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Torque de inser??o e resistência ao arrancamento dos parafusos vertebrais com alma cilíndrica e c?nica

DOI: 10.1590/S0102-36162008001000005

Keywords: spine, bone screws, biomechanics, orthopedic fixation devices.

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objective: to evaluate insertion torque and pullout strength of three different screws used in the anterior fixation of the spine, considering the influence of the diameter of the pilot hole (dop), the test specimen density (cdp), and the screw thread design. methods: the authors used polyurethane test specimens with two densities: 0.16 and 0.32 g/cm3, and three types of screws (uss i, uss ii posterior, and uss ii anterior). in the first stage, the pilot hole was made with a 3.8 mm probe for all screws; in the second stage, with a probe smaller than the inner diameter of the screws (3.5 mm for screws uss i; 3.4 mm for uss ii posterior screws, and 3.0 mm for uss ii anterior screws). 12 experimental groups were formed with ten specimen tests in each group, according to the polyurethane density, dop, and the type of screw used. torque was measured during insertion of the screws and the pullout strength by a mechanical assay in a universal test machine. results: the maximum insertion torque presented a decreasing value in test specimens of 0.16 g/cm3 and 0.32 g/cm3 and in all pilot hole diameters. maximum pullout strength in test specimens of 0.16 g/cm3 and 3.8 mm of perforation diameter was greater in uss ii posterior screws than in uss i screws. with the perforation diameter smaller than the inner screw diameter, uss ii posterior and anterior screws presented higher values than the uss i screw. in test specimens with 0.32 g/cm3 of density and perforation diameter of 3.8 mm, the pullout strength of uss ii posterior and uss i screws was greater than that of uss ii anterior screws. with the smaller perforation diameter than the inner diameter, the values were decreasing between the uss ii posterior screw, then the uss ii anterior screw, and then the uss i screw. conclusion: insertion torque and pullout strength of the screws used in the anterior fixation of the vertebral spine are influenced by the test specimen density, by the screw thread design, and by the diameter of


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