Dental Precious Alloys Research Articles

Galvanic Corrosion between Dental Precious Alloys and Magnetic Stainless Steels Used for Dental Magnetic Attachments

In this study, we examined the corrosion behavior of dental precious alloys and magnetic stainless steels, namely SUS 444, SUS XM27, and SUS 447J1, used for dental magnetic attachments. Their galvanic corrosion behavior was evaluated from the viewpoint of corrosion potentials when they were in contact with each other. Rest potentials of the precious alloys were constantly higher than those of magnetic stainless steels. Since most gold alloys raised the corrosion potential more significantly than silver alloys did, silver alloys seemed to be better suited than gold alloys for combination with magnetic stainless steels. However, all corrosion potential values were sufficiently lower than the breakdown potentials of the stainless steels and existed within their passive regions. Based on the findings of this study, SUS XM27 and SUS 447J1--which exhibited higher breakdown potentials than SUS 444--emerged as the preferred choices for combination with gold alloys.

Experimental Binder-free Investments Reused to Cast Dental Precious Alloys

This study aimed to develop reusable dental investments. SiO2 and MgO were selected as refractory materials to prepare three types of investment (coded as 60S-40M, 80S-20M, 100S) with 40, 20, and 0 wt% of MgO. Each type of investment was reused twice. Thermal expansion and compressive strength were examined and statistically evaluated by ANOVA. To evaluate fit of castings, full crowns were cast by using a commercial Au-Ag-Pd alloy with all investment types. Marginal fit was statistically analyzed by cement thickness. It was found that although MgO strengthened the mold, it had little influence on expansion. The strength of 60S-40M was the highest, and 100S had the greatest advantage with regard to thermal expansion. In the evaluation for clinical applicability, all investments were able to cast successfully, but their castings might be undersized. Among the experimental binder-free investments reused for dental casting in this study, 100S in particular showed to be a good candidate for repeated fabrication of precision fit castings.

Laser Welding of Titanium and Dental Precious Alloys

The performance of laser welding of Ti and two dental precious alloys (Ag-Pd-Au, Au-Pt-Ag) was investigated by mechanical testing and microscopic observation, using butt joint as design. The laser irradiation was done using a commercial Nd:YAG dental laser-welding device in a single pulse mode with output currents 150, 200, 250, 300 A, spot diameters 0.6, 0.9, 1.2 mm, and pulse duration 10 ms. The average welding fracture strength of the dissimilar metals were 108.9 and 137.2 MPa for Ti and Ag-Pd-Au alloy, and Au-Pt-Ag alloy, respectively. The average welding fracture strength of the same metals were 594.9, 648.8 and 312.9 MPa for Ti, Ag-Pd-Au alloy and Au-Pt-Ag alloy. The hardness increased in weld zone, compared with the base metals. Penetration depths were affected by the welding conditions such as the output currents and spot diameters. The welding cracks and porosity were observed in microstructures of the welds. Mapping by EPMA showed the remarkable heterogeneity of the component metals concerned. The welding cracks, porosities and granular precipitates similar to metallic compounds in the weld zones were suggested as the cause for lower welding fracture strength in the dissimilar welds, compared with the similar metals.

金属酸化物をコーティングする接着用表面処理法の研究 Ｉ 貴金属合金に対するＣｕターゲットの効果について

Ion sputtering is a phenomenon in which ions or other high energy particles strike at a target electrode causing emission of atoms from the electrode. It takes placein a grow discharge in a relatively low vacuum chamber. We studied the application of this phenomenon to surface treatment of dental precious alloys for adhesion.Nine pure metals were examined the aptitude as a target which was the source of metal oxide supply. As the result of adhesion endurance test, Cu target showed favorableadhesive strength, and following studies were conducted applying Cu target. In the next study to decide the optimum ion coating time, best result was obtained by 10 minutes treatment.Type IV and Au-Ag-Pd alloys ion coated for 10 minutes with Cu target showed excellent adhesive durability in endurance test and after subjection to thermal cycling of 50, 000 times, adhesive strength of above 250 kgf/cm2 were maintained.