The O-ring is used to increase retention of implant complete and partial overdenture prostheses. They possess a number of advantages, including ease of use and maintenance, low cost, and possible elimination of a superstructure bar. O-rings wear over time, gradually lose retention, and must be replaced periodically. It is essential that O-ring abutments be parallel to each other. Two cases are presented showing the use of O-rings with a complete mandibular implant overdenture and a maxillary removable partial denture.