## 4 Discussion  
Additive manufacturing (AM) is widely applied in the medical field and it is becoming popular in oral surgery. However, only a few studies have analyzed the effect of the laser melting and sintering process (defined as additive manufacturing techniques) on the metal alloys in terms of mechanical and chemical properties [20,21]. Considering that the implant has to be placed in the oral cavity, a variety of factors can influence the final outcome: masticatory function and applied stress on the device, chemical action of the saliva, and, in the case of partial exposure, of foods and beverages, including also any endogenous pathologies, like gastro-esophageal acid reflux. AM technology offers some advantages compared to conventional techniques [22], such as digital planning and design of the customized mesh, shorter surgical times, and easy adaptation of the device to the bone defect [23, 24, 25, 26]. [PERSON] et al. [27] evaluated the dimensional accuracy of customized AM Ti mesh. The thickness of the polished device was 0.3 mm with perforations of 1.0 mm. The results obtained demonstrated that the \(x\)- and \(y\)-axes representation showed higher accuracy compared to the \(z\)-axis. The mean accuracy error value reported was 139 \(\upmu\)m.  
[PERSON] et al. [28] compared the clinical performance of customized AM with conventional Ti meshes for bone augmentation procedures in 26 patients. The customized AM meshes were manufactured with a thickness of 0.5 mm and with 1.0-mm diameter pores. The screw perforations for positioning the AM mesh had a 1.5-mm diameter, and the mesh was manually polished until 0.3-mm thickness was achieved. During implant placement, the Ti meshes were positioned with autogenous bone. The authors reported a higher surgical time for conventional Ti mesh compared to customized AM mesh. Furthermore, conventional meshes were associated with 15.4% of mucosal dehiscence with infection compared to AM procedures. [PERSON] et al. [29] evaluated the feasibility of the customized Ti mesh sheets for alveolar bone reconstruction in two patients. A customized SLM Ti mesh sheet was positioned at the same time as placing a commercial implant. None of the abovementioned studies investigated whether the additive manufacturing process may influence the mechanical properties. From the results of this study, there is a clear difference between perforated and non-perforated samples, with an obvious higher resistance, calculated as ultimate flexural strength, for the samples without any kind of perforation. An adult human male can produce an occlusal force that averages from 45-68 kg (441.3-666.8 MPa) on molar sites. The values of the ultimate flexural strength for non-perforated samples are much higher, but perforated samples break at 503 MPa and start bending with alteration of the initial shape at 300 MPa. The samples, both perforated and not, from BoneEasy (BE) seem to have a higher resistance than the BTK ones. The elastic modulus of perforated samples is lower than the full samples and more similar to the bone's Young's modulus (10-20 GPa). Although the shape of the customized mesh was different from the samples, with a noticeable difference also of the mechanical properties, this aspect should be considered after the implantation in order to avoid potentially dangerous stresses on the device. Partial exposure of the mesh is one of the most common complications and it has been demonstrated by several studies that it may average from 0 to 66% [28], regardless of the site and the extension of the bone augmentation. The existing evidence does not report whether the part exposed to the oral cavity and, thus, to contaminants such as food and beverages but also to sudden and extremely variable chemical conditions, may influence or not the surface of the device, affecting the bone response. In this study, several conditions were simulated, from the immersion of the sample in saline solution (pH 7) up to the extreme acid buffering with pH 4 for a maximum time of 21 days.