Mechanical and biomechanical measurements of five currently available osteosynthesis systems of self-tapping screws

Pressure force, uniaxial 'pullout', minimum torque, and peak torque tests were done to evaluate the effectiveness of three popular monocortical and non-compressing self-tapping screw systems 2 mm in diameter (Champy, Centre-Drive, and Wuerzburger) and two systems 1.5 mm in diameter (Champy and Wuerzburger). The screw systems were all tested on polyvinylchloride plate, skull, and molar mandibular bone from fresh human cadavers. The Champy screw 2 mm in diameter and 7 mm long produced the highest pressure force (mean (SD) 153.4 (58.5) N, n=40) of the systems tested. The Centre-Drive screw of the same size showed the highest retentive force in pullout tests (619.5 (169.9) N, n=40) and also the largest difference between minimum and peak torque in skull and molar mandibular bone (1.86 (0.65) kpcm, n=40). This was clinically relevant compared with reported human bite-force (range 216-740 N). The results showed that, the screw diameter and number of threads were the most important and significant of the mechanical variables tested. The skull bone also exerted more retentive force than the molar mandibular bone. The overall data indicate that there is no need to use screws more than 7 mm long or wider than 2 mm in diameter for monocortical non-compressive osteosynthesis in the craniofacial and the mandibular region.