## 4 Discussion  
Regarding orthodontic extrusion for implant site development, most studies [7; 8; 9; 10; 12; 13; 14; 29; 30] were case reports, except two, which were case series [5; 11]. The studies reporting on regenerative procedures for implant site development included five case reports [16; 18; 19; 20; 27], three case series [17; 24; 25] and one RCT [15]. The majority of studies comparing ridge preservation procedures with spontaneous healing after tooth loss were RCT [22; 23; 26; 28; 31], except one, which was a prospective study [21]. Patients undergoing orthodontic extrusion ranged from 23 to 62 years old; patients treated with regenerative surgery ranged from 18 to 68 years old; and, finally, patients included in the studies comparing spontaneous tissue healing versus extraction alone ranged from 20 to 76 years old. The mean age of patients treated with orthodontic extrusion or regenerative procedures was 40 years, and it was a little lower than the one of patients included in the studies about spontaneous tissue healing after tooth loss and delayed implant placement (52 years); it is not known if this was due to the fact that older patients prefer not to submit to surgery or orthodontic procedures prior to implant placement, or to the clinician's preference. In all studies, most of the patients were women. The presence of a systematic disease before Implant placement has been discussed in the literature. A retrospective study [31] that investigated the correlation between systemic diseases and implant treatment found a failure rate of 3.6% and concluded that osteoporosis and [PERSON]'s disease were significantly associated with early implant failure. Furthermore, the same authors [32] concluded that these factors were not associated with late implant loss. The literature suggests that the level of evidence regarding the association between systemic diseases and implant loss is low [33], but the control of any systemic disease before an implant therapy is considered important [34], and any systemic disease in the patients included in the study should be reported. Regarding health conditions, most patients of the studies included in the systematic review were in good health, but not all studies provided enough information on this subject. Two retrospective studies [35; 36] identified a correlation between smoking and implant complications. For what concerns the smoking habit, both smokers and nonsmokers were included in the studies about regenerative procedures and in the studies comparing ridge preservation procedures with spontaneous healing after tooth loss, as soon as the smoking addiction was moderate (fewer than 10 cigarettes per day). The information provided about patient smoking habits in the group of patients treated with orthodontic extrusion was insufficient. The biological and functional result of implant treatment is very important regardless of the implant's position; however, the esthetic outcome is fundamental in the anterior maxilla, especially in patients with a high lip line. The quality and quantity of alveolar bone and soft tissue in the future implant site is essential for proper tridimensional implant placement to achieve esthetic and functional outcomes; therefore, several techniques have been employed to develop the implant site. Both mandibular and maxillary anterior and posterior teeth were treated with orthodontic extrusion or regenerative procedures to enhance the implant site, but the majority were anterior maxillary teeth. Periodontitis was the primary reason for tooth extraction in the studies reporting on orthodontic extrusion, whereas in the studies reporting on regenerative procedures, many causes can be identified, such as periodontitis, non-restorable tooth, traumas, fractures and endodontic complications. The randomized studies comparing spontaneous tissue healing after extraction with ridge preservation procedures provided no details about the reason for the extractions.