are three schools:
1- Wax bite should be within the inter occlusal distances.

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Dr. Mohammed Alruby
2- Wax bite should beyond the inter occlusal distances.
3- Wax bite should vary according to the individual patients.
Graf Observed that for each mm forward mandibular displacement 100gm of force were created.
= masticatory function; Ahlgren reported that, activator therapy helps in normalization the
chewing cycles. Other studies by Sander advised use of activator until adaptation to normal
chewing pattern occur
= Swallowing pattern: functional appliances within the mouth cause contraction of mandibular
elevators during swallowing which is the same neuromuscular pattern seen in normal swallowing
(teeth together swallowing). Thus the use of activator is very useful in correction of abnormal
swallowing pattern.
= furthermore, the activator is loose removable appliances thus when worn, it would alter the lip
and tongue activities toward normal pattern.
= during swallowing, the lips seal around the margins of appliances and the tongue raise to
support the palatal plate to prevent displacement of appliances. These position and activities of
the lips and tongue done primarily to retain the appliance are the ideal activities of normal
swallowing, so that we can say without doubt that functional appliances are the best in correction
of tongue thrusting and abnormal swallowing behavior
Effect of functional orthopedic appliances on cranio-facial:
1- Stimulation or enhancement of mandibular growth.
2- Changes were in the direction of growth and in the mandibular position but the total volume
of the mandible is not affected.
3- Restraining the midface growth.
4- Alter the morphology of skeletal structure.
Uses of functional orthopedic appliances
1- Anteroposterior discrepancy on normal or mild disproportional bases as in Class II and III
2- Vertical discrepancies on normal or mild disproportional skeletal bases as, deep bite or
open bite.
Classification of orthopedic functional appliances;
Graber classification:
1- Myotonic appliances: which depends primarily on mandibular displacement
anteroposterior or vertically thus initiate.
2- Myo-dynamic appliances: elastic appliances: which not only translate the mandible
anteroposteriorly and vertically but also transmit muscular forces to move the teeth and
reshape the dental arches.
NB: tissue reaction to orthodontic forces are influenced by direction, duration and magnitude of
force as: sutures affected by application of orthopedic forces using high pull headgear are different
from those affected during rapid maxillary expansion.
NB: during high pull headgear treatment, compression is applied mainly to zygomatico maxiilary,
zygomatico-temporal and ptreygomaxillary sutures, while during rapid maxillary expansion
massive tension is applied to mid palatal sutures. This tension stimulates cellular proliferation and
differentiation into osteoblast and fibroblast. Subsequently new osteoid tissue is laid down from
the bone edges toward the midline. Within 3—4 months, the gap is completely obliterated with
mature bone and the mid palatal suture return to appear in its original form and structure.

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Dr. Mohammed Alruby