Medical Engineering & Physics 20 (1998) 565–572 Stress analysis of the human temporomandibular joint J. Chen a,b,* , U. Akyuz a , L. Xu a , R.M.V. Pidaparti a a Department of Mechanical Engineering, Indiana University, Purdue University at Indianapolis, 723 W. Michigan St., Indianapolis, IN 46202, USA b Department of Orthodontics, School of Dentistry, Indiana University, Biomechanics and Biomaterials Research Center, IUPUI, Indianapolis, IN 46202, USA Received 9 July 1998; received in revised form 14 August 1998; accepted 9 September 1998 Abstract Stress analysis of the human temporomandibular joint (TMJ) consisting of mandibular disc, condyle and fossa–eminence complex during normal sagittal jaw closure was performed using non-linear finite element analysis (FEA). The geometry of the TMJ was obtained from magnetic resonance imaging (MRI). The tissue proportion was measured from a cadaver TMJ. Contact surfaces were defined to represent the interaction between the mandibular disc and the condyle, and between the mandibular disc and the fossa– eminence complex so that finite sliding was allowed between contact bodies. Stresses in the TMJ components (disc, condyle and fossa–eminence complex), and forces in capsular ligaments were obtained. The results demonstrated that, with the given condylar displacement, the stress in the condyle was dominantly compressive and in the fossa–eminence complex was dominantly tensile. The cancellous bone was shielded by the shell shaped cortical bone from the external loading. The results illustrate the stress distributions in the TMJ during a normal jaw closure.  1998 IPEM. Published by Elsevier Science Ltd. All rights reserved. Keywords: Stress analysis; Temporomandibular joint; Finite element analysis 1. Introduction Previous research has shown that the temporomandib- ular disorders (TMDs) are closely related to overload of the joint. Overload may be due to clenching, bruxism, trauma, and stress induced muscle tension. Irregular con- dyle–disc relation (internal derangement) is also corre- lated to TMDs [1]. It may be the consequence of the joint overload, and may significantly increase the load within the TMJ. To understand the TMJ overload, the relationship between the condylar displacement and TMJ load needs to be established, and the resulting stresses in the joint need to be understood. Unfortunately, the information is not available at present. Previous analytical or computational investigations of TM joint biomechanics have been restricted to finding the reaction force on the condyle [2–8]. These studies assumed TMJs as hinges and joint reactions were calcu- lated based on equilibrium equations. Only few studies have been done on the state of stress within the condyle * Corresponding author. Tel.: (317) 274-5918; Fax: (317) 274-9744 1350-4533/98/$19.00  1998 IPEM. Published by Elsevier Science Ltd. All rights reserved. PII:S1350-4533(98)00070-8 and the fossa–eminence complex [9–11]. Iwata et al. [9], Korioth et al. [10] and Tanaka et al. [11] created FEA models of the entire human mandible, including the TM joint. No sliding was allowed along the disc–condyle and the disc–fossa interfaces, which violated the boundary constraints of the disc. In the above mentioned studies, the muscle forces were represented by force vectors. The assumed muscle recruitment pattern was never validated. Thus, estimates of TMJ forces from these models were thought to be too imprecise [8,12]. Chen and Xu [13] have created a 2-D FEA model of the human TMJ disc to calculate the stresses and the contact stresses along the upper and lower articulating surfaces. By using measurable condylar displacements as input, this model does not need to estimate the muscle forces and stresses in the disc can be calculated. How- ever, the model did not include the other joint compo- nents such as the condyle and fossa–eminence complex as well as the non-linear material behavior of the disc. In this study, stresses in the TMJ components con- sisting of disc, condyle, and fossa–eminence complex were investigated using FEA. The non-linear geometric and material behavior of the cartilage and ligaments