Stresses, friction, and wear on different materials and design for temporomandibular joint total joint replacement (TMJ TJR)

The purpose of the present study was to evaluate the coefficient of friction, wear volume, surface damage, and contacting stresses regarding different materials and condyle design for alloplastic temporomandibular joint total joint replacement (TMJ TJR). Spherical- and anatomical-shape condyle specimens were prepared from CoCrMo or Ti6Al4V alloys which were assessed against ultra-highly molecular weight polyethylene (UHMWPE) square specimens. On the wear assessment, reciprocating sliding pin-on-plate wear tests were performed considering usual TMJ TJR motion on 30 N normal loading, 1 Hz sliding frequency, and 4-mm linear stroke length for 60 min. Wear tests were performed in Ringer's solution at 37^o C to mimic the surrounding environment. The coefficient of friction and wear volume were recorded for the two condyle design and materials’ pairs. The von Mises stresses and displacement were calculated using a 3D finite element model (FEM) simulation built on tetrahedral linear elements, performed relatively to the condyle-to-UHMWPE central axis. On anatomical TMJ TJR condyle, von Mises stresses were lower when compared to standard TMJ TJR condyle. Wear tests showed a low wear volume of UHMWPE against Ti6Al4V although the volume loss recorded for UHMWPE was lower on the anatomical-shape condyle than that for the spherical design. Scanning electron microscopy revealed plastic deformation on the UHMWPE resulting in ploughing and materials’ degradation after wear testing. Thus, an anatomical TMJ TJR condyle design revealed lower stress distribution and wear volume when compared to a standard TMJ TJR condyle that could improve the long-term mechanical integrity of TMJ TJR over cyclic loading.