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BACKGROUND Retention and stabilization of a single-implant mandibular overdenture (SIMO) are influenced by the biomechanical properties and clinical performance of the attachment system. PURPOSE To compare clinical and patient-reported outcomes following the use of two retention systems, a ball and a stud-type Equator attachment, used for SIMO. MATERIAL AND METHODS 18 fully edentulous participants were treated with a SIMO opposing to a maxillary complete denture. They received two retentive attachments (ball and Equator) in alternate periods (sequences A-B and B-A) and outcomes were assessed after the 1 week (initial) and 3 months (final) periods. In the final assessment, patients were also asked about their preferred retention system. RESULTS Compared to baseline there was an improvement in patient satisfaction using both attachments, whilst no difference was observed between initial and final periods. Similarly, no significant differences were observed when comparing the Ball and Equator at the initial (p=0.330) and final (p=0.08) periods. The multilevel mixed model analysis revealed that the patients' satisfaction was predicted only by their satisfaction with dentures before implant placement. Although no significant difference was found between attachments regarding patient preference, this may be biased by the sequence of attachment use, which suggests that a learning effect might be present in this crossover study design. CONCLUSION The use of a single midline implant to retain a mandibular overdenture significantly improves patient satisfaction irrespective of the attachment used, but patients' preference for the second treatment suggested a learning effect in this study.