Effects of Extra-Oral Force

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Effects of extra-oral appliances Dr. Mohammed Alruby
Effects of extra-oral appliances
And
Forces
Prepared by
Dr. Mohammed Alruby

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Factors affect extra-oral force
Studies of maxillary protraction force
Results of extra-oral force
Effects of extra-oral appliances

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The effects of extra-oral forces on dentofacial structure depend on the following factors:
- Direction of force
- Magnitude of force
- Duration of force
- Growth
- Patient cooperation
1- Direction of force:
Kloehn 1953, Gould 1975, Greenspan 1970, Merrifield and Cross 1970, and Worms et al 1973,
all give an adequate description for the direction of force application and their effect on maxillary
molar position, tipping, bodily, extrusion, intrusion movement
The direction of force should be adjusted according to the patient needs and objective of treatment
as:
- When bodily movement is required, the force should pass through the center of resistance
of molars (at the tri-furcation of roots) and the extra-oral tube should be placed gingivally
as possible
- When bodily displacement of maxilla is required, the force should pass through the center
of maxillary resistance (zygomatic bone)
- When extrusion of molars is required, (in case of deep bite) the force should pass below the
center of resistance (below the level of occlusal plane)- cervical headgear is the best choice
- When intrusion is required (open bite cases) the force should pass above the level of
occlusal plane
- In occipital headgear, the vector of force may pass through the center of resistance of 1st
molar and thus causes: -------------- distal translation of 1st
molar
- If the vector of force passes above the center of resistance causing:
a- Distal root torque
b- Mesial crown tipping
c- Intrusion of maxillary 1st
molar ---- that, ----- closing the bite and same can occurs in
the vertical or high pull headgear
== the direction of force can be determined by adjusting the outer bow in relation to the occlusal
plane or center of resistance
== the best method for recording the force direction is the lateral cephalometric radiograph with
the appliance in place, then the outer bow is adjusted in relation to the occlusal plane and the
center of resistance of tooth or jaw
= in Kloehn’s face bow, the direction of force is 25 – 30 degree below the occlusal plane so that,
the vector of force is far away from the center of resistance of 1st
molars, thus cervical headgear
causes distal tipping and extrusion of 1st
molars and open bite
The direction of force depends upon the following variables:

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I- Vertical position of the outer bow relative to the center of resistance:
= force applied by oblique headgear passing through the center of resistance will cause translation
of the tooth and make intrusion at the same time
= force applied by oblique headgear passing above the occlusal plane
but below the center of resistance will cause:
a- Distal crown tipping, mesial root torque
b- Extrusion of mesial marginal ridge and intrusion of distal marginal ridge --- open bite
= force pass parallel to occlusal plane will produce:
a- More distal crown tipping and less mesial root torque
b- Extrusion
= force applied by cervical headgear pass below the occlusal
plane and away from center of resistance will cause:
a- Distal crown tipping with less root torque
b- Extrusion ------ intrusion
It was noted that the types of movement depend upon the relationship between the vector of force
and center of resistance expressed by the perpendicular distance between line of force and center
of resistance
When the vector of force passes through the center of resistance, the perpendicular distance equal
zero and the teeth will be translated
When the force line passes Coronally to the center of resistance, ----------- the center of rotation
will move apically to the center of resistance that produce:
a- Tipping of crown in one direction
b- Slight tipping of the root in opposite direction
AS: the vector of force moves Coronally, the center of rotation moves apically with consequent:
Increase crown tipping ----- and --- decrease root torque
Until the center of rotation become at the root apex, then the crown tipped without torqueing
N: B:
Kloehn reported that:
a- Placing the outer bow in high position above the center of resistance will causes:
- Mesial crown rotation
- Distal root torque
- Extrusion of distal marginal ridge and intrusion of mesial marginal ridge
b- Placing the outer bow in low level below the occlusal plane will causes:
- Distal crown rotation
- Mesial root torque
- Extrusion of the mesial marginal ridge
c- Placing the outer bow parallel to the occlusal plane will causes:
- Distal crown rotation
- Extrusion

