## 3 Results
### Types of Treatment
#### 3.3.3 Spontaneous Healing of the Extraction Socket and Delayed Implant Placement  
Regarding the delayed implant placement in an untreated edentulous ridge, five studies were included in the systematic review: one prospective study [21] analyzed the spontaneous healing of the extraction socket and a delayed implant placement; the other four randomized controlled studies [22; 23; 26; 28] compared extraction alone with ridge preservation procedures before delayed implant placement (Table 4). In the prospective study [21], no ridge preservation procedure was performed after tooth extraction, but the extraction was astraumatic as possible, and the granulation tissue was left in situ to help the healing process. Implants were placed three months after tooth extraction. In the RCT studies ridge preservation procedures were performed after tooth extraction to limit the resorption of hard and soft tissues: one study [22] used a freeze-dried bone allograft and a collagen membrane; one study [23] used a xenograft; one study [26] used a cortical or collagenated corticocancellous porcine bone graft; finally, one study [28] used a corticocancellous porcine bone graft and a collagen membrane, which remained exposed in the oral environment for an intentional secondary soft tissue healing. A delayed implant placement followed all these ridge preservation procedures: in one study [26], implants were inserted 3 months after tooth extraction; in two studies [22; 28] implants were placed 4 months after extraction; and in another study [23], implants were inserted 7 months after tooth extraction. Two studies [21; 26] only reported data about the type of implants used. The follow-up period was different: in three studies [22; 23; 28], it was 6, 7, and 8 months long, respectively, 3 years in the prospective study [21], and 4 years in another randomized study [26]. Regarding complications, only one study [22] reported the presence of little dehiscences at the time of implant placement in the group of patients treated with ridge preservation procedures. The other studies reported no complications. All studies reported data about hard tissue changes. In the prospective study [21], no statistically significant differences were found in the ridge width before the extraction and 3 years after implant placement (11.44 \(\pm\) 1.80 mm and 11.59 \(\pm\) 1.61 mm, respectively), whereas the vertical ridge dimension showed a statistically significant increase (from 8.05 \(\pm\) 2.12 mm to 12.48 \(\pm\) 2.04 mm). The RCT studies showed that all ridge preservation procedures limited the horizontal and vertical resorption of hard tissue after tooth extraction, compared to extraction alone. In one study [22], the ridge width decreased from 9.2 \(\pm\) 1.2 mm to 8.0 \(\pm\) 1.4 mm in the group treated with ridge preservation procedures (RP), while it decreased from 9.1 \(\pm\) 1.0 mm to 6.4 \(\pm\) 2.2 mm in the extraction-alone (EXT) group, a difference of 1.6 mm. Most of resorption occurred from the buccal. The vertical change for the RP group was a gain of 1.3 \(\pm\) 2.0 mm versus a loss of 0.9 \(\pm\) 1.6 mm for the EXT group. Histologic analysis revealed more bone in the RP group. In another study [23], a significantly greater horizontal resorption was observed at EXT sites (4.3 \(\pm\) 0.8 mm) compared to RP sites (2.5 \(\pm\) 1.2 mm). The ridge height reduction at the buccal side was 3.6 \(\pm\) 1.5 mm for the EXT group, whereas it was 0.7 \(\pm\) 1.4 mm for the RP group. Moreover, the vertical change at the lingual sites was 0.4 mm in the RP group and 3 mm in the EXT group. The histologic analysis showed a significantly higher percentage of trabecular bone and total mineralized tissue in ridge-preservation sites compared to extraction-alone sites. One study [28] reported that in the grafted group changes in horizontal dimension showed an average resorption of 1.6 \(\pm\) 0.55 mm.