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

Abstract

Background: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.

Finite Element Simulation and Additive Manufacturing of Stiffness-Matched NiTi Fixation Hardware for Mandibular Reconstruction Surgery

“…The bite force created by masticatory muscles is the greatest source of stress that is usually applied to the mandible [ 4 , 51 , 52 ]. Our FEA models the peak masticatory load.…”

Fixation Release and the Bone Bandaid: A New Bone Fixation Device Paradigm

“…Previous studies have demonstrated the stress shielding effect, using FE analysis, on a reconstructed mandible with standard of the care Ti-6Al-4V fixation plates [ 4 ]. In a recent work, the use of stiffness matched porous fixation plates have been proposed for the reconstruction surgery to address the stress shielding problem [ 25 ]. However, using low stiffness plates decreased the level of immobilization during the healing period.…”

“…These grafts often resorb if they are placed in areas that have little load and a poor blood supply. When the chips are used in combination with a vascularized graft, the microsurgically implanted vascular fibular graft includes a vascular predicle (i.e., a blood supply) [ 25 ].…”

Metals for bone implants: safety, design, and efficacy

“…These muscles maintain their tone even when the mandible is at rest. The amount of muscle force applied during chewing depends on many factors including food hardness, occlusion state (repositioning or chewing), biteloading conditions (balanced or unbalanced loading, bilateral or unilateral loading, grinding, or clenching), and the location of the teeth which are relative to the muscles and the balancing side jaw joint [121][122][123]. Hence, mastication is a complicated process involving motion of the mandible in multiple directions.…”