下颌升支矢状劈开截骨术对颞下颌关节功能影响的生物力学研究

Maxillofacial deformities are related with unpretty appearance and oral dysfunction. Sagittal split ramus osteotomy (SSRO) is used to treat mandibular deformities with the superior stability and masticatory function. However the effects of SSRO on the function of the temporomandibular joint (TMJ) were controversial. Condylar displacement and the changes of mandibular shape and occlusion after SSRO caused the changes of biomechanics in the TMJs, which induced the adaptive remodeling of TMJ or the additional temporomandibular joint dysfunction (TMD). This project is a biomechanical study about the influence of SSRO on the function of TMJs, which is divided into four aspects. (1) The TMJs of the volunteer patients will be clinically examined to identify TMD symptoms before and after SSRO. (2) According to remodeling of the MRI of the patients, the influence of SSRO on the structure of the TMJs will be analyzed. (3) The finite element models will be developed according to the MRI images of the patients before and after SSRO. The interaction of the discs and the articular cartilages was treated as contact. The loads corresponding to opening mouth and major occlusions, such as centric occlusion, anterior occlusion and unilateral occlusion, will be applied on the models. The effects of SSRO on the contact region between articular discs and cartilages and their maximum and minimum principal stress distributions will be researched. Moreover the relationship of those parameters and TMD symptoms will be attempted to analyse. (4) Based on the preoperative models, the numerical simulation of SSRO will be carried out. The contact region between articular discs and cartilages and their maximum and minimum principal stress distributions will also be analysed via finite element method. The effects of SSRO on the function of the TMJs will be predicted, and the osteotomy could be slightly adjusted to obtain better biomechanics of TMJs.

颌骨畸形影响容貌，并可引发一些功能性病变。下颌升支矢状劈开截骨术（SSRO）是矫治下颌骨畸形的常规手术，术后稳定性和咀嚼功能都优于其他手术。然而SSRO对颞下颌关节（TMJ）功能的影响存在争议，术后髁突位移、颌骨形状和咬合关系的变化会引起TMJ内力学环境的改变，导致TMJ的适应性改建或引发新的颞下颌关节功能紊乱（TMD）症状，而目前缺少相关的生物力学研究。本项目围绕SSRO对TMJ功能的影响展开生物力学研究，包括：1）通过临床检测，研究手术前、后下颌骨畸形患者TMD的症状；2）通过MRI的三维重建，研究手术对TMJ结构的影响；3）采用有限元方法，研究张口和各种咬合工况下关节盘和关节软骨层的接触区域、面积及最大/最小主应力分布与TMD症状的关系，以及SSRO对这些力学参数的影响；4）采用数值模拟手术和有限元方法，研究以上力学参数的分布规律，预测拟定手术方案对TMJ功能的影响，并可优化截骨线。

颌骨畸形不仅影响患者的容貌，而且也会导致一些功能性病变。临床上对颌骨畸形的治疗目前常采用下颌矢状劈开截骨术（SSRO），且该手术术后的稳定性很好，患者的咀嚼功能也得到了很大的改善。然而SSRO对颞下颌关节（TMJ）功能的影响却存在争议，术后髁突位移、颌骨形态和咬合关系的变化都会引起TMJ内力学环境的改变，这将导致TMJ的适应性改建或引发新的颞下颌关节功能紊乱（TMD）症状，而目前缺少相关的生物力学研究。本项目围绕SSRO对TMJ功能的影响展开生物力学研究，得到以下结果和结论：1）通过临床检测，发现大多数颌骨畸形（偏颌、前突、后缩等）患者术前都伴随有轻微至严重的TMD病征，SSRO手术后，这些TMD病征则随之消失或减弱；2）通过对颌骨畸形患者头部CBCT和MRI影像的三维重构，对比术前、术后TMJ的形态和位置关系，发现SSRO能够对患者的髁突角、关节间隙等产生显著性影响。3）通过有限元分析，发现在各种咬合工况下，颌骨畸形患者术前关节盘和关节软骨层都有明显的应力集中区，其接触应力、最大/最小主应力、von Mises应力值都较高，甚至高于关节盘和关节软骨层的破坏应力，SSRO手术后，这些应力水平都有显著性降低，且都低于其破坏应力。4）通过数值模拟手术并进行有限元分析，得出各种咬合工况下，数值模拟手术后的TMJ各力学参数的分布规律与术后模型的一致，且应力分布更加均匀。.总之，SSRO能够显著地改善颌骨畸形患者TMJ的形态，减少TMJ内的高应力区，使TMJ内的应力分布更加均匀合理；此外，SSRO的数值模拟手术还能预测临床手术对TMJ功能的影响，并可优化截骨线。