Effect of Simulated Toothbrushing on the Surface Topography and Electrochemical Stability of Ta2O5- and ZrO2-Coated Commercially Pure Titanium

Ti owes its clinical durability to a protective passive oxide film; however, repetitive toothbrushing and fluoride exposure may disrupt this interface and increase its susceptibility to tribocorrosion. This in vitro study investigated the electrochemical behaviour and surface integrity of commercially pure titanium (CpTi) grade II coated with Ta2O5 or ZrO2 after simulated toothbrushing. CpTi discs were divided into three groups: CpTi, CpTi/Ta2O5, and CpTi/ZrO2. The coatings were deposited by reactive DC magnetron sputtering. Film thickness and adhesion were assessed by step-height and tape tests. Simulated toothbrushing was performed for 22,080 cycles/2 Hz under a load of 200 gf in either Fusayama artificial saliva (AS) or a fluoridated dentifrice (FD) slurry with AS (1:2 w/w). Surface morphology, elemental composition, topography, roughness, crystalline structure, and wettability were evaluated using SEM/EDS, AFM, XRD, and static and dynamic contact angle (CA) measurements. Electrochemical behaviour was assessed by OCP, EIS, and potentiodynamic polarisation. Toothbrushing induced cyclic OCP shifts consistent with depassivation and repassivation, with surface- and medium-dependent electrochemical responses (p ≤ 0.001). CpTi exhibited a more active electrochemical state, higher icorr, and more pronounced surface alterations. Both coatings significantly improved icorr and corrosion rate (CR) (p < 0.001). Ta2O5 provided the greatest electrochemical protection, reducing the CR by approximately 95% versus 77% for ZrO2. Topographical response to F brushing was also surface-dependent (p < 0.001). Roughness was unchanged after corrosion but surface-dependent after toothbrushing (p < 0.001), while wettability increased after corrosion (p ≤ 0.003) and CAH was surface-dependent (p = 0.003). Within the limitations of this in vitro study, Ta2O5 and ZrO2 coatings enhanced the electrochemical response of CpTi under simulated oral-hygiene challenges, with Ta2O5 providing the strongest overall protection, suggesting that oxide surface modification is a promising strategy for improving the tribocorrosion behaviour of Ti-based dental materials.