The biomechanical aspects of reconstruction for segmental defects of the mandible: A finite element study to assess the optimisation of plate and screw factors Péter Bujtár a, b, * ,1 , János Simonovics c,1 , Károly Váradi c , George K.B. Sándor a, d , C.M.E. Avery e a Department of Oral and Maxillofacial Surgery, University of Oulu and Oulu University Hospital, Oulu, Finland b Department of Oral and Maxillofacial Surgery, Southern General Hospital, Glasgow, United Kingdom c Department of Machine and Product Design, Budapest University of Technology and Economics, Faculty of Mechanical Engineering, Budapest, Hungary d BioMediTech, Institute of Biomedical Sciences, University of Tampere, Tampere, Finland e Department of Oral and Maxillofacial Surgery, University Hospitals of Leicester, Leicester, United Kingdom article info Article history: Paper received 7 September 2013 Accepted 13 December 2013 Keywords: Mandible Modelling Biomechanics Stability Finite element analysis abstract A bone plate is required to restore the load-bearing capacity of the mandible following a segmental resection. A good understanding of the underlying principles is crucial for developing a reliable recon- struction. A finite element analysis (FEA) technique has been developed to study the biomechanics of the clinical scenarios managed after surgical resection of a tumour or severe trauma to assist in choosing the optimal hardware elements. A computer aided design (CAD) model of an edentulous human mandible was created. Then 4 common segmental defects were simulated. A single reconstruction plate was designed to span the defects. The hardware variations studied were: monocortical or bicortical screw fixation and non-locking or locking plate design. A standardized load was applied to mimic the human bite. The von Mises stress and strain, spatial changes at the screw-bone interfaces were analysed. In general, the locking plate and monocortical screw fixation systems were most effective. Non- locking plating systems produced larger screw “pull-out” displacements, especially at the hemi- mandible (up to 5% strain). Three screws on either side of the defect were adequate for all scenarios except extensive unilateral defects when additional screws and an increased screw diameter are rec- ommended. The simplification of screw geometry may underestimate stress levels and factors such as poor adaptation of the plate or reduced bone quality are likely to be indications for bicortical locking screw fixation. The current model provides a good basis for understanding the complex biomechanics and devel- oping future refinements in plate or scaffold design. Ó 2014 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved. Introduction The creation of a segmental defect of the mandible is dis- figuring and associated with a significant decrease in oral cavity and upper airway function. Free tissue transfer has become established as the optimum method for reconstructing segmental defects in order to restore bone continuity and recreate form together with function (Goh et al., 2008; Bak et al., 2010). The fibula and DCIA composite flaps are most frequently used whilst the scapula or radial flaps are less commonly appropriate (Urken et al., 1998; Cordeiro et al., 1999; Avery, 2010; Bak et al., 2010). A heavy reconstruction plate, or several lighter plates, is applied to secure the bone element. A single heavy reconstruction plate without a bone graft may occasionally be used for a delayed reconstruction or when a pectoralis major myocutaneous (PMMC) flap is preferred because of advanced disease and substantial co-morbidity (Salvatori et al., 2007; Avery et al., 2010; Onoda et al., 2012). * Corresponding author. Oral and Maxillofacial Surgery, University of Oulu, 90650 Oulu, Finland. Tel.: þ44 7592973847; fax: þ358 5375560. E-mail addresses: bujpet@yahoo.co.uk (P. Bujtár), janos@simonovics.hu (J. Simonovics), varadik@eik.bme.hu (K. Váradi), sandor_george@hotmail.com (G.K.B. Sándor), chrisavery@doctors.org.uk (C.M.E. Avery). 1 Péter Bujtár and János Simonovics equally contributed to the current work and both would act as first author. Contents lists available at ScienceDirect Journal of Cranio-Maxillo-Facial Surgery journal homepage: www.jcmfs.com 1010-5182/$ e see front matter Ó 2014 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jcms.2013.12.005 Journal of Cranio-Maxillo-Facial Surgery xxx (2014) 1e8 Please cite this article in press as: Bujtár P, et al., The biomechanical aspects of reconstruction for segmental defects of the mandible: A finite element study to assess the optimisation of plate and screw factors, Journal of Cranio-Maxillo-Facial Surgery (2014), http://dx.doi.org/10.1016/ j.jcms.2013.12.005