Pacific Coast Society of Orthodontists Bulletin Summer 2020 - 58

Special Section: Class II Correction

Faculty Files

Dr. Janet Kim Interviews Dr. Jae Hyun
Park: Essential Considerations in Class
II Treatment

Dr. Janet Kim
Resident, Postgraduate
Orthodontic Program
Arizona School of Dentistry &
Oral Health

Dr. Jae Hyun Park
PCSO Bulletin Editor-in-Chief

What do you consider as the most important
parameters for mandibular growth rotation in
Class II patients?
One of the most widely recognized classic studies
on the key parameters that determine the direction and degree of mandibular growth rotation
was conducted by Skieller and colleagues1 in
1984. They employed a total of 44 morphologic
variables and analyzed them with a multivariate
statistical method to identify the variables that
showed the highest predictive value on mandibular rotation (alone or combined). They identified
four relevant parameters: mandibular inclination,
intermolar angle, shape of the lower border of
the mandible, and inclination of the symphysis
(Figure 1A-D).1 When these parameters were combined, the prognostic estimate was at its highest
(86%). Of these four parameters, the mandibular
inclination was the most important in the prediction of the direction and amount of mandibular
rotation. In this report, the mandibular inclination was represented by Index I. This is the ratio
between the posterior and anterior facial height
and ranges from 57.2% to 70%. Index I is the most
significant indicator of rotation because it can
explain 62% of mandibular growth rotation when
used alone, and as much as 86% when combined
with the three other values.
In 1985, Siriwat and Jarabak2 categorized facial
morphology based on three distinct patterns
defined by the facial height ratio, or the Jarabak
Quotient.2 Like Index I, this is also the ratio of posterior facial height to anterior facial height and
is measured by the equation (S-Go/N-Me)/100.
They reported that these patterns were commonly associated with rotational growth changes that
tend to accentuate the pattern characteristics
with growth, so these static evaluations were
used in terms of growth, as shown in Figure 2.
When the ratio is between 59% and 63%, the
mandible is expected to present a neutral growth
pattern of downward and forward movement,
which is the most prevalent. If the ratio is less
than 59%, mandibular growth may be hyperdivergent, while if it is greater than 63%, it may be

58	

hypodivergent. Thus, both the mandibular inclination as represented by Index I and the facial
height ratio (Jarabak quotient) are expressions
of the ratio of posterior facial height to anterior
facial height, which is considered to be the most
important parameter for predicting the direction
of rotation in orthodontic treatment planning.
Recently, in my book titled Temporary Anchorage Devices in Clinical Orthodontics, Buschang
and Tadlock3 listed seven indicators of growth
patterns in skeletal Class II malocclusion to help
determine if patients have favorable or unfavorable growth patterns with skeletal Class II
malocclusions (Figure 3).
What are the effects of contemporary Class II
biomechanics? What are their advantages and
disadvantages?
Throughout the history of contemporary orthodontics, various removable and fixed appliances
have been used to treat Class II patients. When
the goal was to treat maxillary dentoalveolar
protrusion, molar distalizing appliances were
used, but when the goal was to correct mandibular skeletal retrusion, then mandibular enhancing
appliances were adopted. The use of removable
appliances, such as headgear, for holding or distalizing maxillary molars, has been reported since
the 1950s, while various removable appliances
such as Bionator and Twin Block have also been
used for mandibular skeletal retrusion cases.
However, these removable appliances were often
not very effective because of the lack of patient
compliance. To overcome this issue, a variety of
fixed, noncompliance appliances were developed.
Many types of maxillary molar distalizing fixed
appliances have been introduced, including the
pendulum appliance, Jones jig, and distal jet,
along with many mandibular enhancing fixed
appliances such as Herbst, Forsus, and MARA.
These appliances were able to successfully correct
overjet and molar occlusal relationships, but they
produced untoward movements that caused anterior anchorage loss, which led to incisor proclination and increased overjet, forward movement

PCSO Bulletin    Summer 2020



Pacific Coast Society of Orthodontists Bulletin Summer 2020

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