Abstract: Objective: To compare the stress of implant and cortical bone and the deformation of titanium framework, using different design of All-on-Four and zygomatic implants with various thickness of cortical bone , via finite element analysis in the maxillary edentulous with severe insufficient vertical bone in the posterior region. Methods: An CBCT data of an maxillary edentulous was selected to establish four different cortical bone thickness models. The model also included implant, abutment and titanium framework. The stress of the implant and cortical bone and the deformation of the titanium framework were calculated with a vertical load of 200N bilaterally in the posterior region. Results: With the increase of cortical bone thickness, the stress of implant and cortical bone and the deformation of the titanium framework gradually decreased. In the All-on-Four model. When the thickness of cortical bone increased from 0.5mm to 1.5mm, the stress and the deformation decreased significantly while the thickness of cortical bone increased from 1.5mm to 2.0mm, the decrease tended to level off. Both of the stress and the deformation had reached a very low level at 1.5mm cortical thickness point.However, in zygomatic implant model ,the change appeared slightly from various cortical bone thickness. Being compared with each other, the stress of implant and cortical bone and the deformation of titanium framework in the zygomatic implant model are smaller than those in the All-on-Four model, and there was a statistical difference in the stress of cortical bone and the deformation of titanium framework at the sites of second premolar and lateral incisor (P<0.05). Conclusion: For maxillary edentulous with insufficient vertical bone in the posterior region, the increase in the thickness of cortical bone is beneficial to reduce the stress distribution of implant and cortical bone and deformation of titanium framework. The zygomatic implant is a more suitable design in the thin cortical bone(<1.5mm). If the cortical bone is thick（≥1.5mm）, though the zygomatic implant model is better than the All-on-Four model, the distribution of the stress and deformation decrease significantly in the All-on-Four model. Thus, we can take the All-on-Four into consideration for patients in this condition.

Key words: edentulous maxilla, fixed implant prosthesis, finite element analysis, all-on-four, zygomatic implant