The effect of DLC-coating deposition method on the reliability and mechanical properties of abutment's screws

Objective: To characterize the mechanical properties of different coating methods of DLC (diamond-like carbon) onto dental implant abutment screws, and their effect on the probability of survival (reliability). Methods: Seventy-five abutment screws were allocated into three groups according to the coating method: control (no coating); UMS – DLC applied through unbalanced magnetron sputtering; RFPA-DLC applied through radio frequency plasma-activated (n = 25/group). Twelve screws (n = 4) were used to determine the hardness and Young's modulus (YM). A 3D finite element model composed of titanium substrate, DLC-layer and a counterpart were constructed. The deformation (μm) and shear stress (MPa) were calculated. The remaining screws of each group were torqued into external hexagon abutments and subjected to step-stress accelerated life-testing (SSALT) (n = 21/group). The probability Weibull curves and reliability (probability survival) were calculated considering the mission of 100, 150 and 200 N at 50,000 and 100,000 cycles. Results: DLC-coated experimental groups evidenced higher hardness than control (p < 0.05). In silico analysis depicted that the higher the surface Young's modulus, the higher the shear stress. Control and RFPA showed β < 1, indicating that failures were attributed to materials strength; UMS showed β > 1 indicating that fatigue contributed to failure. High reliability was depicted at a mission of 100 N. At 200 N a significant decrease in reliability was detected for all groups (ranging from 39% to 66%). No significant difference was observed among groups regardless of mission. Screw fracture was the chief failure mode. Significance: DLC-coating have been used to improve titanium's mechanical properties and increase the reliability of dental implant-supported restorations.