# Virtual Zirconia Implants Replace Titanium Implants?
## 4 Osteointegration  
Osseointegration is a term from the Latin language where osseous means \"bony\" and integrare \"to make whole\", and it is defined as a \"function ankylosis\" [49]. Similar to in titanium implants, the osseointegration of zirconia implants is a dynamic process composed of primary stability and secondary stability. Immediately after implant placement, mechanical fixation of the implant provides primary stability, which is direct contact between the bony walls and the implant. It is considered biomechanical stability as there is no biological activity. On the other hand, the secondary biological stability results from the cellular activity with new bone deposition on the implant surface, giving rise to the functional ankylosis [50; 51]. Figure 2: Schematic illustration of advantages and drawbacks of titanium implants. At the histological level, osteointtegration is an active process that evolves basically two phases: the establishment of the implant in the recipient site and its maintenance. A classical study performed by [PERSON] and colleagues [52] elucidates the implant wound healing progression. Briefly, after the titanium is placed in the drilled site, the implant bed is filled with blood from the marginal tissue, and threads of the implant assure the primary stability in direct contact with the surrounding bone. A water molecule forms a pellicle in the implant surface, which facilitates the adhesion of intracellular matrix proteins provided by the blood cells and interstitial fluid [53]. These proteins assist cell adhesion, migration, and differentiation. Next, when hemostasis is achieved and the blood clot is formed, the inflammatory cells are attracted to the wound site, and give rise to the granulation tissues, and fibroblast-like cells can be encountered in the implant zone area. One week after the implant placement, the provisional matrix replaces the granulation tissues, and the first signs of woven bone are present. Between one and two weeks, the bone tissues between the threads, responsible for primary mechanical stability, began to be reabsorbed by osteoclasts, and new viable bone became deposited. Between eight to twelve weeks, the mature bone can be found to be surrounded by bone marrow [52; 54; 55]. Overall, titanium and zirconia implants present the same bone tissue integration [56]. However, microstructure and implant surface modification methods play a key role in osseointegration. These implant modifications are made to improve mechanical properties of the implants like strength, ductility, biological function, bacterial adhesion, wear, and fracture toughness. This has been well demonstrated in the literature for titanium implants [57; 58; 59; 60; 61]. Basically, the surface modifications can be prepared by physical or chemical methods. Among physical modifications can be cited maching, grit-blasting, acid-etching, laser ablation, and nanocomposite. Regarding the chemical modification, examples that can be mentioned are crystalline deposition, oxidation, fluoride treatment, UV treatment, and hydroxyapatite addition [62; 63]. Surfaces with proper roughness and hydrophilicity are prone to promote more osseointegration than other surfaces. The most common surface modifications in clinical practice are SLA, SLAActive, Osseotite, and TiUnite. SLA has a rough surface produced by sandblasting with large grit followed by mixed acid etching with hydrochloric and sulfuric materials. The SLAActive surface is prepared by rinsing SLA-treated implants under a nitrogen atmosphere and storing them in NaCl solution rather than placing them in dry storage. The Osseotite surface is a rough surface with a uniform micro-texture produced by the dual-acid (HCl-H\({}_{2}\)SO\({}_{4}\)) etching method. Lastly, TiUnite results from the oxidation process in which implants are treated in a galvanic cell containing phosphoric acid electrolyte. The TiUnite surface is characterized by a thick TiO\({}_{2}\) layer enriched with highly crystalline calcium phosphate [19; 64; 65; 66].