## 4 Discussion
Therefore, there are also disadvantages, such as the risk of fracture of the mandible, fracture of the transport segment, difficulties in finishing the osteotomy on the lingual side, incorrect direction of distraction, perforation of the mucosa by the transport segment, suture dehiscence, bone formation defects and pain during the activation of the distraction device. In conclusion, based on the available results, all these regenerative procedures allow an enhancement of a future implant site, with satisfying esthetic and functional outcomes. No study reported a failure and no complications emerged in almost all studies. Nevertheless, we must keep in mind that some bias of non-published data may occur in cases with technical failures, and that makes it difficult to establish an accurate success/failure ratio of the employed techniques [61; 62]. Compared to orthodontic extrusion, the regenerative surgical techniques appear more complex, with a higher risk of complications and with a limited ability to develop soft tissues. Regarding the regeneration of hard tissue, most studies reported qualitative results, and for this reason, it is not possible to calculate the real efficacy of the different techniques in the formation of new bone and it is not possible to compare the results with those obtained through orthodontic extrusion [63; 64]. Finally, the authors have evaluated randomized studies comparing ridge preservation procedures with spontaneous healing of the dedentulous ridge after tooth loss and a delayed implant placement. Overall, the different ridge preservation procedures reduced post-extraction alveolar ridge dimensional changes, compared to extraction alone, but they were unable to prevent resorption. Another systematic review [65] confirmed these results, but also suggested the use of barrier membranes, flap surgical procedures and full flap closure to achieve better results. The obtained results, however, could not indicate which type of surgical procedure or biomaterial is most suitable for this approach. Regarding hard tissue volume, even if ridge preservation procedures appear to be better than extraction alone followed by a delayed implant placement, one prospective study [21] showed that, if tooth extraction is atraumatic and the granulation tissue is left in situ, both horizontal and vertical dimension could be maintained, because the granulation tissue contains new small blood vessels and pluripotent stem cells that contribute to tissue healing. Regarding soft tissue volume, the authors found discordant results. One study [22] reported a loss of soft tissue thickness on the buccal aspect in the ridge preservation group of patients. [PERSON] et al. previously showed that using a resorbable membrane for ridge augmentation decreased soft tissue thickness; the same phenomenon occurred in this study. Soft tissue thickness loss occurs together with hard tissue loss; the greatest loss is on the buccal side; therefore, it has important relevance in the esthetic zone. This loss of soft tissue thickness is most likely due to the interference with flap vascularity by the membrane and the graft; since the membrane is interposed between the flap and the bone surface, the vascular supply for the flap comes only from the flap base rather than the dual blood supply from the underlying osseous and flap base found in non-grafted sites. On the contrary, two other studies [26; 28] reported a greater soft tissue volume in the grafted groups. Further studies are needed to confirm these results, and split-mouth studies would be the most indicative to compare these different approaches.