Pacific Coast Society of Orthodontists Bulletin Spring 2020 - 37

Let's Talk About That

in posterior tooth positions or posterior maxillary
height changes, but this is not equivalent to modifying its fundamental size or length.

PT: Patients with deficient mandibles are probably our most common AP malocclusion. How do
you treat these patients?

For us, growth modification is targeted only to
the maxilla. This means headgear (always high
pull) to restrict AP maxillary growth or reverse
headgear to promote it. Although both are
tooth-borne appliances, the associated dental
side effects, if unwanted, can be mitigated by
limiting use of the appliance to 10 hours or
less. Many times, a purely skeletal response is
desired without mesial or distal movement of the
maxillary molars. This would be the case if the
maxilla was classified red (excessively prominent)
but the ICD in the maxillary arch was zero. Using
headgear (or reverse headgear) for 10 continuous
hours or less will affect the maxillary sutures, so
normal growth is modified, but little or no tooth
movement will occur. It is extremely important to
be able to separate the orthopedic effects from
the dental effects of whatever appliance is being
used. We find that we are able to control the
effects of our applied force systems much better
with headgear than with functional appliances,
which almost always encourage unwanted dental
side effects. There are certainly instances in which
the known side effects of a particular functional
appliance might be desirable, providing justification for its use. For example, when the AP
position of the maxilla is classified red, the ICD
in the maxillary arch is negative (requiring distal
movement of the posterior teeth), and the ICD in
the mandibular arch is positive (requiring mesial
movement of the posterior teeth).

WA: You are absolutely right about the prevalence of mandibular deficiency. In our patients,
we find that as many as 84% walk through our
door with this problem. If you look at only those
for whom the deficiency is greater than 4 mm,
it is still 34%-a pretty large chunk of patients.
Confounding this is that 63% of all patients
examined had a concurrent AP deficiency of the
maxilla. This presents a real dilemma when it
comes to treatment. Using conventional toothborne functional appliances in growing patients
with intent to augment mandibular projection
will come at a cost to the AP position of the
maxilla and to tooth positions within the arches.
Most patients who need enhanced mandibular
projection unfortunately already have a maxilla
that is deficient, which will become even more
deficient from the headgear effect of the functional appliance. Any modest gain in mandibular
length must be weighed against this inevitable
cost. The ideal patient for functional appliance
therapy is one with a maxilla that is mildly (2
mm) in the red zone (excessively prominent) and
a mandible that is mildly (2 mm) in the black
zone (insufficiently prominent). Unfortunately,
patients who fit this profile are about as rare as
unicorns in our office.

Following our usual protocol with headgear or
reverse headgear, we expect roughly 2 mm of net
jaw (maxilla) position change to occur in 1 year if
the patient is growing at an average rate. Rarely
do we attempt or expect to achieve more than 3
mm of total effect. In more extreme conditions,
dramatic AP maxillary skeletal changes are possible, particularly protraction, without concurrent
dental side effects, using bone-borne appliances
as popularized by DeClerck et al.26

Spring 2020 PCSO Bulletin

Short of orthognathic surgery, I'm afraid that
our options for significantly elongating the mandible are pretty limited. Distraction osteogenesis
is reserved for very extreme problems that are
beyond the limits of correction by conventional
orthognathic surgery. Like most orthodontists,
the majority of our patients are not particularly
interested in undergoing jaw surgery, so we
are often faced with having to compromise our
treatment goals. Compromised treatment is not
necessarily a bad thing, so long as the patient
ends up with a condition that is on balance
superior to having had no treatment at all. This
means that health, function, and appearance,

Pacific Coast Society of Orthodontists Bulletin Spring 2020

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