Effects of the taper shape, dual-thread, and length on the mechanical properties of mini-implants

Abstract

Objective: To analyze the mechanical effects of the length and the various shapes such ascylindrical shape, taper shape, and dual-thread shape on the insertion and removal torque of miniimplants.Materials and Methods: Mini-implants (diameter 1.6 mm and length 6 mm and 8 mm) consistingof cylindrical, taper, and dual-thread groups were inserted and removed in Sawbones while measuringthe torque and time. Mechanical analysis was done of maximum insertion torque (MIT),maximum removal torque (MRT), torque ratio (TR; MRT/MIT), insertion angular momentum (IAM),removal angular momentum (RAM), and time of MIT. Measurements were statistically evaluatedto analyze any differences of shapes and lengths.Results: The cylindrical shape had the lowest MIT and MRT in each length. Although taper shapeshowed the highest MIT in each length, dual-thread shape showed significantly higher MRT, TR,and RAM in each length (P - .05). Dual-thread groups showed a gentle increase of insertiontorque and a gentle decrease of removal torque in contrast to the other shape groups. However,it had higher IAM and time of MIT. The long length group showed significantly higher measurementsexcept for TR.Conclusions: Dual-thread shape provided better mechanical stability with high removal torqueon the broad range than other shapes. However, dual-thread shape may need improvement forreducing the long insertion time to decrease the stress to the surrounding tissue. (Angle Orthod.2009;79:908-914. © 2009 by The EH Angle Education and Research Foundation, Inc.