Finite element analysis of patient-specific TMJ implants to replace bilateral joints with simultaneous correction of facial deformity

Abstract

Introduction: Finite element analysis (FEA) is a method to mimic the biomechanical behaviour of an object under various loading scenarios, and may be used during virtual planning of the TMJ prosthesis. Here we present an interesting case report where FEA was done to biomechanically evaluate patient specific total joint replacement prosthesis for bilateral TMJ replacement.

Case report: A 22 year old young girl visited our outpatient clinic with a chief complaint of retruded chin and limited mouth opening for the last 15 years. After clinical and radiographic examination, her corrective surgery was virtually planned on Mimics software. The Implants were studied under simulated loading scenarios in ANSYS to understand the structural integrity of the implant for different loading conditions.

Results: Maximum Von-Mises Stress on Condylar component is 151.9 MPa and Maximum Von-Mises Stress on Fossa component is 0.377 MPa. The minimum safety factor of the fossa component was about 15, which is safe enough to complete 100 million cycles. The maximum von-mises stress were detected at the screw holes in the condylar components of the implant. The screw holes were therefore the areas prone to highest chance of failure in the design.

Conclusion: We conclude that FEA based biomechanical analysis is important prerequisite during customized reconstruction of TMJ. In today's scenario of patient specific TMJ reconstruction, FEA based designing and planning of stress distribution along the bone and calculation of maximum strain in the prosthesis, further aids in the proper designing of this implant and enhances the post-operative clinical results.

Keywords: Alloplastic TMJ reconstruction; Facial deformity; Finite element analysis; Maxillary cant; Patient specific TMJ implant; TMJ Ankylosis.

Fig. 1a

Virtual planning includes counterclockwise rotation of maxillomandibular complex to increase posterior midfacial height, ramus height and chin.

Fig. 1b

Virtual model for FEA.

Fig. 1c

The loading scenario when a 360 N load acted on the a). Molars, b). Incisors in a downward direction.

Fig. 2a

Von mises stress on fossa and condylar component after maximum loading forces on molars.

Fig. 2b

Von mises stress on fossa and condylar component after maximum loading forces on incisors.

Fig. 2c

Safety Factor: Condyle and glenoid fossa- Loading at molars and Loading at incisors.