Dental implants osseointegration: in vitro, preclinical and clinical research results.

Osseointegration is described as the close contact between bone and an implant surface, and the interest on surface engineering has to be understood as an important and natural trend. The biological fixation between the dental implant surfaces and jaw bones should be considered a prerequisite for the long-term success of implant-supported prostheses. In this context, the implant surface modifications gained an important and decisive place in implant research over the last years. The bone response, which means rate, quantity and quality, is related to the implant surface properties. For example, the composition and charges are critical for protein adsorption and cell attachment. Hydrophilic surfaces seem to favor the interactions with biological fluids and cells when compared to the hydrophobic ones, and hydrophilicity is affected by the surface chemical composition. Various techniques of surface treatments have been studied and applied to improve biological surface properties, which favors the mechanism of osseointegration. This strategy aims at promoting the mechanism of osseointegration with faster and stronger bone formation, to confer better stability during the healing process, thus allowing earlier loading of the implant. Some of the objectives for the development of implant surface modifications are to improve the clinical performance in anatomical sites characterized by poor quantity or quality of bone, to accelerate the bone healing and thereby allowing immediate or early loading protocols and also stimulating bone growth in order to permit implant placement in sites that lack sufficient residual alveolar ridge, thus providing them a jumping gap ability, for example. Implant morphology influences bone metabolism: rougher surfaces stimulate differentiation, growth and attachment of bone cells, and increase mineralization; furthermore, the degree of roughness is important. Implants may have "smooth" (machined) or rough surfaces. The main methods that are reported in the literature to create implant roughness are acid etching, sandblasting, titanium plasma spraying and hydroxyapatite (HA) coating. A current tendency is the manufacturing of implants with micro and submicro (nano) topography. Furthermore, the biofunctionalization of implants surfaces, by adding different substances to improve its biological characteristics, has also been recently investigated. In this contex, aim of the present project has been focused on dental implant surface modifications in order to improve the clinical performance in areas with poor quantity or quality of bone. In detail this aim has been reached trough 3 steps: 1) in vitro studies: a) in vitro studies of osteoproperties of glass and titanium surfaces grafted with fibronectin sequence motif for integrin binding (Arg-Gly-Asp, RGD)/ human vitronectin protein (HVP) b) development of an in vitro model to evaluate the degree of implants osteointegration by passing in vivo test. 2) in vivo studies, in big animal model, dogs, of osteointegrative properties of implants with different degree of surface modification. 3) clinical research on short implants, to underline the effect of surface modifications on dental implant survival in the long term in the clinic. As final results of these studies, we can conclude that there are a huge number of types of implant surfaces in the market, from different implant manufacturers, all of them claiming to have better clinical results. It is important that the clinician choose the surface that have shown the best results in the scientific literature. The majority of currently available in vitro and in vivo studies seem to indicate that implant surfaces with micro and submicro (nano) topography bring forward benefits to the process of interaction between bone cells and implant surfaces, accelerating and increasing the quality of bone-to-implant-contact (BIC). Finally, based on the state of the art of implant development, it is possible to predict that, within some time, implant surfaces coated with substances with biomimetic capacity will be available for clinical use. This process of implant bio-functionalization aims at modulating new bone formation around implants, and it represents the next step in implant development.