The aim of this study is threefold: i) to evaluate within-subject response to complete lower dentures retained by 1 or 2 or 3 implants fitted with independent overdenture attachments; ii) laboratory evaluation of the retention force generated with 1-2 or 3-implants and study its correlation to patients' response; iii) study the wear pattern of the plastic inserts on the overdenture abutments during each retention mode (i.e. the number of implants used to retain the dentures) and correlate its effects to denture stability.