Purpose: This study aimed to compare between using four implants in the inter foraminal region, and using four implants (two in the anterior region and two short implants in the posterior region) to retain mandibular dentures regarding implant stability.

Materials and methods: Fourteen completely edentulous patients were selected and divided into two groups (seven patients for each group). Group A ,Each patient was rehabilitated with four implants in the inter foraminal region retaining mandibular denture. Group B, Each patient was rehabilitated with four implants (two conventional were inserted in the inter foraminal region and two short implants were inserted on each side at the first molar regions) retaining mandibular denture. Immediate loading was done. Implant stability was evaluated using osstell at time of insertion, after two months and after four months. Independent sample t-test was used to compare between two groups in non-related samples. Repeated measure was used to compare between follow up periods within groups.

Results: Group A showed higher implant stability compared to group B. However, t-test showed no statistical significant difference. Also, there was an increase in implant stability through out the study period.

Conclusion: From the result obtained from this study, it could be concluded that: Implants stability have no relation with their distribution or length. So, using of short implants in the resorbed posterior mandible is a reliable treatment option.

Key words: screw retained dentures, implant stability, mandibular denture.