## 4 Discussion  
This case report analyzed radiographical and histological data of two ARP sites from one to two years post-operation. The first case was diagnosed as Stage II, Grade B periodontitis on the upper-right second premolar while the second case was diagnosed as Stage II, Grade B periodontitis on the upper-right second molar. Both patients had severe alveolar bone resorption extended to the apical aspect and ARP proceeded usingxenogeneic graft materials to reduce the dimensional alterations of the alveolar ridge after tooth extraction. The radiographical analysis using CBCT, taking place from one to two years after ARP, presented that the alveolar bone heights remained comparable to the adjacent area and the volume was sufficiently maintained to place an implant without additional horizontal augmentation. Moreover, the high insertion torque achieved in the grafted sites not only provided a reliable primary stability, but also indicated higher initial bone-to-implant contact and ultimately achieved a predictable treatment outcome [18,24]. Previous studies suggested that an intact extraction socket wall may promote hard tissue formation and better outcome for the grafting biomaterials after tooth extraction [8,25]. Despite the large apical bone defect that appeared on the two presented cases, all of the socket walls at the coronal part were intact. However, due to inflammatory bone resorption, only the thin layers of the facial walls remained. It is known that facial walls present a more pronounced reduction after tooth extraction compared to lingual/palatal walls. This is because they are comprised mainly of bundle bones [1,3] and that facial wall thicknesses of less than 2 mm are prone to greater amount of bone loss [26]. Although the thickness of the facial walls was less than 2 mm in both cases, lateral and cross-sectional radiographic images of CBCT exhibited that the alveolar bone heights were comparable to the adjacent area and were maintained one to two years after ARP (Figure 3). With these findings, the authors agree that the biomaterials successfully preserved the socket dimension for a longer period of time. Histomorphological analysis of the bone samples shows slightly higher NFB (23.5-25.3%) and RGM (17.5-29.0%) percentages compared to a previous clinical study, which evaluated an extraction socket graft that was collected 4 months after the surgery [17]. In this previous study, the mean percentages of NFB and RGM in the DBBM group were 15.1% and 12.7%, respectively. In the DPBM group, the mean percentages of NFB and RGM were 18.5% and 12.2%, respectively. However, a careful interpretation of the data is demanded since the percentages of the previous study analyzed the whole area of the collected sample from a trephine, while this report only analyzed the apical third. With this limited sample, the authors are unable to conclude whether the percentages of NFB increased over time; however, newly formed mineralized bone around the grafted biomaterials appears to be intact for longer period to period. Comparing the histological samples of the two present cases, the residual graft materials of the premolar site (Case I) is more condensed and newly formed bone closely fills the gap between the grafted materials adjunct to the fibrous tissue. Despite the apical lesion that appeared on the premolar, the marginal proportions of the walls were intact and collagenated DBBM enhanced the stability of the grafted material. On the other hand, residual graft materials are more sparsely dispersed in the molar site (Case II) with mineralized bones forming around biomaterials and fibrous tissues filling the gap in between. One possible hypothesis for this that can explain this difference is that, in the molar case, the apex of the socket was exposed to the sinus floor. Therefore, during the condensation process, a minimal amount of pressure was applied to impede the biomaterials from entering the maxillary sinus.