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

Objectives: 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. Methods: 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. Results: 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). Conclusions: 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. (C) 2008 Elsevier Ltd. All rights reserved.