Anisotropic elasticity of cortical and cancellous bone in the posterior mandible increases peri-implant stress and strain under oblique loading

The aim of this study was to compare implant-bone interface stresses and pe riimplant principal strains in anisotropic versus isotropic three-dimension al finite element models of an osseointegrated implant in the posterior man dible. We obtained anisotropic (transversely isotropic) elastic constants f or mandibular bone and derived equivalent isotropic constants by averaging over all possible spatial orientations. A finite element model was construc ted using ten-node tetrahedral p-elements, providing curved edges where nec essary and increasing the accuracy of the results in regions of high stress gradients. Perfect bonding was assumed at the implant-bone interface. An o blique load was applied at the coronal aspect of the crown with 100 N verti cal and 20 N bucco-to-lingual components. Implant-bone interface stresses e xceeded reported bond strengths and principal strains reached yield strain levels in the cortical crest. Anisotropy increased what were already high l evels of stress and strain in the isotropic case by 20 to 30% in the cortic al crest. In cancellous bone, anisotropy increased what were relatively low levels of interface stress in the isotropic case by three- to four-fold to exceed bond strength levels. Anisotropy has subtle, yet significant effect s on interface stresses and peri-implant strains and careful consideration should be given to its use in finite element studies of dental implants.