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II- The length of the outer bow:
Gould and Greenspan showed that, the length of outer bow may change the direction of force on
the teeth
Regarding the length of the outer bow, there are 3 possible varieties:
a- Short bow: ending mesial to maxillary molar tubes
b- Long bow: ending distal to molar tubes
c- Medium bow: ending at the level of molar tubes
Effect of short bow:
a- Mesial crown tipping
b- Distal root torque
c- Intrusion of mesial marginal ridge
d- Extrusion of distal marginal ridge
Effect of long bow:
a- Distal crown tipping
b- Mesial root torque
c- Intrusion of distal marginal ridge
d- Extrusion of mesial marginal ridge
Effect of medium bow:
a- Intrusion
b- Distal translation
III- Types of anchorage:
a- Cervical headgear:
The primary vector of force, provides distal and extrusive tooth movement
b- Occipital headgear:
The primary vector of force, provides distal and intrusive tooth movement
c- High- vertical pull or parietal headgear:
The primary vector of force provides an intrusive movement with less distal movement
So that, cervical headgear is the best choice for treatment of class II deep bite
Occipital headgear is the best choice of treatment of class II open bite
Vertical headgear is the best choice for treatment of open bite cases
2- Magnitude of force:
= force between 250 – 400gm / side will cause only dento-alveolar changes and teeth movement
= force about 800gm will be sufficient for anchorage purpose because the extra-oral appliance
worn only half time 12 hour / day, so that, use double amount of force more than delivered by the
intra-oral appliance for successful anchorage
= force more than 800gm / side will sufficient to produce skeletal changes in the dentofacial
complex
Force can be measured by Zebco Fishman gauge or spring scale
It was found that, the magnitude of force depends on the following:
1- Time of treatment: growing bone is more responsive than mature one so that, treatment
during active growth period require less force and produce more pronounced effects
2- Severity of discrepancy: sever discrepancy require more force over long period

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3- The amount of expected growth: if there is enough amount of growth, extra-oral force may
be used in minimum range only for guiding of growth
4- Direction of growth: favorable growth direction requires small amount of force for guiding
while unfavorable growth may require greater amount of force for inhibition or redirection
5- Duration of force application: either less force over longer duration or more forces over
short duration
6- Individual sensitivity and pain threshold: the applied force should not cause pain or
discomfort to the patient
=== force more than 3 pounds will cause soreness of the teeth and cervical region
3- Duration of force application:
There is much variability in the daily wear
The range between the sleeping hours to 24 hours
The range required to produce skeletal changes is 12 -16 hours
4- Growth (time of treatment):
= Treatment should be carried during the active growth periods to take a benefits of pubertal
growth spurt. It starts between 10.5 – 12.5 and lasts 2 years in boys
= By age 13 years, girls become an adult while boys don not reach adulthood until 16 years
Orthopedic force is effective only during active growth period and more particularly during
pubertal spurt. Use of orthopedic force in adult is of little significance
= actually, the maxillary growth ceases early so that, the best results of orthopedic correction on
maxilla can achieved in early age 6 – 9 years
5- Patient cooperation:
The effect of orthopedic force depends to great extent on patient cooperation in wearing the
appliance as instructed
Many failures were found due to lake of patient cooperation to wear the appliance. At the same
time, there is no definite way to detect the patient cooperation
By positive re-enforcement and education, some patients are very responsive to therapy
N: B:
A major negative side effects of maxillary protraction procedure is maxillary dental movement that
detract from skeletal change
Shapiro and Kokich used the ankylosed primary canine as natural implant. With traction against
maxillary arch stabilized by these teeth, they were able to demonstrate approximately 3mm of
maxillary protraction in one year, with minimal dental change
Studies for maxillary protraction
Teuscher 1978 has postulated a center of resistance of maxillary complex lying in the region of the
zygomatico-maxillary suture and suggested that maximum restraint of growth without downward
rotation of ANS could be obtained only by ensuring that the force vector passed anterior to this
center of resistance
Cozzani: SNA angle increased by average of 3.5 degree, SNB angle increased 1.02 degree and the
large changes occurred in patients who were 9 years of age or younger when treatment started

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Rune et al, studied the effect of posterior anterior traction in an 11 year- old boy with maxilla-
nasal dysplasia (retrusion of midface and hypoplasia of ANS). The advancement of maxilla is
0.6mm and this limited response due to insufficient growth capacity of circum-maxillary sutures.
Ishii et al, studied the effect of combined maxillary protraction and chin cup appliance in severe
class III cases, they found:
Pogonion moves backward by 1.68mm and downward by 1.15mm
Point B moved backward by 2.0mm
These changes means that there was a backward displacement and downward and backward
rotation of the mandible by chin cup
Chong and Ive evaluated treatment effects and post treatment changes following class III
malocclusion, they found: that the early correction of class III with maxillary protraction headgear
induces significant skeletal and dental changes
Chen and Lai-ying evaluated sagittal skeletal and dental changes of severe headgear treatment in
unilateral cleft lip and palate.
After 7 months’ treatment with reverse headgear wear:
1- There is a normalization of the sagittal maxilla-mandibular relationship
2- Significant skeletal changes in maxilla and mandible
MacNamara, described technique combining a bonded rapid palatal expansion appliance, with
orthopedic facial mask, the effects include:
1- Forward and downward movement of maxilla
2- Forward and downward movement of maxillary dentition
3- Downward and backward redirection of mandibular growth
4- Lingual tipping of lower anterior teeth
5- Inhibition of mandibular growth
Baik 1995, studied the protraction of maxilla in 60 subjects from 8 – 13 years of age with 47
subjects with RME and 13 with labio-lingual appliance, he concluded the following results:
1- After maxillary protraction, the maxilla and maxillary dentition moved forward and
downward, and mandible and mandibular dentition moved backward and downward
2- Maxilla moved more in RME cases than labio-lingual appliance
3- Palatal plane angle decreased more in case of protraction during palatal expansion than
protraction after palatal expansion
Itoh et al 1985, study the orthopedic effects of maxillary protraction appliance in treatment of
anterior cross bite, and found the following:
1- Parallel protraction forces applied to the molars caused anti-clock wise rotation of the
teeth. force 20 degree downward to occlusal plane decreased the tipping and cause some
extrusion
2- Parallel and downward tractions caused constriction of anterior portion of maxilla
3- Forward pull from molars and 1st
premolars caused anti-clockwise opening rotation of the
palatal plane
Maxillary deficiency is a deficiency not only in width and height but also in depth.
Protraction of maxilla has been found to increase the sagittal depth.

