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Although offering superior resistance to corrosion, titanium is unable to withstand discoloration with exposure to peroxide or fluoride. The mechanism of this discoloration, however, remains to be clarified. The purpose of this study was to investigate the mechanism underlying discoloration of titanium with immersion in peroxide- or fluoride-containing solutions based on electrochemical quartz crystal microbalance (EQCM) analysis. A 9-MHz titanium-deposited quartz crystal was used as for the electrodes. Four test solutions were prepared for immersion of the electrodes: 154 mM (0.9%) NaCl; 150 mM H2O2+154 mM NaCl (pH=4 by addition of lactic acid); 150 mM H2O2+154 mM NaCl (pH=8 by addition of sodium hydroxide solution); and 48 mM (0.2%) NaF+154 mM NaCl (pH=5.0 by addition of lactic acid). A WinEchem electrochemistry software-controlled quartz crystal analyzer (QCA922) and the Potentiostat/Galvanostat (Princeton Applied Research) on Windows XP were used to measure concurrently the resonance frequency and potential of the electrodes. The EQCM data differed among solutions. In the acidulated fluoride-containing solution, the electrode showed lower open circuit potential and a gradual increase in electrode frequency, indicating a loss of mass by titanium dissolution. In the peroxide-containing solution, although open circuit potential showed no marked difference, electrode frequency showed a gentle decrease in acidic solution, indicating a gain in mass by oxidation; but an increase in alkaline solution, indicating a loss of mass by dissolution. These results confirmed that exposure to acidulated fluoride- or alkaline peroxide-containing solutions causes dissolution-induced discoloration, while that to acidulated peroxide-containing solutions resulted in the formation of an oxide film together with discoloration.

The objective of this study was to compare corrosion behavior in several titanium alloys with immersion in acidulated saline solutions containing hydrogen peroxide. Seven types of titanium alloy were immersed in saline solutions with varying levels of pH and hydrogen peroxide content, and resulting differences in color and release of metallic elements determined in each alloy. Some alloys were characterized using Auger electron spectroscopy. Ti-55Ni alloy showed a high level of dissolution and difference in color. With immersion in solution containing hydrogen peroxide at pH 4, the other alloys showed a marked difference in color but a low level of dissolution. The formation of a thick oxide film was observed in commercially pure titanium showing discoloration. The results suggest that discoloration in titanium alloys immersed in hydrogen peroxide-containing acidulated solutions is caused by an increase in the thickness of this oxide film, whereas discoloration of Ti-55Ni is caused by corrosion.

The objective of this study was to evaluate change in color in experimental titanium-20mass% chromium (Ti-20Cr) alloy in an oral environment. Pure Ti and Ti-6Al-7Nb and Co-29Cr-5Mo alloys, as references to compare change in color, were prepared by casting. The cast specimen was mirror-polished. Each specimen was affixed to a palatal plate and the plate then worn by a volunteer for up to 300 h. A few specimens showed a change in color. These changes and the median values among the tested alloys were not significant. Larger amounts of carbon, nitrogen, and oxygen were observed in the discolored alloys than in the slightly-discolored alloys. The spectra of the constituent elements of the alloys revealed no corrosion. In conclusion, the experimental Ti-20Cr alloys showed a level of resistance to change in color and corrosion similar to that in commercially available Ti and Co-29Cr-5Mo alloys.

The mechanical properties of a series of binary Ti-Cr alloys were investigated. Chromium content ranged from 5 to 20 mass%. Dumbbell- and disk-shaped specimens of each alloy were obtained by casting for mechanical testing and microstructural observation. Yield strength (YS) at 0.2%, tensile strength (TS), elongation (EL) and Vickers hardness (Hv) were determined. The TS and YS of Ti-15Cr were similar to those of Ti-20Cr at approximately 880 or 900 MPa and higher than those of cp-Ti by nearly 55%. Among all Ti-Cr alloys, Ti-10Cr showed the lowest EL. At 50 µm below the surface, Hv ranged from 370 to 420. Addition of 15 or 20 mass% chromium to titanium yielded sufficient strength and relatively high elongation values. Judging from the results of the mechanical properties, the suitability of Ti-Cr alloys with 15 or 20 mass% chromium for use in dental prostheses.

The purpose of this study was to determine whether the brushing durability of a titanium dioxide coating on a polymethyl methacrylate (PMMA) substrate was improved by prior treatment with an acryloxypropyl trimethoxysilane-based agent. Titanium dioxide coatings were obtained by spray-coating substrates with or without prior treatment. Structure was investigated using IR, SEM, and an EPMA. Effect on durability against brushing was determined with a brush-wear test machine utilizing a commercial denture brush. A thin layer comprised of siloxane and TiO(2) was formed on a PMMA substrate by prior treatment with an acryloxypropyl trimethoxysilane-based agent and spray-coating of TiO(2). Prior treatment demonstrated improved stability against brushing, whereas the titanium coating was removed after less than 1x10(5) brushing cycles without prior treatment. This suggests that prior treatment with an acryloxypropyl trimethoxysilane-based agent would confer improved durability against brushing-induced stress on a TiO(2) coating in its application to dentures.

