Data sources Cochrane Oral Health's Trials Register, the Cochrane Central Register of Controlled Trials (CENTRAL), Medline, Embase, the US National Institutes of Health Ongoing Trials Register (ClinicalTrials.gov) and the World Health Organization International Clinical Trials Registry Platform. Study selection Randomised controlled trials (RCTs), including cross-over trials on maxillary or mandibular implant overdentures with different attachment systems with at least one-year follow-up were considered. There were no restrictions on language or date of publication. Data extraction and synthesis Data were abstracted by four reviewers with risk of bias being assessed using the Cochrane tool. Data were combined using a fixed effects meta-analysis. The GRADE approach was used to assess the overall body of evidence. Results Six RCTs with a total of 294 mandibular overdentures were included. All of the trials were considered to be at high risk of bias. No studies on maxillary overdentures were included. For bar and ball attachments there was low quality evidence [two studies] that short-term re-treatment (repair of attachment system) was higher with ball attachments; RR =3.11(95%CI; 1.68 to 5.75) but no difference RR = 1.18(95%CI; 0.38 to 3.71) for replacements of attachment systems. There was no difference between ball and magnet systems in medium-term prosthodontic success or repair of attachment systems, but prosthodontic maintenance costs were higher when magnet attachments were used [one study - very low quality evidence]. Only one trial compared ball and telescopic attachments providing very low quality evidence. Conclusions For mandibular overdentures, there is insufficient evidence to determine the relative effectiveness of different attachment systems on prosthodontic success, prosthodontic maintenance, patient satisfaction, patient preference or costs. No trial evidence was available for maxillary overdentures.
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