Objective: This study was conducted to evaluate the masticatory efficiency in immediately loaded implant retained mandibular complete over denture with two different occlusal schemes namely opposing conventional maxillary complete denture. Patients and Methods: Fourteen completely edentulous patients with age ranged from 51-61 years were selected from outpatient clinic of Removable Prosthodontics, Faculty of Dental Medicine, Al-Azhar University. One stage octa titanium implants with 3.75mm diameter and 14mm length were used. All Patients sharing in this study receive
immediately loaded implant reteined mandibular overdenture. They were randomly divided into two equal groups (7 patients in each), the first group had the artificial teeth arranged in a median lingualized occlusio, while the second group had the artificial teeth arranged in a bilateral balanced occlusion. Masticatory efficiency measurements were
taken at the first time of overdenture placement and after six months of over denture use. Paired t-test was used to evaluate the masticatory efficiency before and after adaptation period for each group. Independent t-test was used to compare the masticatory efficiency measurements between both groups. Results: At the time of denture placement, there
was no significance difference in masticatory efficiency measurements between both groups. Masticatory efficiency was increased considerably after six months of denture use, and it was significantly higher than masticatory efficiency recorded at the time of new prosthesis placement in the same group. After six months of denture use, there
was a significance difference in masticatory efficiency measurements between both groups. Conclusions: It was concluded that using lingualized occlusion concepts was resulted in increased masticatory efficiency more than bilateral balanced occlusion after six months of denture use in patients received immediately loaded implant retained mandibular overdenture with ball and socket attachment.