Comparison of the primary stability of orthodontic mini-screws manufactured by the Computer Numerically Control and Selective Laser Melting manufacturing methods: An exploratory study

Background: This study was to assess the primary stability of orthodontic mini-screws of the same design produced by a conventional and a novel manufacturing method. Methods: A total of 150 orthodontic mini-screws with a body length of 8 mm, a diameter of 1.6 mm, a button head, and a self-drilling feature were used in the study. Mini-screws were manufactured through computer numerically controlled (CNC) and selective laser melting (SLM) manufacturing methods. Titanium (T) and stainless steel (SS) alloys were used as manufacturing materials. The study was conducted on three groups; CNC-T, SLM-T and SLM-SS. Mini-screws were placed at 60- and 90-degree angles in fresh bovine femur bones, where the cortical bone thickness was 2 mm. With the radiofrequency analysis (RFA) technique, the stability of the mini-screws was determined immediately after they were placed (F0), immediately after applying orthodontic force to the mini-screw (F1), after six hours (F6), and after 24 hours (F24). Three-way robust ANOVA was used to compare the data, and the Bonferroni correction was statistically applied. Results: Except for the insertion angle of the mini-screw, the group and time factors had statistically significant effects on the RFA values. The highest RFA value was detected in the SLM-T group. Conclusion: Orthodontic mini-screws manufactured from titanium or stainless steel alloys using the SLM technology can be an alternative to mini-screws manufactured using the traditional manufacturing method. The mini-screws manufactured using the SLM technology demonstrated adequate primary stability when subjected to an orthodontic force. Keywords: Orthodontic mini-screw, Primary stability, Selective laser melting, Computer numerical control, Radiofrequency analysis