PubMed · 6962552
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F Nikolopoulou. [Construction materials for complete denture bases].. https://pubmed.ncbi.nlm.nih.gov/6962552/
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This in vitro study evaluated the efficacy and safety of six different nickel-titanium engine-driven instruments used with a torque-controlled engine device and nickel-titanium hand and stainless steel hand instruments in preparation of curved canals. A total of 80 curved (36 degrees) simulated root canals were prepared. Images before and after were superimposed, and instrumentation areas were observed. Time of instrumentation, instrument failure, change in working length and weight loss were also recorded. Results show that stainless steel hand instruments cause significantly less transportation towards the inner wall of the canal than do nickel-titanium hand instruments. No instrument fracture occurred with hand instruments, but 30-60% breakage of instruments was recorded during instrumentation with the engine-driven devices. The working length was maintained by all types of instruments. Newly developed nickel-titanium rotary files were not able to prevent straightening of the severely curved canals when a torque-controlled engine-driven device was used.
The age-hardening reactions in a commercial type III dental gold alloy were studied by means of hardness test, X-ray diffraction study and scanning and transmission electron microscopic observations. The hardening was attributed to the formation of the metastable AuCu 1' type ordered phase in the grain interior by the isothermal ageing at 225 and 450 degrees C at which two hardness peaks were observed by the isochronal ageing. By ageing at 450 degrees C, the hardening did not begin immediately because the incubation period was required. The age hardening at 225 degrees C was characterized by a slow growth rate of the metastable AuCu 1' type ordered phase. The overageing with softening which occurred following prolonged ageing at 450 degrees C was due to the formation of the lamellar structure composed of the Ag-rich alpha1 and AuCu 1 type ordered phases at grain boundaries.
The purpose of this study was to investigate the bond strength between porcelain and experimental cast titanium alloys. Eleven binary titanium alloys were examined: Ti-Cr (15, 20, 25 wt%), Ti-Pd (15, 20, 25 wt%), Ti-Ag (10, 15, 20 wt%), and Ti-Cu (5, 10 wt%). As controls, the bond strengths for commercially pure titanium (KS-50, Kobelco, Japan) and a high noble gold alloy (KIK, Ishifuku, Japan) were also examined. Castings were made using a centrifugal casting unit (Ticast Super R, Selec Co., Japan). Commercial porcelain for titanium (TITAN, Noritake, Japan) was applied to cast specimens. The bond strengths were evaluated using a three-point bend test according to ISO 9693. Since the elastic modulus value is needed to evaluate the bond strength, the modulus was measured for each alloy using a three-point bend test. Results were analyzed using one-way ANOVA/S-N-K test (alpha = 0.05). Although the elastic moduli of the Ti-Pd alloys were significantly lower than those of other alloys (p = 0.0001), there was a significant difference in bond strength only between the Ti-25Pd and Ti-15Ag alloys (p = 0.009). The strengths determined for all the experimental alloys ranged from 29.4 to 37.2MPa, which are above the minimum value required by the ISO specification (25 MPa).