The implants that have been used are made from titanium with a microrough surface (Astra Tech Implant System, Dentsply Implants, Mølndal, Sweden). All implants have been placed according to the manufacturer's instructions (http://www.dentsplyimplants.no/nb-NO/Implantatsystem/Prosedyrer/Treatment-planning) and fitted with precision attachments (Locator, ZEST Anchors, Escondido, CA, USA. The removable prostheses were made from heat cured poly-methyl-metacrylate (PMMA) incorporating three active matrices).