Castability evaluation and effect of recasting of ceramo-metal alloys.

This study was conducted to assess the castability of four ceramo-metal alloys including three base metal alloys (nickel-chromium, cobalt-chromium, and titanium) as well as a gold alloy as control. The mesh test pattern was used to produce a total of 20 cast samples, five for each. The percent castability value was calculated by counting complete segments of a cast alloy grid. Effect of recasting on the castability was evaluated using fresh and cast alloys in the ratio of 50:50, cast into the mesh design. Results revealed a superior percent castability values for gold alloy with comparable results produced by the Ni-Cr alloy while Titanium alloy displayed the least values. Recasting elicited a significant decrease in castability for Titanium alloy whereas other investigated alloy systems were not significantly affected. Laboratory castability evaluation is a valuable tool for both selecting and using dental materials for producing cast restorations.

Resistance to fracture of high-strength porcelain crowns versus metal ceramic crowns under different conditions.

Although the good appearance and biocompatibility of dental porcelains, failures are still of considerable concern because of the limited properties to all ceramic system. Physical properties that might be considered ideal include high strength, resistance to abrasion, and resistance to the hostile oral environment. Porcelain has been considered by many of its physical characteristic are similar to those of enamel. In 1983 a new modality of treatment, the etched porcelain restoration was introduced by Simonsen and Calamia. Numerous investigations have shown the strength of the etched porcelain bonded to composite resin and also the clinical success of this porcelain to be used as laminated veneers and etched inlays and onlays.