Wear and Bond Strength of Diamond Coatings on TMJ Devices

Diamond coatings have been shown previously to increase the wear resistance of articulating titanium alloy surfaces. Objective: The purpose of this study was to measure the bonding strength and wear properties of two types of diamond coatings on implant prototypes for TMJ applications. Methods: Nanocrystalline (NCD) and multi-layer (MLD) diamond coatings (5-layer coating consisting of alternating nano- and micro-crystalline diamond) were deposited on 4 condyle and 4 fossa Ti alloy components using a chemical vapor deposition (CVD) process. The diamond-coated implants were subjected to 500,000 cycles of wear testing (equivalent to 4.4 years of clinical usage) using a predesigned mandibular simulation machine. An electronic profilometer recorded wear depth tracks and SEM micrographs were used to provide visual evidence of material lost. Bond strength/interfacial toughness of the two types of diamond coatings (2-3µm thickness) on titanium alloy disks (20 indentations total) was determined using a brale indenter at 150 Kg, and a Micro-VU visual measuring microscope was used to measure indention diameter and to note delamination of the coating when it occurred. Results: The mean measured wear track depth on the single layer (nanocrystalline) and the multi-layer (micro+nano) diamond coatings was 0.669 µm and 0.235 µm, respectively. The interfacial toughness calculations were 122 and 130 J/m2 for NCD and MLD, respectively. Only two delaminations were found for both the NCD and MLD specimens. Conclusions: NCD and MLD coatings showed very high wear resistance and extremely high interfacial toughness (bonding strength to Ti alloy) when used as a coating on simulated TMJ substrates. The wear resistance of the multi-layer diamond coatings was significantly higher than the nanocrystalline diamond coatings, indicating that this type of coating is preferred for use on TMJ devices to minimize wear debris. This study was supported by NIDCR Grant # 1 R01 DE 13952-01A1.