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Plast Reconstr Surg Glob Open. 2016 Sep 8;4(9):e858. eCollection 2016 Sep.

Metallic Fixation of Mandibular Segmental Defects: Graft Immobilization and Orofacial Functional Maintenance.

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1
Department of Mechanical Industrial and Manufacturing Engineering, University of Toledo, Toledo, OH; and Department of Plastic Surgery, The Ohio State University, Columbus, OH.

Abstract

The aim of this study is to investigate the behavior of the healthy mandible under maximum molar bite force to demonstrate the problems associated with the current standard of care procedures for mandibular segmental defect reconstruction (ie, use of Ti-6Al-4V hardware and either a single- or double-barrel fibular graft). With current Ti-6Al-4V mandibular reconstruction hardware, there is a significant stiffness mismatch among the hardware, graft, and the remaining host anatomy. How the distribution of mechanical forces through the mandible is altered after a segmental bone loss and reconstruction is incompletely understood.

METHODS:

We studied a healthy adult mandible for stress, strain, and reaction force distribution during normal mastication. Stress distribution of this model was then used to study problems encountered after mandibular segmental defect reconstructive surgery. We model the use of both single- and double-barrel fibular grafts to repair the loss of the left M1-3 containing segment of the mandible. These simulations were done using 2 sets of plates with different thicknesses.

RESULTS:

We found that the stiffness mismatching between the fixation hardware and the graft and host bone causes stress shielding of that bone and stress concentrations in the fixation hardware and screws. These effects are expected, especially during the bone healing period. However, long term, this abnormal stress-strain distribution may lead to either the hardware's failure due to stress concentration or graft failure due to bone resorption as a result of stress shielding. We found that the stress-strain distribution is more normal with a double-barrel fibular graft. Additionally, we found that thinner fixation plates can reduce stress shielding.

CONCLUSION:

The proposed model can be used to evaluate the performance and optimization of the fixation device.

Conflict of interest statement

The authors have no financial interest to declare in relation to the content of this article. This study was supported by Ohio Third Frontier Technology Validation and Startup Fund (TVSF) grant 15-791. The Article Processing Charge was paid for by the Department of Plastic Surgery, The Ohio State University (Columbus, OH).

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