Abstract
Mandibular fracture fixation and reconstruction are usually performed using titanium plates and screws, however, there is a need to improve current fixation techniques. Animal models represent an important step for the testing of new designs and materials. However, the validity of those preclinical models in terms of implant biomechanics remains largely unknown. In this study, we investigate the biomechanics of the sheep mandible as a preclinical model for testing the mechanical strength of fixation devices and the biomechanical environment induced on mandibular fractures. We aimed to assess the comparability of the biomechanical conditions in the sheep mandible as a preclinical model for human applications of fracture fixation devices and empower analyses of the effect of such defined mechanical conditions on bone healing outcome. We developed 3D finite element models of the human and sheep mandibles simulating physiological muscular loads and three different clenching tasks (intercuspal, incisal, and unilateral). Furthermore, we simulated fractures in the human mandibular body, sheep mandibular body, and sheep mandibular diastema fixated with clinically used titanium miniplates and screws. We compared, at the power stroke of mastication, the biomechanical environment (1) in the healthy mandibular body and (2) at the fracture sites, and (3) the mechanical solicitation of the implants as well as the mechanical conditions for bone healing in such cases. In the healthy mandibles, the sheep mandibular body showed lower mechanical strains compared to the human mandibular body. In the fractured mandibles, strains within a fracture gap in sheep were generally not comparable to humans, while similar or lower mechanical solicitation of the fixation devices was found between the human mandibular body fracture and the sheep mandibular diastema fracture scenarios. We, therefore, conclude that the mechanical environments of mandibular fractures in humans and sheep differ and our analyses suggest that the sheep mandibular bone should be carefully re-considered as a model system to study the effect of fixation devices on the healing outcome. In our analyses, the sheep mandibular diastema showed similar mechanical conditions for fracture fixation devices to those in humans.
Highlights
IntroductionFixation with plates and screws at the mandible is used as gold-standard in patients with fractures (Champy et al, 1978; Sauerbier et al, 2008; Munante-Cardenas et al, 2015) and segmental resections due to tumors or osteonecrosis (Evans et al, 1995; Shaw et al, 2004; Isler et al, 2018; Rendenbach et al, 2018)
The fixation methods must provide at the fracture site adequate stability, restoring the physiological biomechanical conditions to promote bone healing and provide rapid recovery of the patient
We investigated sheep mandible as an animal model for testing fixation devices and their potential influence on the healing outcome
Summary
Fixation with plates and screws at the mandible is used as gold-standard in patients with fractures (Champy et al, 1978; Sauerbier et al, 2008; Munante-Cardenas et al, 2015) and segmental resections due to tumors or osteonecrosis (Evans et al, 1995; Shaw et al, 2004; Isler et al, 2018; Rendenbach et al, 2018). Standard fixation of simple fractures is performed through load-sharing devices, which is usually achieved with titanium miniplates and monocortical screws along Champy’s ideal lines of osteosynthesis (Champy et al, 1978) The latter helps to reduce the empiricism behind the choice of plate positioning, neutralizing the shear strains exerted at the fracture site, and restoring the physiological strain patterns in the bone tissue. Despite high success rates in both maxillofacial trauma and reconstructive surgery, fixation-related complications remain These include material failure, non-union, and plate-related infections (Shaw et al, 2004; Robey et al, 2008; Seemann et al, 2010; van den Bergh et al, 2012; Gutta et al, 2014; Liu et al, 2016; Rendenbach et al, 2019). To improve current treatment options and to develop and test new approaches, including innovative implant materials, e.g., magnesium alloys (Byun et al, 2020), profound basic research is necessary
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