Effects of washer on the stress distribution of mini-implant A finite element analysis

Objective: To investigate the biomechanical effects of 'washer' designed for improving mini-implant stability. Materials and Methods: Four three-dimensional finite element models of the mini-implant and surrounding bone were constructed with washers in different spike lengths (1.5 mm, 2.0 mm, and 2.5 mm). The force was applied in two directions (45 degrees and 90 degrees). The stress distribution on surrounding bone and the displacement of the mini-implant were analyzed. Plots of tensile stress, compression stress, and displacement were calculated, and maximum values in each category were analyzed. Results: The stress distribution was different between the models with washer and without washer. However, no remarkable differences in stress distribution were observed among the models with washer, regardless of spike length. A significantly greater displacement value was observed in the model without washer compared to the models with washer, but no notable difference in displacement value was found among the models with washer. The plots of the displacement distribution of the models with washer presented notable pattern differences as compared with that of the model without washer. Conclusion: With the use of the washer, a more homogeneous distribution of bone stress and less displacement of the mini-implant can be achieved. (Angle Orthod. 2012;82:137-144.)