Biomecanical evaluation of miniscrew implants in vitro

Background: Bone quality plays an important role in the success of orthodontic miniscrew implants. The mechanical properties of bone are highly related to the mineral content, which varies widely according to function and histology. However, in vitro methods for evaluating biomechanical properties of miniscrew implants have not been reported. Purpose: The aim of this study was to assess the biomechanical performance of miniscrew implants using bone samples which were demineralized by timed chemical immersion to alter the mineral content. Materials and Methods: Sections of fresh rib bones from adult pigs were selectively demineralized by timed immersion in 1 % ethylenediamine-tetraacetic (EDTA). Specimens were removed from the solution after 0 (control), 6, 10, 16, 30 and 50 days and embedded in acrylic blocks. Quantification of bone density was performed using radiographic images processed with Photoshop software. Fifty miniscrew implants (8 mm long and 1.6 mm in diameter, BKM, Korea) were inserted. Maximum insertion torque was recorded with a toque gauge. Pullout strength was tested using an Instron Universal testing machine. Statistical analysis was performed using Kruskal-Wallis Test and Spearman correlation coefficients. Results: There was a systematic decrease in bone density that was followed by a significant decrease in the biomechanical properties of the miniscrews. High correlation (r = 0.91) was observed between maximum insertion torque and maximum pullout strength. Conclusions: The biomechanical properties of miniscrew implants can be evaluated in vitro using bones obtained from a single species prepared with the selectively demineralized bone technique. The proposed method can be used to facilitate comparison between different miniscrew implant systems, avoiding the inaccuracy observed in conventional methods. Keywords: miniscrew implants, orthodontics, biomechanics, in vitro