Medline, Cochrane Library.English articles published from 1966 to June 2007, in which the masticatory performance of subjects with implant-supported or retained dentures was assessed by objective methods and compared to performance with conventional dentures, were included. Single-tooth implants studies were excluded.Characteristics of subjects, type of dentures, and quantitative results were extracted from original articles. Level of evidence was rated by 2 authors following the United States Agency for Healthcare Research and Quality (AHRQ, www.ahrq.gov/) recommendations.18 articles met the criteria for inclusion. Experimental studies showed: 1. fixed implant-supported partial dentures do not provide significant improvement in masticatory performance compared to conventional removable partial dentures for Kennedy Class I and II partially edentulous mandibles; 2. the combination of a mandibular implant-supported or retained overdenture (IOD) and maxillary conventional complete denture (CD) provides significant improvement in masticatory performance compared to CDs in both the mandible and maxilla for a limited population having persistent functional problems with an existing mandibular CD due to severely resorbed mandible; and 3. the type of implant and attachment system for mandibular IODs has a limited impact.Well-designed; quasi-experimental studies showed ;1. mandibular fixed implant-supported complete dentures provide significant improvement in masticatory performance compared to mandibular CDs in subjects dissatisfied with their CDs; and 2. implant-supported mandibular resection dentures have an advantage over conventional dentures in masticatory performance on the defect side of the mouth.While a number of studies on masticatory performance have been conducted in patients with various designs of implant-supported or retained dentures, high-level evidence supporting advantages in masticatory performance of implant-supported or retained dentures over conventional dentures is limited.