The Effect of Casting Procedures on Rotational Misfit in Castable Abutments

Purpose: Misfit of implant components has been linked to restorative complications such as screw loosening. Although previous studies have shown a correlation between rotational misfit and screw loosening, the impact of casting procedures on rotational misfit is lacking. The aim of this in vitro study was to evaluate the effect of casting procedures on rotational misfit of cast abutments when compared to machined titanium abutments. Materials and Methods: Forty-eight external hexagonal implants and 48 abutments were placed in 4 groups of 12 samples each: (1) machined titanium abutments, (2) premachined palladium abutments cast-on with palladium, (3) plastic burnout abutments cast with nickel chromium, and (4) plastic burnout abutments cast with cobalt chromium. Rotational misfit between the external hexagon of the implant and the internal hexagon of the abutment was measured using standardized techniques and recorded in degrees. Mean values for each group were analyzed with analysis of variance and Tukey test. Results: The mean rotational misfit was 1.21 ± 0.57 degrees for machined titanium abutments, 1.77 ± 130 degrees for cast-on abutments, 1.98 ± 0.72 degrees for cast NiCr abutments, and 2.79 ± 1.13 degrees for cast CoCr abutments. Significantly greater rotational misfit was recorded with cast CoCr abutments when compared to machined titanium abutments (P .05). Conclusion: Rotational misfit was less than 2 degrees for all groups except for cast CoCr abutments, which demonstrated a significantly greater rotational misfit. Keywords: abutments, implants, misfit, rotational misfit