## 1 Introduction  
The use of dental implants is a very common procedure [1]. For ideal prosthetic design, implants must be inserted in a correct 3D plan [2]. Patients may present alveolar ridge defects as a consequence of periodontal disease, dental trauma, traumatic extraction, or genetic anomalies, which do not allow the correct implant position [3, 4].  
Different treatment options have been described to reconstruct these defects, which may include inlay and onlay block bone grafts, crestal splitting, osteogenic distraction, and guided bone regeneration (GBR) using resorbable and non-resorbable barrier membranes [5]. Of these, GBR seems to be the most reliable and predictable, providing excellent long-term stability [6, 7].  
The basic principle of GBR involves placing a mechanical barrier to protect the blood clot and to isolate the bony defect from the surrounding connective and epithelial tissue invasion. This space is needed to allow the osteoblasts to access the space intended for bone regeneration. The use of a barrier membrane, especially a resorbable one, has the advantage of facilitating the procedure, but often the shape of the defect itself may create a collapse of the barrier and the loss of the \"space maintaining\" effect [8].  
Titanium meshes, as an alternative to membranes, have been used for a long time as a predictable technique for bone regeneration and, owing to their rigidity, the adaptation onto the defect and maintenance of their shape can be more stable [9]. To overcome the main drawbacks, which are the remaining sharp margins after cutting and the increased surgical time required for their shaping and fitting, pre-shaping of the mesh on a stere-olithographic model (STL) of the patient's jaw can be an alternative to significantly shorten the intraoperative time, but with a significant cost increase [10]. More recently, 3D-printed, custom-made titanium devices have been introduced as a modern alternative [11].  
Regardless of the production technique for any implantable devices, it is mandatory to control the characteristics to optimize their biological performance [12]. The stiffness of titanium meshes can damage the soft tissue, and the mechanical strength is related to the thickness of the material and pore dimensions. More specifically, the surface properties direct the cellular interactions [13]. These properties, including surface topography and chemical composition, are usually derived by the surface treatments applied [14].  
Surface topography and roughness are aspects that can be easily manipulated by post-production surface treatments and that play a strategic role in the determination of cellular interactions, influencing adhesion and differentiation [15,16]. High degrees of roughness represent a major risk for ionic leakage from the material [17] and the bacterial adhesion can be increased, with the consequence of implant failures [18].  
Smooth surfaces are able to reduce the biological processes at the interface, keeping the titanium oxidized layer properties unaffected for periods [16]. Thus, the correct micro- and nano-roughness levels can stimulate osteoblast differentiation and maturation, proliferation, and production of both matrices [19]. Although the mesh characteristics should be highly controlled, it is important to note that the biological response depends also on the correct diagnosis and clinical indication. Moreover, if an exposure during the healing phase occurs, it is relevant to demonstrate if, beside the unfavorable outcome, chemical modifications of the exposed surface may affect the bone growth.  
The present study investigated two different commercial customized devices, comparing their mechanical properties (flexion test and internal friction) and their macro- and microstructural changes after exposure to different degrees of pH to observe if the modifications of the material were coherent with the clinical findings. Further evaluations were made using SEM with profiles analysis and chemical composition.