Effect of Cantileverd Bar Length on Strain Around Two and Four-Implants Supporting A Mandibular Over-Denture

Statement of problem There is little information as to how the cantilevered bar length affect the strain around two and four implants supporting a mandibular over denture Purpose measure the effect of cantilevered bar length on strain produced around two-implant and four-implant supporting a mandibular over denture, and evaluating the amount of stress reaching the supporting structures. Materials and methods Two root-form implants were placed bilaterally in the canine region of an edentulous acrylic mandibular model (group A). Also four root-form implants were placed in the canine & bicuspid region of another edentulous acrylic mandibular model (group B). The implants on each model were connected with a resilient bar/clip attachment with the following lengths of cantilevered bar length 11mm, 9mm and 7mm. Four linear strain gauges were bonded to the acrylic resin at the mesial & distal surface of each implant. Each gauge was wired separately into a 1/4 Wheatstone bridge of a multichannel digital bridge amplifier. Strains were measured on each model. Strain measurements were performed under central loading using a loading device. Results when using two or four implants, the 11mm cantilevered bar length generated the highest peri-implant strain values, while the 7mm cantilever length recorded the lowest under central loading conditions. A positive correlation between the cantilever length and the peri-implant strain was found. The same effect was found on the supporting structures. Conclusion The 7mm cantilevered bar with clips placed on the cantilevers was recommended when 2 or 4 implants were used to support mandibular over dentures as it demonstrated the lowest magnitude of strains with no significant differences between peri-implant sites