Influence of Surface Roughness on the Adhesion of Hydroxyapatite Coatings to Titanium and Titanium Alloy Surfaces: A Systematic Review of in vitro Experimental Studies

This systematic review gathered evidence to identify the influence of roughness on titani-um surfaces on the adhesion of hydroxyapatite coatings. This research followed the PRISMA guidelines and was registered on the Open Science Framework (osf.io/cxrsf). In vitro stud-ies were searched on Science Direct, PubMed, Embase, Scopus, Google Scholar and in the references of the articles included. Two independent reviewers selected the studies based on the inclusion and exclusion criteria. The risk of bias analysis was carried out using the adapted Joanna Briggs Institute quasi-experimental study tool. 2890 articles were found and after applying the selection criteria 22 were chosen to be read in full. 9 studies were excluded because they did not evaluate substrate roughness or coating adhesion. Finally, 13 studies composed this systematic review. Of these, 4 indicated that greater titanium rough-ness provides better adhesion of the hydroxyapatite coating, 7 that in addition to roughness, other factors play a role in this process, and 2 other studies presented divergent results. Surface roughness has influence on the adhesion of hydroxyapatite coatings to titanium. However, the type of titanium alloy, the thickness of the coating and other characteristics also affect the adhesion process and should be considered