Biomechanical Study on the Stability of Mini-Implants in the Infrazygomatic Crest Region

Abstract

Objective: To determine insertion angles and force directions that minimize micromotion of infrazygomatic crest (IZC) mini-implants while accounting for the curved lateral wall and the non-parallel bicortical anatomy.

Methods: We built 20 three-dimensional finite element models that preserved full thread geometry and the true IZC bicortical relationship. Two force directions (horizontal vs. vertical), five insertion angles (15°-70°), and single vs. double cortical engagement were tested under a 2 N load. Outcomes included implant displacement and von Mises stress in the screw and surrounding bone.

Results: Vertical loading consistently halved displacement compared with horizontal loading (mean 7.3 ± 2.9 μm vs. 14.7 ± 6.2 μm). Under horizontal forces, 45° minimized displacement (8.1 μm) and cortical stress (92 MPa); under vertical forces, 15° performed best (4.6 μm). Effect sizes were substantial: vertical vs. horizontal displacement ratio ≈ 0.50; 45° vs. 70° cortical stress reduction ≈ 33-40% under horizontal loading. Penetrating the thin sinus floor (∼0.45 mm) did not improve stability.

Conclusion: For IZC anchorage, 15-45° insertion with predominantly vertical force reduces stress and micromotion; thin bicortical engagement provides no additional benefit. These anatomy-aware rules are readily applicable chairside.

Keywords: biomechanical; finite element analysis; infrazygomatic crest region; mini-implants; orthodontic anchorage.