## 4 Discussions
The horizontal bone gain (width) was similar and without significant statistical differences between the implant sites reconstructed by the S-GBR technique and the bovine-derived xenograft and those reconstructed by the S-GBR technique and the porcine-derived xenograft. However, the osteodensity gain was higher in the implant sites reconstructed with the bovine-derived xenograft, but without significant statistical differences in comparison with the test group. These results could be related to the differences related to the structure and the physicochemical properties between the two categories of the xenografts. The porcine-derived xenograft used in the personal study (Purgo, Purgos Biologics, Seongnam-si, Korea) has a high degree of porosity (78.4%), a large specific surface area (SSA; 69.9 m\({}^{2}\)/g), a high degree of surface roughness (4.47 um), and a significant percentage of pores with a diameter <100-nm. The degree of porosity is higher than that detected in the case of the bovine-derived xenografts and very close to the porosity of the human trabecular bone (79.3%), while the micropores and macropores play a crucial role in new bone formation [28]. The osteoblasts have higher proliferation rates, higher rates of alkaline phosphatase synthesis, and mineral deposition on the extracellular matrix if they adhere to surfaces with micropores less than 100 nm diameter [29]. The degree of hydrophilicity and the surface energy of the porcine-derived xenograft leads to high protein absorption rates, increased cell adhesion rates, and the stimulation of cell proliferation processes [30; 31]. The statistical tests determined the absence of significant statistical differences between the control and test groups at 6 months follow-up for all measured alveolar bone parameters. The average results of the horizontal bone gains (width) for the bovine-derived xenograft augmentation procedures obtained in our study were comparable with data reported by similar research [21; 32; 33; 34; 35]. [PERSON] et al. (2018) have reported in a comprehensive review of the literature a net horizontal bone gain at follow-up of 2.86 \(\pm\) 0.23 mm [21]. [PERSON] et al. (2016) have reported in a systematic review a mean horizontal gain of 4.5 \(\pm\) 1.0 mm after alveolar bone augmentation techniques with mixtures of autogenous bone and xenogeneic grafting material [32]. [PERSON] et al. (2013) have found an average value of 5.68 mm horizontal bone gain in the lateral ridge augmentation techniques performed with autogenous bone and bovine bone-derived xenografts [33]. [PERSON] et al. (2014) have reported for lateral ridge augmentation with bovine-derived xenograft and autogenous bone (90:10) a mean value of the horizontal bone gain of 5.7 \(\pm\) 1.0 mm [34]. [PERSON] et al. (2021) have found a mean horizontal gain of 3.6 \(\pm\) 0.8 mm and a mean vertical gain of 5.2 \(\pm\) 1.1 mm in the augmentation of the mandibular alveolar defects using a combination of autogenous bone and bovine xenografts [35]. [PERSON] et al. (2021) have recorded, at 6 monthsfollow-up, in a study that investigated the effectiveness of horizontal augmentation with the bovine-derived xenograft, the increase of the alveolar bone width with 1.34 \(\pm\) 0.14 mm, 2.49 \(\pm\) 0.24 mm, and 2.97 \(\pm\) 0.24 mm at 2 mm, 4 mm, and 6 mm, respectively, below to the implant shoulder [36]. [PERSON] et al. (2014) have reported a significant increase of the osteodensity mean values (390 HU) following the alveolar augmentation procedures with the bovine-derived xenograft [37]. A systematic review of the effectiveness of the natural and synthetic bone grafts used in the alveolar bone augmentation reported the absence of significant differences in the percentage of new bone between any two grafts and recommended the use of any category of xenografts in the enhancement of alveolar bone quality and volume prior to the insertion of the dental implants [38]. Moreover, a recent review performed by [PERSON] et al.