Use of an axisymmetric finite element method to compare maxillary bone variables for a loaded implant.

PURPOSE This study determined the effect of various bone models on the stresses and strains generated under occlusal loading of a dental implant. MATERIALS AND METHODS A two-dimensional finite-element model was created for stress analysis. The geometric and elastic properties of a 3.8 x 10-mm Steri-Oss implant embedded in a segment of premaxilla were modeled. Computed tomography scanning of a dried maxilla half was used to determine representative geometry and density of this region. Material properties for bone were varied to simulate the following: all-cancellous bone, cancellous bone with a thin (1.5-mm) crestal isotropic cortical layer, cancellous bone with a thick (3-mm) crestal isotropic cortical layer, and cancellous bone with a thick (3-mm) layer of transversely isotropic (orthotropic) cortical bone. RESULTS Low stresses and high strains surrounded the fixture apex for the all-cancellous bone model. When a layer of cortical bone was added, higher crestal stresses and lower apical strains were observed. The thicker layer of isotropic cortical bone produced stresses at least 50% less than the thinner layer. The assumption of transverse isotropy (orthotropy) increased stresses and strains by approximately 25% compared with isotropic bone. CONCLUSIONS Crestal cortical layer thickness and bone isotropy have a substantial impact on resultant stresses and strains. Clinical assessment of these parameters is recommended.