## 4 Discussion
Tooth extraction was followed by immediate post-extractive implant placement in all studies, except two [9; 12], where a delayed implant placement was performed 4-6 weeks after extraction. Immediate post-extractive implant placement is suggested to keep the hard and soft tissue volume obtained through the orthodontic technique. All studies showed good treatment outcomes, with satisfying esthetic and biological results and successful implant osteointegration, but two studies [7; 11] only reported the implant survival rate (100% and 96%, respectively). Regarding the amount of bone and/or soft tissue augmentation obtained through the orthodontic extrusion, only a few studies [5; 7; 11; 12; 30] gave quantitative data, and only one study [11] indicated the percentage of the efficacy of the technique in the regeneration of bone and soft tissue in the future implant site (70% and 65%, respectively). Most studies reported qualitative results, and for this reason, it is not possible to calculate the real efficacy of the orthodontic technique in the regeneration of hard and soft tissues in a future implant site. 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 technique. At the moment, based on the available results, it is only possible to say that orthodontic extrusion appears as an interesting non-surgical technique to develop a future implant site using hopeless teeth, with apparently fewer disadvantages and risks than the traditional surgical techniques (GBR, ridge splitting, distraction osteogenesis, and bone grafting). The only constraints to the use of this technique are the presence of hopeless teeth to be extruded with a sufficient quantity of residual periodontal attachment and a sufficient anchorage unit [31; 32; 33; 34; 35; 36; 37]. Some recommendations to optimize the clinical results can be given: low and controlled (<100 g) extrusive forces must be used; an extrusion ratio < 1 mm/month should be performed; it is important to use an anchorage on the teeth adjacent to the ones planned to be extruded; the extrusion should be performed according to the long tooth axis; regular follow-up of patients should be scheduled every month; a post-extrusion retention period is suggested; immediate post-extractive implants are suggested to keep the hard and soft tissues volume obtained through the orthodontic technique. Further studies are necessary to evaluate the efficacy of the technique in the regeneration of hard and soft tissues, to compare the different extrusive biomechanics and to create an evidence-based clinical protocol. Another aspect to investigate is the resorption rate of the orthodontically regenerated bone to compare the quality and quantity of bone regenerated through orthodontic extrusion with that obtained using regenerative procedures. For implant site development, different regenerative procedures were used: four studies [15; 17; 19; 20] performed a one-stage or two-stage guided bone regeneration (GBR), three studies [16; 18; 25] performed a bone graft procedure, and two studies [24; 27] performed alveolar distraction osteogenesis.