Influence of Micro Threads Alteration on Osseointegration and Primary Stability of Implants: An FEA and In Vivo Analysis in Rabbits.

PURPOSE To describe the early bone tissue response to implants with and without micro threads designed to the full length of an oxidized titanium implant. MATERIALS AND METHODS A pair of two-dimensional finite element models was designed using a computer aided three-dimensional interactive application files of an implant model with micro threads in between macro threads and one without micro threads. Oxidized titanium implants with (test implants n=20) and without (control implants n=20) micro thread were prepared. A total of 12 rabbits were used and each received four implants. Insertion torque while implant placement and removal torque analysis after 4 weeks was performed in nine rabbits, and histomorphometric analysis in three rabbits, respectively. RESULTS Finite element analysis showed less stress accumulation in test implant models with 31Mpa when compared with 62.2 Mpa in control implant model. Insertion and removal torque analysis did not show any statistical significance between the two implant designs. At 4 weeks, there was a significant difference between the two groups in the percentage of new bone volume and bone-to-implant contact in the femur (p< .05); however, not in the tibia. CONCLUSIONS The effect of micro threads was prominent in the femur suggesting that micro threads promote bone formation. The stress distribution supported by the micro threads was especially effective in the cancellous bone.

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