Miniscrew Composition, Transmucosal Profile, and Cortical Bone Thickness: A Three-dimensional Finite-element Analysis...

The aim of this study was to use the finite-element method (FEM) to analyze the stress fields generated in miniscrews (MSs) and surrounding bone on applying a force perpendicular to the MS according to variations in the cortical bone thickness and changes in the transmucosal profile length and MS composition.

Miniscrews with stainless steel (SS) and titanium alloy mechanical properties with a 1 to 2 mm transmucosal profile inserted in bone blocks with cortical bone of varying thickness (1 and 2 mm) were three-dimensionally modeled using computer-aided design (CAD) and examined using FEM. A 3.5 N force perpendicular to the long axis of the MS was applied in the four mechanical tests: EM1: SS MS and a 1 mm transmucosal profile; EM2: titanium MS and a 1 mm transmucosal profile; EM3: SS MS and a 2 mm transmucosal profile; and EM4: titanium MS and a 2 mm transmucosal profile.

The stress distributions in all mechanical tests were highest at the MS, especially at the MS-cortical bone interface. A greater stress concentration occurred in cortical bone measuring 1 mm thick than in the cortical bone measuring 2 mm thick. The MSs with a 2 mm transmucosal profile showed higher stress than those with a 1 mm transmucosal profile.

The titanium alloy MSs showed higher stress fields and deflection voltages than the SS MSs at the same cortical bone thickness and with the same transmucosal profile.

From a mechanical perspective, this study showed the stress field generated in MSs with SS and titanium alloy (Ti) mechanical properties and surrounding bone. The stress distribution was concentrated at the MS, mainly at the interface with the cortical bone, and the difference between the stress values for the Ti and SS MSs was very small. Under this condition, the two types of MSs are suitable for orthodontic applications because their yield limits are much higher.