Aim of the study: to compare between two different denture base materials regarding their effect on the retention of complete dentures in patients with severely resorbed lower edentulous ridges. Material &methods: seven completely edentulous patients with age ranged between 55 and 65 years were selected for this study; each patient received three types of lower dentures to use it for four months, in addition to one week in between as a washing period before wearing the new one. Denture bases classified into three groups, heat cured acrylic resin denture base (Group I), heat cured acrylic resin denture base where the lower denture was lined by soft liner material (Group II) and a combination base of heat cured acrylic resin and Co-Cr denture base (Group III). Retention was evaluated after one month and three months from dentures delivery. Results: the results of this study revealed that a significant differences between group I,
group II and group III denture bases during the follow up study period after one month, and non-significant differences between group I, group II and group III denture bases during the follow up study period after three months. Conclusion: from this study it is concluded that the Co-Cr denture base and Conventional heat cure acrylic resin denture
base lined with soft liner material could be used as alternative treatment modalities to conventional heat cure acrylic resin denture bases in complete edentulous cases suffering from severely resorbed lower ridges.