Effect of alloy type and casting technique on the fracture strengthof implant-cemented structures

ABSTRACT

Objectives: To evaluate the influence of alloy type and casting procedure on the fracture strength (FS) of metallicframeworks for implant-supported fixed prostheses.Study design: Thirty three-unit structures for lower posterior bridges were waxed-up and randomly assigned totwo groups (n=15) according to alloy type and casting technique Group 1 (C) cobalt-chromium cast in a centrifugalmachine (TS1, Degussa–Hüls); Group 2 (T) titanium cast in a pressure-differential device (Cyclarc II,Morita). Each structure was cemented onto two prefabricated abutments under a constant seating pressure. After6 months of water aging, samples were loaded in a static universal testing machine (EFH/5/FR, Microtest) untilfracture. Axial compressive loads were applied at the central fossa of the pontics. FS data were recorded and surfacetopography of the fractured connectors was SEM-analyzed. A Chi-Square test was performed to assess thedependence of pores on the alloy type and casting procedure. ANOVA and Student–Newman–Keuls (SNK) testswere run for FS comparisons (p<0.05).Results: One third of the C structures showed pores inside the fractured connectors. T frameworks demonstratedhigher FS than that of C specimens exhibiting pores (p=0.025). C samples containing no pores recorded the greatestmean FS (p<0.001).Conclusions: Fracture strength of metallic frameworks depended on the alloy type and casting procedure. Cobaltchromiumcasts often registered pores inside the connectors, which strongly decreased the fracture resistance.An accurate casting of titanium with a pressure-differential system may result in the most predictable techniqueunder the tested experimental conditions (AU)