Pacific Coast Society of Orthodontists Bulletin Summer 2020 - 69

Presentation Summary

The zygomaticomaxillary sutures are the most
resistant ones. Dr. Nguyen saw no distraction
at the pterygoid plates, although this would be
quite difficult to detect. The thickest bone in the
palate is along the midpalatal raphe, branching
laterally in the canine and first premolar areas.
The MARPE may be more stable in that anterior
region, where the bone is thickest, but more research is needed. With the V-shaped expansion,
there is more overjet created in the canine regions, appearing at a greater level with a 6-8 mm
expansion versus a 3 mm expansion level. The
vomer is not distracted; it stays on one side or
the other. There is less expansion laterally on the
side that contains the vomer, and the difference
can be as large as 2 mm. This has the potential to
create a skeletal and/or dental discrepancy with
nasal septum deviation if the expansion is large.
The nonvomer side tips more while the vomer
side expands less.
SARPE Versus MARPE
SARPE appears to provide a more uniform anteroposterior expansion, but it is still V-shaped.
MARPE produces a higher level of expansion,
similar to the transverse expansion results when
SARPE and TSADs are combined. Should MARPE
be used in adolescents to obtain greater orthopedic expansion? On 14-year-olds, both traditional
RPEs and MARPEs have reduced buccal bone
at the molars, but it was less with TSAD-borne
expanders at the premolars. Because both types
had similar expansion outcomes, Dr. Nguyen feels
that it is appropriate to use a standard RPE rather
than MARPE in 14- to 15-year-olds.
How does one go about retaining bone-borne expansion? A bone-borne transpalatal arch between
two of the miniscrews has been tried in Europe.

Summer 2020    PCSO Bulletin	

There is limited evidence of bone-borne expanders being better than tooth-borne expanders,
especially because there are major differences in
protocols, design of TSAD placements, and even
in the use of hybrids. The speaker likes to use
8-10 mm length screws. In a a Class III correction
study, the use of regular RPEs and face masks or
MARPEs and face masks showed no significant
clinical differences in outcomes for a sample of
average 16-year-olds. With MARPE, point A comes
forward less than 1 mm but does tend to relapse
posteriorly.
Dr. Nguyen personally experiences an estimated
20% failure rate with MARPE. When this occurs,
of the four RPE TSADs, it is generally one of the
two more posterior screws that fails. This may be
related to the palatal bone being less thick there.
Sometimes he can remove the expander and
switch to elastics to "finish" the transverse management. There is no new data to support the use
of corticopuncture to help relieve the stress of
expansion or of adding microtrauma to facilitate
expansion. A partial corticotomy with MARPE
does not seem to help uniformly because some
patients do not respond more positively.
Predictors for Success of MARPE
Age, length of the palate, and sutural maturation appear to affect the success rate of MARPE.
Patients younger than 30 appear to demonstrate
the best success, while there is a 50% failure
rate in those older than 40. Males tend to have
more failures, probably because their sutures are
thicker and longer. Success is better with sutural
stages A - C but poorer with more mature sutures
of stages D and E. In conclusion, one must assess
whether the risk is worth the reward when selecting MARPE as the modality of expansion.

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Pacific Coast Society of Orthodontists Bulletin Summer 2020

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