| Objective:The purpose of this study was to use finite element method to construct a suture marked 3-dimension finite element model of human craniofacial complex for future biomechanical study. The perspective of biomechanics was used to explain a disputed problem that if the rapid maxillary expansion is necessary before maxillary protraction. The results of this study would provide powerful biomechanical support ,and help us to orthotherapy classâ…¢malocclusion with maxillary growth deficiency by protraction . Meanwhile, the first being constructed model can develop the further study of craniofacial complex biomechanics .Methods:In this study the analytical model was developed from a dry skull of 10- year-old girl (mandible not included). Before CT scanning, firstly the sutures were exactly marked by zinc oxide eugenol because they were invisible in CT films. Make a simple stent , metallic bar was vertical to frankfort horizontal plane, fixed on craniofacial bone, then scan craniofacial bone and reconstruct CT 3-D image. The ANSYS software was used to construct the finite element method which included the craniofacial sutures. When the model was constructed , we set parameters and boundary condition, simulate RME and maxillary protraction . At last, we test and analysis theperameter of model and application of model.Results:1 The suture marked 3-dimension finite element model established in this study was highly coincide with the dry skull and 3-dimension CT image. And the total number of elements and nodes created was 83688 an d 21480,respectively.The mesh generation of this model is accurate and reasonable, which can be rotated,cut,deleted or extracted from it freely .2 Simulating clinical rapid maxillary expansion, the maximum transverse displacement appeared at node of 12911, and the displacement was 5.31mm. Observe from coronal plane , maxillary was opened like pyramid. The bottom was palatal plate near to oral, the top direction nasal bone.The maximum sagittal displacement value appeared at node of 2314, it's -1.16mm(backward in the level direction),this node was corresponding to palatal shelf of zygomatic bone. The maximum value forward in level direction appeared at node of6022, it's 1.08mm, it was corresponding to piriform aperture anterior inferior point. Maxillary complex(including alveolar bone, A point ,ANS point) all shift forward in level direction. But zygomatic bone shift backward.The maximum vertical displacement value(downward in vertical direction) appeared at node of 52, it's -1.22mm. This node was corresponding to nasal cavity posterior upperside. The maximum value (upward in vertical direction)appeared at node of 241, the value was 1.76mm, it's corresponding to zygoma.3 After simulating clinical rapid maxillary expansion, the maximum compressive stress value appeared at alveolar bone near to maxillary first permanent molar, which is 57.19N/mm~2.In addition, all the related sutures in maxillary have stress concentration phenomenon, among them, the value of nasalmaxilla suture and frontonasal suture reached 32.68 N/mm~2. Frontal process of zygomatic bone, zygomatic arch , zygomaticofrontal suture, and so on showed higher stress value.4 After simulating clinical maxillary protraction ,node of 6297 and its vicinity showed highest tensile stress, 39.86N/mm~2. This node is corresponding to alveolar bone around maxillary first permanent molar. The value of alveolar bone, processus zygomaticus maxillaeta and maxillary tuberta also show high level. Anterior of palate and inferior wall of orbit presented as compressive stress.All the related sutures in maxillary have stress concentration phenomenon .Conclusions:1 Using the methods of CT scanning and ANSYS software, constructing a suture marked 3-D FEM of human craniofacial complex is feasible, advanced and reliable. The suture marked 3-dimension finite element model proved to be a suitable procedure for comparing the biomechanical influences of various therapeutic measures.2 After rapid maxillary expansion, craniofacial bone especially the maxilla moving downward would reduce the angle, and the rotation of mandibula . The antedisplacement of A point induced ANB angle's decreasing,which will be condutive to improve the relation between maxillary and mandibula of classâ…¢patients.The related sutures in craniofacial bone restrict transverse displacement as well as zygoma and sphenoid bone. So when RME is used ,growth and development , especially sutures calcification and fusion must be considered.3 Maxillary protraction can improve growth and development of maxilla.The relation of maxillary and mandibula in sagittal direction would be improved , too. Rapid maxillary expansion and maxillary protraction would make up with bad changes, and the maxilla could obtain real translation.
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