Mini-implant behavior to shear tensile forces in the porcine mandible.

Aim: To determine the tangential tensile force loading behavior of mini-implants relative to cortical bone thickness in the porcine mandible.

Methods: Eighteen mini-implants were placed both anteriorly and posteriorly perpendicular to the bone surface in porcine mandibles and subjected to shear tests using a Universal Testing Machine (Instron). Further, cone beam CT was used to measure cortical bone thickness at each mini-implant site.

Results: The shear strength differed significantly between the anterior (mean 89.05 ± 35.9 N) and posterior (mean 179.85 ± 29.01 N) sites. The same was true for the cortical bone thickness (anteriorly, mean 3.59 ± 0.49 mm; posteriorly, mean 4.24 ± 0.5 mm).

Conclusion: The shear forces required to dislodge mini-implants were much higher than forces typically applied for orthodontic purposes. Therefore, mandibular cortical bone supporting monocortical orthodontic mini-implants would most likely withstand immediate loading with tangential shear forces. In addition, it seems that mini-implants loaded tangentially continue to exhibit adequate anchorage for orthodontic forces even after they are displaced.