Effect of splinting and interproximal contact tightness on load transfer by implant restorations.

STATEMENT OF PROBLEM To circumvent the difficulty of achieving a passive framework fit, some authors have suggested that multiple adjacent implants be restored individually. This protocol requires that each unit be able to withstand mastication forces. Non-splinted restorations have numerous interproximal contacts that require adjustments prior to placement, with an unknown outcome relative to load transfer. PURPOSE This in vitro simulation study examined the effect of splinting and interproximal contact tightness on passivity of fit and the load transfer characteristics of implant restorations. MATERIAL AND METHODS A photoelastic model of a human partially edentulous left mandible with 3 screw-type implants (3.75 x 10 mm) was fabricated. For non-splinted restorations, individual crowns were fabricated on 3 custom-milled titanium abutments. After the units were cemented, 5 levels of interproximal contact tightness were evaluated: open, ideal (8 microm shim stock drags without tearing), light (ideal +10 microm), medium (ideal + 50 microm), and heavy (ideal + 90 microm). For splinted restorations, five 3-unit fixed partial dentures were fabricated, internally adjusted with silicone disclosing material, and cemented to the model. Changes in stress distribution under simulated non-loaded and loaded conditions (6.8 kg) were analyzed with a polariscope. RESULTS In the simulated alveolar structures, non-splinted restorations with heavier interproximal contacts were associated with increased tensile stresses between implants; occlusal loads tended to concentrate around the specific loaded implant. Splinted restorations shared the occlusal loads and distributed the stresses more evenly between the implants when force was applied. The load-sharing effect was most evident on the center implant but also was seen on the terminal abutments of the splinted restorations. CONCLUSION The results of this in vitro study suggest that excessive contact tightness between individual crowns can lead to a non-passive situation. In this experiment, splinted restorations exhibited better load sharing than non-splinted restorations.