RESUMEN
Objective Aiming at the 3D skull model with great difference in initial posture and resolution, a skull registration method based on feature contour line is proposed in the paper. Methods Firstly, contour lines which include eye, nose, temporal bone, maxilla and jawbone are extracted; Secondly, the types of contour are distinguished according to their length and shortest distance between them, and the corresponding relationship is established between the two skulls needed to register, thus the coarse registration of skulls is completed; Finally, an improved iterative closest point (ICP) algorithm is proposed by integrating weight into ICP, which is used to complete fine registration of skulls, thus the accurate registration of skulls is achieved at last. Results Registration between a unknown skull and 300 reference skulls is done, and the experimental results show that the proposed registration method could complete 3D skull registration, which could get high accuracy and speed in fine registration. Conclusion So the skull registration method based on local contour line is an accurate and fast 3D skull registration method.
RESUMEN
The three-dimensional (3D) changes of bone, soft tissue and the ratio of soft tissue to bony movement was investigated in 8 skeletal Class III patients treated by mandibular setback surgery. CT scans of each patient at pre- and post-operative states were taken. Each scan was segmented by a threshold value and registered to a universal three-dimensional coordinate system, consisting of an FH plane, a mid-sagittal plane, and a coronal plane defined by PNS. In the study, the grid parallel to the coronal plane was proposed for the comparison of the changes. The bone or soft tissue was intersected by the projected line from each point on the gird. The coordinate values of intersected point were measured and compared between the pre- and post-operative models. The facial surface changes after setback surgery occurred not only in the mandible, but also in the mouth corner region. The soft tissue changes of the mandibular area were measured relatively by the proportional ratios to the bone changes. The ratios at the mid-sagittal plane were 77 ~ 102% (p < 0.05). The ratios at all other sagittal planes had similar patterns to the mid-sagittal plane, but with decreased values. And, the changes in the maxillary region were calculated as a ratio, relative to the movement of a point representing a mandibular movement. When B point was used as a representative point, the ratios were 14 ~ 29%, and when Pog was used, the ratios were 17 ~ 37% (p < 0.05). In case of the 83rd point of the grid, the ratios were 11 ~ 22% (p < 0.05).