QUANTIFICATION OF DENTAL MOVEMENTS IN ORTHODONTIC FOLLOW-UP: A NOVEL APPROACH BASED ON REGISTRATION OF 3D MODELS OF DENTAL CASTS
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Table 1. Details of dental modifications between the two casts in the three analysed patients, and comparison of correspondent RMS values with the control group.
Patient 1
First cast Second cast RMS value
malposition of 3 teeth distal rotation of central incisors removal of two teeth adjustment of malposition realignment of central incisors
Average pointto-point distance
1.61 mm 1.07 mm
Patient 2 malposition of a tooth adjustment of malposition 1.13 mm 0.24 mm Patient 3
Control group distal rotation of central incisors right canine in eruption correction of central incisors right canine erupted
--
0.98 mm 0.26 mm
0.26 mm( SD: 0.06 mm)
0.02 mm
Figure 6. Second 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. Figure 7. Second patient. Chromatic map of modifications of dental surfaces between the two casts: blue areas are more vestibularized in the second cast, vice versa for the red and yellow areas. Green areas remained unchanged.
t test( p < 0.01). In addition the technical error of measurement( TEM) was evaluated.
3. Results In the group of control subjects, on average the RMS value was 0.26 mm( SD: 0.06). No statistically significant differences were observed between measurements taken by the same operator or different observers( p > 0.01).
The technical error of measurement( TEM) was respectively 6.1 % for intra-observer error and 9.6 % for inter-observer error. The first analysed patient was a female aged 12 years. She had a malposition involving both the canines and the second premolar on the right side. The orthodontic treatment was based on the removal of the second premolar on the right side and the first on the left side and the application of an orthodontic device, as shown by the second cast performed after one year( Fig. 4). The registration and calculation of point-to-point distances between the two models highlights the mesial rotation of the lateral incisors and realignment of the canine, whereas the molars did not show any appreciable modification( Fig. 5). In addition the method was able to verify the novel orientation of the second premolar; mean RMS value between the dental profiles from the two 3D scans amounted up to 1.61 mm. The second patient, a female aged 11 years, showed a malposition of the left canine: the application of an orthodontic device was able to produce an adjustment of the canine position, as shown by the second cast taken after four years( Fig. 6). The procedures of registration were able to verify the vestibular translation of all dental elements,
58 Stoma Edu J. 2017; 4( 1): 55-61. http:// www. stomaeduj. com