Facial growth assessment and anatomical relationship analysis are conducted through cephalometric evaluation. Utilizing 2D radiographic images in sagittal or coronal planes forms the basis of this assessment, yet the introduction of 3D imaging methods like computed tomography and magnetic resonance imaging has significantly enhanced accuracy. The realm of 3D cephalometry provides a more precise quantification of craniofacial morphology, longitudinal growth patterns, and occlusal transformations. Nevertheless, the development of a reliable protocol for this analysis continues to be a subject of widespread research. This study introduces a protocol for 3D cephalometric evaluation aimed at identifying the natural head position (NHP) and precisely measuring facial growth and asymmetry, with a phantom investigation conducted to assess its efficacy.
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The findings demonstrate the protocol’s capacity for consistent alignment with the NHP, showcasing minimal discrepancies across various regions. Moreover, the protocol’s capability for accurate measurement of facial growth and asymmetry is highlighted.
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The 3D skull alignment protocol furnishes a precise and landmark-free estimation of head symmetry, allowing for accurate alignment with NHP and assessment of facial growth and asymmetry.
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Cephalometric analysis plays a crucial role in evaluating facial growth, anatomical correlations, and facilitating treatment planning in dental and surgical fields. However, the potential inaccuracies associated with 2D cephalometrics, such as image quality variations and landmark identification challenges, are mitigated with the widespread availability of 3D imaging technologies. These advancements enable a more detailed analysis of facial morphology, especially in the realms of pre-operative planning and evaluation.
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In order to assess the accuracy and reliability of the geometric morphometric analysis applied to craniofacial structures, it is crucial to consider potential sources of error and variability. Factors such as image acquisition techniques, landmark digitization, and software algorithms can all impact the outcomes of the analysis. Therefore, validation studies utilizing known standards or reference datasets can help validate the methodology and ensure consistency in the results.
Furthermore, the utilization of 3D imaging techniques, such as cone-beam computed tomography (CBCT) or stereophotogrammetry, can provide a more comprehensive and detailed assessment of craniofacial structures compared to traditional 2D cephalometric imaging. These advanced imaging modalities allow for the visualization of facial asymmetry in three dimensions, offering valuable insights into the complexity of craniofacial growth and development.
Overall, integrating advanced imaging technologies with geometric morphometric analysis techniques can enhance our understanding of craniofacial morphology and contribute to the improvement of clinical practices in orthodontics and craniofacial surgery.
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The reliability of restoring NHP was verified by subjecting the target model to random rigid transformations and comparing it with the gold standard model (Figure 1g). The process was repeated 15 times, with the results summarized in Table 2. For full data, the mean symmetric distance (MSD) and Hausdorff distance (Hd) between the gold standard and target models amounted to 0.17 and 0.52 mm, respectively. Vertical restoration presented an error of merely 0.21 mm for N and 0.30 mm for Pog markers. For part of the data, MSD and Hd were 0.27 and 0.52 mm, with N and Pog errors of 0.32 mm and 0.23 mm, respectively. The final craniofacial alignment involved random transformation and repositioning with full and partial craniofacial data sets. Discrepancies between moved landmarks in the gold model and distorted face models are presented in Tables 3 and 4. The methodology for comprehensive 3D cephalometric analysis offers an accurate assessment of facial symmetry and NHP, along with the application of a basal cranium for overlaying various craniofacial skeletons. The algorithm successfully repositioned distorted models to match corresponding gold standard geometries. In the phantom study conducted, the level of accuracy and reliability in evaluating minor morphological differences was quantified. The assessment provided a distinct determination of the craniofacial symmetry plane and vertical direction. The primary advantage of utilizing a basal cranium becomes evident in the presence of facial growth and asymmetry, particularly when the Pog marker does not lie in the symmetry plane.
The alignment protocol allowed for an accurate evaluation of facial growth with an error ranging from -11.38 to 9.31% over 2 years and from -11.38 to 2.77% over 4 years. Similarly, excellent skull alignment was achieved when examining facial asymmetry. Linear measurements between points revealed errors ranging from -1.50 to 9.31% for asymmetry 1, -11.38 to 2.77% for asymmetry 2, and 0.89 to 3.65% for asymmetry 3. The results demonstrate that the protocol can be invaluable in quantifying subtle asymmetric changes in craniofacial anatomy, especially in patients with cleft lip and palate. Facial asymmetry in cleft lip and palate patients typically ranges from 0.79 mm in the lower face to 1.15 mm in the middle face, with all error estimates below the mentioned values.
A new protocol for determining the true plane of symmetry of the craniofacial skeleton has various clinical applications, including: 3D cephalometric analysis for assessing morphology, growth, and asymmetry, determining the orientation of the dental occlusal plane relative to craniofacial skeleton morphology, quantifying asymmetry of the lower jaw, biomechanical studies of chewing asymmetry, virtual surgery planning for lower jaw reconstruction, and developing mandibular implants. The protocol enables reliable determination of the true plane of symmetry of the craniofacial skeleton. The accuracy of symmetrical alignment is confirmed and not dependent on user-defined landmark errors. An important advantage is the ability to align morphologically different skulls using the cranial base surface instead of the traditional sella turcica point. This significant improvement aligns with the modern trend towards three-dimensional imaging and the need for reliable quantitative evaluation of longitudinal changes in 3D. It is also non-invasive, clinically useful in orthodontics and maxillofacial surgery, versatile, and applicable to other anatomical areas and even to other areas of interest.
A fully automated protocol has been proposed for 3D skull alignment, which provides an accurate assessment of the true plane of symmetry of the human skull without using characteristic points. It allows precise alignment of the skull in a standard anatomical position, regardless of user-defined input data. The algorithm provides accurate quantitative characteristics of facial growth and asymmetry, making it useful for clinical applications.
⚑ Protocol proposed for the field of engineering and computer science, University of Hull, Hull, United Kingdom. Manuel Pinheiro, Synhwai Ma, and Michael Fagan.
Department of Orthodontics, Dental School, University of Dundee, Dundee, United Kingdom