Dental implants have become a well-established treatment method for oral rehabilitation after tooth loss. Pure titanium is still the material of choice when it comes to dental intraosseous implants and has been used for decades. However, titanium implants have esthetic limitations, especially in the front aspect of the maxillary jaw. The recession of the gingiva can lead to visible implant necks. Furthermore, titanium may cause immunological reactions with early local infection and possible risk for implant loss [1]. Ceramic implants are proclaimed as a new alternative to titanium implants. The first tooth-colored ceramic implants were inferior to titanium-based implants due to their biomechanical characteristics such as low fracture toughness [2]. In the 1980s, the Tübinger immediate implant was introduced, fully made of aluminum oxide (AL₂O₃), but was withdrawn from the market because of high fracture rates [3]. Other investigations on different AL₂O₃ implants found less bone-implant contact compared to titanium [4] as well as reduced survival rates [2, 5]. Since the introduction of yttrium-stabilized tetragonal zirconia polycrystalline (Y-TZP)-based implants, it could be shown that these implants show high similarity in osseointegration compared to titanium implants [2].

Titanium implants with smooth or roughened surfaces have shown high success rates in various indications [2, 6, 7]. Surface characteristics of dental implants, as a new development over the last decades, are seen as an important factor that affects osseointegration, especially in compromised patients (e.g., following radiation therapy, bone augmentation, class D4 bone) [8]. By improving the implant design, implant material, and implant surface characteristics as well as surgical techniques and implant loading conditions, osseointegration can be affected [9]. Several new techniques are performed nowadays to speed up the osseointegration process by altering the surface of the implant chemically (incorporating inorganic phases onto the titanium oxide layer) or physically (increasing the level of roughness) [10, 11]. Advantages of surface-modified implants include (a) establishing a greater contact area followed by better primary stability, (b) providing surface-retaining blood clots, and (c) stimulating bone formation [10, 12]. In vitro tests of surface roughness showed higher proliferation, cytokine, and growth factor production of osteoblast-like cells. Those factors are known to affect proliferation, differentiation, and matrix synthesis of chondrocytes [13,14,15,16]. Many studies on surface characteristics of titanium implants were performed over the last years. Due to the renaissance and new development of zirconia implants, it is now necessary to study their behavior and surface characteristics and to compare them to titanium implants. However, data regarding the surface characteristics of these zirconia implants are very rare. Therefore, the aim of this study was to examine the surface characteristics, element composition, and surface roughness of the five different commercially available dental zirconia implants.