Microstrains around standard and mini implants supporting different bridge designs

The purpose of the study was to analyze microstrains around small- versus standard-diameter implants used in restoration of thin wiry ridge through different bridge designs. Additionally, influence of the site of occlusal vertical loading was evaluated using strain gauges. Two models simulating mandibular unilateral free-end saddle were fabricated. Two standard-size implants (3.75 × 13 mm) were inserted in one model in the position of the second premolar and first molar to support 2 3-unit cantilever bridges (NiCr alloy). On the other model, a standard implant and a mini implant (3.0 × 13 mm) were inserted in the position of the second premolar and second molar, respectively, to support 2 fixed-fixed 3-unit NiCr bridges. Four strain gauges were mounted buccally, lingually, mesially, and distally adjacent to each implant. The prostheses were temporarily cemented. A 300 N vertical load was applied on the middle of the horizontal runner bar connecting the prosthetic units and on the center of the pontics. Microstrains were recorded and analyzed. Cantilever bridges recorded higher microstrains than fixed-fixed bridges for both loading conditions. Yet, for both designs, loading on the horizontal runner bars, which apply an equal load on all bridge units simultaneously, resulted in significantly lower microstrain values than applying the load only on the pontics. Mini implant revealed greater strain values than standard implant supporting the same fixed partial denture. The best treatment option that produced the least microstrains was the fixed-fixed bridge with a mini implant as a terminal abutment. Mini implants induced higher microstrains than standard implants.