Maxillary Implant Overdentures Retained by Bars or Locator

* Background Patients experiencing problems with their conventional maxillary denture can benefit from implant- retained overdentures. Several retention systems are available. These retention systems can be roughly divided into bar-retained implant overdentures, in which multiple implants are splinted and the overdenture is attached through retentive clips, and into retention systems using non-splinted solitary attachments (locators). Evidence on maxillary implant overdenture attachment systems has been mostly short to medium term, non-comparing or retrospective. Even more, 10-years data of comparative studies are lacking. * Main research question To compare treatment outcomes of fully edentulous patients with maxillary overdentures, supported by four implants, retained by either bars or locators . The primary objective of the study is to analyze marginal bone level changes by radiological assessments at 10-years follow-up. Secondary objectives are implant and overdenture survival, condition of peri- implant mucosa and patients' satisfaction. * Design (including population, confounders/outcomes) The study design is an observational study of a group of patients which were treated 10 years ago with dental implants and an overdenture in the maxilla because of problems with retention and stability with their conventional denture. Outcomes: primary outcome is the change in marginal peri-implant bone level 10 years after placing the overdenture. Secondary outcome measures will be implant and overdenture survival, peri-implant mucosa health and patients' satisfaction using a questionnaire.