Objective: The objective of this study was to clarify the influence of chromium content on surface reaction of Ti-Cr alloys in an acidic fluoride-containing saline solution., Methods: Four Ti-Cr alloys containing 5, 10, 15 or 20 mass% chromium were characterized in terms of dissolution of metals in an acidic fluoride-containing saline solution and surface structure by X-ray photoelectron spectroscopy and Auger electron spectroscopy., Results: Total amount of metals dissolved from each alloy decreased with increase in chromium content. The surface oxide films of Ti-Cr alloys before and after immersion in an acidic fluoride-containing saline solution consisted of titanic and chromic species, such as oxide, hydroxide, and hydrate. The [Cr]/([Ti]+[Cr]) ratio in the surface oxide film on as-polished Ti-Cr alloys was closely correlated with chromium content. However, the ratio in any alloy approximately doubled after immersion. Although thick oxide films were observed after immersion, all alloys showed a thinner oxide film than commercially pure titanium., Significant: In all alloys, concentration of chromic species such as oxide and hydroxide in the surface oxide film was associated with chromium content, and chromic species improved corrosion resistance to fluoride.

Although fluoride induces corrosion in titanium in an oral environment, the influence of protein on this corrosion remains to be clarified. The objective of this study was to investigate suppression of fluoride-induced corrosion of titanium where albumin was either present in a solution or where albumin was preadsorbed on titanium. Titanium dissolution in titanium specimens and surface characterization of each specimen were determined. Dissolution in a saline solution containing both albumin and fluoride was less than that in only fluoride-containing saline solution. The titanium specimen was covered in an albumin film. The morphology of the titanium in the fluoride-containing saline solution revealed jagged edges, whereas titanium immersed in the saline solution containing albumin and fluoride showed a round and plate-like morphology. When albumin-adsorbed titanium was immersed in a fluoride-containing solution, dissolution within 6 h was less than that in non albumin-adsorbed titanium. Dissolution increased with desorption of adsorbed-albumin from the titanium surface. The results suggest that albumin in a solution suppresses dissolution of titanium compounds, thus influencing their morphology. Albumin adsorbed on titanium reduces fluoride attack and suppresses dissolution.

This study compared differences in discoloration and dissolution in several titanium alloys with immersion in peroxide- or fluoride-containing solution. Commercially pure titanium (CP-Ti) and six titanium-based alloys were used: Ti-0.15Pd, Ti-6Al-4V, Ti-7Nb-6Al, Ti-55Ni, Ti-10Cu, and Ti-20Cr. Two test solutions were prepared for immersion of polished titanium and titanium alloys: one consisting of 0.2% NaF + 0.9% NaCl (pH 3.8 with lactic acid) and the other of 0.1 mol/l H2O2 + 0.9% NaCl (pH 5.5). Following immersion, color changes were determined with a color meter and released elements were measured using ICP-OES. Discoloration and dissolution rates differed between the two solutions. In the hydrogen peroxide-containing solution, color difference was higher in Ti-55Ni and Ti-6Al-4V than in any of the other alloys, and that Ti-55Ni showed the highest degree of dissolution. In the acidulated fluoride-containing solution, CP-Ti, Ti-0.15Pd, Ti-6Al-4V, Ti-7Nb-6Al, and Ti-10Cu alloys showed remarkable discoloration and dissolution with immersion. On the contrary, Ti-20Cr alloy showed very little discoloration and dissolution in either solution.

It has recently been found that alloying with copper improved the inherently poor grindability and wear resistance of titanium. This study characterized the corrosion behavior of cast Ti-6Al-4V alloyed with copper. Alloys (0.9 or 3.5 mass % Cu) were cast with the use of a magnesia-based investment in a centrifugal casting machine. Three specimen surfaces were tested: ground, sandblasted, and as cast. Commercially pure titanium and Ti-6Al-4V served as controls. Open-circuit potential measurement, linear polarization, and potentiodynamic cathodic polarization were performed in aerated (air + 10% CO(2)) modified Tani-Zucchi synthetic saliva at 37 degrees C. Potentiodynamic anodic polarization was conducted in the same medium deaerated by N(2) + 10% CO(2). Polarization resistance (R(p)), Tafel slopes, and corrosion current density (I(corr)) were determined. A passive region occurred for the alloy specimens with ground and sandblasted surfaces, as for CP Ti. However, no passivation was observed on the as-cast alloys or on CP Ti. There were significant differences among all metals tested for R(p) and I(corr) and significantly higher R(p) and lower I(corr) values for CP Ti compared to Ti-6Al-4V or the alloys with Cu. Alloying up to 3.5 mass % Cu to Ti-6Al-4V did not change the corrosion behavior. Specimens with ground or sandblasted surfaces were superior to specimens with as-cast surfaces., ((c) 2005 Wiley Periodicals, Inc.)

