Assessment of stiffness and load deflection of orthodontic miniscrews used for palatal anchorage: An in vitro biomechanical study

Objective: The purpose of this study was to evaluate the biomechanical properties of miniscrews of 5 different lengths, 2 different diameters, and different combinations of insertion used for palatal skeletal anchorage. Materials and methods: Twenty-four different combinations of a total of 120 miniscrews of two different diameters (2.0 mm and 2.3 mm) and five different lengths (9 mm, 11 mm, 13 mm and 15 mm) were tested at different angles of insertion (90° and 45°) and distances from a synthetic bone block (3 mm, 5 mm, 7 mm). Samples were fixed in an Instron Universal Testing Machine and a load was applied in single cantilever mode to the neck of each miniscrew. The stiffness and maximum load before permanent deformation were recorded. Model-based recursive partitioning testing (CART) was used to evaluate differences between groups. Results: Significantly higher forces were necessary to deform miniscrews of diameter 2.3 mm than those of 2.0 mm, those inserted at an angle of 45° with respect to 90°, and at smaller distances between the miniscrew neck and block; in addition, the maximum load and stiffness increased with increasing screw length. Conclusion: This in vitro experimental study showed strong correlations between deformation load and miniscrew geometry, insertion angle and distance from the synthetic block, results that should be considered when planning miniscrew insertion in order to reduce the risk of unwanted fracture.