Pilot study of the relationship between the hardness and abrasion resistance of two base metal alloys used for metal-ceramic restorations.

STATEMENT OF PROBLEM: Base metal alloys present high values of strength and hardness, which have been associated with the greater abrasion resistance and polishing of metal-ceramic restorations. However, surface hardness has been shown to be a poor indicator of abrasion resistance. PURPOSE: The study aimed to compare the hardness and abrasion resistance of Ni-Cr alloys and determine whether there is a correlation between these 2 properties. MATERIAL AND METHODS: Two Ni-Cr alloys for metal-ceramic restorations with different hardness values were subjected to the following procedures: (1) initial measurement of Vickers hardness, (2) a series of abrasion cycles, (3) measurement of mass loss after each cycle, and (4) Vickers hardness measurements after each cycle. RESULTS: For each alloy, linear regression revealed a negative correlation between hardness and reduction in mass. The higher hardness of alloy A was associated with higher mass loss during abrasion when compared with alloy B. CONCLUSION: There was no significant correlation between hardness and mass loss for either alloy.

Corrosion-fatigue life of commercially pure titanium and Ti-6Al-4V alloys in different storage environments.

STATEMENT OF PROBLEM: Removable partial dentures are affected by fatigue because of the cyclic mechanism of the masticatory system and frequent insertion and removal. Titanium and its alloys have been used in the manufacture of denture frameworks; however, preventive agents with fluorides are thought to attack titanium alloy surfaces. PURPOSE: This study evaluated, compared, and analyzed the corrosion-fatigue life of commercially pure titanium and Ti-6Al-4V alloy in different storage environments. MATERIAL AND METHODS: For each metal, 33 dumbbell rods, 2.3 mm in diameter at the central segment, were cast in the Rematitan system. Corrosion-fatigue strength test was carried out through a universal testing machine with a load 30% lower than the 0.2% offset yield strength and a combined influence of different environments: in air at room temperature, with synthetic saliva, and with fluoride synthetic saliva. After failure, the number of cycles were recorded, and fracture surfaces were examined with an SEM. RESULTS: ANOVA and Tukey's multiple comparison test indicated that Ti-6Al-4V alloy achieved 21,269 cycles (SD = 8,355) against 19,157 cycles (SD = 3, 624) for the commercially pure Ti. There were no significant differences between either metal in the corrosion-fatigue life for dry specimens, but when the solutions were present, the fatigue life was significantly reduced, probably because of the production of corrosion pits caused by superficial reactions.