Dental implants are widely used as a treatment option to replace a defective prosthesis. In recent years, treatment using short implants, which are ≤ 8 mm in length, has been increasing in cases with vertical bone resorption [1]. It is thought that this will become more popular as the number of patients who require minimally invasive treatment, such as older patients and those with chronic disease, is increasing [2,3,4,5].

There are two major implant designs; tissue level (TL) implants, where the platform is located under the soft tissue level, and bone level (BL) implants, where the platform is placed at the crestal bone level. TL implants are often avoided in the esthetic area, but there are no clear criteria for the selection of either implant design. Conversely, TL implants are more structurally favorable for a shorter implant body than BL implants because of the submerged design and shorter abutment screw. Clinically, the 4-mm-long TL implant is the shortest used [6, 7]. However, no report has been previously undertaken on the difference between the mechanical behavior of TL and BL implants, so it is not clear which design is more advantageous.

Recently, a titanium–zirconium alloy (TiZr) has been developed, which contains approximately 15% zirconium in titanium and has high biocompatibility, similar to commercially pure titanium (cpTi). Furthermore, TiZr has higher mechanical strength when compared with cpTi and is expected to be effective for preventing fracture of the implant body [8,9,10,11]. Clinically, it has been reported that TiZr implants have no significant difference in marginal bone resorption and survival rate when compared with cpTi implants, and their use is equivalent to cpTi implants [12,13,14]. However, the difference in stress distribution to the surrounding bone and within the implant body between cpTi and TiZr implants has not been elucidated.

Finite element analysis (FEA) is often used to predict the long-term prognosis of a device in an intraoral environment simulating loading conditions [15,16,17]. Therefore, we conducted a mechanical study of implant using three-dimensional FEA, with the purpose of clarifying the differences between cpTi and TiZr implants, TL and BL implants, and their length.