| The construction of 3-D finite element models of human craniofacial complex is quite complicated and still in a confused state. Up to now, there is not yet any complete and precise 3-D finite element model in the world, of which 22 bones, all teeth and temporomandibular joints in craniofacial region should be included. Without question, if this problem can not be well settled, the biomechanical study on craniofacial region will be heavily restricted. Class III malocclusion is one of commonly encountered oral clinical diseases, which usually results in serious damage to the visage, physiological function and even mental health of patients. As for Class III malocclusion caused by maxillary retrusion, one of the best treatments is maxillary protraction.From the point of precise and rate of model construction, this article analyzes merits and disadvantages among all modeling methods, then deals with how to develop the ideal 3-D geometrical & 3-D finite element craniofacial complex model, and finally provides valuable experience of the most convenient, precise and the best clinical applicable modeling method. At the same time, on the base of self-developing 3-D finite element models of craniofacial complex, this article explores the change rule of stress, strain and displacement of craniofacial complex against different strength and direction of maxillary protraction.This article includes the following two parts:Part One: 3-D Finite Element Modeling Method Exploration Objective: To investigate the feasibility of constructing the 3-D finite element model of craniofacial complex with the original DICOM data of CT; develop the craniofacial complex 3-D finite element model of precise biomechanical characteristic, and provide a reliable and convenient model base for related biomechanical study. Methods: 1. Acquired the original DICOM data of 2-D image craniofacial complex bythin-slice high resolution CT scanning.2. Respectively apply the combination of self-programmed, ANSYS and Solidworks software, the combination of Mimics and HyperMesh software, and the combination of Mimics and MSC.Marc software, then develop two different 3-D finite element models of craniofacial complex according to the original DICOM data, and analyze merits and disadvantages among the three modeling methods.Results:1. The precise and detailed 3-D geometrical models of craniofacial complex are obtained.2. Two different 3-D finite element models of craniofacial complex are developed, and the mesh generation is precise and reasonable; the constructed model has good comparability with the morphology of reconstructed organisms' model; the constructed model has great applicability, and; the constructed model is of quite precise mechanics characteristic.Conclusion: It is proved that the most precise model construction method is the combination of applying the original DICOM data of thin slice CT scanning, self-programmed, ANSYS and Solidworks software, but it is hard to realize the analysis of 3-D finite element at present; the most convenient method is the combination of applying the original DICOM data, Mimics and HyperMesh software, and; the most detailed is the combination of applying the original DICOM data, Mimics and MSC.Marc software, of which the bone suture is also included.Part Two: 3-D Finite Element Method Study on Maxillary Protraction Objective: To explore the change rule of stress, strain and displacement of craniofacial complex against different strength and direction of maxillary protraction, so as to provide the scientific basis for the selection of force system in clinical treatment.Methods: On the basis of the 3-D finite element model constructed in Experiment four, to simulate the boundary conditions of craniofacial complex protraction with MSC.Marc software, and analyze influence to the craniofacial complex against different strength and direction of protraction, then calculate the stress, strain and displacement values at 320 different conditions, and finally protract the stress anddisplacement nephograms. Results:1. When the angle of maxillary protraction is small, the stress distribution in the whole maxilla is balanced, but when the angle against function occlusion plane is larger than 40°, it will result in stress concentration zone in maxilla.2. Within an effective range, the larger the protraction angle forms, the better for the advancement of maxilla.3. When protraction force value is totally at 800g, and the protraction angle is between 20°~25°, it seems that the palatal plane just parallel move forward without rotation.4. When the protraction angle is between -15°~+40°, it seems that the whole pars palatalis are compressed and narrowed, in which the anterior palate changes most notably. With the protraction angle's augmentation, the phenomenon of narrowing weakens.5. The change rule of effectiveness of different force value of protraction in the same direction differs in different stress zone.6. When taking brow and chin as pivots to protract the maxilla, the whole lower mandible will rotate downward and backward while the drawing stress and compressive stress are coexisted, and the neck of condyle bears the strongest force.Conclusion:1. The force direction of maxillary protraction should be less than 40°. Within this range, the larger the protraction angle forms, the better for the advancement of maxilla.2. It should be careful to select the appropriate force value when the protraction angle augments, and the force value should be less than 1600g when the protraction angle is larger than 40°.3. When protraction force value is at 800g, and the protraction angle is between 20°~25°, it seems that the palatal plane just parallel move forward without rotation.4. Maxillary protraction will result in tension on median palatine suture, it seems that the whole pars palatalis are compressed and narrowed, but the effect is not enough to prove that if maxillary expansion should be combined with inclinical treatment.5. When taking brow and chin as pivots to protract the maxilla, the mandible will rotate downward, and the direction of mandible growth will also change. The mandible's growth must be influenced by relative restraining factors.
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