## 4 Discussion  
As documented in various studies in the literature, despite the numerous advantages of custom-made membranes, such as precise adaptation to the individual bone defect, shorter surgical intervention time, and the ability to plan the percentage and shape of the desired bone augmentation, exposure remains a challenging problem. Indeed, custom-made titanium membranes exhibit greater rigidity compared to standard membranes, which may lead to exposure, reaching a percentage of up to 20%. Other studies report exposure rates ranging from 14.8% to 59%. The heterogeneity in these results may be related to various factors, including mechanical stress on the soft tissue flap, post-surgical prosthesis placement, the learning curve of digital software and mesh placement procedure, surgeon skills, and the inability to modify the membrane shape during surgery. However, in most cases of exposure, it is mild and limited to specific points [18]. According to [PERSON] et al. and [PERSON] et al., exposure rates for custom-made membranes were found to be lower than traditional titanium membranes [13; 19]. The negative effect of mesh exposure depends on the complication timing and any associated infection. Compared to late exposure, early exposure compromises bone regeneration outcomes, leading to significantly lower osteogenesis at the exposed site and an increased need for removal. Late exposure, occurring after 4 weeks post-intervention, \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Exposure** & **No Exposure** \\ \hline Average Vertical Bone Increase (mm) & 5.2 mm & 5.5 mm \\ Average Horizontal Bone Increase (mm) & 3.8 mm & 4.5 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Average bone increase values with and without membrane exposure. has minimal or no effect on bone regeneration outcomes, allowing for successful implant placement in the regenerated bone. Successful bone regeneration can still be achieved in cases of early exposure if promptly treated with proper disinfection [13; 20]. Another factor that could influence the outcome of bone regeneration is the mechanical properties of titanium mesh, particularly the presence or absence of pores and their size [9]. According to [PERSON] et al., titanium meshes without pores can prevent fibroblast growth at the defect site, but inadequate blood supply may delay bone regeneration, leading to membrane exposure three weeks after guided bone regeneration (GBR) surgery [21]. [PERSON] et al. demonstrated that the presence of holes in materials is a crucial factor for the penetration of cellular elements and capillaries into the grafted material, with a recommended size \(>100\) um to ensure soft tissue healing and provide an extensive network of blood vessels [22]. On the other hand, the presence of holes makes it challenging to achieve selective cell isolation, often resulting in the growth of soft tissues beneath the membrane. Several studies have investigated the relationship between hole size and soft tissue growth. However, the relationship between pore size and bone formation remains controversial [9]. In this study, four occlusive meshes and six membranes with pores were used. Membrane exposure was noted in three cases where a non-perforated occlusive membrane was used. Due to the limited sample size, it is not possible to definitively attribute the exposure to a specific membrane property, but it is likely that the lack of holes on the mesh's surface affected the outcome. Other drawbacks associated with custom-made membranes include the need for a second intervention for removal and the cost associated with device design and prototyping [23]. Several studies have demonstrated that GBR with titanium mesh achieves a good percentage of both horizontal and vertical bone gain, facilitating implant placement. However, clinical outcomes depend on the type of defect, making bone gain percentage case-specific and reliant on the specific clinical characteristics.