A dynamic study of the effect on the maxillofacial complex of the face bow: analysis by a three-dimensional finite element method.

In order to investigate the effects of a face bow on the maxillofacial complex, we applied an analysis by a finite element method. To create a skull model, we measured an adult skull sample, and constructed a left lateral model without a mandible with 11 bones of 11 types, 30 sutures, and 3 synchondroses. The numbers of elements and nodes in the model were 1,207 and 1,539, respectively. The numbers of elements in the face bows used were 16 for the short type and 22 for the long one, respectively. Both of them were directly connected to the first molar tooth. To establish the constraining conditions, a symmetrical condition at the center of the model was chosen, and the basal part of the occipital bone was completely fixed. Each 1 kg loading was applied in three directions: 30 degrees post-superior, 0 degree posterior, and 30 degrees post-inferior. The results from this face bow loading experiment showed that the direction of displacement and the stress distribution were significantly different among the kinds of the face bows and the loading directions. For the short type face bow, simple compression appeared due to the post-superior loading and bending deformation due to the posterior and post-inferior ones. For the long type face bow, some bending deformations appeared, including anterior-elongation and posterior compression due to the post-superior loading. Post-inferior bending due to posterior loading and post-inferior bending and inferior displacement due to the post-inferior loading also appeared. Thus it is feasible to dynamically control the maxillofacial complex form by changing the type of the face bow and the direction of the loading traction.