Data sources Pubmed and EMBASE databases were searched from 2000 to 2017 and complemented by manual searching of the references of reviews and the full-text articles assessed for inclusion.

Study selection The inclusion criteria were: (i) Randomised clinical trials (RCT), prospective or retrospective studies, and case series or case reports including at least ten totally edentulous patients rehabilitated with maxillary implant-supported overdenture; (ii) analysed one of the following outcomes: survival rate of the implants, survival rate of the overdenture and patient-reported results; (iii) had at least two years of follow-up; (iv) and were written in English language.

Data extraction and synthesis The data extraction was performed by two independent reviewers. The comparison of the analysed outcomes was performed by nonparametric Fisher Test for unpaired data according to the number of implants and to the splinting technique. A meta-analysis was performed for the odds ratio (OR) for implant failure between four splinted implants and more than four splinted implants.

Results Twenty-eight studies were included in the systematic review. The survival rate of implants appeared to be higher when at least four implants were placed to support the overdenture, compared to less than four implants. The survival rate of overdentures and the patient satisfaction were not influenced by the number of implants.

The metanalysis could only be performed to compare the implant survival rate of a four splinted implants group and more than 4 splinted implants group, without significant differences between both groups (OR = 0.39; 95 % CI: 0.14, 1.14; p = 0.09).

Conclusions Although the placement of at least four implants to support a maxillary overdenture seems to report higher implant survival rates, further studies are needed to confirm this conclusion. No differences were found for overdenture survival rates or patient satisfaction according to the number of implants.

数据来源从2000年至2017年搜索Pubmed和EMBASE数据库，并通过人工搜索评论的参考文献和评估纳入的全文文章作为补充。

研究选择纳入标准为：（i）随机临床试验（RCT），前瞻性或回顾性研究，以及病例系列或病例报告，包括至少十名上颌种植体支持的覆盖义齿修复的完全无牙龈缺牙的患者；（ii）分析了以下结果之一：植入物的存活率，覆盖义齿的存活率和患者报告的结果；（iii）至少有两年的随访；（iv）并以英语书写。

数据提取和合成数据提取由两个独立的审阅者进行。根据植入物的数量和夹板技术，通过非参数Fisher检验对未配对数据进行分析结果的比较。对四个夹板植入物和四个以上夹板植入物之间的植入物失败的比值比（OR）进行了荟萃分析。

结果系统评价包括28项研究。与少于四个植入物相比，当至少放置四个植入物以支撑覆盖义齿时，植入物的存活率似乎更高。覆盖义齿的存活率和患者满意度不受植入物数量的影响。

进行荟萃分析只能比较四个夹板植入物组和四个以上夹板植入物组的植入物存活率，两组之间无显着差异（OR = 0.39； 95％CI：0.14、1.14； p = 0.09）。

结论尽管为支持上颌覆盖义齿放置至少四个植入物似乎报告了较高的植入物存活率，但仍需进一步研究以证实这一结论。根据种植体的数量，对于覆盖义齿的存活率或患者满意度没有发现差异。