Pacific Coast Society of Orthodontists Bulletin Spring 2020 - 33

Let's Talk About That

basal bone (WALA ridge). It is entirely possible
to achieve the six keys to optimal occlusion yet
have an unhealthy treatment result because the
roots are not in harmony with supporting tissues.
Such is the case when the dental arches are made
too wide or too narrow relative to supporting
bone or if the arches are too long or too short; for
example, an arch where premolars were inappropriately extracted and the incisors subsequently
retracted using torque control, into positions
that might satisfy some arbitrary cephalometric
parameter but not element I.
PT: How do you evaluate transverse skeletal
relationships?
WA: Evaluating jaw widths is element III of the
six elements of orofacial harmony. The transverse dimension is often overlooked, in our
opinion. Because we place a high priority on
root positions, archwire width and shape must
be customized for each patient so that tooth
inclinations are corrected without altering the
faciolingual positions of the centers of rotation. If
done in this way, essentially by decompensating
posterior tooth positions, the corrected arches
themselves will indirectly represent the width
of the underlying basal bone of each jaw. The
difference in width between opposing corrected arches, if any, reveals the transverse skeletal
discrepancy quite precisely; no radiographs are
needed. Transverse skeletal discrepancies are
found in a very high percentage of our patients,
as high as 75%, virtually all of which consist of the
maxilla being narrower than the mandible. Many
of these discrepancies are small, meaning 3 mm
or less, but ignoring them clinically will usually
mean that a fair amount of torque will have to be
applied when trying to correct posterior occlusal
interfacing, which in turn moves the roots out of
the sweet spot within the alveolar bone.
Adherents to philosophies advocating the creation of very broad arches using broad archwires
to reduce or eliminate premolar extractions often
find that negative crown torque is needed to

Spring 2020 PCSO Bulletin

control maxillary posterior crown inclinations.
In contrast, those that espouse the notion that
the width of the mandibular arch should never
be changed often find a need to apply positive
torque to mandibular posterior teeth. Neither
approach will produce ideal root positions within
alveolar bone.
Recognizing and correcting transverse skeletal
discrepancies in the early stages of orthodontic
treatment vastly simplifies subsequent orthodontic strategies aimed at correcting occlusal
relationships between opposing arches. In the
end, an ideal occlusion can be created with the
roots in desired positions relative to supporting
tissues with little or no torque applied.
PT: You mentioned that you are using a new
system of classification. Can you explain how it
works?
WA: Unlike any previously proposed system, we
classify individual arches, not malocclusions.
Arches are classified using a discrepancy index
called the interim core discrepancy (ICD), which
quantifies the lack of or the excess mesiodistal
space for teeth within an arch after the width,
shape, and depth of an arch have been corrected (actually or virtually) and the incisors
have been set, actually or virtually, into their
optimal AP positions within the jaws. Of course,
quantifying the ICD is meaningful only if the
optimal width, shape, depth, and length of an
arch are well defined. This is element I of the six
elements of orofacial harmony. ICD quantifies
the difference between an arch in its current
condition and optimality. When the ICD is
resolved through treatment, an arch becomes
optimal (element I).
Element I arches then set the stage for jaw and
chin classification. This is because teeth (arches)
that are in element I positions indirectly reflect
the AP positions, the widths, and the heights of
their respective jaws. Element I teeth thus serve
as referents for assessing the positions of the

Pacific Coast Society of Orthodontists Bulletin Spring 2020

Table of Contents for the Digital Edition of Pacific Coast Society of Orthodontists Bulletin Spring 2020