Voxel-based superimposition of serial craniofacial CBCT for
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A voxel-based 3-D superimposition method is user-friendly and reproducible in detecting 3D soft tissue changes. Superimposition and segmentation error are both considered minimal with this method.

The aim of this investigation was to evaluate the reproducibility of a voxel-based 3-D superimposition method and the effect of segmentation error on determining soft tissue surface changes.

A total of 15 pairs of serial cone-beam computed tomography images from growing subjects were selected from an existing digital database. Each pair was superimposed on the anterior cranial base, in 3 dimensions with Dolphin 3D software. The reproducibility of superimposition outcomes and surface segmentation were tested with intra- and interoperator comparisons.

The outcomes were;
--Median differences in inter-and intrarater measurements at various areas presented a range of 0.08-0.21 mm. In few instances, the differences were larger than 0.5 mm.

--In areas where T0-T1 changes were increased, the error did not appear to increase. However, the method error increased the farther the measurement area was from the superimposition reference structure.

--For individual images, the median soft tissue segmentation error ranged from 0.05 to 0.06 at various areas and in no subject exceeding 0.13 mm.

Conclusively, the presented voxel-based superimposition method was efficient and well reproducible. The segmentation process was a minimal source of error; however, there were a few cases in which the total error was more than 0.5 mm and could be considered clinically significant. Therefore, this method can be used clinically to assess 3-dimensional soft tissue changes during orthodontic treatment in growing patients.

American Journal of Orthodontics & Dentofacial Orthopedics
Source: https://doi.org/10.1016/j.ajodo.2020.04.022
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