Clinical and Experimental Investigation on Load-related Reconstruction Plate Deformation after Segmental Mandibulectomy

Introduction: Segmental mandibulectomy is indicated for primary tumors of the oral cavity which involve the mandible. Several methods of mandibular reconstruction after ablative surgery are described. One basic step is bone bridging of the defect by reconstruction plates. Whereas the mechanical behaviour and material characteristics of plate system are well described, less is known about the dynamic load related behaviour to of the plate systems under in vivo conditiones. Fracture of the plates and screws are a major problem in the long term clinical outcome of patients. Insight into the load related biomechanics under experimental conditions and in the clinical setting is important to improve the design of plating systems. Material and methods: We studied experimentally the load dependent plate deformation (Synthes Unilock 2,4 plate) after mandibulectomy and reconstruction of human mandibles in a specially designed device. Definitive loads were applied and the subsequent plate deformation recorded by strain gauges. Additionally we investigated in vivo the load related reconstruction plate deformation after segmental mandibulectomy (anterior segment and corpus segment resection). Patients were reconstructed with rigid plates and strain gauges were applied extraorally to the reconstruction plate. Plate deformation was determined in dependence of mastication loads and compared to the biomechanics found in the experimental setting. Results: Our investigation allows numerical quantification of plate deformation after segmental mandibulectomy in vivo and in vitro. We found maximun deformations near the plate angle under experimental settings about 400 to –200 µstrains. Under in vivo settings maximum deformations between 1000 to –500 µstrains were measured during mastication load at different strain gauges localisation. Conclusion: The determination of load related reconstruction plate deformation by strain gauges allows quantification of surface deformation during mastication. Knowledge about the complex strain behaviour after segmental mandibulectomy is important to improve the design of plating systmes.