## 4 Discussion  
This study involved 100 consecutive cases of GBR performed by applying a 3-D preformed Ti mesh to the non-contained horizontal defects around the implant simultaneously with implant placement. We evaluated and compared the clinical and radiologic results. We also grouped the cases using a cross-linked resolvable collagen membrane from those using a non-crosslinked collagen membrane with a 3-D preformed Ti mesh. We compared the exposure rate of the mesh and the hard tissue gain rate after 6 months to evaluate the effect of using an additional resorbable collagen membrane. Conventional titanium meshes have an excellent self-space-making capacity, which provides predictable results when performing extensive bone grafting, and they are less susceptible to bacterial infection. In addition, they permit the supply of sufficient blood, nutrients, and oxygen, among others, because of their macropore sizes, which facilitate bone and soft tissue regeneration [14]. However, the conventional titanium mesh needs to be cut and bent to an appropriate size and shape before application, because complete fixation is required for positioning the mesh properly; the sensitivity of the technique is very high, and the mesh exposure frequency is high [15]. The mesh exposure rates reported in previous studies, such as those conducted by [PERSON] that summarized the clinical studies on guided bone regeneration using the conventional titanium mesh, ranged from 14.28% to 52.7% [16]. Previous studies that used 3-D preformed Ti mesh have reported membrane exposure rates as high as 20-25%, which are similar to those reported for the conventional titanium mesh [17; 18]. However, [PERSON] et al. reported that the 3-D preformed Ti mesh can reduce the duration of surgery and trauma to the flap because it does not need to be cut or bent differently from the existing Ti mesh, and there is no sharp margin [18]. In this study, mesh exposure was observed in 7 of the 100 patients and 7 of the 129 sites, and the exposure rate was as low as 5.4%. The exposure rate of the 3-D preformed Ti mesh only group (Group 1) was 11.8%, which was lower than that observed for the conventional titanium mesh. Despite these advantages, it is necessary to consider its relatively higher price than that of the traditional Ti mesh, and caution should be exercised when excessive vertical ridge augmentation is required. Some studies have recommended the additional use of a resorbable collagen membrane above the titanium mesh to compensate for the limitations of the conventional titanium mesh [19; 20; 21]. [PERSON] et al. reported that when a resorbable collagen mem  
Figure 3: Comparison of the hard tissue gain rates (HGR) of the groups. There was a statistically significant difference between the rates of Groups 1 and 2, as well as Groups 1 and 3. HGR, the percentage of HG compared with BA (HG/BA); BA, bone augmentation immediately after surgery; HG, hard tissue gain after 6 months of healing; Group 1, only three-dimensional preformed titanium mesh (3-D-PFTM) used; Group 2, 3-D-PFTM + cross-linked collagen membrane used; Group 3, 3-D-PFTM + non-cross-linked collagen membrane used. * Statistically significant difference (\(p<0.05\); Kruskal–Wallis test). brane was used, fibrous tissue grew within the collagen membrane, thereby preventing dehiscence [22]. [PERSON] et al., who studied this through animal experiments, reported that the additional use of a resorbable collagen membrane did not significantly decrease the exposure rate [21]. However, the exposure rate of the group using only a 3-D preformed Ti mesh (Group 1) was 11.8%. In Groups 2 and 3, which additionally used the resorbable collagen membrane, the exposure rates were 5.0% and 4.2%, respectively, which were lower than those of Group 1, regardless of whether the resorbable collagen membrane was cross-linked.