* Background Patients experiencing problems with their conventional maxillary denture can benefit from implant- retained overdentures. Bar-retained implant overdentures can be supported by 4 or 6 implants, splinted by a bar. Evidence on maxillary implant overdentures has been mostly short to medium term, non-comparing or retrospective. Even more, 15-years data of comparative studies are lacking. It is important to evaluate treatment outcomes, such as implant survival, peri-implant bone changes and patient satisfaction at the long-term.
* Main research question The aim of this 15-years study is to evaluate a patient group treated 15 years ago in a prospective study with a maxillary overdenture on 4 or 6 implants in an edentulous maxilla. The primary objective of the study is to analyze marginal bone level changes by radiological assessments at 15-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 15 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 15 years after placing the overdenture. Secondary outcome measures will be implant and overdenture survival, peri-implant mucosa health and patients' satisfaction using a questionnaire.
* Expected results Stable peri-implant bone levels, high implant and overdenture survival rate and satisfied patients.