Evaluation of stability and stress distributions of titanium and resorbable plates used in genioplasty by finite element analysis

Objective: This study aims to compare the stability and stress responses of titanium and resorbable plates used in genioplasty using the finite element analysis method, and to evaluate the applicability of resorbable plates in this surgical context. Material and Method: Within the scope of the study, a 5 mm anterior advancement genioplasty was performed on a mandibular model. Following the osteotomy line, six different finite element models were created using three different materials (titanium, self-reinforced poly-L/DL-lactic acid [SR-P(L/DL)LA], and hydroxyapatite-reinforced poly-L-lactic acid [HA-PLLA] and two different plate designs (straight plate, genioplasty plate): Model-1: Fixation was achieved using two 4-hole 1 mm thick titanium straight plates (one on each side of the midline) and eight 2×7 mm titanium mini screws. Model-2: Two 4-hole 1 mm thick resorbable SR-P(L/DL)LA (70/30) straight plates and eight 2×7 mm resorbable SR-P(L/DL)LA (70/30) mini screws. Model-3: Two 4-hole 1 mm thick resorbable HA-PLLA straight plates and eight 2×7 mm resorbable HA-PLLA mini screws. Model-4: A 6-hole 1 mm thick titanium genioplasty plate and six 2×7 mm titanium mini screws. Model-5: A 6-hole 1 mm thick resorbable SR-P(L/DL)LA (70/30) genioplasty plate and six 2×7 mm resorbable SR-P(L/DL)LA (70/30) mini screws. Model-6: A 6-hole 1 mm thick resorbable HA-PLLA genioplasty plate and six 2×7 mm resorbable HA-PLLA mini screws. 3D modeling was performed using Blender software, and meshing and analysis were conducted using Altair HyperMesh and Altair OptiStruct programs, respectively. von Mises stress distributions, displacement values, and stress concentration points were examined on the models. Results: The analyses revealed that all plate systems transferred stress and displacement to the bone within physiological limits. The highest amount of displacement was observed in the SR-P(L/DL)LA genioplasty plate model, while the lowest displacement was observed in the titanium straight plate model. The highest von Mises stress value was found in the titanium straight plate model, and the lowest was in the SRP( L/DL)LA genioplasty plate model. The highest tensile and compressive stress values were observed in the SR-P(L/DL)LA genioplasty plate model. Regarding plate design, straight plates provided a more controlled stress distribution and exhibited lower displacement values compared to genioplasty plates. Conclusion: In this study, titanium plates were found to provide high mechanical strength and to result in lower displacement values at the osteotomy site. However, the rigid nature of titanium (due to its high elastic modulus) may lead to bone atrophy in the long term. Resorbable plates, on the other hand, offer a more physiological stress distribution owing to their elastic modulus being closer to that of bone and their ability to gradually transfer load to the bone as they degrade. Among these systems, HA-PLLA plates demonstrated lower stress and displacement values compared to SR-P(L/DL)LA. Furthermore, flat plate designs were found to be more effective than genioplasty plates in terms of stress distribution and stability. Based on these findings, we recommend the use of resorbable flat plate-screw fixation systems due to their superior biomechanical compatibility and physiological stress management. Keywords: Genioplasty, Orthognathic surgery, Resorbable plate, Titanium plate