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Haskell and Farman stated that, non-surgical maxillary protraction has ability to displace the A
point anteriorly. The protraction ranges of A point 2.5 -5mm was reported in limited number of
cases. They hypothesized that variation in success of advancing A point can be explained by the
presence or absence of partial patency of the pre-maxillary maxillary suture.
Ricketts has observed the forward movement of point A in response to treatment of class III and
cleft palate cases. The effect of forward traction of maxilla has been documented in unilateral cleft
lip and palate patients by use of implant
The Net results of extra-oral forces
If there is full cooperation in wearing the appliance and the growth is still active, the following
results can occur:
I- Cervical headgear:
a- Face bow:
Dental effects:
- Distalization of molars and bicuspids to class I
- Increase the arch parameters
- Extrusion of molars
- Reduce over bite
- Reduce over jet
Skeletal effects:
- Inhibit the forward growth of maxilla, ANS hold in position
- Posterior displacement of maxilla, ANS and A point moves posteriorly (movement of maxilla
backward 4 – 7mm)
- Upward rotation of maxilla, PNS moves downward and ANS remains in position or moves
upward
- Downward and backward rotation of mandible – due to molars distalization
- Increase lower face height and increase FMA
b- J – hooks:
Dental effects:
- Distalize incisors
- Extrude incisors
- Reduce over jet
- Increase over bite
- Decrease arch parameters
Skeletal effects:
- ANS rotate downward
- ANS held in position or moves distally
- A point moves distally

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II- Oblique headgear:
a- Face bow:
Dental effects:
- Distalize the molars
- Intrude molars
- Reduce over jet
- Increase over bite
- Increase arch parameters
Skeletal effects:
- ANS rotate downward and PNS upward
- Rotate the maxilla downward
- Inhibit the forward growth of maxilla or moves the maxilla posteriorly
- Mandible rotate upward and forward
- Forward position of symphysis
- FMA remain unchanged or reduced
- Decrease lower face height
b- J hooks:
Dental effects:
- Distalize incisors
- Intrude incisors
- Decrease arch parameters
- Decrease over bite
- Decrease over jet
Skeletal effects:
- Prevent forward growth of maxilla, ANS held in position
- Move the maxilla, ANS moves distally and may rotate upward
- A point moves distally
III- High pull or vertical headgear:
a- Face bow:
Dental effects:
- Intrude molars
- Reduce open bite
Skeletal effects:
- Rotate maxilla downward, ANS rotate downward and PNS upward
- Mandible rotate upward and forward with chin moves anteriorly
- FMA remain unchanged or reduced
- Lower face height is decreased
b- J hooks:
Dental effects:
- Intrude incisors
- Reduce over bite
Skeletal effects:
- ANS moves upward

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N: B:
Indication of extra-oral forces:
1- Skeletal class II malocclusion in growing children
2- Skeletal class III malocclusion in growing children
3- Open bite
4- Deep bite
5- Retraction of incisors and canine
6- Distalization of molars
 In case of mandibular correction:
The force is directly applied against the mandible using oblique occipital chin cup in correction of
------------- class III and high pull (vertical) chin cup for correction ----- open bite
 In case of maxillary correction:
The force is directed against maxilla, through an intra-oral appliance to effect the desired changes,
it used for correction of:
1- Class II skeletal using cervical or occipital headgear according to over bite
2- Excessive over bite or over jet
3- Class III using face mask
N: B:
Advantages of orthopedic correction:
1- Correct the basic skeletal mal-relationships
2- Improve facial esthetics
3- Reduce the time of treatment
4- Reduce need for extraction
5- Rapid correction of over jet and over bite and molar relationship
6- Reduce needs for complex mechanics in treatment and preparation of anchorage
7- Less damaged the periodontium
8- More stable results

Effects of Extra-Oral Force

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