Implant survival in 1-versus 2-implant mandibular overdentures: a systematic review and meta-analysis

Objective: This systematic review was performed to compare the survival of 1- vs. 2-implant overdentures (IODs) in the edentulous mandible. Materials and methods: Manual and electronic database (PubMed, EMBASE and CENTRAL) searches were performed to identify scientific articles, published in English, reporting on mandibular IODs utilizing unsplinted attachments. Studies were included if they were prospective human studies reporting on two-piece microrough surface implants with a diameter >= 3 mm. Data were extracted by two independent investigators, and an overall inter-investigator kappa score was calculated. A meta-analysis was performed on the included comparative studies. Results: The search shortlisted 30 prospective studies for data extraction and statistical analysis. The included studies comprised of only two randomized controlled trials (RCTs) comparing 1-vs. 2-IODs, and a further 28 prospective studies. The kappa score calculated was between 0.86 and 1 for the various parameters. One RCT favored 1-IODs (RD: 0.08, 95% CI: 0.01, 0.14) while the other favored 2-IODs (RD: - 0.04, 95% CI: - 0.27, 0.19). However, the overall random effects model did not reveal a significant risk difference (RD) for implant failure between the two interventions (I-2 = 36.6%, P = 0.209; RD: 0.05, 95% CI: - 0.07, 0.18). Conclusions: The results of this meta-analysis conclude that the postloading implant survival of 1-IODs is not significantly different from 2-IODs. However, the existing scientific evidence in the literature in terms of prospective comparative studies is scarce. Hence, before recommending the 1-IOD as a treatment modality, long-term observations are needed and a larger range of functional, prosthodontic, and patient-centered outcome measures should be considered.