Soft bone primary stability of 3 different miniscrew for orthodontic anchorage: a resonance frequency investigation

Introduction: Several miniscrews are available for skeletal anchorage. They have different geometries with self-drilling or self-tapping features. The aim of this study was to evaluate the soft bone primary stability of 3 different orthodontic screws by using the resonance frequency analysis. Methods: Aarhus mini-implant (Aarhus Mini-implant, Charlottenlund, Denmark) (A), Mini Spider Screws (HDC, Sarcedo, Italy) (S), and Micerium Anchorage System (Micerium, Avegno, Italy) (MAS) were investigated. To be compatible with the device used for resonance frequency analysis, the screws were modified (an abutment [Astra Tech, Mölndal, Sweden] was soldered on top). Four screws per system were tested. Each screw was placed in 5 excised rabbit femoral condyles, providing experimental models of soft bone. Placement was drill-free for the A screw, whereas the MAS and S screws required a pilot hole through the cortical layer. After each placement procedure, resonance frequency was assessed as a parameter of primary stability. Differences among the systems were analyzed by using analysis of variance for repeated measures, with the level of significance at P < 0.05. Results: The recorded resonance frequencies (in Hz) were (mean ± SD): MAS, 6236.1 ± 192.1; S, 6270.1 ± 99.7; and A, 6193.1 ± 142.4. Differences among the groups were not statistically significant (P > 0.05). Conclusions: The resonance frequency analysis is applicable to comparatively assess the primary stability of orthodontic miniscrews. The 3 systems had similar outcomes in an experimental model of soft bone. © 2009 American Association of Orthodontists.