Ali H. EL Shoukouki^A; EL Sayed A. Abdel-khalek^B; Jameela m. Khalefa^C A-      Professor of prosthodontics, Faculty of Dentistry,Mansoura University, Egypt. B-      Assistant Professor of prosthodontics, Faculty of Dentistry,Mansoura University, Egypt. C-      BDS, Faculty of Dentistry, Al-Zawia University, Libya. Abstract: Introduction:Rehabilitation of edentulous mandible by means of implant-retained dentures is effective treatment modality that, mostly provide sufficient denture retention by two inter foraminal implants. The use of bar attachment allows the splinting of implants and provides better stress distribution with higher level of comfort and long-term stability. Traditionally; metallic, plastic clips or resilient denture liner have been used to anchor the denture to the bar joining the implants (Dos Santos et al., 2014). Aim of the work : This study was aimed to examine the influence of thickness soft lining resilient Molloplast-B bar frame work as related to retentive force for mandibular implant over-denture at (1, 2, and 3mm), thickness, with different bar cross-section (round- oval & Hader) bar attachment. Material and methods:This in vitro study was carried out on squared shape educational edentulous mandibular models. According to the bar cross section and thickness of soft liner around the bar, the models were divided into the test groups as follow:  group A model with Round bar connecting both implants retaining overdenture with 1mm, 2 mm, or 3mm thickness of soft lining resilient Molloplast-B bar frame work. And group Ba model with Hader bar connecting both implants retaining overdenture with 1mm, 2 mm, or 3mm thickness of soft lining resilient Molloplast-B bar frame work. And Group C: a model with Dolder bar connecting both implants retaining over-denture with1mm, 2 mm, or 3mm thickness of soft lining resilient Molloplast-B bar frame work, they connected to installed implants at canine region. Acrylic resin complete mandibular over-dentures were constructed. The retention measured by use digital force meter, data was collected and statistically analysis. Result:this study revealed that the highest retentive force was observed with Dolder bar at 3 mm thickness compared to Hader and round bars design with different soft liner thickness. Conclusion:Molloplast-B resilient bar frame work retention is dependent on its thickness and bar cross section design. A 3mm thickness resilient liner is more retentive than 1 or 2mm thickness for round and Hader bar. Oval cross section bar provide more retentive infrabulge undercut for resilient liner material.