Limitations of reuse for silver-palladium alloys -Evaluating post-recasting heat treatment impact on corrosion resistance.

The aim of this study was to investigate the effect of repeated casting and heat treatment on the corrosion resistance of a commercial Ag-Pd-Cu-Au alloy as evaluated by electrochemical techniques. After repeated casting, the fifth cast of the Ag-Pd-Cu-Au alloy exhibited dramatic degradation of properties, although upon heat treatment, this corrosion resistance did improve. Despite the improvement by heat treatment, after five castings, this alloy may not have satisfactory hardness for clinical use. These results of this study demonstrate that, up to the fourth cast and heat treatment, the Ag-Pd-Cu-Au alloy has acceptable corrosion resistance and hardness.

High-performance scaffolds on titanium surfaces: osteoblast differentiation and mineralization promoted by a globular fibrinogen layer through cell-autonomous BMP signaling.

Titanium has been widely used as a dental implant material. However, it takes several months for the implant body to bind with the jawbone. To develop new bioactive modification on titanium surfaces to achieve full osseointegration expeditiously, we used fibrinogen and fibronectin as bioactive scaffolds on the titanium plate, which are common extracellular matrix (ECM) proteins. We analyzed the features of the surface of ECM-modified titanium plates by atomic force microscopy and Fourier transform infrared spectrophotometry. We also evaluated the effect of ECM modification on promoting the differentiation and mineralization of osteoblasts on these surfaces. Fibrinogen had excellent adsorption on titanium surfaces even at low concentrations, due to the binding ability of fibrinogen via its RGD motif. The surface was composed of a fibrinogen monolayer, in which the ratio of ß-sheets was decreased. Osteoblast proliferation on ECM-modified titanium surface was significantly promoted compared with titanium alone. Calcification on the modified surface was also accelerated. These ECM-promoting effects correlated with increased expression of bone morphogenetic proteins (BMPs) by the osteoblasts themselves and were inhibited by Noggin, a BMP inhibitor. These results suggest that the fibrinogen monolayer-modified titanium surface is recognized as bioactive scaffolds and promotes bone formation, resulting in the acceleration of osseointegration.

Effect of fluoride from glass ionomer on discoloration and corrosion of titanium.

The objective of the study was to examine the effects that fluoride ions released from different dental glass ionomer cements may have on titanium. The study included determination of the amounts of released ions and measurement of the color changes on titanium plates cemented with four kinds of commercial glass ionomer cements due to immersion of such "sandwich specimens" in 1% saline (NaCl) solution. The discoloration of titanium in the presence of glass ionomer cements was observed. In addition, for specimens cemented with two of the cements titanium ions were found in the solution after immersion. The results of the present study show that a low concentration of released fluoride ions and other elements from glass ionomer cements may cause aesthetic problems of discoloration of titanium restorations and appliances.

The effect of recasting on corrosion of a silver-palladium alloy.

OBJECTIVES: Noble and semi-noble dental casting alloys are often reused by recasting. The aim of this study was to determine if repeated casting has a detrimental effect on the corrosion behavior of a silver-based dental alloy. METHODS: A commercial Ag-Pd-Cu-Au alloy was cast and four times recast. Electrochemical tests were performed to determine the effects of recasting on the polarization parameters and the corrosion current density in artificial saliva. Changes in hardness, chemical composition and microstructure were determined. RESULTS: Recasting had little effect on the shape of the polarization curves, but the corrosion current density dramatically increased after the fifth cast. Hardness increased with recasting and the microstructure showed grain growth. Increased subgrain formation was found for the fifth cast. The elemental map showed decreased surface concentration of Au for the fifth cast. The bulk concentrations of Au, Ag and Pd remained constant, but the copper and zinc contents slightly decreased and the content of impurities increased. SIGNIFICANCE: Recasting of an Ag-Pd-Cu-Au alloy initially had little effect on the corrosion susceptibility in artificial saliva, but a severe degradation of properties was observed after the fifth cast. The results indicate that a dental alloy of this type can be safely recast only a small number of times.

Evaluation of corrosion degradation of amalgams by immersion and fracture test.

In this study an immersion and fracture test was used to evaluate the susceptibility of dental amalgams to degradation of their mechanical strength by corrosion. Specimens of each of the six types of high-copper amalgams and one type of low-copper amalgam were prepared and tested. Cylindrical specimens were grooved using a diamond cutoff blade and immersed in 1% NaCl to which H2O2 was added to increase the oxidation power. After two weeks of exposure the specimens and controls were fractured and the loss of strength was calculated. Two amalgams showed a significant loss of strength. The test procedure is relatively simple and does not require sophisticated electrochemical or analytical instrumentation. A higher resolution power might be achieved by increasing the severity of corrosion or the number of replicate tests.