Study by finite element method of the mechanical stress of selected biodegradable osteosynthesis screws in sagittal ramus osteotomy

We tested the stability of the bilateral sagittal split osteotomy using four resorbable osteosynthesis screws (the PLLA screw introduced by Harada and Enomoto, the Isosorb® screw, the BioSorbFX® screw and the Lactosorb® screw) which are all currently in clinical use. The distribution of stress in both the bicortically inserted screws and the adjacent bone of a computer-generated mandible was recorded by the three-dimensional finite element method. The stress of the materials under investigation was postulated to have reached threshold values for stability, and maximum chewing forces of 132 N (Harada and Enomoto), 117 N (Isosorb®), 115 N (BioSorbFX®) and 46.4 N (Lactosorb®) were determined. As far as the postoperative chewing forces were concerned, all four screws were sufficiently stable at the osteotomy gap. Finite element modelling seems to be an appropriate method of investigating these clinical issues when the mechanical stress both in implants and in the adjacent bone is taken into account.