On the Wear Assessment of Multilayer Nanocrystalline Diamond Coated Implants of the Temporomandibular Joint
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On the Wear Assessment of Multilayer Nanocrystalline Diamond Coated Implants of the Temporomandibular Joint Malesela J. Papo1, Shane A. Catledge1, Camilo Machado2, Somaieh Kashef1, Alan E. Eberhardt3 and Yogesh K. Vohra1 1 Department of Physics, University of Alabama at Birmingham, AL 35294-1170, U.S.A. 2 Department of Prosthodontics and Biomaterials, University of Alabama at Birmingham, AL 35294-0007, U.S.A. 3 Department of Biomedical Engineering, University of Alabama at Birmingham, AL 352941170, U.S.A. ABSTRACT We deposited multilayer Nanocrystalline Diamond (NCD) thin films on Ti-6Al-4V substrates that were machined to imitate the shapes of the condyle and fossa of the temporomandibular joint (TMJ). We performed low stress wear assessment experiments on condyle/fossa pairs mounted in a custom-built mandibular movement simulator (MMS) for 5 x 105 loaded cycles at 1.2 Hz, which is equivalent to 4.4 years of clinical use. Analysis of wear surfaces on the control and the NCD-coated pairs indicated that no film delamination occurred on the NCD-coated condyle/fossa couple and that wear damage was extensive on the uncoated condyle/fossa pair. The high stress wear tests performed using the Ortho-POD machine at loads of 80 and 165 N showed that loss of film on the condyle specimens occurred after 3300 and 341 cycles, respectively. A subsequent evaluation of the influence of condyle curvature on wear by articulating a multilayer condyle/disk pair at a load of 50 N and 250 000 cycles at 1.2 Hz, showed that film delamination on the condyle occurred after 12500 cycles and no loss of film was observed on the disk after 250 000 cycles of articulation. Our results show that the observed lower film lifetimes on the condyles at high stresses are not related to intrinsic stresses in the film but probably due to lower film adhesion on the curved surfaces of the condyle. INTRODUCTION One of the common causes of prosthesis failure of the temporomandibular joint is due to excessive wear [1]. This failure markedly reduces implant lifespan from weeks to a few years and normally leads to osteolysis of the surrounding bone tissue as a result of wear particle generation [1]. Wear particle generation is due to surface roughening of the articulating components of the prosthesis. Recent studies at the University of Alabama at Birmingham have shown that such a problem can be solved by coating prostheses with nanocrystalline diamond films fabricated by microwave plasma chemical vapor deposition (MPCVD) [1-3]. This work showed that the deposited films could be optimized for low surface roughness, high hardness, low corrosion, and exceptional film adhesion [4]. Limited work on the evaluation of the mechanical properties of such films on TMJ prostheses under low stress conditions showed that the films remain adhered after an equivalent 2 years of clinical use [3]. In this present work, we report results of the study where the articulation lifespan under low loading conditions was increased to 4.4 years. We also assess mechanical wear beha
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