Pacific Coast Society of Orthodontists Bulletin Summer 2020 - 68

Presentation Summary

Presentation Summary

Possibilities and Challenges With
Skeletal Expansion
Dr. Bruce P. Hawley
PCSO Bulletin Contributor
Dr. Tung Nguyen
University of North Carolina,
Chapel Hill

Presented by Dr. Tung Nguyen at the Washington
State Society of Orthodontists Meeting, Feb 14,
2020
Depending on the study, the prevalence of posterior crossbite in the general population ranges
from 10% to 22%. In addition to the traditional
means of rapid palatal expansion, miniscrew-assisted rapid palatal expansion (MARPE) and surgically assisted rapid palatal expansion (SARPE) can
be used.
Protocols
Dr. Nguyen fits bands and then takes an upper
impression for MARPE, with the laboratory leaving 1 mm between the palate and the expander.
After the RPE is cemented, he anesthetizes and
places 1.8- × 12-mm temporary skeletal anchorage
devices (TSADs). He incorporates the University
of California Los Angeles activation schedule of
two turns per day for patients in their early to mid
20s and as much as is possible for older patients.
A newer protocol starts with four to six turns per
day until a maxillary midline diastema appears.
The University of North Carolina protocol is two
turns per day until a diastema appears, then one
turn per day thereafter. If there is resistance, he
stops turning for one day, but up to one to two
weeks' rest might be needed. Bear in mind that
Korean-manufactured jackscrews are 1/6 mm
per turn, while other jackscrews are 1/4mm per
turn. Using full bands on molars reduces torquing to the miniscrews but adds direct force to
the molars. Some clinicians will cut off the hyrax
extension arm to the molar band if there is molar
tipping.
Outcomes
How does monocortical versus bicortical anchorage compare? A finite element study shows
that the latter results in better implant stability,
less mini-implant deformation and fracture, and
more parallel expansion in the coronal plane. An
unpublished clinical comparison study demonstrated more skeletal expansion with bicortical
anchorage at the zygoma (31%), molars (55%), and

68	

canines (57%), but the difference was only about
1 mm. Another study demonstrated true orthopedic (skeletal) expansion of 41%, bone bending
at 12%, and dental tipping at 48% (which includes
the bone bending). Dr. Nguyen is concerned
about the amount of bone bending and accordingly limits activations to one turn per day.
Skeletal expansion goes up to the zygomaticofrontal suture. For 21-year-old patients, the
zygomaticomaxillary complex bends 0.6 mm
for each 1 mm of expansion. Another sample of
27-year-olds demonstrated more tipping in this
group, 7° versus 4-5° in the 21-year-old sample. Resultant expansion at the tooth apices is less than
the expansion of the cusp tips. The difference
was found to be 50% for the canines and second
molars and 70% for the premolars and first molars. There is a loss of buccal bone thickness with
MARPE, and dehiscences and fenestrations can
be seen, depending on the location of the conebeam computed tomography slices. A skull study
in the general population showed 40% incidence
of dehiscence (with the mandibular canines most
affected) and 61% of fenestration (maxillary first
molar having the greatest incidence). Dr. Nguyen
found that 11% of MARPE patients had dehiscences before expansion while 65% demonstrated them afterward. SARPE expansion went from
14% pretreatment to 69% following treatment,
which was very comparable with MARPE, but
fenestrations decreased as the crowns tipped in,
and fenestrations became dehiscences. Individuals with preexisting dehiscences were at least
four times more likely to develop additional
dehiscences. No relation was found with age, sex,
or right versus left sides. The mesial root of the
maxillary first molar was the most affected root.
In theory, to obtain parallel expansion, the
expander must be placed more posteriorly.
For more anterior expansion, the expander is
placed more anteriorly. No correlation was found
between the position of the expander and the
resulting expansion, with most cases showing
a more anterior (V-shaped) expansion pattern.

PCSO Bulletin    Summer 2020



Pacific Coast Society of Orthodontists Bulletin Summer 2020

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