Bivariate optimization of orthodontic mini-implant thread height and pitch.

Abstract

Mini-implants have been used as anchorage for years, but failure is common in clinical practice. Mini-implant design is a critical factor affecting its stability. The aim of this study was to evaluate the effect of continuous and simultaneous variations of thread height and pitch on the biomechanical properties of an orthodontic mini-implant. A 3D finite element model, composed of a posterior maxilla section and an orthodontic mini-implant, was created. Mini-implant thread height ranged from 0.10 to 0.40 mm, and thread pitch ranged from 0.50 to 2.00 mm. Effects of the implant thread height and pitch on the maximum Von Mises stresses in maxilla and mini-implant, as well as maximum displacements in the mini-implant, were evaluated by a finite element method. Bivariate analysis was used to determine the optimal range of thread height and pitch. Variation of thread height and pitch decreased the maximum Von Mises stresses in cortical bone, cancellous bone and mini-implant by 54.9, 78.4 and 23.6 %, respectively. The maximum displacement in the mini-implant decreased by 21.8 %. Maxillary stress and mini-implant stability were influenced by mini-implant thread height and pitch. Increased thread height with a thread pitch of 1.20 mm was better for orthodontic mini-implant in the maxillary posterior region. Thread height played a more significant role than the thread pitch in reducing maxillary stress and enhancing orthodontic mini-implant stability.