Objective: The aim of this study was to determine predictive values of biomechanical factors influencing primary stability of mini-implants: compacta thickness, mini-implant diameter and length, method of insertion, and components of vertical insertion force. Materials and Methods: Six different types of cylindrical self-drilling mini-implants Dual Top (Jeil Medical Corp., Seoul, Korea) with diameters of 1.4, 1.6 and 2.0 mm and lengths of 6 and 8 mm were manually (hand-driven) and mechanically (machine-driven) inserted into the swine ribs bone samples without pre-drilling a guiding hole. Compacta thickness was measured with sliding caliper, while insertion torque and vertical insertion force were recorded with specially designed device connected with oscilloscope. Maximal insertion torque was used as a measure of primary stability. Analyses of covariance, Sidak post – hoc test and hierarchical multiple linear regression analysis were used in statistical analysis. Results: Statistically significant predictors of better primary stability of orthodontic mini-implants are thicker compacta (explaining for 24.2% of variability), wider diameter of mini-implant (20.6%), manual insertion (9.9%), greater length of mini-implant (3.7%), higher maximal vertical insertion force (2.2%), and lower vertical force at maximal insertion torque (1.4%). A total of 61.5% of variability of primary stability is explained by this model. Conclusions: Compacta thickness, mini-implant diameter, and manual insertion have higher impact on the primary stability of orthodontic mini-implants, while mini-implant length and components of vertical insertion force have lower impact.