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Figure 4. First patient: on the left, the 3D model from the first cast, showing a malposition of both canines; on the
right, the 3D model from the second cast, after one year and the removal of the second premolar on the right side
and the first on the left side, and consequent realignment of canines.
QUANTIFICATION OF DENTAL MOVEMENTS IN ORTHODONTIC FOLLOW-UP:
A NOVEL APPROACH BASED ON REGISTRATION OF 3D MODELS OF DENTAL CASTS
Figure 5. first patient, chromatic map of modifications of dental surfaces from the left side between the two casts
(on the left vestibular surface, on the right lingual surface): blue areas are more vestibularized in the last cast, vice
versa for the red and yellow areas. Green areas (including the first and second molar) remained unchanged.
an orthodontic treatment in a private dental office:
all the patients were IOTN (index of orthodontics
treatment needs) ≤3. 11 At least two dental casts
were available for each patient, taken at different
time periods during the therapy. The casts were
scanned by a 3D laser scanner (iSeries, Dental
Wings©, Montreal, Canada). According to the
manufacter, the precision of the instrument is 15
μm. The 3D models were then elaborated through
VAM© software (Canfield Scientific, Inc., Fairfield,
NJ): first the palatal area including palatal rugae
was manually selected in both surfaces (Fig. 1);
then the software was requested to automatically
register the two models in order to reach the
minimum point-to-point distance between the
selected areas (Fig. 2). Once the registration
between the two surfaces was reached, the
dental arch (dental crown surfaces) was manually
defined on the 3D model obtained from the
more recent cast, and a Region of Interest (RoI)
was obtained. The software was then requested
to select the RoI and to calculate the point-to
point mean distance and RMS value (Root Mean
Square) of the two models within the selected
Stomatology Edu Journal
RoI. Mean values consider together positive and
negative movements, whereas RMS values are all
positive, and can provide a complete evaluation
of the variations between two dental scans.
Together with these quantitative parameters,
a chromatic map of surface modifications of
dental element extracted from the more recent
dental cast is provided, with areas coloured in
blue, green and red: the blue areas are more
vestibularized in the last cast than in the earlier
one, whereas the red areas are less vestibularized.
Green areas do not show modifications between
the two casts (Fig. 3). To test the method on
a control group, the same procedure was
applied on the dental arch models of five
adult patients aged over 18 years who had
longitudinal records taken but where no dental
movements or modifications were expected.
Time elapsed between the two casts was 1.5 years
on average. The same procedures of registration,
RoI selection, and calculation of RMS values on the
control group was repeated by the same operator
and by another observer: intra- and inter-observer
differences were statistically assessed by Student’s
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