Mechanical analysis of the taper shape and length of orthodontic mini-implant for initial stability

Kim, Jong Wan; Cho, Il Sik; Lee, Shin Jae; Kim, Tae Woo; Chang, Young Il

Abstract

Orthodontic mini-implants, despite its usefulness as anchorage, have some limits such as loosening. Therefore, various shapes and lengths have been studied. The aim of this study is to analyze the shape and length of mini-implants mechanically. The shapes of mini-implants (1.6 mm, Dual Top, Jeil Medical Co., Seoul, Korea) were cylindrical and taper. The lengths of mini-implants were 6 mm and 8 mm. The tested groups were 5 groups (cylindrical 6 mm, cylindrical 8 mm, taper 6 mm, taper 8 mm and taper 8 mm modified whose thread is reduced from the middle to upper part). All were inserted and removed on the polyurethane foam with the torque measured. During insertion and removal, the taper shape needed higher torque than the cylindrical shape, and the 8 mm length than the 6 mm length (p < 0.001). The taper 6 mm group showed superior insertion torque (p < 0.001) and similar removal torque to the cylindrical 8 mm group. The taper 8 mm modified group with gradually reduced threads, showed continuous high removal torque after the peak. The initial mechanical stability can be provided by the tapered shape and also, affected by length and thread design.