Thread shape, cortical bone thickness, and magnitude and distribution of stress caused by the loading of orthodontic miniscrews: finite element analysis

Abstract

Cortical bone thickness is assumed to be a major factor regulating miniscrew stability. We investigated stress distribution in two miniscrews with different thread shapes (type A and B) and in cortical bone of three different thicknesses using three-dimensional (3D) finite element (FE) models. More specifically, 3D FE models of two different miniscrews were created and placed obliquely or vertically into a cylindrical bone model representing different cortical bone thicknesses. When force was applied to the miniscrew, the stress distribution on the screw surface and in the peri-implant bone was assessed using FE methodology. Miniscrew safety was evaluated using a modified Soderberg safety factor. Screw head displacement increased with a decrease in cortical bone thickness, irrespective of screw type. The smallest minimum principal stresses on the screw surfaces remained constant in type A miniscrews on changes in cortical bone thickness. Minimum principal stresses also appeared on the cortical bone surface. Lower absolute values of minimum principal stresses were seen in type A miniscrews when placed vertically and with upward traction in obliquely placed type B miniscrews. Both miniscrews had acceptable safety factor values. Taken together, orthodontists should select and use the suitable miniscrew for each patient in consideration of bone properties.

The success rate of mini‐screws for incisors intrusion and patient age, gender, and insertion angle in the maxilla using CBCT and implant‐guided surgery. A split‐mouth, randomized control trail

“…Screw stability was measured clinically by torque measuring tool and the Mandrell attached to it by checking the screw resistance to removal under the torque of 5 Nm. A reading was taken every month to check the screw's stability, [33][34][35][36] (Figure 4).…”

Success rates of single-thread and double-thread orthodontic miniscrews in the maxillary arch

“…Previous studies have investigated the effect of various variables such as length, diameter, and thread features (shape, pitch, depth) on the primary stability of mini-implants in laboratory conditions [ 3 , 4 , 15 – 21 ] or animal studies [ 22 – 25 ]. However, it is essential to note that the mechanical properties of artificial bone and the bone quality of animals differ from humans [ 10 , 14 ].…”