Tensile strength and microleakage of the bond between a nickel-chromium alloy and a visible light-cured resin composite: effect of 4-META, silicoating, and bead retention.

Three retention systems, 4-META adhesive, Silicoating, and a conventional retention beads system, were used for resin-metal bonding. For each group, 40 standard specimens were prepared (20 for microleakage testing and 20 for tensile strength testing). Wax patterns were prepared, invested, and cast with a nickel-chromium alloy. The metal surfaces of the specimens were sandblasted with 250-microns aluminum oxide. Dentacolor Opaque was placed and set in a light curing unit for 90 seconds. Dentacolor resin composite was placed and set in the same unit for 90 seconds. The bonded specimens were subjected to thermocycling process in baths of 5 degrees C and 55 degrees C with 30-second dwell time. The tensile strength test specimens were stored in water, and the microleakage test specimens were stored in 5% basic fuchsin dye for 2 days. The means of the tensile strength test groups were not significantly different. However, the differences in microleakage among groups were found to be statistically significant. As a result, 4-META and Silicoating systems were found to be better than the conventional retention beads system, which allowed the greatest microleakage.

The relations between alveolar ridge and the teeth located in neutral zone.

The neutral zone is defined as the area where the forces of the tongue pressing outward are neutralized by the forces of the cheeks and lips pressing inward. In this study records of neutral zones of 30 edentulous patients were used to establish the relation between teeth arrangement according to neutral zone principles and teeth arrangement according to crest of ridge. These 30 patients were classified according to their ages, edentulous periods and denture experience. The results have shown that the lower molars were positioned a little bit closer to lingual with respect to crest of ridge; premolars were positioned either close to crest of ridge or they were coincided on it. In the anterior zone, the teeth were in accordance with known principles of positioned of anatomic landmarks.

In vitro corrosion behavior of 13 prosthodontic alloys.

The corrosion behavior of 12 high-gold, low-gold, palladium-silver, and nickel-chromium alloys was tested using electrochemical techniques. A 22-carat-gold alloy was used as a control. High-gold alloys were extremely resistant to corrosion, but the resistance of the alloys decreased with decreasing mobility (from high-gold, to palladium-silver, to low-gold, to nickel-chromium alloys). Tests were also made to determine the type of corrosive attack; nickel-chromium alloys exhibited pitting, and palladium-silver alloys demonstrated the selective dissolution of the silver-rich phases. The corrosion resistance of noble alloys was far superior to that of nickel-chromium-based alloys; therefore, the palladium-silver alloys, which have a moderate price range, may be more suitable for restorations.