19 Maxillary implant overdentures: bars or solitary attachments 2.1 INTRODUCTION Patients experiencing problems with their conventional maxillary denture can benefit from implant-retained overdentures (IODs)1-3. Several retention systems are available which can be roughly divided into bar-retained IODs, in which multiple implants are splinted and the overdenture is attached through retentive clips, and into retention systems using non-splinted solitary attachments. Bar-retained IODs on four implants provide good retention, require little maintenance, but are more expensive than solitary attachments. The medium term results of IODs on four implants (4-IOD) with bar retention are promising, with high implant and overdenture survival rate and a low incidence of complications, and may be considered the gold standard1-6. Solitary attachments, an alternative to bars, are more economical and easy to clean by the patient7, but wear more easily, which can cause lack of retention8. However, replacing these attachments can often be done chair side. A recent review reported that, when a maxillary IOD is supported by four implants, both types show equal implant survival rate, overdenture survival rate and patient satisfaction9. However, these conclusions are based on a limited number of randomised controlled trials. Moreover, most studies on solitary attachments were mostly short term, non-comparing or retrospective, and therefore inconclusive. This underlines the need for studies comparing different attachment systems with a longer follow-up. We conducted a randomised controlled trial to compared the treatment outcomes of fully edentulous patients with maxillary IODs, supported by four implants, retained by either bars or solitary attachments. Marginal bone level change, implant and overdenture survival rate, technical and biological complications, clinical characteristics and patient related outcome measures were assessed during a 5-year follow-up. 2.2 MATERIALS AND METHODS Patients Between January 2013 and January 2016, all eligible fully edentulous patients experiencing problems with their maxillary conventional denture that were referred to the Department of Oral and Maxillofacial Surgery (University Medical Center Groningen, the Netherlands) were asked to participate in a randomised controlled trial. The patients were considered eligible to participate if they had been fully edentulous for at least one year and had sufficient bone volume to place four implants in the anterior maxilla. The patients were allowed to have mandibular IODs. The bone volume was assessed using cone beam computed tomography (CBCT). The exclusion criteria were an American Society of Anaesthesiologists score (ASA score10) of ≥III, smoking, former radiotherapy in the head and neck region, pre-prosthetic surgery or previous loss of implants in the maxilla. All the participants received oral and written information about the trial. Signed informed consent was obtained from each participant. The initial 1-year trial was approved by the Medical Ethical Committee of the UMCG and the study was registered in the Dutch Trial Register (NL3813). In the present 5-year follow-up study, no new interventions were carried out and was therefore not considered research performed on test-subjects as meant in the Medical Research Involving Human Subjects Act (WMO) (MEC-reference M20.259187). The 2
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