## 4 Discussion
A variable reporting method on MDIs' follow-up was observed in several studies, which led to a challenging quantitative data extraction as follow: (a) most studies reported a wide follow-up duration (i.e., between 12 months and 60 months); (b) the majority of studies failed to report the number of implants followed during a particular interval of time and did not mention the timing of implant failure; (c) the majority of studies reported follow-up durations of \(<\)3 years; (d) most of the studies (n = 6) described a follow-up duration of 12 months only, indicating that the long-term survival rate of MDIs is unknown;and (3) only one study described the life table survival analysis with an interval survival rate and cumulative survival rate of 94.7% each. It is essential to note that the 1 st year interval survival rate of 94.7% does not indicate the one-year true survival rate of MDIs, since not all MDIs had a minimum follow-up duration of 12 months. McGill consensus suggests the utilization of two SDDIs for retaining mandibular overdentures [53]. With regards to the application of MDIs, most of the articles included in the present review utilized four MDIs for retaining mandibular overdentures, whereas two articles utilized two MDIs, and only one study utilized both two and four MDIs. On assessing the effect of the number of MDIs in the same article [43], higher prosthetic complications were observed for the utilization of two MDIs (n = 64) as compared to four MDIs (n = 52). Moreover, the findings of the present review suggest that four MDIs are linked with higher rates of patient satisfaction and quality of life. Hence, the use of four MDIs might be recommended to retain mandibular overdentures for prosthetic rehabilitation. The findings of the included studies in the present review report that the MBL was well within clinically physiological limits [54], and no study reported an MBL of \(\geq\)1.5 mm. It is imperative to notice that this review examined bone loss scores in the mandibular arch, and this might have affected this variation. Hence, further studies following subjects over longer durations to assess MBL in both the maxillary and mandibular arch should be carried out to compare the bone loss of MDIs with SDDIs. Regarding the surgical technique, most of the studies used the full-thickness flap technique for the placement of MDIs (45.45%), followed by the flapless technique (36.36%). Some authors recommend the use of a flapless procedure since it might decrease discomfort, postoperative pain, and resultantly reducing the morbidity of patients [13; 17; 29]. However, [PERSON] and colleagues [51] compared the flap technique with the flapless technique for installing SDDIs and observed no difference with regards to postoperative morbidity and/or pain. One of the limitations of this systematic review is the inclusion of the studies published in English language only. Although, there has been a remarkable increase in the number of studies that have examined the behavior of immediate loaded MDIs to retain mandibular overdentures, however, there are a very limited amount of randomized controlled/clinical trials. Moreover, the challenge of blinding the research investigators, participants, and outcome assessors might be regarded as a bias of this review. Therefore, caution should be taken while interpreting the outcomes of this study because of lower number of randomized controlled/clinical trials, and further clinical trials should be conducted to better answer in regards to rehabilitation therapy using mandibular overdentures retained by MDIs. Despite this, the utilization of immediate loaded MDIs for retaining mandibular overdentures exhibits viability, high patient satisfaction and quality of life, adequate survival rates, and clinically acceptable peri-implant clinical and radiographic parameters.