Pullout force comparison of selected screws for rigid fixation in maxillofacial surgery

Background. Screws used in open reduction and internal rigid fixation need a large amount of force to effectively stabilize the plate. Currently, there is no worldwide standard screw design and there are no publications available comparing the pullout strength of different maxillofacial osteosynthesis systems. Objectives. The aim of the study was to compare the pullout strength of different screw types. Material and methods. The study used 75 screws made by the main manufacturers (DePuy Synthes, KLS Martin and Medartis). The screws were inserted into polyurethane up to 3.6 mm or 9.6 mm deep. The 1-100 kN Insight Material Testing System (MTS Systems Corporation), a twin-column floor-standing model for high-force applications, was used for the electromechanical measurement of the screws' axial pullout strength from the blocks of polyurethane. The method was based on the standard specification and test methods for metallic medical bone screws (ASTM F543-07 and Annex A3). Results. Among the self-tapping microscrews 6 mm in length and 1.5 mm in diameter, DePuy Synthes screws had the greatest average pullout force (226.0 +/- 7.52 N; p < 0.05). Among the self-drilling 6 mm x 1.5 mm microscrews, DePuy Synthes screws also had the highest score (253.6 +/- 4.39 N; p < 0.05). Among self-tapping miniscrews 6 mm in length and 2.0 mm in diameter, Medartis screws attained the highest scores (228.8 +/- 9.73 N; p < 0.05). Among self-drilling 6 mm x 2.0 mm screws, KLS Martin screws had the best results (320.8 +/- 9.09 N; p < 0.05). Conclusions. There are significant differences in fixing force among screws of the same diameter but originating from different manufacturers.