## 4 Discussion  
In this retrospective clinical study, three different surgical techniques for the rehabilitation of a posterior maxilla with insufficient residual bone height for the placement of axial implants were compared. Sinus lift techniques have been extensively discussed, and several authors have reported good short- and long-term results on implant survival rate. Concerning a lateral sinus lift, [PERSON] et al., in their multicenter prospective study at 2 years of follow-up, reported an implant survival rate of 97% in patients with residual bone height between 1 and 4 mm who were treated with a lateral sinus augmentation using a nano-crystalline hydroxyapatite sole bone filler, simultaneous implant placement, and a deferred loading protocol [29]. Similar results were obtained by [PERSON] et al. in their retrospective clinical study at 10 years of follow-up, in which they reported an implant survival rate of 95.45% in patients undergoing sinus lift via a lateral approach using autologous bone graft, implant placement after a four-month healing period, and a deferred loading protocol [30]. These results are similar to those obtained in this study, where the implant survival rate of fixtures placed by sinus lift via a lateral approach was 95.83%. [PERSON] et al. [31], in their retrospective clinical study at 15 years of follow-up, compared implant survival in patients subjected to sinus lift with that in patients subjected to a lateral approach, depending on the implant placement protocol and biomaterial used. Implants placed at the same time as the sinus lift (residual bone height above 4 mm) provided similar results to implants placed after the healing period; autologous bone, according to other studies [32], provided better results than a heterologous bone graft. Although autologous bone is currently considered the gold standard in bone regeneration [33], good medium- and long-term results have been obtained in both sinus lift techniques even without bone grafting [34]. Considering these results, in the present study, autologous bone chips obtained from the lateral bone window were applied as the only bone regeneration material. Concerning transcrestal sinus lift, [PERSON] et al., in their retrospective clinical study at 10.43 \(\pm\) 5.01 years (ranging from 5 to 16 years) of follow-up, reported a survival rate of 95.45% [35]. Similar results were obtained by [PERSON] et al., in their randomized controlled trial at 10 years of follow-up, in which they reported an implant survival rate of 90.7% in the case of osteotome sinus floor elevation with deproteinized bovine bone mineral and 95.0% without bone grafting [36]. According to these authors, the transcrestal sinus lift, applied when residual bone height was at least 5 mm, was performed through an osteotome-mediated technique and without biomaterials, recording an implant survival rate of 95.65%. Concerning tilted implants applied to bypass the sinus floor, the implant survival rate recorded in our study (98%) could be compared with those in other studies. [PERSON] et al., in their retrospective clinical study at 5 years of follow-up, reported an implant survival rate of 95.2% in immediate-loading rehabilitations of posterior edentulous maxilla with the placement of one axial and one tilted implant, concluding that tilted implants, longer than traditional ones, could increase the implant-to-bone contact area, promoting primary stability, reducing the prosthetic cantilever, and engaging basal bone [37]. Similar results were obtained by [PERSON] et al. [38] and [PERSON] et al. [39], who reported implant survival rates of 100% at 5 years of follow-up and 96.3% at 3 years of follow-up, respectively, in the absence of intra- or post-operative surgical complications. Regarding marginal bone loss, as reported by [PERSON] et al. in their systematic review and meta-analysis of clinical trials [40] and as confirmed by our results, implants placed via sinus lift techniques show values similar to those of implants placed via traditional methods.