Optimal selections of orthodontic mini-implant diameter and length by biomechanical consideration: A three-dimensional finite element analysis

A finite element analysis was carried out to evaluate continuous and simultaneous variations of orthodontic mini-implant diameter and length, and to identify their optimal ranges in the maxillary posterior region. Within the ranges of diameter from 1.0 mm to 2.0 mm and the length from 6.0 mm to 16.0 mm, our results showed that the increases of the diameter and length reduced the maximum equivalent stresses in cortical, cancellous bones and mini-implant by 80.94%, 91.84% and 86.11%, respectively, and the maximum displacement in the mini-implant by 81.29%. When the diameter exceeded 1.5 mm and the length exceeded 11.0 mm, the mini-implant achieved the best stability and the lowest levels of stress and displacement. At the similar increment, the change in the diameter was more effective than the change of length in reducing bone-implant complex stresses and enhancing mini-implant stability. Diameter exceeding 1.5 mm in combination with the longest length in safety range were the optimal biomechanical choice for the maxillary posterior region in a screwed orthodontic mini-implant.