Bolandzadeh, N., Bischof, W. F., Flores-Mir, C., and Boulanger, P. (2013). Multi-modal registration of 3D maxillodental CBCT and photogrammetry data over time. DentoMaxilloFacial Radiology, 42(2), 22027087.

Objective: In recent years, one of the foci of orthodontics has been on systems for the evaluation of treatment results and the tracking of tissue variations over time. This can be accomplished through analyzing three dimensional (3D) orthodontic images obtained before and after the treatments. Since complementary information is achieved by integrating multiple imaging modalities, cone-beam computed tomography (CBCT) and stereo-photogrammetry technologies are used in this study to develop a method for tracking bone, teeth, and facial soft tissue variations over time. Methods: We propose a two-phase procedure of multi-modal (phase one) and multi-temporal (phase two) registration, which is aligning images taken from the same patient by different imaging modalities and at different times. Extrinsic (for phase one) and intrinsic (for phase two) landmark-based registration methods are employed as an initiation for a robust iterative closest points (ICP) algorithm. Since mandible moves independently to the upper skull, the registration procedure is applied separately on the mandible and the upper skull. Results: The results show that the signed error distributions of both mandible and skull registrations follow a mixture of two Gaussian distributions, corresponding to alignment errors (due to our method) and temporal change over time. Conclusion: We suggest that the large values among the total registration errors correspond to the temporal change resulting from: 1) the effect of treatment (i.e., the orthodontic changes of teeth positions); 2) the biological changes such as teeth growth over time, specially for teenagers; 3) the segmentation procedure and CBCT precision change over time.

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