A Comparison of Torque Forces Used to Apply Intermaxillary Fixation Screws

When establishing intermaxillary fixation (IMF) using bone screws, fracture of a screw is a potential complication. This study was conducted to investigate the forces that arise at bone screw insertion and to determine safety margins between torque for manually tightened insertion and torque until breakage for 3 different IMF screw systems, which could ultimately favor the use of 1 IMF screw system based on decreased risk of complications.

IMF screws were placed into porcine mandibles by 3 oral and maxillofacial surgeons. The porcine mandibles were evaluated for cortical thickness and suitable insertion sites by cone-beam computed tomography. Measurements of torque until failure were performed on predrilled aluminum plates by the primary author. A digital torque screwdriver measured 180 data points per second as continuous data and recorded the measurements.

Measurements indicated clear differences in torsion forces between manually tightened insertions and torque until breakage for all 3 IMF screw systems. No statistical difference in safety margins was found among the IMF screw systems.

Because no statistical differences in safety margins were found among the IMF screw systems, this study indicates that IMF screw selection should be based on other clinical factors, such as ease of use or economic factors. Future prospective studies are necessary to fully determine evidence-based criteria for IMF screw selection.