107 Maxillary implant overdentures: retreatment after failure 7.1 INTRODUCTION Even though implant surgery has become a safe and predictable treatment for replacing teeth1, peri-implantitis has evolved to a common condition, occurring in 28 to 56% of all patients2. Peri-implantitis results in loss of marginal bone, which can eventually lead to implant loss and is an example of late implant failure, while early implant failure is caused by lack of osseo-integration3. Since a late failure site is exposed to a longer infection period, this results in a larger amount of bone loss and changes in bone quality4. Additionally, patients with a late failure tend to show signs of multiple failures3. Since there is no fixed prosthetic alternative for most failing implant cases4,5, retreatment with implants is often considered. Retreatment, however, is associated with lower implant survival because the retreated sites are still subject to some, if not all, of the previous factors that led to the failure6. Maxillary retreatment7, as well as of sites with a lower bone quality and quantity8, have been shown to result in a lower survival rate. Current research on retreatment is limited to studies describing predominantly early failures with survival rates between 71.0 and 94.6%9, while results of retreatment after late implant failure are sparsely reported. A separate analysis of early and late implant failure in studies incorporating both types of implant failures has, unfortunately, not been performed 7,8,10 and no studies have reported solely cases with a history of late failure sites11. Therefore, the purpose of the present retrospective study was to assess the outcome on retreating a group of patients with multiple late maxillary implant failures after full arch rehabilitation. 7.2 MATERIALS AND METHODS This retrospective, observational cohort study included all consecutive patients referred to the Department of Oral and Maxillofacial Surgery (University Medical Center Groningen, the Netherlands) between 2008 and 2018, regarding late failure of all maxillary implants supporting their fixed dental prosthesis (FDP) or implant overdenture (IOD) were asked to participate. The study was approved by the UMCG Medical Ethical Committee (METc 2018/030) and was carried out in accordance with The Code of Ethics of the World Medical Association (Declaration of Helsinki). Informed consent was obtained from all the participants. Surgical protocol All patients were treated according to protocol for a new IOD. Smokers were instructed to cease smoking for at least 2 months prior to treatment. Patients were retreated by one surgeon (GMR) during two surgical sessions: reconstructive and implant surgery. In case of a failed FDP, a temporary removable denture was made prior to implant removal. During reconstructive surgery, the implants were removed under general anaesthesia using forceps and implant retrieval tools. The maxilla was reconstructed using bone grafts harvested from the anterior iliac crest, calvaria or retromolar region. A maxillary sinus floor elevation procedure was performed and the bone defects were augmented with particulate bone grafts, as described by 7
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