Factorial analysis of variables affecting bone stress adjacent to mini-implants used for molar distalization by...

The aim of this study was to investigate the stresses on mini-implant, cortical bone, and cancellous bone for maxillary molar distalization using an orthodontic implant in a finite element model for different angulations and depths of insertion.

A three-dimensional finite element method was used to simulate overall orthodontic tooth movements by using ANSYS software. The maxillary bone and the molars were reproduced using CT scan images and conversion of the same into STL file was done. Finite element model was generated and the effect of forces was studied on the model for different depths and angulations of mini-implant insertions. The distalization force was exerted by an open-coil spring and the direct skeletal anchorage was provided by a mini-implant. Mini-implants were placed in depths of 5 mm, 7 mm, and 9 mm inside the bone and insertion angles of 30°, 60°, and 90°. Stresses on mini-implant and extent of stress on the surrounding bone were assessed by the software.

1. Least stress was found when the mini-implant was inserted at an angle of 30°, as it is nearer to the stronger cortical bone. 2. As the length of the mini-implant increases, accompanied by the increase in the depth of insertion, a decrease in stress in the mini-implant, cortical bone, and cancellous bone was noticed.

An increase in the insertion angle from 30° to 90° increases the stresses on both the implant and the cortical bone. A higher depth of thread in the bone helps in reducing the stress on the implant, cortical bone, and cancellous bone. This helps in improving the primary stability of the mini-implant and its life.