Abstract：
BACKGROUND: There is currently no consensus in the literature whether the aetiology of a Class II subdivision is dental, skeletal or both. The aim of this study was to identify and quantify skeletal and dental asymmetries in Class II subdivision malocclusions.
METHODS: CBCTs from 33 Class II subdivision malocclusion patients were used to construct 3D volumetric label maps. Eighteen landmarks were identified. The original scan and associated 3D volumetric label map were mirrored. Registration of the original and mirrored images relative to the anterior cranial base, maxilla and mandible were performed. Surface models were generated, and 3D differences were quantified. Statistical analysis was performed.
RESULTS: Anterior cranial base registration showed significant differences for fossa vertical difference, fossa roll, mandibular yaw, mandibular lateral displacement and lower midline displacement. Regional registrations showed significant differences for antero-posterior (A-P) mandibular length, maxillary roll, A-P maxillary first molar position, maxillary first molar yaw and maxillary first molar roll. Class II subdivision patients also show an asymmetric mandibular length as well as an asymmetric gonial angle. Moderate correlations were found between the A-P molar relationship and fossa A-P difference, mandibular first molar A-P difference, maxillary first molar A-P difference and maxillary first molar yaw.
CONCLUSIONS: This study suggests that Class II subdivisions can result from both significant skeletal and dental factors. Skeletal factors include a shorter mandible as well as posterior and higher displacement of the fossa on the Class II side, resulting in mandibular yaw. Dental factors include maxillary and mandibular first molar antero-posterior asymmetry.
METHODS: CBCTs from 33 Class II subdivision malocclusion patients were used to construct 3D volumetric label maps. Eighteen landmarks were identified. The original scan and associated 3D volumetric label map were mirrored. Registration of the original and mirrored images relative to the anterior cranial base, maxilla and mandible were performed. Surface models were generated, and 3D differences were quantified. Statistical analysis was performed.
RESULTS: Anterior cranial base registration showed significant differences for fossa vertical difference, fossa roll, mandibular yaw, mandibular lateral displacement and lower midline displacement. Regional registrations showed significant differences for antero-posterior (A-P) mandibular length, maxillary roll, A-P maxillary first molar position, maxillary first molar yaw and maxillary first molar roll. Class II subdivision patients also show an asymmetric mandibular length as well as an asymmetric gonial angle. Moderate correlations were found between the A-P molar relationship and fossa A-P difference, mandibular first molar A-P difference, maxillary first molar A-P difference and maxillary first molar yaw.
CONCLUSIONS: This study suggests that Class II subdivisions can result from both significant skeletal and dental factors. Skeletal factors include a shorter mandible as well as posterior and higher displacement of the fossa on the Class II side, resulting in mandibular yaw. Dental factors include maxillary and mandibular first molar antero-posterior asymmetry.
摘要：
背景：目前文献中没有共识II类细分的病因是否为牙科，骨骼或两者。这项研究的目的是识别和量化II类细分错牙合中的骨骼和牙齿不对称性。
方法：使用来自33例II类细分错牙合患者的CBCT来构建3D体积标记图。确定了18个地标。原始扫描和相关的3D体积标记图被镜像。相对于前颅基部的原始图像和镜像图像的配准，进行上颌骨和下颌骨。生成了表面模型，并对3D差异进行了量化。进行统计分析。
结果：前颅底配准显示窝垂直差异显着差异，窝辊，下颌偏航，下颌外侧位移和下中线位移。区域配准显示下颌前后（A-P）长度存在显着差异，上颌辊,A-P上颌第一磨牙位置,上颌第一磨牙横摆和上颌第一磨牙横滚。II类细分患者还显示出不对称的下颌长度以及不对称的角。发现A-P磨牙关系与窝A-P差异之间存在中等相关性，下颌第一磨牙A-P差值,上颌第一磨牙A-P差与上颌第一磨牙偏航差。
结论：这项研究表明，II类细分可由显著的骨骼和牙齿因素引起。骨骼因素包括下颌骨较短以及II类侧窝的后部和较高位移，导致下颌偏航。牙齿因素包括上颌和下颌第一磨牙前后不对称性。
方法：使用来自33例II类细分错牙合患者的CBCT来构建3D体积标记图。确定了18个地标。原始扫描和相关的3D体积标记图被镜像。相对于前颅基部的原始图像和镜像图像的配准，进行上颌骨和下颌骨。生成了表面模型，并对3D差异进行了量化。进行统计分析。
结果：前颅底配准显示窝垂直差异显着差异，窝辊，下颌偏航，下颌外侧位移和下中线位移。区域配准显示下颌前后（A-P）长度存在显着差异，上颌辊,A-P上颌第一磨牙位置,上颌第一磨牙横摆和上颌第一磨牙横滚。II类细分患者还显示出不对称的下颌长度以及不对称的角。发现A-P磨牙关系与窝A-P差异之间存在中等相关性，下颌第一磨牙A-P差值,上颌第一磨牙A-P差与上颌第一磨牙偏航差。
结论：这项研究表明，II类细分可由显著的骨骼和牙齿因素引起。骨骼因素包括下颌骨较短以及II类侧窝的后部和较高位移，导致下颌偏航。牙齿因素包括上颌和下颌第一磨牙前后不对称性。
