Figure 8. Third patient: on the left, the 3D model from the first cast, showing a malposition of the left
canine; on the right, the 3D model from the second cast, after orthodontic therapy.
Interestingly, RMS value increased with the entity
of dental displacement and number of involved
teeth, and was in every case significantly higher
than the same parameter shown by the control
group (Table 1).
Figure 9. Third patient, chromatic map of
modifications of dental surfaces between the two
casts: blue areas are more prominent in the last
cast, vice versa for the red and yellow areas. Most
of modifications can be observed on the left central
incisor and the left canine.
but for the left canine which remained in the same
position and was realigned within the dental
arch (Fig. 7). In addition, the method was able to
accurate describe the novel presence of brackets
and wire in the second cast, correctly assessed in
blue areas (more vestibularized in the second cast
than in the first one). The average RMS value was
1.13 mm.
The third patient was an 11 year old girl, who was
chosen in order to test the detectability of lesser
dental displacements like pathological overjet
value. In detail, the central incisors were distally
rotated, whereas the right canine was still erupting
with the exposition of the tip. In the second cast,
after orthodontic therapy, the central incisors were
medially oriented, whereas the canine crown was
erupted and in correct occlusion. The second cast
was taken after four years.
The registration procedure correctly assessed the
change in orientation of the left central incisor: in
addition, the eruption of the canine was detected
as well (Fig. 9); RMS value was 0.98 mm.
Stomatology Edu Journal
QUANTIFICATION OF DENTAL MOVEMENTS IN ORTHODONTIC FOLLOW-UP:
A NOVEL APPROACH BASED ON REGISTRATION OF 3D MODELS OF DENTAL CASTS
4. Discussion
In the last century orthodontics has seen a
progressive update of technologies and clinical
procedures, with an amelioration of dental position,
functionality and aesthetics. 1 On the other side, a
parallel issue concerns the assessment of dental
displacement powered by orthodontic therapy,
in order to verify the clinical success and provide
corrections. Surprisingly, although the constant
development of 3D image acquisition systems
has represented a crucial revolution in dentistry,
their application to the field of orthodontics is still
at the beginning and most of their potentiality
remains to be explored. 8 An example is provided
by Thirvenkatachari et al. who proposed a
protocol for the registration of 3D surfaces and
calculation of displacement of the center of
mass of dental elements. 8 This type of approach
provides a metrical information but is not able
to predict the modifications of the entire dental
surfaces, especially where the movements do not
consider dental translation. Another important
aspect concerns the morphological assessment of
dental movements, which may give an additional
information for the evaluation of orthodontic
therapies.
The present protocol may represent a proposal
for an innovative analysis of dental movements:
registration is based on the morphology of palatal
rugae which are stable with time 12,13 and have
been already used as reference point in 3D-3D
superimposition of dental arches. 14 The procedure
is repeatable and provides both morphological
and metrical analyses of dental movements.
The chromatic map of dental arches can give
information concerning the specific movement
of each dental element (rotation, translation or
inclination), immediately readable by the operator.
59