What is the optimal number of implants for removable reconstructions? A systematic review on implant-supported overdentures

Objectives The aim of this systematic review was to assess the optimal number of implants for removable reconstructions. Material and methods Medline and The Cochrane Central Register of Controlled Trials were searched and complemented by hand searching. All trials published in English to October 2011 were included, in which overdentures, supported by a various number of implants, in adult edentulous individuals were compared. Only randomized controlled trials with at least 12 months follow-up were selected. The outcomes of interest were implant loss, the amount of peri-implant bone loss, the incidence of complications and the patient satisfaction. Results No articles were found providing information regarding the maxilla. Eleven studies on the mandible were included for the final comparative analysis. It was possible to make a comparison among four categories: (i) 1 vs. 2 implants; (ii) 2 implants with ball attachments vs. 4 implants with a bar; (iii) 2 implants with a bar vs. 4 implants with a bar; (iv) 2 implants splinted with a bar vs. 2 unsplinted implants. Conclusion For the maxilla there are no studies, at the present time, that can be utilized to address the question of how many implants should support an overdenture. For the mandible, it cannot be concluded that bone loss, patient satisfaction, or number of complications is significantly related to the number of implants supporting the overdenture. Furthermore, splinting two implants does not seem to offer additional value. Well conducted research is needed to identify the prognostic factors for long-term success.