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.

Finite element analysis of a tandem screw configuration in sagittal split osteotomy using biodegradable osteosynthesis screws.

The goal of the present study was to determine the mechanical stability of selected osteosynthesis screws in a paired linear configuration in cases of bilateral sagittal split osteotomy of the mandible. A mandible model was created that consisted of 22,846 elements and 4,879 nodes. The following screws were tested in the tandem screw configuration: the poly-L-lactic acid (PLLA) in accordance with Harada and Enomoto, the Isosorb screw (Aesculap, Germany), the BioSorbFX screw (Bionix Implants, Finland), and the Lactosorb screw (WL. Lorenz, USA). The mechanical parameters of the materials studied were adopted from the literature or were based on manufacturer information. With the precondition that the materials each be stressed to the ultimate tensile strength, the following chewing forces could be neutralized: 100 N by 2.0-mm titanium mini-screws, 117.5 N by PLLA screws in accordance with Harada and Enomoto, 90.0 N by Isosorb screws, 89.0 N by BioSorbFX screws, and 35.0 N by Lactosorb screws. Here the peri-implant bone was stressed within limiting values with the titanium miniscrew, and the PLLA screw according to Harada and Enomoto, but not the osteosynthesis material itself. The finite element method (FEM) appears suitable for simulating complex mechanical stress situations in the maxillofacial area. As a result, significant time and materials (animal tests) can be saved when developing new or modified materials

[Finite element assisted study of the mechanical stability of 2 selected osteosynthesis systems for mandibular osteotomy]. / FEM-gestützte Untersuchung zur mechanischen Stabilität zweier ausgewählter Osteosynthesesysteme bei der sagittalen Unterkieferosteotomie.

The aim of this study was to use the finite element method (FEM) to compare the stability of 2.0 mm titanium screws in a triangular configuration with that of a 2.0 mm titanium miniplate as osteosynthesis material following bilateral sagittal split osteotomy. To this end, a model of the mandible was produced, consisting of 19,854 elements and 4285 nodes. The mechanical parameters of the materials investigated were taken from the literature or notified by the manufacturer. On condition that the materials were subjected only to their respective ultimate tensile stress, it was possible to neutralise the following masticatory force: 124.6 N with the miniplate and 167.5 N with the bicortical triangular screw configuration. The limitation of stress ensued from the peri-implant bone and not from the osteosynthesis material per se. The finite element method (FEM) appears to be suitable for simulating complex mechanical stress situations in the maxillofacial area, as also demonstrated by the fact that our data agree with those in the literature and with clinical experience. It will enable considerable savings to be made in terms of time and materials (animal experiments) in the future development of osteosynthesis materials and techniques.

Finite-element-analysis of different screw-diameters in the sagittal split osteotomy of the mandible.

A three dimensional finite element model of the mandible was developed to simulate and study the biomechanical loads of osteosynthesis screws in bilateral sagittal osteotomy. Using the finite-element method clinical conditions were simulated. Different bicortical screw configurations and diameters were evaluated. When bite forces were applied, the most stable configuration was found to be a triangular one. This confirms the results found in the literature. A mini screw of 2.0 mm diameter can provide sufficient stability at the osteotomy site after ramus split osteotomy. Even screws with a diameter of 1.5 mm would withstand forces up to 89.5 N, which would not normally be reached by patients after ramus split osteotomy in the early period of healing. Forces exerted by patients after bilateral ramus split osteotomy do not exceed these values. The finite-element analysis appears to be an adequate method to evaluate this clinical question of interest. It might well replace mechanical models and the results are comparable with those reported in the International literature.