Bond strength of three porcelains to two forms of titanium using two firing atmospheres

Statement of problem. Problems with casting and porcelain bonding are encountered when titanium is used in metal-porcelain restorations. The oxidation characteristics of titanium are the main problem. The bending mechanisms in titanium-porcelain systems are complex and poorly understood. Purpose. An in vitro investigation was performed to evaluate the bonding characteristics of 3 titanium-porcelain systems in various firing conditions. Material and methods. This study evaluated the bonding strength of 3 commercial titanium porcelains fired in a vacuum and in an argon atmosphere to cast and noncast commercially pure titanium, using a a-point bending test according to DIN 13927 and SEM with energy dispersive spectrometry analysis. The results were compared with an Ni-Cr alloy and a conventional porcelain that was chosen as a control. Results. The Ni-Cr-conventional porcelain system fired in an argon atmosphere had significantly higher bond strength than the other systems (P<.001). In addition, the bond strength of the titanium-spark erosion-Noritake Ti22 combination, fired in an argon atmosphere, was significantly higher than the other titanium-porcelain groups, which had results similar to those obtained with the vacuum-fired, Ni-Cr-conventional porcelain and argon-fired titanium-cast-Noritake Ti22 groups. On the other hand, the bond strength of the titanium-TiBond and titanium-Vita Titankeramik groups was below the lower limit value in the DIN 13927 standard for the 3-point bending test (25 MPa). Although the results of the Duncan multiple range test showed that firing in an argon atmosphere did not affect the bond strength of the titanium-Vita Titankeramik groups, the titanium-spark erosion-TiBond group, or the titanium-cast-Noritake Ti22 group, argon firing improved the bond strengths of the Ni-Cr-conventional porcelain group, the titanium-cast-TiBond group, and the titanium-spark erosion-Noritake Ti22 porcelain group. It was also found that there were no significant differences between the bond strengths of cast and non cast titanium groups; an exception was the titanium TiBond groups in which the porcelain was fired in a vacuum. Conclusion. The oxide layer produced on titanium was considered to have a potentially adverse effect on titanium-porcelain bonding. It was also concluded that matching the titanium-porcelain combination is the main determinant for optimal bonding. Firing in an argon atmosphere that limited the oxidation of titanium improved the titanium-porcelain bond in some of the groups.