Effectiveness of Screw Surface Coating on Zirconia Abutment Stability after Loading

Objective: In an attempt to prevent screw-loosening problem, abutment screws with surface treatment were developed. Thus, the aim of the current study was to evaluate comparatively the effectiveness of titanium alloy screws with tungsten-doped diamond-like carbon (W-DLC) coating and non-coated screws on the stability of ZrO₂-ceramic abutments before and after cyclic loading, as soon as observe possible microdamaging in the structure of the components using a scanning electron microscope (SEM). 

Method: Twenty prefabricated ZrO₂-ceramic UCLA abutments (Neodent – Implante Osteointegrável) were tightened to 20 Ncm on their respective external hex implants and divided equally into 2 groups (n=10), according to the type of screws used: (A) non-coated titanium alloy screw (Ti); (B) titanium alloy screw with W-DLC coating (W-DLC/Ti). The reverse torque value (preload) of the abutment screw was measured before and after loading. The tests were performed according to ISO norm 14801. A cyclic loading (0.5 x 10⁶; 15 Hz) between 11 - 211 N was applied. Group means were calculated and compared using ANOVA and F tests (α=.05). SEM analysis was conducted before and after loading at the implant-abutment interfaces and screw surfaces. 

Result: Before cyclic loading, the mean of Ti group was significantly higher than the W-DLC/Ti group (p=0.021). After cyclic loading, both means decreased significantly, with no significant differences between them (p=0.499). The SEM images showed structural damage when the matting surfaces of the abutments were compared before and after loading. 

Conclusion: (1) the reverse torque before loading for Ti screws required higher force than W-DLC/Ti screws; (2) the two abutment screw types presented similar effectiveness in maintaining preload after loading; (3) the significant decrease in reverse torque values and the microdamaging detected at SEM analysis indicate that patient follow-up is needed to ensure the integrity of the ZrO₂-ceramic single-implant restorations.