Metals for implantation in the human body

Cytocompatible tantalum films on Ti6Al4V substrate by filtered cathodic vacuum arc deposition

Tantalum films were deposited on negatively biased Ti6Al4V substrates using filtered cathodic vacuum arc deposition to enhance the corrosion resistance of the Ti6Al4V alloy. The effect of substrate voltage bias on the microstructure, mechanical and corrosion properties was examined and the cytocompatibility of the deposited films was verified with mammalian cell culturing. The Ta films deposited with substrate bias of -100V and -200V show a mixture of predominantly β phase and minority of α phase. The Ta/-100V film shows adhesive failure at the Ti/Ta interface and a cohesive fracture is observed in Ta/-200V film. The Ta/-100V showed a significant improvement in corrosion resistance, which is attributed to the stable oxide layer. The in-vitro cytocompatibility of the materials was investigated using rat bone mesenchymal stem cells, and the results show that the Ta films have no adverse effect on mammalian cell adhesion and spreading proliferation.

Comparison of ion release from new and recycled orthodontic brackets

Bracket corrosion can occur in the oral environment. The purpose of this study was to compare the release of metal ions from new and recycled brackets in artificial saliva and buffers with different pH values over a 12-week immersion period. The brackets were divided into 2 groups: new and recycled. The recycled bracket bases were coated with adhesive and the brackets were heat treated. Nickel, chromium, iron, and manganese ions were detected by atomic absorption. The surface characteristics of the brackets were examined by energy dispersive radiographic analysis. The results were as follows: (1) Recycled brackets released more ions than did the new brackets. (2) Greater amounts of nickel, iron, and manganese ions were released in artificial saliva than in the other buffers tested. (3) Ion release from brackets in a pH 4 buffer was greater than that observed in pH 7 or pH 10 buffers. (4) The total amount of ion release increased with time. (5) After a 12-week immersion, the total ion release averaged over the period did not exceed the recommended daily intake.

Corrosion of resin-bonded orthodontic brackets

The objective was to identify the nature and origin of indelible black and green stains found in enamel after the removal of bonded orthodontic brackets. Several brackets were examined by scanning electron microscopy and energy-dispersive x-ray analysis. Irrespective of the type of bracket or resin, morphologic evidence of corrosion activity was found. Brackets were pitted, and in some cases large amounts of metal were missing. Cracks were found in the resin which led to sites of destruction in which structures resembling microorganisms were also found. X-ray analysis showed the presence of chromium, nickel, iron, and chlorine in significant amounts in the bonding, discolored resin. It was concluded that the cracks were favoring crevice corrosion. In the presence of organisms and a lowered pH, together with a chloride environment and an oxygen gradient, conditions conducive to corrosion are established.

A statistical treatment of fatigue of the cast Co-Cr-Mo prosthesis alloy

Fatigue tests have been conducted on commercially produced cast Co-Cr-Mo alloy in tension-tension while surrounded by a physiological solution at 37 degrees C. The data have been analyzed by statistical techniques to yield an allowable stress such that there is 95% confidence of less than one failure in 1,000 after 5 X 10(7) cycles of stress fluctuation. These results are valid for a substantially sounder material than may be common in commercial use and therefore a more conservative allowable stress probably ought to be used for design purposes.

Brain tissue reaction to some chronically implanted metals

✓ The toxicity of certain metals, namely, platinum, platinum-8% tungsten, platinum-10% rhodium, platinum-10% iridium, platinum-10% nickel, platinized platinum, a gold-nickel-chromium alloy, a gold-palladium-rhodium alloy, a chromium-nickel-molybdenum alloy (Vitallium), stainless steel, silver, rhenium, and gold, was evaluated histologically following chronic implantation for 2 months in the brains of cats. Of the above metals, all but silver were found to be nontoxic. Boron was also evaluated and found to be nontoxic.