Pacific Coast Society of Orthodontists Bulletin Fall 2021 - 42

Let's Talk About That
RR: The digital approach to orthognathic surgery
was really enabled by a convergence of three
technologies. It was essentially a trifecta. First,
we needed a readily available, affordable, and
relatively low exposure means of obtaining 3D
radiographic imaging of the entire face, and that
arrived with the CBCT scanners that have become
so ubiquitous in many of our offices. Second,
we needed powerful segmentation software
that could process large digital imaging and
communications in medicine (DICOM) data sets
into high-resolution 3D images on which virtual
surgery could be carried out. Dolphin Imaging in
Chatsworth, California, and Materialise in Louven,
Belgium, were two of the early providers of this
technology. Finally, we needed 3D printing to generate
the surgical guides we take to the operating
room to ensure that the virtual surgical planning
is realized accurately. We can thank Chuck Hull,
the inventor of stereolithography, for this technology
that many of us now have sitting on the
lab bench in our office. Without these 3D printers,
the images created from the virtual planning
would just be colorful pictures. The process has
continued to advance to where we can now integrate
intraoral optical scans with the segmented
CBCT for even higher-resolution dental anatomy
than what is possible with X-rayed casts from
poured impressions. Surgical guides generated
from the digital process can even be used to fit
custom-fabricated titanium fixation plates that
reposition the bony anatomy precisely according
to the surgical plan.
PT: Can you describe the digital orthognathic
workflow and how it differs from what you used
to do?
RR: Prior to digital, our orthognathic surgery
workflow consisted of measurements taken diFigure
1. Traditional orthognathic surgery workflow. (a) Dental casts are mounted on
an articulator with a face bow transfer and a bite registration. (b) The maxilla is repositioned
according to the surgical plan. (c) The final occlusion is established. (d) Acrylic
splints are made.
42
rectly from the patient and the usual two-dimensional
cephalometric prediction tracings. A face
bow and bite registration were needed to mount
casts. We did our model surgery using an Erickson
Model Block, and then there was the smelly
polymethylmethacrylate surgical guide-making
process (Figure 1a-d). Each case required multiple
hours of preparation. With digital, the process
involves obtaining a CBCT scan carefully registered
to the adjusted natural head position (NHP)
using a simple laser level and some adhesive radiopaque
labels (Figure 2a-d). A 3D image is then
rendered on the computer and oriented to the
NHP (Figure 3a). Measurements referenced to the
facial midline, horizontal, and vertical reference
planes are made from the rendered image (Figure
3b). The imaging software makes this a relatively
easy process, and I do this chairside with the patient.
An intraoral optical scan is taken. Prediction
tracings are completed from a rendered cephalometric
profile oriented to the NHP, and then the
digital data set and all of my measurements and
PCSO Bulletin
Fall 2021

Pacific Coast Society of Orthodontists Bulletin Fall 2021

Table of Contents for the Digital Edition of Pacific Coast Society of Orthodontists Bulletin Fall 2021