coatings Article Nanotubular Oxide Layer Formed on Helix Surfaces of Dental Screw Implants Magdalena Ja ˙ zd˙ zewska * and Michal Bartma ´ nski   Citation: Ja˙ zd ˙ zewska, M.; Bartma ´ nski, M. Nanotubular Oxide Layer Formed on Helix Surfaces of Dental Screw Implants. Coatings 2021, 11, 115. https://doi.org/10.3390/ coatings11020115 Received: 11 December 2020 Accepted: 18 January 2021 Published: 20 January 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Faculty of Mechanical Engineering and Ship Technology, Gda´ nsk University of Technology, Narutowicza 11/12, 80-233 Gda ´ nsk, Poland; michal.bartmanski@pg.edu.pl * Correspondence: magdalena.jazdzewska@pg.edu.pl; Tel.: +48-58-347-17-96 Abstract: Surface modification is used to extend the life of implants. To increase the corrosion resistance and improve the biocompatibility of metal implant materials, oxidation of the Ti-13Nb- 13Zr titanium alloy was used. The samples used for the research had the shape of a helix with a metric thread, with their geometry imitating a dental implant. The oxide layer was produced by a standard electrochemical method in an environment of 1M H 3 PO 4 + 0.3% HF for 20 min, at a constant voltage of 30 V. The oxidized samples were analyzed with a scanning electron microscope. Nanotubular oxide layers with internal diameters of 30–80 nm were found. An analysis of the surface topography was performed using an optical microscope, and the Sa parameter was determined for the top of the helix and for the bottom, where a significant difference in value was observed. The presence of the modification layer, visible at the bottom of the helix, was confirmed by analyzing the sample cross-sections using computed tomography. Corrosion tests performed in the artificial saliva solution demonstrated higher corrosion current and less noble corrosion potential due to incomplete surface coverage and pitting. Necessary improved oxidation parameters will be applied in future work. Keywords: nanotubular oxide; helix surfaces; dental implants; roughness; corrosion properties 1. Introduction Titanium and its alloys are nowadays among the most popular biomaterials, called the “gold standard” for endosseous dental implants, even if some adverse reactions may be expected. They possess a lot of important properties, such as their low density, suitable fatigue strength, Young’s modulus and specific tensile strength, high resistance to brittle cracking, high corrosion resistance, and the best biocompatibility. Despite that, titanium and its alloys need surface modifications for early osseointegration [1,2]. The type of commercial implant determines surface topography and differences in geometry [3]. Surface modification is nowadays an obligatory treatment of dental implants. Bioac- tivity of the surface resulting in adhesion of osteoblasts and bone ingrowth can be achieved by the development of surface roughness, creation of bioactive films, and deposition of coatings [2]. Many different methods have been used to change the surface roughness of dental implants, including mechanical techniques such as grinding, polishing, machining, sandblasting and attrition, chemical etching in acids, alkali and fluorides, electrophoretic deposition, and laser treatments [4–11]. The interaction of cells and adsorption of proteins depends on surface structure and is significant in the presence of nanometric pores, which increase the rate of osseointegra- tion and biomechanical fixation [2,7,8,12–17]. A significantly higher bone contact of 27% (p < 0.05) was observed in nanotextured compared to machined implants [18]. However, reproducibility of nanoscale surface profiles of titanium with chemical modifications such as acid-etching is quite difficult to achieve and unreliable, and knowledge on the ideal surface roughness parameters for rapid osseointegration is still lacking [19,20]. Coatings 2021, 11, 115. https://doi.org/10.3390/coatings11020115 https://www.mdpi.com/journal/coatings