Diamond-Like-Carbon Coating Over Prosthetic Screws: Analysis Of The Torque Maintenance After Retorque

Background: The retorqueing of fixing screws has become a routine in clinical practice, aiming to reduce the risk of screw loosening; however, there are not in vitro studies that evaluate the effect of this clinical practice in nanofilm-coated screws. The objective of this study was to verify the torque maintenance of prosthetic pillar screws coated with diamond-doped diamond-like nanofilm (DD-DLC), submitted to retorque, after mechanical fatigue, in external (EH) and internal hexagonal connections (IH). Materials and Methods: Different implants and treatments of the prosthetic screws resulted in eight experimental groups (n=5): untreated and not submitted to fatigue (EH-CON) (IH-CON); untreated and fatigued control (EH-F) (IH-F); with DLC nanofilm and fatigued (EH-DLCF) (IH-DLCF) and with DD-DLC nanofilm and fatigued (EH-DD-DLCF) (IH-DDDCLF). The coatings were plasma-deposited through the Plasma Enhanced Chemical Vapor Deposition method. The samples were exposed to one million fatigue cycles; samples were submitted to reverse torque; samples were retorqued; then samples were re-submitted to another one million mechanical cycles. After fatigue, the reverse torque of the screws was performed to determine the torque maintenance. The screws were qualitatively analyzed through a scanning electron microscope. The statistical analysis used ANOVA. Results: There was no interaction between the studied factors. The treatment of screws and connection type did not present significant differences. The coatings did not interfere in the adaptation of the screw to the implant. Conclusion: The prosthetic screws with DLC and DD-DLC nanofilms, after retorque, did not present increased torque maintenance.