[The effect of bacteria reaction time on corrosion properties of Ni-Cr alloys pretreated with different proteins].

PURPOSE: To evaluate the corrosion properties of absorbed protein on the surface of NiCr alloys, and provide experimental base for corrosion resistance of dental casting alloys. METHODS: NiCr alloy specimens were divided into 3 groups: one group was exposed to the artificial saliva(control group), and the other 2 groups were exposed to the artificial saliva with 1% bovine serum albumin(BSA), or 0.22% lysozyme(LSZ). Group of BSA and group of LSZ were the experimental group. Specimens in 3 groups were cultured in solution of Streptococcus mutans for 12 h, 24 h, 36 h and 48h, and investigated with electrochemical impedance spectroscopy measurement(EIS) and potentiodynamic polarization measurement(POT) to determine the corrosion resistance of the alloys. The data was analyzed with SPSS 17.0 software package. RESULTS: The results indicated that the corrosion resistance of both BSA group and LSZ group were higher than that of the control group (P<0.05) and LSZ group was superior to BSA group cultured in the solution of Streptococcus mutans for 12 h. When cultured for 24 h, the corrosion resistance of BSA group and LSZ group had no significant difference (P>0.05), but was still higher than that of the control group. After 36 h culture time, the control group and the BSA group had no statistical difference in corrosion resistance （P>0.05), while the LSZ group had the poorest corrosion resistance. When the culture time extended to 48 h, the control group had a better corrosion resistance compared with the BAS group and the LSZ group(P<0.05), but BSA group had displayed lower corrosion properties than LSZ group. The potentiodynamic polarization curve and electrochemical impedance spectroscopy had similar results. CONCLUSIONS: The adhesion of BSA and LSZ on the surface of the NiCr alloys in the early time could effectively inhibit the corrosive effect of Streptococcus mutans. The LSZ had better effect than BSA. With the continuing role of bacteria and the consumption of the absorb protein, the corrosion resistance of NiCr alloys toward Streptococcus mutans becomes lower than the alloys without absorb protein, which demonstrated that the adhesion of protein would change the surface structure of NiCr alloys and BSA had a greater effect.

Mechanical properties of SEI silicone for maxillofacial prosthesis / 上海第二医科大学学报

Objective To evaluate the mechanical properties of SEI silicone for maxillofacial prosthesis before and after heat aging and explore its clinical value. Methods Two kinds of silicones, SEI and A-2186, were performed heat aging for 24, 48 and 72 h. The parameters of tear strength, tensile strength, elongation at break and hardness of them were detected under ordinary state and at different time points after heat aging. Statistic comparison and analysis were conducted. Results Tear strength, tensile strength and elongation at break of A-2186 silicone were more favorable than those of SEI silicone under ordinary state, while the parameter of hardness was an exception (P < 0.05). After heat aging and with time progress, tear strength, tensile strength and elongation at break significantly decreased and hardness significantly increased for both A-2186 silicone and SEI silicone (P < 0.05). After heat aging, tear strength and tensile strength of A-2186 silicone were more favorable than those of SEI silicone, while the latter had a minor change in hardness. Conclusion Compared with the worldwide commonly used A-2186 silicone, there is room for improvement in tear strength and tensile strength for SEI silicone. Given the favorable property of minor change in hardness after heat aging, SEI can be used as a prosthetic material for facial soft tissue defect.

Silicone elastomers for maxillofacial prosthesis / 上海第二医科大学学报

Current materials used for maxillofacial prostheses are far from ideal,and how to develop a final prosthetics material is a significant topic in the research of maxillofacial prostheses.In this paper,some pertinent research of silicone elastomeric materials,such as mechanical properties and colorant are reviewed.