3-d Reconstruction And Fe Analysis Of Soft Tissue And Mandible

Maxillofacial surgery, especially orthognathic surgery, is widely used for the treatment of patients suffering from maxillofacial dysmorphosis, such as the disequilibrium between the mandible, the upper jaw and the face. The purpose of the surgery is to improve the oral function, as well as the appearance of the patients. However, incapability to accurately predict the soft tissue deformation resulting from bone repositioning after surgery is a major obstacle for the current orthognathic surgery. The traditional method, namely, teeth plaster casts, planning the surgical procedure and post-operative prediction based on two dimensional images, is far from precise. How to precisely predict soft tissue deformation before the surgery is the major concern of patients and surgeons for many years.Based on 3D CT images acquired from maxillofacial region, this paper has established 3D FE models for the mandible and facial soft tissue. Using the realistic models, the interaction between mandible and soft tissue and the effect of bone on the deformation of soft tissue, under different conditions of bone displacement, have been explored.(1) To build up a more accurate soft tissue model, skin of 1.5mm thickness was extracted manually based anatomical features. Then skin, muscle and fat were separated respectively using gray scale thresholding. Finally, different material properties were assigned to different types of soft tissue considering their CT values, leading to a multi-layer model for facial soft tissue.(2) To establish a finite element model for the mandible. According to the relationship between the CT value, apparent density and the elastic modulus of bone, bone's apparent density and elasticity modulus were calculated based on the grey level of bone pixels.(3) To establish contact pairs between bone and soft tissue models. Nonlinear contact analysis method was used to explore the interaction between bone and soft tissue.(4) Based on the established FE model, we analyzed the deformations of soft tissue after different displacements of the bone with FEA.