ABSTRACT
The use of reduced angle of insertion during miniscrew implant placement has been reported to increase the mechanical retention of miniscrew implants. However, the effects of the insertion angulation in the dentoalveolar bone have not been investigated. The purpose of this study was to investigate the effects of insertion angulation on the biomechanical performance of miniscrews implanted in the dentoalveolar bone. Three hundred and sixty self-tapping miniscrew implants (1.6 x 8 mm) (BMK, Seoul, Korea) were systematically inserted in fresh maxillary and mandibular dentoalveolar bone (anterior, middle and posterior sites) of minipigs at 30, 60 and 90 degrees to the bone surface, aided by a 3-D Surgical Guide (Y\&B Products, Chiangmai, Thailand). Maximum insertion torque and pullout strength were assessed with the Imada torque wrench and the Instron Universal Testing Machine, respectively. Results were recorded and analyzed by One way analysis of variance; ANOVA and Pearson correlation coefficients. It was found that maximum insertion torque and pullout strength had significant correlation (r = 0.81). In the maxilla, no significant difference in the maximum insertion torque and pullout strength was observed between miniscrews implanted at 30, 60 or 90 degrees. Although miniscrews inserted at 30 degrees exhibited the highest mechanical performance than those inserted at 60 and 90 degress in the anterior portion of the mandible, they exhibited significantly reduced insertion torque and pullout strength values than those inserted at 60 and 90 degress in the middle and posterior sites. No significant difference was observed between miniscrews inserted at 60 and 90 degrees. In conclusion, insertion angulation did not improve the mechanical performance of miniscrews implanted in the maxillary dentoalveolar bone. Reduced insertion angulation (30 degrees) was effective only in the anterior portion of the mandible.