## 1 Introduction  
Three-dimensional printing is an additive manufacturing technology (AM) that represents an alternative method of production with respect to traditional casting and subtractive methods for producing tridimensional tools. This novel technology permits freeform fabrication, so in the biomedical field, custom-made tools can be fabricated, starting from patients records, such as X-rays or CT-scans [1, 2]. AM can be applied in the production of bone substitutes and metallic meshes for guided bone regeneration, facilitating adaptation and immobilization of the tool in the bony defect, reducing surgical times and post-surgical sequelae, and increasing the success rate of surgery [3; 4; 5]. A further advantage of AM is the possibility to plan the production of infinite complex geometries characterized by different porosities in order to mimic natural tissues [6]. With respect to the traditional process of fabrication, 3D printing represents an economic alternative that minimizes the amount of material wasted, reduces the number of steps needed in production, and influences the technician's ability to produce high-quality products [3]. An interesting review by [PERSON] et al. described the different technologies adopted by recent 3D printers for the production of metallic biomedical devices [1]. In power bed fusion techniques, a high energetic beam, such as LASER, can be used to sinter (selective laser sintering, SLS) or melt (selective laser melting, SLM) different layers of metal powder deposited consecutively, based on a computer-aided design (CAD) project. The metal powder is delivered by a nozzle via the laser direct metal deposition (LDMD), so this technique permits a user to use different mixtures of metal powder to produce structures with different pores and gradients of metals, with the possibility to fabricate a large number of parts, and with a precision limit that is above 1 mm [7; 8]. In selective electron beam melting (SEBM), the laser is substituted by a high-energy electron beam, with high efficiency of production and smaller deformation [9; 10]. The metallic powder can also be trapped in a binder, which could be a plastic such as in atomic diffusion additive manufacturing (ADAM), or in a liquid ink, such as in the nanoparticle jetting (NP): in both techniques, the binder evaporates during the heating of the structure [11; 12]. Laser-induced forward transfer (LIFT) involves applying a pulsed laser beam to a thin metallic film that melts and is deposited as droplets, which after cooling, solidify [13]. On the contrary, in inkjet 3D binder jetting, a water jet is layered on a metallic bed, forming a 3D structure that is sintered on a furnace. Three-dimensional printing permits a user to modulate many parameters during the process of manufacturing, such as the energy power source, the temperature reached during manufacturing processes, the metallic powder adopted (composition and morphology), and the thickness of the deposited layers. It is important to highlight that the manufacturing method is able to affect the final product, especially in the chemical composition, the porous microstructure, and the mechanical properties. Another important point to consider is the bacterial interaction with this novel surface: recent literature has highlighted the importance of surface topography in the contrast or in the establishment of a mature biofilm, which could protect or predispose to perip-implatitis [14; 15; 16]. Peri-implantitis is associated with complex microbiota profiles and the process of biofilm formation on the implant surface is comparable with biofilm formation on natural teeth. The species _Streptococcus oralis_ and _Streptococcus sanguinis_ followed by _Neisseria pharyngis_ and _Gemella haemolysans_ are considered the first colonizers of the implant surface. Changes in the biofilm composition of _Streptococci_ species are observed between the fourth and eighth hours of biofilm formation.