The objective of this study was to demonstrate the role of albumin on the corrosion behavior of titanium in a solution containing 2.0 g/l fluoride and either 0.1 or 1.0 g/l albumin. The corrosion behavior and surface characterization of passive films on titanium immersed in such a solution were examined. In addition, the change in pH and the concentration of dissolved titanium in the solution were examined. The results showed that the corrosion of titanium in a solution containing fluoride was distinct, and that adding albumin to the solution containing fluoride suppressed corrosion. Fluorine was detected on the titanium surface immersed in the solution containing fluoride, and dissolution of the titanium was confirmed. The titanium immersed in a solution containing both fluoride and albumin had an albumin film regardless of the albumin concentration. In addition, the amount of dissolved titanium from the titanium immersed in the solution was less than when the solution contained no albumin. It was suggested that the formation of adsorbed albumin films on or in the passive film acted to not only protect the titanium from attack by the fluoride but also suppressed dissolution of the titanium-fluoride compounds.

The purpose of this study was to investigate the correlation between corrosion resistance and surface composition of an experimental Ti-20 mass% Cr casting alloy in a saline solution containing fluoride. The alloy had a greater resistance to corrosion in a fluoride-containing saline solution than did commercially pure titanium. However, with confirmed dissolution of titanium and chromium, it meant that the fluoride in the saline solution corroded the alloy slightly. X-ray photoelectron spectroscopy analysis revealed that the surface composition of the alloy consisted of titanium and chromium oxides containing hydroxide. The [Ti]/([Ti] + [Cr]) ratio in the surface oxide film decreased when immersed in fluoride-containing saline solution, that is, the surface oxide film became chromium-rich oxide. Therefore, the alloy obtained good corrosion resistance to fluoride due to formation of a chromium-rich oxide film.

Proteins can interact with corrosion reactions in several ways. In this study, we investigated the effect of albumin on the corrosion resistance of titanium in the presence of fluoride. The effects of the NaF concentration, albumin concentration, and pH on the corrosion characteristics of commercially pure titanium (CP-Ti) were examined by means of electrochemical techniques. The corrosion resistance of titanium decreased as the NaF concentration increased and as pH decreased. The corrosion resistance of titanium in NaF solutions was improved in the presence of albumin. The natural electrode potential was elevated, and the passive current density was reduced by albumin at a concentration of 0.01%. The polarization resistance rose with increased concentrations of albumin in fluoride solution. These results showed that the albumin in saliva and dental plaque affected the corrosion resistance of CP-Ti in fluoride solution.

This study evaluated the microtensile bond strength (μTBS) of 1-step self-etch adhesives (1-SEAs) and 2-step self-etch adhesives (2-SEAs) to pulp chamber dentin immediately after bleaching with 2 types of common bleaching techniques. Pulp chamber dentin of bovine teeth was bleached using 30% hydrogen peroxide (H2O2) solution with quartz-tungsten-halogen light-curing unit (Group 1) and 3.5% H2O2-containing titanium dioxide (TiO2) (Pyrenees®) activated with 405-nm violet diode laser for 15 min (Group 2). Unbleached specimens were placed in distilled water for 15 min and used as controls. After treatment, dentin was bonded with resin composite using 1-SEA or 2-SEA and stored in water at 37°C for 24 h. Each specimen was sectioned and trimmed to an hourglass-shape and μTBS was measured. Fractured specimens were examined under a scanning electron microscope to determine fracture modes. All specimens in Group 1 failed before proper bonding tests. In Group 2, the μTBS of 2-SEA was significantly greater (with no failed specimens) than 1-SEA (where 21 out of 36 failed). These results indicate that 2-SEA is a better adhesive system than 1-SEA on bleached dentin. Our results also demonstrated that application of H2O2 significantly decreases bond strength of resin to dentin; however, in the case of nonvital tooth bleaching, Pyrenees® is a better alternative to the conventional 30% H2O2 bleaching. [ABSTRACT FROM AUTHOR]

To optimize the properties of titanium for use in dentistry, alloying is necessary. This study reports on the characterization of some titanium alloys for grindability, wear, and corrosion resistance. Improvements in grindability and wear seemed to occur with the presence of the eutectoid in the alloy. [ABSTRACT FROM AUTHOR]