Three-Dimensional Analysis of Mini-Screw Implants

Introduction: The purpose of this study was to evaluate the effects of surface modifications of mini-screw implants (MSIs) and force application on peri-bone-implant contact. Methods: Using randomized split-mouth design in 7 skeletally mature male foxhound dogs, 21 MSIs with a sand-blasted, large-grit and acid etched (SLA) surface were compared with 21 machine surfaced MSIs placed in the mandible. Twenty eight of the MSIs were immediately loaded with 200g using NiTi coil springs, and compared to unloaded controls. The percentages of bone-implant contacts were measured in two zones from a distance of 6-to-24 µm and 24-to-42 µm from the MSI surface for both cortical and non-cortical bone using micro-computed tomography (µCT) with an isotropic resolution of 6 µm. Results: A 100% clinical success rate attained for SLA surfaced MSIs, compared to the 95% for machine surfaced MSIs. Mean insertion torque was higher for SLA surfaced MSIs (39 Ncm) compared to machine surfaced MSIs (42 Ncm), but was not statistically significant (p = .875). Peri-bone-implant contact was significantly higher (p < .05 ) for the loaded SLA surfaced MSIs than machine surfaced MSIs. Peri-bone-implant contact ratios assessed by µCT demonstrated higher overall percentages in the SLA surfaced MSIs in both cortical and non-cortical segments. SLA surfaced MSIs under force load also demonstrated statistically significant differences in implied bone-implant contact compared to machine surfaced MSIs. BV/TV ratios evaluated at distances from 6-to-24 µm were significantly less compared to ratios from 24-to-42 µm. Conclusion: SLA surfaced MSIs compared to machine surfaced MSIs demonstrated the following: 1) 100% clinically successful; 2) peri-bone-implant contact significantly higher; 3) insertion torque higher, but not statistically significant different from machine surfaced MSIs; 4) force application demonstrated a significant increase in peri-bone-implant contact for SLA surfaced MSIs