Electrochemical Behavior of Alloys for Fixed Partial Denture
The electrochemical behaviors of eight parent alloys and four post-solder alloys used in dental prostheses were specified in a (pH=7.4; (NaCl)=9g/L)-aqueous solution at 37°C. For each alloy, the free potential was followed during two hours, and a cyclic polarization between the cathodic domain and the solvent's oxidation was performed. The gal- vanic corrosion between each parent alloy and its usual post-solder was also studied. The free potentials stay in the immu- nity domain of the alloy's base-elements (precious metals) or in their passivation domain (nickel, chromium). A relatively strong oxidation of the alloys is possible only for high values of applied potential. Corrosion of the noblest alloys is al- most inexistent. It occurs for the nickel-base alloys but it is very slow. Most of the elements present can be oxidized, but only for high potentials which cannot be really achieved by dissolved oxygen. Galvanic corrosion can occur between the parent alloy and the post-solder alloy in some cases. The realization of frameworks for fixed partial denture (FPD) often involves the use of more or less noble metallic alloys and their assemblage by soldering. The latter is called pre-ceramic soldering or post-ceramic soldering, this de- pending on the step of the fabrication of the prostheses at which this soldering is realized. Soldering is well used to correct distortion of the framework which occurs during the casting process (1), to improve the seating accuracy (2) and to correct a possible movement of teeth before prosthesis cementation (3). The solder joint is often the weakest part of a fixed partial denture (4, 5). While some defects can be due to the process of fabrication (6), others can appear during the use of the prosthesis in the mouth, because of corrosion by saliva which can generate additional cavities on alloy sur- face. Indeed, the metallic framework may partly remain exposed to the buccal milieu, notably a part of the parent alloy and the post-ceramic solder which is not covered by ceramic. These are the reasons why the individual behaviors of main alloy of the framework and of the post-solder alloys in contact with saliva need to be better known, as well as the behavior of this parent alloy coupled with its usual post- solder. The purpose of this article is first to specify the separate behaviors of the parent alloy and of the post-ceramic solder, and second to study the possible galvanic corrosion which could be due to the association of the two materials, by using electrochemical techniques. The electrolyte used in this study, is characterized by a NaCl concentration of 9 g/L and
Accuracy of one-piece castings, preceramic and postceramic soldering.
An investigation was conducted to evaluate the relative accuracy of one-piece castings of FPDs of three, four, and five units with those assembled by preceramic soldering and postceramic soldering. The preceramic soldered FPDs were subjected to six simulated porcelain firing cycles to assure a homogeneous sample. A total of 15 FPDs, five of each length, were evaluated for each test condition. A three-piece aluminum mold with stainless steel dies, which allowed for varying the length of the prosthesis, was used to fabricate the FPDs in 52% gold-palladium alloy. Marginal discrepancies of the castings on the dies were compared for the three test techniques. The mesiodistal length of the FPDs that were pre- and postsoldered were also measured at the occlusal and at the gingival margins and compared with the restorations before soldering.
Catalytic hydrogenolysis of poly-iodinated recombinant human insulin-like growth factor II (IGF-II): a potentially useful method for the tritiation of IGF-II.
A method has been developed to prepare, purify, and fully characterize poly-iodinated insulin-like growth factor II (IGF-II) which can then be catalytically deiodinated to produce IGF-II with its native disulfide bonded structure. This method can potentially be adapted to prepare tritiated IGF-II with the use of tritium gas in the hydrogenolysis step. IGF-II was iodinated at all three tyrosines using lactoperoxidase with a three-fold excess of sodium iodide. The iodinated products were purified using reversed-phase HPLC and characterized by peptide mapping. The tyrosine-containing peptides generated by pepsin digestion were characterized by amino acid sequence analysis. Mono- and di-iodinated phenylthiohydantoin tyrosine derivatives were synthesized and used to identify the iodination state of the modified tyrosine residues in the sequence analysis. Purified poly-iodinated IGF-II was deiodinated by hydrogenolysis, over a prereduced palladium (II) oxide catalyst to form IGF-II with its native disulfide bonds intact, as shown by peptide mapping.