Orthotown November 2023 - 40

This discrepancy in growth leads
to an imbalance in the relationship
between the upper and lower jaws,
resulting in a Class III malocclusion.
The treatment of these malocclusions
often requires a combination of
orthodontic and surgical interventions.
However, recent advancements in
orthodontic techniques have provided
alternative treatment options that can
minimize or even eliminate the need
for surgery.
A bit of history
Maxillary protraction +/rapid
palatal expansion
Studies have shown that traditional
rapid palatal expansion (RPE) and
facemask therapy can achieve significant
forward movement of the maxilla
and improvement in the skeletal
Class III malocclusion in growing
patients.7
However, the amount of forward
movement is related to the age
of the patient; in general, the younger
the patient, the greater the potential
for maxillary advancement via growth
modification.
In 2005, Vaughan et al.8
published
a randomized controlled clinical
trial demonstrating the effectiveness
of maxillary protraction with and
without maxillary expansion. Participants
had a mean age of 7-8 years old
and wore a protraction facemask for
an average of 14 months (full time in
the beginning and 14 hours per day
once an end-to-end molar relationship
was achieved). Force of elastics
was 300-500 g (10-18 ounces) per
side. In both groups, A-point moved
forward approximately 2.5 mm, with
associated counterclockwise rotation
of the maxilla and clockwise rotation
of the mandible.
Miniplates + maxillary protraction
In 2010, Heymann et al.9
published a
pilot study where they used maxillary
and mandibular miniplates and
intermaxillary traction in six 10- to
13-year-olds. Average treatment time
was 12.5 months and the elastic force
used started at 150 g (5.3 ounces)
per side and progressed up to 250 g
(8.8 ounces) per side. They noted an
average SNA change of 2 degrees,
indicating forward movement of the
maxillary complex. They also noted
changes at the level of zygoma, which
they suggested may be because of the
location of the miniscrew placements
closer to the zygomaxillary suture.
for Class III malocclusion. To evaluate
dental and skeletal alterations
(changes), pretreatment, progress and
posttreatment CBCT images were
obtained using an iCat FLX (Dexis).
The field of view covered the mandible,
maxilla, upper and lower dentition,
and anterior cranial base.
The 3D surface models of the manCorrecting
Class III
malocclusions can
be a challenge
for orthodontists,
because the
underlying cause
can be a small
retrognathic maxilla,
a prognathic
mandible or both.
MARPE + facemask
Maino et al.10
dible, maxilla, cranial base, and upper
and lower dentition were generated
using the Segment Editor module in
the 3D Slicer software. Image analysis
was conducted using Slicer3D with the
CMF module software (Maurice Müller
Institute) installed.11
The head position of T1 images was
adjusted in the coronal and sagittal
views using the palatal plane. In the
axial, coronal and sagittal views,
images were reoriented based on
palatal plane reference. Voxel-based
registration was employed to superimpose
T2 and T1 images. The anterior
cranial base, which completes growth
by age 7, served as the reference region
for 3D segmented anatomical structures.
The registration process aimed
to achieve the best anatomical fit of
the anterior cranial base structures.
The CMF software overlaid 3D
reported on average, the
A-point of the maxilla was brought
forward 3.4 mm in 28 Class III patients
who underwent bone-anchored RPE
facemask therapy (ALT-Ramec protocol).
Most notable with these changes
was that the treatment duration for the
protraction was only four months on
average with a 14-hour wear time. The
elastic force used with the facemask
was 400 g (14 ounces) per side.
Case studies
We will now review three cases
from my practice of patients who
have undergone orthodontic care
NOVEMBER 2023 | 40 | ORTHOTOWN.COM
surface models registered within the
same coordinate system. Closest-point
3D linear distance measurements
were taken, and the resulting surface
distances were computed and stored
as color-coded 3D linear distances.
We utilized the Markups module,
a feature in 3D Slicer, to facilitate the
creation and management of markups
in both 2D and 3D. This allowed us
to obtain measurements such as the
distance from point A (T1 image)
to point A' (T2 image), as well as the
measurement between the right and left
maxillary points (Mx Right to Mx Left).
A big thanks to Dr. Alexander Plaksin
and his team at Imprind Imaging
Services for the 3D superimposition
workups and data analysis.
http://www.ORTHOTOWN.COM
Orthotown November 2023

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