RESUMO
BACKGROUND:Diameter and length of mini-implant have effects on its stability, which has been reported mostly in I and II osteoid, but less in IV osteoid. OBJECTIVE:To optimize the design of mini-implant diameter and length in IV osteoid by a three-dimensional finite element analysis. METHODS:Implant-mandible solid model was established. A 2 N orthodontic force that was perpendicular to the long axis of the implant and at a 30° angle with the distal central axis was applied onto the top of the implant. The implant was designed for different diameters (1.2-2.0 mm) and lengths (6-10 mm). Peak stress and peak displacement of the mandible were mechanicaly assessed, and stress sensitivity variables were analyzed. RESULTS AND CONCLUSION:The stress and displacement of the implant were mainly concentrated in the neck of the implant. The stress of implant-bone interface mainly focused on the contact area of the implant-cortical bone interface, and the stress of the cancelous bone was relatively smal, but the stress of the cortical bone was weakened faster. When the implant length was constant, the implant diameter had a great effect on stress changes, and the stress of bone tissue was reduced with the increase of implant diameter. When the implant diameter was constant, the implant length had no significant effect on the stress of bone tissue. To sum up, the stress of bone tissue and displacement were sensitive to the change of implant diameter rather than the change of implant length. These findings indicate that implant diameter has a greater effect on stress distribution of bone tissue than the implant length, and the implants with > 1.5 mm in diameter are suitable for IV osteoid.