Third Clinical Division, Peking University School and Hospital of Stomatology, Beijing, China.
National Engineering Laboratory for Digital and Material Technology of Stomatology, Beijing Key Laboratory of Digital Stomatology, Peking University School and Hospital of Stomatology, Beijing, China.
BMC Oral Health. 2023 Sep 8;23(1):655. doi: 10.1186/s12903-023-03367-3.
Assessment of growth-related or treatment-related changes in the maxilla requires a reliable method of superimposition. Such methods are well established for two-dimensional (2D) cephalometric images but not yet for three-dimensions (3D). The aims of this study were to identify natural reference structures (NRS) for the maxilla in growing patients in 3D, opportunistically using orthodontic mini-screws as reference; and to test the applicability of the proposed NRS for maxillary superimposition by assessing the concordance of this approach with Björk's 'stable reference structures' in lateral projection.
The stability of the mini-screws was tested on longitudinal pairs of pre- and post-orthodontic cone-beam computed tomography (CBCT) images by measuring the distance changes between screws. After verifying the stability of the mini-screws, rigid registration was performed for aligning the stable mini-screws. Then, non-rigid registration was used to establish the dense voxel-correspondence among CBCT images and calculate the displacement of each voxel belonging to the maxilla relative to the mini-screws. The displacement vectors were transformed to a standardized maxillary template to categorize the stability of the internal structures statistically. Those voxels that displaced less relative to the mini-screws were considered as the natural reference structures (NRS) for the maxilla. Test samples included another dataset of longitudinal CBCT scans. They were used to evaluate the applicability of the proposed NRS for maxillary superimposition. We assessed whether aligning the maxilla with proposed NRS is in concordance with the maxillary internal reference structures superimposition in the traditional 2D lateral view as suggested by Björk. This was quantitively assessed by comparing the mean sagittal and vertical tooth movements for both superimposition methods.
The stability of the mini-screws was tested on 10 pairs of pre- and post-orthodontic cone-beam computed tomography (CBCT) images (T1: 12.9 ± 0.8 yrs, T2: 14.8 ± 0.7 yrs). Both the loaded and the unloaded mini-screws were shown to be stable during orthodontic treatment, which indicates that they can be used as reference points. By analyzing the deformation map of the maxilla, we confirmed that the infraorbital rims, maxilla around the piriform foramen, the infrazygomatic crest and the hard palate (palatal vault more than 1 cm distal to incisor foramen except the palatal suture) were stable during growth. Another dataset of longitudinal CBCT scans (T1: 12.2 ± 0.63 yrs, T2: 15.2 ± 0.96 yrs) was used to assess the concordance of this approach with Björk's 'stable reference structures'. The movement of the maxillary first molar and central incisor showed no statistically significant difference when superimposing the test images with the proposed NRS or with the classic Björk maxillary superimposition in the lateral view.
The infraorbital rims, maxilla around the piriform foramen, the infrazygomatic crest and the hard palate (palatal vault more than 1 cm posterior to incisal foramen except the palatal suture) were identified as stable regions in the maxilla. These stable structures can be used for maxillary superimposition in 3D and generate comparable results to Björk superimposition in the lateral view.
评估上颌骨的生长相关或治疗相关变化需要一种可靠的叠加方法。这种方法在二维（2D）头颅侧位片上已经得到很好的建立，但在三维（3D）上尚未建立。本研究的目的是确定生长患者上颌骨的自然参考结构（NRS），并利用正畸微型螺钉作为参考；并通过评估该方法与 Björk 稳定参考结构在侧位投影中的一致性，来检验所提出的上颌骨叠加的 NRS 的适用性。
通过测量螺钉之间的距离变化，在正畸前后的锥形束计算机断层扫描（CBCT）图像的纵向对中测试微型螺钉的稳定性。验证微型螺钉稳定后，进行刚性配准以对齐稳定的微型螺钉。然后，使用非刚性配准在 CBCT 图像之间建立密集的体素对应关系，并计算每个属于上颌骨的体素相对于微型螺钉的位移。将位移向量转换到标准化的上颌模板中，以统计方式对内部结构的稳定性进行分类。相对于微型螺钉位移较小的那些体素被认为是上颌骨的自然参考结构（NRS）。测试样本包括另一组纵向 CBCT 扫描。它们用于评估所提出的 NRS 在上颌骨叠加中的适用性。我们评估了通过与建议的 NRS 对齐，是否与 Björk 建议的传统二维侧位的上颌骨内部参考结构叠加一致。这通过比较两种叠加方法的上颌切牙和尖牙的平均矢状和垂直牙齿移动来定量评估。
对 10 对正畸前后的锥形束计算机断层扫描（CBCT）图像（T1：12.9±0.8 岁，T2：14.8±0.7 岁）进行了微型螺钉的稳定性测试。结果显示，加载和未加载的微型螺钉在正畸治疗过程中均稳定，这表明它们可以用作参考点。通过分析上颌骨的变形图，我们证实眶下嵴、梨状孔周围的上颌骨、眶下嵴和硬腭（除腭缝外，切牙孔后 1cm 以上的腭穹隆）在生长过程中是稳定的。另一组纵向 CBCT 扫描（T1：12.2±0.63 岁，T2：15.2±0.96 岁）用于评估该方法与 Björk 的“稳定参考结构”的一致性。当用建议的 NRS 或经典 Björk 上颌骨叠加在侧位上对测试图像进行叠加时，上颌第一磨牙和中切牙的移动没有统计学上的显著差异。
眶下嵴、梨状孔周围的上颌骨、眶下嵴和硬腭（除腭缝外，切牙孔后 1cm 以上的腭穹隆）被确定为上颌骨的稳定区域。这些稳定结构可用于 3D 上颌骨叠加，并产生与 Björk 侧位叠加可比的结果。
