A systematic review of implant-supported overdentures in the edentulous maxilla, compared to the mandible:How many implants?

Background and aim: There is now overwhelming evidence from systematic reviews that a two-implant overdenture is the first choice of treatment for the edentulous mandible. Conversely, consensus is lacking for implant-supported maxillary overdentures. Therefore, we systematically reviewed the treatment outcome of concepts used for implant-supported maxillary overdentures, focusing on the survival of implants, survival of maxillary overdentures and condition of the implant surrounding hard and soft tissues after a mean observation period of at least 1 year.Material and methods: MEDLINE (1950 to December 2013), EMBASE (1966 to December 2013) and CENTRAL (1800 to December 2013) were searched to identify eligible studies. Two reviewers independently assessed the articles using specific study design-related quality assessment forms.Results: Out of 195 primarily selected articles, 24 studies fulfilled the inclusion criteria. A meta-analysis showed an implant survival rate of 98.1% and overdenture survival of 99.5% per year in the case of 6 implants and a splinted (bar) anchorage. In the case of 4 implants and a splinted (bar) anchorage, implant survival rate and overdenture survival were 97.0% and 96.9% per year, respectively. In the case of 4 implants and a non-splinted anchorage (ball, locator, telescopic crown), implant survival rate and overdenture survival were 88.9% and 98.8% per year, respectively. The condition of the pen-implant tissues was not reported in most studies.Conclusions: An implant-supported maxillary overdenture (all studies 4 implants) provided with a splinted anchorage is accompanied with a high implant and overdenture survival rate (both >95% per year), while there is an increased risk of implant loss when 4 implants with a non-splinted anchorage are used.