3-Dimensional Finite Element Analysis Of Superstructure Of An Implant Under Functional Occlusions

Object: Implant is an important method for repairing missing teeth. How to design the implant superstructure to distribute the stress reasonable is an attractive topic to researchers now. Their main research method is three-dimensional finite element method (3-D FEM). However, many 3-D finite element models include maxillary and mandible separately. The relation between them is not established. Furthermore, their loads are simple forces with single direction or pressures with single location. This paper established a 3-D finite element model with maxillary complex, mandible, and full dentition simultaneously. The upper and lower dentition has a functional occlusion relationship. This will help the further analysis of implant stress under functional occlusion.Methods: A volunteer's head was scanned using helix computer tomography, and then we got the marginal data of the maxillary complex, mandible and teeth in digital instrument. We wrote ANSYS program files using these data. The program is preceded in finite element software (ANSYS 6.1) to create key points, lines, areas and volumes sequentially. The model includes maxillary complex, mandible, and full dentition simultaneously, and a centric relation occlusion is established between upper and lower teeth. Then the left lower molars, implant, and relevant mandible are selected out to establish a new model. We meshed the model and analyze the stress around the implant with 9 cusp inclinations(5,10,15,20,25,30,35,40,45degree) under 4 functional occlusions. Result: 1) A 3D-FEM including maxillary complex, mandible and fulldentition was established, which consisted of 44,052 nodes and 192,873 elements. The upper and lower dentition has a functional occlusion relationship. Then we created a local 3D-FEM including the left lower molars, implant, and relevant mandible, which consisted of 5,216 nodes and 27,143 elements. 2) The stress on and around the implant is related to the shape of the implant superstructure, and is also related to occlusion contact form with the opposite teeth. With 45 degree cusp inclination under ABC contacts, the stress of the cancellous bone around the implant is 3.376MPa, which is the lowest at the same location under different cusp inclinations and different contact forms. With 25 degree under AB contacts, the lowest stress of the cortical bone is 10.959MPa. With 45 degree under ABC contacts, the lowest stress of the upper part of the implant is 14.662MPa. With 20 degree under AB contacts, the lowest stress of the neck of the implant is 19.076MPa. With 45 degree under ABC contacts, the lowest stress of the root of the implant is 19.801 MPa.Conclusion: 1) The 3D-FEM we created has a good geometry similarity. It can be used to analyze many situations of the teeth and the jaw. It is also a base for the further analysis of stress under dynamic occlusion. 2) The design of the implant superstructure is related to the location of implant in the bone, shape of the opposing teeth, and occlusion contact relations. 3) The decrease of cusp inclination do not always lead to the decrease of the stress of the implant. 4) Under a centric occlusion, a greater cusp inclination can reduce the stress on and around the implant, but under a lateral occlusion, it will mean to a great rise of the stress. Therefore, we recommend a cusp inclination is limited between 20 to 25 degree, and the compatible occlusion contact is AB two points contact.