Introduction:  Many case reports and retrospective studies related implant placement to     mandibular weakness and fracture. 
Objectives:This study aimed to investigate the effect of number and positions of dental implants on structure integrity of completely edentulous mandible.
Material and Methods:Thirty-two synthetic edentulous polyurethane mandibles were divided in 4 groups: First group (I) was unaltered eight fully intact replicas representing control group acting as reference. Second group (II) was eight replicas where only single symphysial implant was placed representing single implant group. Third Group (III) was eight replicas with inserted double implants in canine area representing double implant group, while fourth group (IV) was eight replicas with inserted triple implants (two implants in premolar area, one implant in symphysis) representing triple implant group. Vertical loads were simulated by universal testing machine under conditions simulating trauma, with a compression force acting laterally on the ramus of the mandible with displacement rate up of 5 mm/min until failure. The primary outcome variable was maximum load to failure. Other outcome variables were Fracture locations and displacement to failure. Scanning electron microscope was utilized to evaluate the changes in the implant surfaces in fracture sites.
Results: the results of this study revealed that there were significant differences in Maximal failure loads and fracture location across all groups [P = 0.02, P < 0.0001, respectively].
Conclusion:It was assumed from this study that placement of dental implant in canine positions disturbed structure integrity of intact mandibles and acted as point of weakness.