包含骨缝的儿童颅面三维有限元模型的建立及前牵引应力分析初探

Establishment of the craniofacial three-dimensional finite element models with the sutures defined alone

目的 建立包含骨缝的儿童颅面三维有限元模型并进行前牵引应力分析,以期为儿童颅面矫形治疗的生物力学分析提供依据.方法 对1名8岁男性头颅标本自头顶表皮至甲状软骨进行连续CT扫描,扫描层厚0.625 mm,将获得的CT扫描数据依次导入Mimics 10.0、Geomagic 9.0及Ansys 13.0软件处理后,参考此头颅标本的铣切图像,绘制腭中缝、颧上颌缝、额上颌缝、颧额缝和颧颞缝,模拟腭中缝打开与未打开两种状态,建立包含9条骨缝、8颗牙齿（6ⅣⅡ1｜1ⅡⅣ6）的儿童颅面三维有限元模型.模仿临床前牵引,于颅面三维有限元模型眉弓上1 cm处（F1）、颞下颌关节窝处（F2）、上颌第一乳磨牙与第一恒磨牙联合成1个整体后的上颌第一乳磨牙近中牙颈部（F3）的矢状面上加载载荷.分析载荷F1 ～ F3分别为2、1、1N,加力方向与（牙合）平面平行时两种颅面三维有限元模型的等效应力分布及力值.结果 建立了腭中缝打开和未打开两种状态的儿童颅面三维有限元模型,模拟前牵引加载时两种颅面三维有限元模型的等效应力分布范围相似；应力集中于鼻梁及鼻翼外侧部.腭中缝打开时等效应力最大值在鼻尖点,为18916.00×10-4 MPa;最小值在恒上中切牙近中切缘点,为1.61 ×10-4 MPa.腭中缝未打开时等效应力最大值在鼻尖点,为19244.00×10-4 MPa;最小值在恒上中切牙近中切缘点,为1.62×10-4 MPa.结论 将骨缝视作一种实体进行单独定义,可建立包含部分骨缝的儿童颅面三维有限元模型.前牵引模拟加载时腭中缝打开与未打开两种状态下模型等效应力分布相似,等效应力最大值在鼻尖点.

Objective To develop a child craniofacial three-dimensional（3D） finite element model （FEM） with sutures defined alone.Methods The CT data for this study was developed from sequential computed tomography scan images taken at 0.625 mm intervals of an 8 years children skull.Data set was imported into Mimics 10.0 and processed with Geomagic 9.0,and exported as initial graphics exchange specification（IGES） files.The IGES files were then imported into Ansys 13.0 to set up two FEM with or without the median palatine suture being opened.The FEM contained nine craniofacial sutures and eight teeth which were defined alone.For simulating orthopedic maxillary protraction,three forces（F1-F2） were loaded on FEM.F1 （1 N） was loaded at 1 cm above the geison.F2（1 N） was loaded at articular fossa of temporal bone.F3（2 N） was directed anteriorly and paralleled with occlusal plane near the canine.The stress distribution and the values distributed in each point gained in the two models were compared.Results Two craniofacial 3D FEM of the child were developed with the median palatine suture opened or not.With median palatine suture being opened or not,the two models showed the similar von Mises stresses（VMS）.The distribution of the VMS was in the bridge of the nose and dextro-ala nasi.When the median palatine suture was opened,the max VMS value was 18916.00 × 10-4 MPa which appeared in the nose point and the min VMS value was 1.61 × 10-4 MPa which appeared in the maxillary central incisor point.At the same time,the max stress value at the direction Y was-3985.30 × 10-4 MPa and appeared in the frontomaxillary suture point,and the min Y value was 0.08 × 10-4 MPa which appeared in the maxillary central incisor point.When the median palatine suture was not opened,the max VMS value was 19 244.00 × 10 4 MPa and appeared in the nose point.The min VMS value was 1.62 × 10-4 MPa and appeared in the maxillary central incisor point.At the same time,the max stress value at the direction Y was-4258.20 × 10-4 MPa and appeared in the frontomaxillary suture point,and the min Y value was 0.08 × 10-4 MPa which appeared in the maxillarv central incisor point.Conclusions To define the sutures as entities alone contributed to develop child craniofacial 3D FEM which consist nine sutures.There was tiny difference in stress distribution in both the VMS and in Y direction with the median palatine suture being opened or not.