materials Article Critical Role of Etching Parameters in the Evolution of Nano Micro SLA Surface on the Ti6Al4V Alloy Dental Implants Pankaj Chauhan 1,2 , Veena Koul 2 and Naresh Bhatnagar 1, *   Citation: Chauhan, P.; Koul, V.; Bhatnagar, N. Critical Role of Etching Parameters in the Evolution of Nano Micro SLA Surface on the Ti6Al4V Alloy Dental Implants. Materials 2021, 14, 6344. https://doi.org/10.3390/ ma14216344 Academic Editor: Bruno Chrcanovic Received: 30 August 2021 Accepted: 9 October 2021 Published: 23 October 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/). 1 Mechanical Engineering Department, Indian Institute of Technology, Delhi 110016, India; dr.prachichauhan@gmail.com 2 Centre for Biomedical Engineering, Indian Institute of Technology, Delhi 110016, India; veenak_iitd@yahoo.com * Correspondence: nareshb@mech.iitd.ac.in Abstract: The surface of dental implants plays a vital role in early and more predictable osseointegra- tion. SLA (sandblasted large grit and acid-etched) represents the most widely accepted, long-term clinically proven surface. Primarily, dental implants are manufactured by either commercially pure titanium (CP-Ti) or Ti6Al4V ELI alloy. The acid etch behavior of CP-Ti is well known and its effects on the surface microstructure and physicochemical properties have been studied by various researchers in the past. However, there is a lack of studies showing the effect of acid etching parameters on the Ti6Al4V alloy surface. The requirement of the narrow diameter implants necessitates implant manufacturing from alloys due to their high mechanical properties. Hence, it is necessary to have an insight on the behavior of acid etching of the alloy surface as it might be different due to changed com- positions and microstructure, which can further influence the osseointegration process. The present research was carried out to study the effect of acid etching parameters on Ti6Al4V ELI alloy surface properties and the optimization of process parameters to produce micro- and nanotopography on the dental implant surface. This study shows that the Ti6Al4V ELI alloy depicts an entirely different surface topography compared to CP-Ti. Moreover, the surface topography of the Ti6Al4V ELI alloy was also different when etching was done at room temperature compared to high temperature, which in turn affected the behavior of the cell on these surfaces. Both microns and nano-level topography were achieved through the optimized parameters of acid etching on Ti6Al4V ELI alloy dental implant surface along with improved roughness, hydrophilicity, and enhanced cytocompatibility. Keywords: dental implants; osseointegration; titanium alloy; acid etching; microtopography; nanotopography 1. Introduction Dental implants were introduced by Brånemark in 1960 for the replacement of missing teeth [1]. The well documented long term clinical result favors titanium and its alloy as the gold-standard material for dental implant application [2–4]. Titanium exhibits the best combinations of properties like strength, corrosion resistance, and biocompatibility as desirable for the bone–implant application. According to the ASTM standard, six types of titanium are available for biomedical implant applications including four grades of commercially pure titanium and two alloy forms (Ti6Al4V and Ti6Al4VELI grade). CP-Ti is an unalloyed pure form of titanium that contains only traces of other elements (i.e., carbon (C), nitrogen (N), oxygen (O), and iron (Fe). From Grades 1–4, there is an increase in oxygen content, which improves the mechanical properties of titanium. However, the alloy exhibits better mechanical properties than all grades of CP-Ti [3]. Ti6Al4V and Ti6Al4V-ELI alloys have a biphasic composition consisting of alpha and beta phases. Aluminum in these alloys act as an alpha phase stabilizer and vanadium acts as a beta phase stabilizer. Ti6Al4V ELI has a low concentration of interstitial elements O and C, which improves ductility compared to Ti6Al4V [3]. Materials 2021, 14, 6344. https://doi.org/10.3390/ma14216344 https://www.mdpi.com/journal/materials