Bending resistance of prefabricated titanium posts following molten cast core attachment

Posts and cores are used to restore endodontically treated teeth that have substantial loss of the coronal tooth structure. This in vitro study was designed to determine the mechanical properties of prefabricated titanium posts following attachment of their metal cores by molten casting (caston). Prefabricated tapered titanium posts (ER post-restoring system, Komet, Lemgo, Germany) in three diameter sizes (ISO 50, 90, 110) (n=9) were cast over with the metal cores of three different alloys (Au-Ag-Pt, Au-Pt-Pd, Co-Cr-Mo). Also, posts of each size were precision fit into the central core channels of the different cast metal cores to serve as control specimens. The 0.2% yield strengths (R0.2) of all specimens were tested on a universal testing machine. Statistical analyses of the results were carried out with an analysis of variance (ANOVA, one-way, two-way) and Bonferroni-Dunn's multiple comparisons post-hoc analysis for test groups (alpha=0.05). There was a significant decrease in yield strength (p<0.05) as a result of casting the various metals over the different post sizes, considered to be due to the detrimental thickening and porosity formation of the titanium surface oxide layer. Twenty-one percent, 51% and 33% reduction in yield strength, respectively, was obtained for the ISO 50, ISO 90 and ISO 110 cast-on groups relative to controls (p<0.05). Statistically significant differences in various core alloys were found only for the Au-Ag-Pt alloy compared to the Co-Cr-Mo alloy (post size ISO 50) and the Au-Pt-Pd alloy compared to the Co-Cr-Mo alloy (post size ISO 110) (p>0.05). Prefabricated titanium posts with metal cores cast over them showed inferior mechanical properties compared to precision-fit posts. These results indicate greater strength of the titanium posts when their cast cores were attached mechanically rather than by the molten casting method.