## 4 Discussion  
In this randomized prospective study using serial stone cast scans and CBCT images obtained at baseline and at a 4-month follow-up assessment, we evaluated the alteration of alveolar morphology after ridge preservation following tooth extraction. We assessed the effectiveness of autogenous tooth bone graft, either alone (DDM only) or in combination with rhBMP-2 (rhBMP-2/DDM), on ridge preservation, compared to conventional bovine xenografts (DBBC). To the best of our knowledge, this is the first randomized controlled study to compare rhBMP-2/DDM and xenografts in human subjects. Similar clinical trials using DDM as a scaffold for rhBMP-2 have recently been published, but most of these studies were conducted on animals [31; 32]. Natural reduction of the alveolar ridge after tooth extraction can be demanding, and it is challenging to rehabilitate the aesthetic and functional value of the implants. Since the clinical purpose of extraction socket is mainly implant placement, it is fundamental for clinicians to minimize postextraction bone atrophy. The ridge preservation technique includes the placement of biomaterials and substitutes in an extraction socket to prevent ridge atrophy. Many studies on ridge preservation have documented the structural changes that occur around the alveolar ridge following ridge preservation [13; 33; 34; 35]. It is well-known that ridge preservation can limit and delay alveolar bone alteration [36; 37]. Not all studies have reported beneficial effects from reducing alveolar ridge atrophy [36; 38] which implies that ridge atrophy occurs in almost all the extraction sockets regardless of ridge preservation. In this study, we reported negative postextraction remodeling changes (approximately 80% of original soft tissue volume) in all three groups after tooth extraction accompanied with ridge preservation (\(p<0.05\)). These results are consistent with those obtained in previous studies which have shown that horizontal bone loss of approximately 30-60% and vertical bone loss of approximately of 10-20% is inevitable after 6 months [39]. Despite the ridge preservation technique, postextraction bone atrophy appears to be entirely unavoidable [40]. In this study, extraction was done by two surgeons. However, atraumatic extraction was performed with minimal damage to the bone during extraction, and there was no difficulty in extraction. Therefore, it is considered that this did not significantly influence the study outcomes. Study outcomes may be affected by extraction causes such as pulpitis and periodontitis. In order to control for this bias, patients with severe periodontitis with a vertical bone loss of more than 50% were excluded from the study and the inflammatory tissue was debrided with the extraction. In this study, 3D volumetric alteration of both soft and hard alveolar tissue was recorded at baseline and 4 months after extraction, and comparative analyses were performed between the DBBC-treated group, DDM-treated group, and the group treated with DDM and rhBMP-2. From a quantitative perspective, we did not observe any significant differences in volume between the three groups at 4 months postoperation (\(p>0.05\)). Although our study did not include a control group, this result implies that the DDM groups exhibited similar changes in ridge volume as the conventional DBBC grafting. Consequently, this result may indicate that DDM grafting on the extraction socket might lead to lesser alveolar atrophy compared to cases without postextraction grafting. According to radiographic assessment performed in this study, there were no statistical differences between the three groups in vertical bone height. Similarly, previous studies did not show statistical differences between DBBC and DDM in vertical bone height after 6 months of ridge preservation [14]. The 4-month postoperative ridge width at 1 mm (RW-1) from the marginal crest was significantly reduced in the DBBC group (9.00 \(\pm\) 2.76 mm), the DDM group (11.74 \(\pm\) 1.57 mm), and the rhBMP-2/DDM group