Plateau implants- would cancellous bone withstand the functional loading when involved in bone loss?

Background

Crestal cortical bone at the implant neck is the key structural element of the jaw, which withstands the functional loading. Bone loss progression results in overloading of ìsoftî cancellous bone with the risk of implant failure. Comparing to conventional ones, short implants should be more sensitive to this issue. Plateau implants reduce the impact of bone loss, but there is no quantitative confirmation to this.

Aim/Hypothesis

The aim of this study was to assess the load-bearing ability of cancellous bone on several levels of bone loss after it propagates through the crestal cortical bone.

Material and Methods

Cancellous bone von Mises stresses (MESs) were proposed to evaluate load-bearing ability of fully and partially osseointegrated 4.5 (N), 5.0 (M), 6.0 mm (W) diameter and 5.0 mm length Bicon SHORT® implant on 5 levels of bone loss from 1.2 to 2.0 mm. Implant 3D models were placed crestally and bicortically in posterior maxilla segment models with type III bone and 1.0 mm cortical crestal and sinus bone. Bone models were drawn in Solidworks 2016 software. Materials were assumed to be linearly elastic and isotropic. Elasticity moduli of cortical cancellous bone were 13.7 1.37 GPa. Bone-implant assemblies were analyzed in finite element (FE) software Solidworks Simulation. 4-node 3D FEs were generated with a total number of up to 2,516,000. 120.92 N oblique load was applied to the center of 7 Series Low 0° abutment. MESs were evaluated in cancellous bone-implant interface for fully and partially osseointegrated implant and were compared.

Results

6.0, 5.0, 3.5 MPa maximal MESs for the osseointegrated N, M, W implants were found in cancellous bone at the first fin. For 1.2, 1.4, 1.6, 1.8, 2.0 mm bone loss, maximal MESs were calculated in migrating critical points of cancellous bone-implant interface, which were located on the border of disosseointegrated-osseointegrated cancellous bone- 8.0, 10.0, 12.5, 15.0, 17.5 MPa for N, 7.3, 9.3, 11.5, 13.5, 16.0 MPa for M, 4.5, 7.5, 8.5, 10.3, 12.0 MPa for W implant. For N, M, W implants after 6 years in function (1.2 mm bone loss), 33, 46, 58% MESs increase was determined, for 7 years (1.4 mm bone loss) – 67, 86, 114%, for 8 years (1.6 mm bone loss) – 108, 130, 143%, for 9 years (1.8 mm bone loss) – 150, 170, 194%, for 10 years (2.0 mm bone loss) – 192, 220, 243%.

Conclusion and Clinical Implications

The studied Bicon SHORT® implants were found extremely sensitive to bone loss after 5 years in function, when it has spread outside the cortical bone (1.2Ö2.0 mm) and cancellous bone has become the only load-bearing element, since maximal MESs have exceeded the ultimate strength of dense cancellous bone (5.0 MPa). Therefore, implantologists should consider the obtained data in treatment planning.