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Objective To compare the initial stability difference between a new designed torque-resisted orthodontic miniscrew anchorage and commercial miniscrew anchorage by torque tests and resonance frequency analysis (RFA). Methods After predrilled 4 mm⁃deep holes with a diameter of 1.0 mm, two different miniscrews were implanted into the swine ribs for measurement of maximum insertion torque (MIT), maximum removal torque (MRT) and RFA which was recorded as implant stability quotient (ISQ). Statistical analysis was done for all data by SPSS 13.0. Results The mean value of MIT, MRT, ISQ for new miniscrews were (11.86±1.58) N•cm, (8.45±2.24) N•cm and 61.80±2.9 while for commercial miniscrews were (10.36±1.42) N•cm, (6.76±1.78) N•cm and 58.15±2.98. The differences be-more stable than commercial miniscrews.

Objective: To investigate the influence of the diameter and length of the mini-implant on the primary stability after loading with composite forces (CF) which contained torque and horizontal forces (HF)., Methods: Ninety-six finite element models were established by the combination of mini-implant and bone, diameters (1.2 mm, 1.6 mm, 2.0 mm) and length (6 mm, 8 mm, 10 mm, 12 mm). There were 12 sizes, each size corresponded with 8 models. Group HF (each size n = 4) was loaded with 1.96 N horizontal force and Group CF (each size n = 4) was loaded with composite force which contained 6 N·mm torque and 1.96 N horizontal force. The maximum displacement of mini-implant with different force directions, implant diameters and lengths were evaluated., Results: The effect of force direction on the displacement related to diameter of mini-implant. The maximum displacement under load with HF respectively was changed with the changing of diameter[1.2 mm: (7.71 ± 0.49) µm; 1.6 mm: (3.94 ± 0.31) µm; 2.0 mm: (2.32 ± 0.43) µm], which were smaller than the maximum displacement of Group CF [1.2 mm: (9.22 ± 0.63) µm; 1.6 mm: (4.62 ± 0.52) µm; 2.0 mm: (2.69 ± 0.49) µm] (P < 0.05). When diameter was 1.2 mm, the difference of the maximum displacement [(1.61 ± 0.22) µm] between Group HF and CF was more obvious than that when the diameter was 1.6 mm or 2.0 mm [(0.64 ± 0.12), (0.49 ± 0.06) µm] (P < 0.05)., Conclusions: The composite force had unfavorable effect on the primary stability of the mini-implant. The diameter of the mini-implant had better be larger than 1.2 mm when the composite forces were applied.