Pacific Coast Society of Orthodontists Bulletin Spring 2020 - 34

Let's Talk About That

jaws relative to defined landmarks in all three
planes of space. Interestingly, most of the landmarks and referents we use are external, reducing
reliance on radiography.
PT: How do you determine if or when premolar
extractions are needed?
WA: The ICD value is predicated on the width,
shape (including AP incisor positions), and depth
of an arch being optimal, but not necessarily
the length, so it is a measure of the mesiodistal
discrepancy within an arch. The discrepancy is
resolved via mesial and/or distal translation of
posterior teeth to the extent needed to bring
the ICD value to zero. A positive ICD means
that the width, shape, and depth are correct,
yet there remains excess space within the arch.
The only way to eliminate this excess space
without altering the desired parameters of an
arch is by mesial translation of posterior teeth.
Approximately 30% of arches are in this category. An arch with an ICD of zero requires no
mesial or distal translation. In other words, the
arch can be made optimal (element I) simply by
correcting its width, shape, and depth. Only a
small percentage of arches can be successfully
treated in this way, perhaps 5%. An arch with
a negative ICD value requires distal translation
of posterior teeth using temporary anchorage
devices, Nance-supported distalizers, or other
similar methods capable of producing a nonreciprocal effect. The specific mechanics employed
are not as important as understanding the basic
principles of what is needed for the arch to meet
element I standards.
The extent to which anatomic limitations
govern the amount of distalization achievable
determines when extractions of premolar teeth
are required. For example, if you feel confident
that posterior teeth can be bodily distalized up
to 3 mm per side, then you could conceivably
treat an ICD of −6 without extractions. Given
patient demographics in our practice, approximately 20% to 25% have an ICD of −6 or worse

and should probably be treated with extractions.
Without extractions in a patient with an ICD
of −6 or worse, the widths of the arches would
have to be increased beyond optimality and/
or the positions of the incisors within the jaw
will be anterior to the goal (excess arch length).
There are no other possible outcomes unless a
gross amount of interproximal reduction were
to be performed.
PT: How do you classify AP jaw positions?
WA: AP jaw positions constitute element II of the
six elements of orofacial harmony. The referents
are element I maxillary and mandibular central
incisors. Because maxillary incisors are visible
when smiling, profile esthetic goals must be considered when evaluating the AP position of the
maxilla. The landmark for AP diagnosis and classification of the maxilla is the forehead. Once the
AP position of the maxilla is corrected (actually
via orthognathic surgery or growth modification
or virtually as part of diagnosis either digitally or
by conventional cut-and-paste methods), it serves
as the landmark for diagnosing and classifying
the AP position of the mandible.
Studies have shown that the forehead is a good
anatomic landmark from which to assess the attractiveness of the face in profile when the maxillary incisors are bared.1,2,15-24 Clinically, we establish
a frontal plane line called the goal anterior limit
line (GALL), which originates from the forehead
(usually very close to glabella) to determine the
desired AP positions of the maxillary incisors and
maxilla (Figure 6a, b).
When the maxillary incisors are optimally
positioned within the maxilla (inclinations and
root positions) and the maxilla's AP position is in
harmony with the GALL, it is possible to achieve
both an excellent occlusion and an excellent
facial profile. A premium is placed on facial attractiveness when the teeth are displayed, such as
they are in social situations when talking, smiling,
and laughing. We believe this to be equally if not

PCSO Bulletin Spring 2020

Pacific Coast Society of Orthodontists Bulletin Spring 2020

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