Biomechanics 4 /certified fixed orthodontic courses by Indian dental academy

BIOLOGY AND
BIOMECHANICS OF
EXTRAORAL APPLIANCES
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

Effects of protraction mechanics
on the midface
• Valmy Pangrazio et al.
• NOV. 1998 AJO.

• Forty patients with Class III maxillary
deficiencies were each treated with a
bonded maxillary palatal expansion
appliance followed by protraction.
• This group was compared with 24
Class I patients treated solely with
bonded expansion appliance
mechanotherapy.

• The protraction group showed
significant increases in the following
measurements: ANB angle, Wits, A
perpendicular to nasion and in sella to
A point.
• The control group did not demonstrate
any significant changes in the position
of the maxillary complex as a result of
expansion mechanics.

• The present investigation demonstrated
that protraction forces on the maxilla will
result in movement of the maxilla in a
downward and forward direction.

Long-term effects of Class III
treatment with rapid maxillary
expansion and facemask therapy
• By Westwood, McNamara et al.
• AJO march 2003.

• The treated sample consisted of 34
patients who underwent RME/FM
treatment before the pubertal growth
spurt (average age, 8 years 3 months
at the beginning of treatment).
• At the final observation period
(average age, 14 years 10 months), all
patients were in decelerative growth
phase.

• It is concluded that the favorable
skeletal change observed over the long
term is due almost entirely to the
orthopedic correction achieved during
the RME/FM protocol.
• During the posttreatment period that
includes the pubertal growth
spurt, craniofacial growth in RME/FM
patients is similar to that of untreated
Class III controls.

• Aggressive over-correction of the Class
III skeletal malocclusion, even toward a
Class II occlusal relationship, appears
to be advisable, with the
establishment of positive overbite and
overjet relationships essential to the
long-term stability of the treatment
outcome.

Biomechanical and clinical
considerations of a modified protraction
head-gear.
• By Ravindra Nanda.
• AJO 1980 vol.78
• The ages of the patients ranged from 9 to
13 years. All patients were selected prior
to attainment of the circumpubertal
height growth peak.

• in majority of patients the maxilla was
small or retropositioned. The mandible
was either of normal dimensions or
slightly larger.
• None of the patients had an excessively
large mandible. In addition, none of the
patients exhibited an underjet larger
than 2 mm.

• The results showed that a modified
protraction headgear with a chin cup
helps in the correction of Class III
malocclusion by the anterior
displacement of the maxilla, and
possibly restricting or changing the
direction of the growth of the mandible.

Individual growth in Class III
malocclusions and its
relationship to the chin cap effects
• Hiroyuki Ishikawa et al.
• Sept. 1998 AJO.
• Longitudinal cephalograms of six
untreated Japanese Class III
subjects were used for the analysis
of jaw growth from 8 to 14 years of
age.

• Among the six subjects, inhibition of
maxillary forward growth was found in
four subjects at ages before the
maximum pubertal growth in body
height occurred.
• One subject with growth
characteristics of strong mandibular
downward growth showed backward
growth of the mandible by chincap.

• One of the remaining sample showed
the strongest mandibular forward
growth where chin cap was not
effective.
• It was concluded that effects of chin
cap therapy are closely related to
growth characteristics of the mandible
in Class III treatment.

The effects of chin cup therapy on
the mandible: A longitudinal study
• By P. Wendell ,R. Nanda.
• 1985 apr. AJO.
• The patients selected for this study were
Japanese females treated with the
extraoral chin cup appliance.

• Lateral ceph. were taken on the
average of 6 months for the treatment
group and every year for the control
group.
• Ten treated patients and seven control
patients were studied. The duration of
chin cup therapy averaged 3 years 1
month.

• The mandible exhibited less downward
displacement relative to cranial base
during treatment. The skeletal profile
was improved with treatment.
• This study indicates that the chin cup
may be a viable mode of treatment for
the preadolescent and adolescent
mandibular prognathism patients.

Long-term effects of chincap therapy
on skeletal profile in mandibular
prognathism
• By Junji Sugawara et al.
• 1990 Aug AJO.
• The sample consisted of 63 Japanese
girls who had skeletal Class III
malocclusions before treatment. All
underwent chincap therapy from the
beginning of treatment.

• The duration of chincap therapy varied
but averaged 4 1/2 years. The samples
were divided into the following three
groups according to their ages when
chincap therapy was started: A group
that started at 7 years of age (n =
23), a group that started at 9 years of
age (n = 20), and one that started at 11
years of age (n = 20).

• The skeletal profile was greatly
improved during the initial stages of
chincap therapy, but such changes
were not permanent.
• chincap therapy did not necessarily
guarantee positive correction of
skeletal profile after complete growth.

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Biomechanics 4 /certified fixed orthodontic courses by Indian dental academy

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