In vitro vertical misfit evaluation of cast frameworks for cement-retained implant-supported partial prostheses

To evaluate the influence of the alloy type and the associated investing and casting techniques, on the marginal adaptation of bridge structures luted onto prefabricated implant abutments.

Thirty frameworks for three-unit posterior-lower bridges were waxed and cast (10 of cobalt-chromium, 10 of titanium and 10 of palladium-gold). Each structure was cemented onto two prefabricated implant abutments with a special clamp designed to maintain constant seating pressure. The vertical discrepancy around the abutments' margins was assessed by scanning electron microscopy (SEM). One-way ANOVA for independent samples and Scheffe's test were applied to analyze the effect of the alloy type and its recommended investing and casting system on vertical misfit. Student's t-test for independent samples was used to compare misfit values concerning the abutment design (premolar and molar). The significance level was set at alpha=0.05.

Cobalt-chromium samples recorded the greatest vertical discrepancies, revealing significant differences with respect to both titanium and palladium-gold structures (p<0.0001). Vertical gaps of the palladium-gold and the titanium casts were not significantly different (p=0.292). Neither statistically significant differences were found between the anterior and posterior abutments' vertical misfit independently from the alloy type and nor within each group of alloys tested (p>0.05).

The vertical fit of the frameworks cast for implant-cemented bridges was influenced by the alloy type and the investing and casting methods. The marginal discrepancy of the three tested alloys could be considered clinically acceptable. A polished technique in the management of titanium could optimize the accuracy of this cast frameworks.