2014 IR&D Annual Report

The Development of a Dynamic Finite Element Model of the Temporomandibular Joint (TMJ) and Study of Joint Mechanics, 18-R8386

Principal Investigators
Daniel P. Nicolella
Jessica S. Coogan
Travis D. Eliason
Todd L. Bredbenner

Inclusive Dates: 04/01/13 – 10/01/14

Background — Disorders of the temporomandibular joint (TMJ) result in an annual cost of $4 billion and affect approximately 16 to 59 percent of the population. TMJ disorder (TMD) causes pain in the jaw when speaking or chewing that is often associated with clicking and popping of the jaw and can limit a person's ability to open their mouth. Women ages 20 to 40 are the most prevalent suffers of TMD. Various studies indicate that women with TMD outnumber men anywhere from 3:1 to 8:1. While the causes of TMD are not completely understood, it is thought that alterations in joint mechanics due to osteoarthritis (OA) or trauma results in degradation and inflammation of the joint soft tissues (cartilage and disc), which then results in pain and limited motion. In addition, displacement of the TMJ disc is also associated with TMD. The dynamic mechanical environment within the TMJ during chewing or clenching is not well characterized due to the complexity of the anatomy and materials. Within the TMJ research community, the question of how soft tissue properties and geometry of the joint affect the mechanical environment has gone unanswered and is the focus of this project.

Figure 1. Dynamic finite-element model of the skull mandible, TMJ and associated active 
			muscles.
Figure 1. Dynamic finite-element model of the skull mandible, TMJ and associated active muscles. Muscle activation dynamics are determined using a novel feedback controller incorporated directly into the finite element analysis code.

Approach — The primary objectives of this program were to:

  • Develop a detailed dynamic finite element model of the TMJ and mandible from head CT scans.
  • Determine muscle activation timings and magnitude to achieve dynamic mouth opening and closing using a new a proportional–integral–derivative (PID) controller method.
  • Perform sensitivity analyzes of TMJ disc properties to determine the importance of those properties in the resulting forces and stresses of the TMJ during normal mandible movements.
  • Implement an element erosion or damage material model for the TMJ disc to investigate the effects of disc degeneration on the muscle forces required for normal mandible movements.
  • Develop a statistical shape model of the TMJ coupled with the dynamic finite element model.
  • Using the FE-coupled statistical shape model, investigate the effect of gender differences on TMJ stress.

Accomplishments — There are three major accomplishments resulting from this project that significantly advance the field of TMJ biomechanics and will form the basis of a new research project. First, we have developed a high-fidelity, anatomically accurate, finite-element model of TMJ mechanics that is governed by the internal generation of muscle forces to achieve a specific functional goal (such as chewing), paralleling how functional joint motion is produced in vivo (Figure 1). Second, we have modified this new model by incorporating statistical shape modeling methods to efficiently describe variation in human anatomy that occurs between individuals and within populations and to investigate how these variations, particularly anatomical differences between TMD patients and normal individuals, affect TMJ mechanics. Third, we have developed and implemented a new method of determining the time history of internal muscles forces using a feedback model paradigm that improves model efficiency by more than an order of magnitude compared to current muscle force optimization methods. In combination, these new capabilities will allow us to investigate TMJ mechanics both at the length scale of the tissues comprising the joint while simultaneously accounting for anatomical variability at the population level that has been heretofore impossible but nonetheless necessary to understand the link between joint mechanics and disease.

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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 10 technical divisions.
04/15/14