Comparison of compression screws used for mandible head fracture treatment-experimental study

Objectives: Compression screws that can fix a fracture of the condylar head of the mandible are available. Although typical titanium lag screws are generally used, a series of headless screws have been designed for this purpose. The "headless" advantage derived from the complete submergence of the screw in the bone after fixation is the lack of irritation of the lateral ligament of the temporo-mandibular joint by the screw head. The aim of this study is to compare the compression force of typically used lag screws with that of newly developed headless compression screws.

Materials and methods: This study tested five types of screws with a 14-mm length: 10 2.0-mm lag screws and 40 headless screws (four groups of equal size: 1.5-mm H screws, 1.8-mm H screws, 2.0-mm H screws, and 1.8-mm W screws). Two cuboid blocks of standardized polyurethane foam were fixed by one screw. The maximal compression force (F in N) and torque at maximal compression force (T in Ncm) were tested according to the guidelines of the American Society for Testing and Materials (ASTM F1839-08).

Results: The test results were as follows: 2.0-mm lag screw: F = 211.5 ± 20.7 and T = 21.1 ± 1.6; 1.5-mm H screw: F = 47.2 ± 5.6 and T = 18.2 ± 1.1; 1.8-mm H screw: F = 95.5 ± 9.8 and T = 18.2 ± 1.1; 2.0-mm H screw: F = 145.1 ± 18.4 and T = 25.5 ± 1.5; and 1.8-mm W screw: F = 180.5 ± 8.7 and T = 26.4 ± 2.8. Each type of screw significantly differed from one another as far as compression forces (F) were considered (p < 0.05): the best is the lag screw contrary to the thinnest H screw which is the worst one. For all tested screws, the compression force depended on the torque (S curve relationship was revealed, p < 0.05) and screw diameter (a larger diameter yielded greater compression, p < 0.05).

Conclusions: The 8-mm headless screws featured only a small loss of compression ability compared to the titanium lag screws.

Clinical relevance: Headless screws are mechanically attractive fixation materials for condylar head fracture treatment.